Contents. 4 Project Planning...4-1

Transcription

1 4 Project Planning

2 Contents 4 Project Planning River Planning Overview and Project Development Purposes Analysis on Power Supply Range and Power Market Potential Calculation of Water Resources and Energy Economy Selection of Normal Pool Level Selection of Minimum Pool Level Selection of Installed Capacity Selection of Rated Head Selection of Type and Number of Units Navigation Scale Calculation and Analysis of Sedimentation by Mathematical Model Calculation of Reservoir Backwater Operation Mode of Reservoir and Power Station Analysis on Impact of Paklay Reservoir on Upstream and Downstream Reaches 4-184

3 4 Project Planning 4.1 River Planning Overview and Project Development Purposes River Overview As the 4 th cascade power station in the hydropower development of the Mekong River, the PakLay Hydropower Project (HPP) is located in the Laos reach of the main stream of the Mekong River. The dam site of the project is at the Stake No km of main stream of the Mekong River (i.e km from the estuary) at the border of Sayaboury Province and Vientiane Province of Laos. It is about 20 km from PakLay county town in the downstream and about 230 km from the Vientiane, capital of Laos. See the Attached Figure Paklay-FS-General-01 for PakLay Hydropower Project Geologic Sketch. Originating from the north piedmont of Tanggula Mountains in Qinghai Province of China, the Lancang-Mekong River passes Qinghai, Tibet and Yunnan and is known as the Mekong River since it leaves China at Mengla County, Xishuangbanna Prefecture, Yunnan Province. As a famous international river in Southeast Asia, the Mekong River passes Laos, Myanmar, Thailand, Cambodia and Vietnam and enters into the South China Sea at the vicinity of Ho Chi Minh City, Vietnam. According to relevant statistics, the main stream of Lancang River Mekong River is about 4,850 km in total length with a catchment area of about 795,000 km 2. Lancang River within Chinese territory is 2,130 km long in its mainstream; Boundary River between China and Myanmar is 31 km long, Boundary River between Laos and Myanmar is 234 km long, Boundary River between Laos and Thailand is 976 km long, the river within the borders of Laos is 789 km long, the river within the borders of Cambodia is 490 km long, the river within the borders of Vietnam is 230 km long. The basin profile of Lancang Mekong River looks like a strip with narrow top and wide bottom. It overpasses 25 latitudes with big diversity in physical geographic conditions within basins. Divided by the Mekong River Basin Research and Coordination Commission (hereinafter referred to as "the Mekong River Commission" (the MRC)), the 4-1

4 Mekong River can be divided into the upper Mekong River and the lower Mekong River. The upper Mekong River Basin means the Lancang River within the borders of China and the Mekong River within the borders of Myanmar. The lower Mekong River Basin mainly means the Mekong River within the borders of Laos, Thailand, Cambodia and Vietnam. The upper and lower Mekong River Basins are approximately divided by the Chiang Sean Hydropower Project. The upper Mekong River Basin mostly lies in the Tibetan Plateau, subject to the obvious three-dimensional climate. Affected by the monsoon climate, the lower Mekong River Basin is mainly subject to dry season and rainy season. Generally, the dry season starts from November and ends to May of the next year, at a relatively low temperature due to the northeast monsoon climate. Affected by Annamite Mountains and Central Highlands, the rainfall generally occurs within the borders of Vietnam during this period, with a relatively low quantity. The rainy season generally starts from June and ends to October, mainly affected by the southwest monsoon climate. The highest quantity of rainfall occurs between August and October. The main stream of Lancang River within the borders of China is about 2,160 km in total length, with a natural fall of 4,583 m and an average gradient of This river flows from north to south, across 12 latitudes. The basin is of the stripped shape, and the area within the borders of China is about 174,000 km 2. The Lancang River has an abundant and stable water quantity, with a big fall, being one of the rivers with the most abundant hydropower resources and good development conditions in Yunnan Province. According to the check results of hydropower resources in China in 2003, the theoretic reserves of hydropower resources in the Lancang River Basin in Yunnan Province are 24,900 MW, the annual energy output is billion kw h. The theoretic reserves of main stream of the Lancang River are 17,420 MW, accounting for about 70% of the reserves of the whole basin. The technically exploitable amount of water power resources in this basin is 27,560 MW, 25,610 MW for the main stream. The development of hydropower project on the Lancang River basin is the most important composition for construction of southwest hydropower energy base and implementation of the energy strategy of "West-East 4-2

5 Electricity Transmission Project" in China. The Mekong River is about 2,720 km long and covers a basin of 621,000 km 2 with the fall about 480 m and the average gradient of At the point since which the river leaves China, the average annual discharge is 2,030 m 3 /s and annual runoff is 64 billion m 3 ; while at the estuary, the average discharge is 15,062 m 3 /s and annual runoff is 475 billion m 3. According to statistics, the theoretical reserve of water resource is about 58,000 MW, the technically exploitable installed capacity is about 37,000 MW, and average annual output is about 180 billion kw h. Most of the technically exploitable water resources of the river are in Laos and Cambodia. In details, Laos has 51%, Cambodia has 33% and other countries (Myanmar, Thailand, and Vietnam) have 16%. So far, the exploited water resources only account for less than 1% of the total resources Planning and Development Overview of Hydropower Projects at Middle and Lower Reaches of the Lancang River In December 1986, the POWERCHINA Kunming Engineering Co., Ltd. (the former HydroChina Kunming Engineering Co., Ltd.) had prepared the Planning Report at Middle and Lower Reaches of the Lancang River in Yunnan Province (Gongguoqiao - Nam Nga River Mouth), in which the eight-cascade development scheme including two reservoirs at middle and lower reaches was recommended, namely, the eight-cascade development scheme covering Gongguoqiao HPP, Xiaowan HPP, Manwan HPP, Dachaoshan HPP, Nuozhadu HPP, Jinghong HPP, Ganlanba HPP and Mengsong HPP and including Xiaowan and Nuozhadu regulation reservoirs. The planning report was accepted in May According to the latest results, refer to Table for major parameters of cascade hydropower stations at middle and lower reaches of the Lancang River. 4-3

6 Table Major Parameters of Cascade Hydropower Stations at Middle and Lower Reaches of the Lancang River Item Unit Gongguoqiao Xiaowan Manwan Dachaoshan Nuozhadu Jinghong Ganlanba Mengsong Catchment area at dam site Average annual discharge Average annual runoff 10 3 km m 3 /s m Normal pool level m Minimum pool level m Effective storage 10 6 m Regulation capability Installed capacity Average annual energy output Current development condition Time of completion Daily regulation Overyear regulation Seasonal regulation Seasonal regulation Overyear regulation Weekly Daily regulation regulation Run-of-river MW kwh Completed Completed Completed Completed Completed Completed Feasibility study Year of 2012 Year of 2010 Year of 2007 Year of 2003 Year of 2014 Year of 2009 Planning Currently, except the Ganlanba and Mengsong HPPs, all the other cascade HPPs at the middle and lower reaches of the Lancang River have already been basically completed, of which Xiaowan was completed in 2010 and Nuozhadu was completed in In the eight-cascade development scheme, the Xiaowan and Nuozhadu reservoirs have the annual regulation function. The two reservoirs have a total regulating capacity of billion m 3, with a significant regulation action on the runoff feeding into the cascade reservoir at the lower reaches Hydropower Planning Overview of Main Stream of the Mekong River In 1957, under the support of the Economic Commission for Asia and the Far East (ECAFE in short and renamed as Economic and Social Commission for Asia and the Pacific since 1987), the MRC was established and comprising of Vietnam, Laos, Cambodia and Thailand. Since 1963, the MRC has carried out large number of basin planning for the Mekong River. In 1970, the commission put forward 1970 Basin Guiding Planning, in which 7 hydroprojects were proposed in the main stream reach as long as over 2,400 km 4-4

7 from Hekou, China to Chiang Saen, Thailand. The 7 cascade power stations had a total installed capacity of 23,300 MW, total reservoir capacity of billion m 3, effective storage of 136 billion m 3, although none of them was realized for they were designed with high dams and large reservoirs, inflicting significant inundation loss and impact on environment and society. In 1994, under the sponsorship of United Nations Development Programme and French Government, the Secretariat of the MRC called out a research team staffed by experts from the member countries to review the hydropower planning of the main stream of the Mekong River and prepared the Study Report for Runoff Type Hydropower Engineering Development of the Main Stream of the Mekong River, altering the original proposal of high-dam plus large reservoir into runoff type development, recommending a 11-cascade runoff type power station development scheme, including PakBeng, LuangPrabang, Sayaboury, PakLay, ChiangKhan, Pamong, BanKoum, DongSabong, StungTreng, Sambor and TonleSap with a total installed capacity of 14,810 MW. See Table for the major technical indexes of 1994 Proposal on Mekong River Runoff Type Hydropower Planning. According to such planning, the normal pool level in the reservoir of PakLay Hydropower Project is m. In 2007, to develop the abundant domestic water resources and attract investment, Laos Government offered 5 hydropower station development projects including Pak Beng, LuangPrabang, Sayaboury, PakLay and ChiangKhan which are all in the main stream of the Mekong River. Development memorandums were signed with enterprises. After that, the developers of the cascade power stations started entrusting design institutes for feasibility study and design. As the proceeding of the feasibility study and design for the cascade power stations, it was found that the original planning (1994 Planning) had proposed seriously overlapped heads (up to 5 ~ 10 m) between the cascade power stations and neither economic efficiency nor rationality was sufficiently considered in the river reach water resource development in a general sense. To address these issues, Laos Government entrusted France CNR Corporation in 2008 to carry out cascade level 4-5

8 optimization study for the above-mentioned 5 hydropower stations and propose more economical and reasonable connection scheme of cascade water levels. In September 2009, CNR Corporation submitted the final report on cascade level optimization study, moving the dam site of ChiangKhan Hydropower Project from Stake No. 1,772 km to 1,737 km and proposing recommended scheme for level optimization of the cascade power stations. The results hereof are shown in Table Table Project Pak Beng Langprabang Results of the Cascade Level Optimization Scheme Recommended by the CNR Corporation Results of Developed by 1994 CNR Recommended Scheme Planning Yunnan Datang International Lixian Hydropower Development Co., Ltd. 345m 337.5m~340m Petro Vietnam Power Corporation (Vietnam) 320m 310m~312.5m Sayaboury CH.Kanchang (Thailand) 270m 275m PakLay ChiangKhan SINOHYDRO Corporation Limited and China National Electronics Import - Export Corporation Yunnan Datang International Lixian Hydropower Development Co., Ltd. 250m 230m 240m~245m 217.5m~220m According to the results of the cascade level optimization scheme recommended by the French CNR Corporation and through coordination by multiple particles, the Lao Government has defined the final level convergence scheme, with the following specific requirements: a) The normal pool level of the Pak Beng reservoir shall be so selected that the backwater level will not exceed the Border between Laos and Thailand; b) The normal pool level of the Langprabang reservoir shall not exceed 310 m a.s.l.; c) The normal pool level of the Sayaboury reservoir shall not exceed 275 m a.s.l.; d) The normal pool level of the PakLay reservoir shall not exceed 240 m a.s.l.; e) The normal pool level of the ChiangKhan reservoir shall not exceed 220 m a.s.l.; According to the final scheme determined by the Lao Government, refer to Attached Figure Paklay-FS-General-02 for the Mekong River Main Stream Laos Reaches Cascade Development Schematic Diagram. 4-6

9 Currently, the construction of the Sayaboury HPP within the borders of Laos was commenced in The Pak Beng, Langprabang, PakLay and ChiangKhan HPPs are all under the preliminary preparation works. The feasibility study reports of the Pak Beng and ChiangKhan HPPs have already been done, and have been evaluated and reviewed by the Lao Government. 4-7

10 Table Major Technical Indicators in the Proposal of 1994 for Planning of Run-of-River Hydroelectric Projects on Mekong River Project Unit Pak Luang Pak Chiang Ban Don Stung Tonle Sayaboury Pamong Sambor Beng Prabang Lay Khan Koum Sabong Treng Sap Total Border Border Border Location Laos Laos Laos Laos Laos between between between Laos and Laos and Laos and Cambodia Cambodia Cambodia Thailand Thailand Cambodia Distance from the estuary km Catchment area 10 3 covered by the 2 km dam site Annual mean discharge at dam m 3 /s site Normal pool level m ~ Installed capacity MW Average annual 10 9 energy output kw h Annual operating hours of installed capacity h Note: 1) Loss on transmission line has been deduced from the mean annual energy output in the table; 2) The dam site of Chiang Khan Hydropower Station has been relocated from the spot which is 1,772 km from the estuary to 1,737 km. 4-8

11 4.1.4 Project Development Purposes As the biggest river in the Southeast Asia and the third biggest river in Asia, the Mekong River flows through Myanmar, Laos, Thailand, Cambodia, Vietnam, etc., its basin almost covers the whole Laos and most regions in Cambodia, Thailand and Vietnam. With a pleasant climate, an abundant rainfall, fertile soil and rich materials, this basin is the most economically active region in the Southeast Asia, and is the mother river for people around to live and develop. The hydropower development of the main stream of the Mekong River involves the benefits of tens of millions of people along the river. The development-protection relation must be effectively solved, so that the environmental and social impacts can be relieved and the hydropower development can be well compatible with the sustainable development in the basin. In order to guide and normalize the hydropower development of the main stream of the Mekong River, the MRC had prepared the Preliminary Design Guidance for Proposed Mainstream Dams in the Lower Mekong Basin in August 2009, requiring that the navigation on the main stream should be also taken into account during the hydropower development, and the affects of the hydropower development on fishery, sediment transport, river morphology, water quality, water environment and aquatic ecosystem should be minimized or avoided. a) Power generation The main stream of the Mekong River is about 2,720 km in total length, with the fall of about 480 m, in which the river course within the borders of Laos is about 789 km long. According to relevant data, the theoretic reserves of the hydropower resources of the Mekong River are about 58,000 MW, the technically exploitable hydropower resources are about 37,000 MW, 51% of which lies within the borders of Laos. The PakLay HPP is the Cascade 4 in the hydropower planning on the main stream of the Mekong River. The catchment area at the dam site is 280,500 km 2, and the annual average discharge is 4,060 m 3 /s (upper dam site). According to the study results in this stage, the normal pool level of the reservoir of the PakLay HPP is m a.s.l., the installed capacity is 770 MW, the annual average energy output is GW h, and the annual operation hours of installed 4-9

12 capacity are 5,357h. The development and construction of the PakLay HPP will provide clean renewable energy sources to Southeast Asian countries such as Laos and Thailand, this will be good for strengthening the energy sources reserves of the Southeast Asian countries and play an very important role for prompting the economic and social development of Laos. Therefore, the purposes of development of the PakLay HPP are dominated by power generation. b) Shipping As the biggest international river in the Southeast Asian region, the Mekong River flows through multiple Southeast Asian countries such as Myanmar, Laos, Thailand, Cambodia and Vietnam. The river has a relatively gentle slope and a large and relatively stable discharge, being the important logistic shipping route among the Southeast Asian countries, and the important shipping route for the economy and trade between China and Southeast Asian countries. Since the beginning of 1990s, China has successively invested more than RMB 10 million to treat more than 260 km of waterways of the lower reaches of Lancang River in Yunnan Province, and built the Simao Port and Jinghong Port, both being the national Grade-I ports. The waterway between the Simao Port and the Guanlei Wharf at the Border between China and Myanmar has already reached the standards of the national Grade-VI waterway of China, and is capable of carrying the 100 t ship all the year round and the 200 t ~ 300 t ship in May ~ December. In August 1994, the shipping experts and government officials from China, Myanmar, Laos and Thailand had together investigated the 886 km waterway from the Simao Port in China to LuangPrabang in Laos, and they had collected mass data about waterways and navigation conditions, laying a foundation for treatment of river course and joint development of navigation on the Mekong River. From December 1994 to January 1997, China had successively signed the Lancang River ~ Mekong River Passengers and Freights Transport Agreement with Laos and Myanmar. In April 2000, China, Laos, Myanmar and Thailand had formally signed the Lancang River ~ Mekong River Merchant 4-10

13 Ship Navigation Agreement of China, Laos, Myanmar and Thailand (hereinafter referred to as the "Four-country Merchant Ship Navigation Agreement"), and held the navigation ceremony at Jinghong Port in June 2001, declaring that the merchant ships of the contracting countries can freely travel on the 886 waterway between Simao Port and LuangPrabang Port. The "Four-country Merchant Ship Navigation Agreement" reached a consensus on improvement and maintenance of the waterway on the Greater Mekong, and aimed to prompt and guarantee the development of shipping between the Lancang River and the Mekong River. In 2003, the China Government had invested more than RMB 90 million to treat the 71 km river course between the Jinghong Port and the No. 243 boundary monument at the Border between China and Myanmar, so that this river course of waterway had been improved from Grade VI to Grade V, with the single-chip navigation capacity reaching 300 t ~ 500 t. From 2002 to 2004, the Chinese Government had invested USD 5 million to treat the 331 km waterway on the Mekong River from the No. 243 boundary monument at the Border between China and Myanmar to Houayxay in Laos, so that the navigation capacity of this river course had been improved from 100 t ~ 150 t to 200 t ~ 300 t. The Lancang River ~ Mekong River international shipping and trade had developed quickly as the Jinghong ~ Houayxay navigation capacity improved. Enterprises participating in the shipping business have increased from 1 Nos. in 1990 to 36 Nos., and ships participating in the international shipping logistics have increased from a few numbers in 1991 to hundreds at present. The major types of ships participating in the international shipping on the Lancang River ~ Mekong River have upgraded from 150 t to 250 t, with the maximum tonnage of 300 t. In addition to the traditional freights transportation, the Lancang River ~ Mekong River is now carrying the refined oil products transportation, scheduled tourists transportation and refrigerated transportation of fresh fruits and vegetables, meaning that the types of logistics and transportation have been further enlarged and optimized. The Houayxay ~ LuangPrabang ~ Vientiane waterway on the Mekong River has never been treated due to the limited economic capability of Laos, so this waterway has a 4-11

14 relatively small navigation capacity. Currently, the river course between Houayxay and LuangPrabang in Laos has the navigation capacity in dry season of 30 t, and the navigation in flood season of 80 t. The river course between LuangPrabang and Vientiane has the navigation capacity in dry season of 15 t and the navigation capacity in flood season of 60 t. Few cargo ships travel on the Houayxay ~ LuangPrabang ~ Vientiane waterway, but this waterway carries the dedicated passenger services. The river course downstream of Vientiane has a relatively steep slope to the Phnom Penh riverbed, with many races and waterfalls. The navigation is intercepted between upper and lower reaches, and the water-land transshipment develops around the Khone Phapheng Waterfall. The river course downstream of Phnom Penh carries seagoing vessel all the year round. According to the Overall Layout Planning for Development of Water Transport in Nine Provinces in the North of Laos, before 2020, it is planned to improve about 1,117km-long waterway from No. 244 boundary monument at the Border among China, Laos and Myanmar to Nong Khai (40 km downstream of Vientiane) by waterway regulation and cascade canalization, such that the waterway is available for navigation of 500t ships. Therefore, navigation must be considered in the development of Paklay HPP. The PakLay HPP lies on the LuangPrabang ~ Vientiane river course on the Mekong River. Currently, the navigation capacity at this river course is about 15 t (dry season) ~ 60 t (flood season), and the waterway treatment and port construction are falling behind, so this river course has a relatively low freight transportation capacity, which seriously affects the development of international shipping on the Lancang River ~ Mekong River. However, there are relatively abundant materials such as agricultural products and woods and relatively considerable minerals and sylvite reserves on both banks of the river course, so there is a huge potential to develop the freight transportation business. As the regional economy develops and the cooperation policies in the China-ASEAN Free Trade Area are being gradually implemented, the trades and shipping business on the Lancang River ~ Mekong River will be subject to the new development opportunities. Upon completion of the Pak Beng, LuangPrabang, Sayaboury, PakLay and ChiangKhan hydropower projects at 4-12

15 the Laos river course of the main stream of the Mekong River, the river course of main stream of the Mekong River in the length of about 550 km within the borders of Laos can be channelized, so as to form a deep waterway. The bottleneck of navigation on the main stream of the Lancang River ~ Mekong River will be broken through, the range of benefits due to the navigation will be enlarged, the navigation conditions will be improved, and this will play an important role in prompting the economic development in the Mekong River region. According to the provisions specified in the "Preliminary Design Guidance of Dam on Main Stream of the Mekong River", the navigation facilities must be arranged for the hydropower projects on the main stream of the Mekong River, so as to ensure the unimpeded navigation on the river and prompt and guarantee the development of navigation on the Lancang River ~ Mekong River. According to the study results, the single-line single-stage ship lock shall be adopted for design of navigation structures for the PakLay HPP. According to the unified requirements of the MRC and the current navigation situation and relevant plans on the main stream of the upper Mekong River, and with reference to the feasibility study design results of each cascade at the upper reaches, the ship lock shall be Grade IV standardized in China, the design ship shall have a tonnage of 500 t and the corresponding ship lock shall have the effective dimension of 120 m 12 m 4 m (length width water depth at lock sill). Therefore, the development of the Project must take the navigation into account. c) Fishery industry As one of a few longitudinal rivers in the world, the Lancang River ~ Mekong River flows through various geographic environments such as glacier, meadow, plateau, canyon, broad valleys at medium and low mountains and alluvial plain, covering almost all climates and geological conditions in the world, including frigid zone in glacier, cold temperate zone, temperate zone, warm temperate zone, subtropical zone, and dry and cold zone, dry and hot zone and wet tropical zone in tropical zone. Complex and diversified biological species live in the basin due to diversified climates and geographic conditions. 4-13

16 The investigation indicates that the biodiversity in the Mekong River basin is second only to that in the Amazon River basin, while the diversity of aquatic organism is the highest all over the world, and many areas in the basin have the unique aquatic species in the world. According to statistics, there are about 1,300 types of fishes in the Mekong River, including the biggest freshwater fish in the world - the pangasianodon gigas, and rare freshwater finless porpoise. As the largest freshwater fish production area in the world, the Mekong River basin has an average annual fish output of about 2.60 million tons, and fishery industry is the basic industry for millions of people along the Mekong River to live. The construction of dam of the Project will affect some types of fishes on the Mekong River in migration and spawning. According to statistics, about 700,000 t ~ 1.60 million tons of project-affected fishes will migrate away if no relevant measures are taken, causing the economic loss of about USD 1.4 billion ~ 3 billion every year. In order to control the affect of hydropower development on fishery industry, the "Preliminary Design Guidance of Dam on Main Stream of the Mekong River" has clearly specified that the fish pass structures must be arranged for the hydropower projects on the main stream of the Mekong River, so as to ensure that 95% of migrant fishes can pass through the dam safely. In summary, according to the achievements of planning related to the main stream of the Mekong River, relevant requirements of the MRC and the actual situation of the Project, the development of the Paklay HPP shall give priority to power generation and combine the comprehensive utilization of shipping etc. Meanwhile, during construction and operation of the Project, effective measures shall be taken to minimize affect on ecological environment (such as arrangement of fish pass structures). In addition, after completion, the Project shall also have benefits for comprehensive utilization, such as developing aquiculture in the reservoir area, promoting tourism and local economic and social development and improving irrigation conditions of the reservoir area. 4.2 Analysis on Power Supply Range and Power Market Potential Power Supply Range and Design Target year The Paklay HPP is located in Laos which lies in the north of Indo-China Peninsula of 4-14

17 Asia. Laos borders China in the north, Cambodia in the south, Vietnam in the east, Myanmar in the northwest and Thailand in the southwest. Its national territory covers 236,800 km 2, 80% of which are mountains and plateaus, mostly covered by forests. Its current population is about 6.9 million. Dominated by agriculture and with weak industrial base, the economic development in Laos lagged behind. Since 1986, Laos has obtained relatively rapid economic and social development through promoting reform and open policy, improving investment environment, adjusting economic structure and improving market economy mechanism. Especially in recent 10 years, Laos has been actively implementing the strategy of "resources for funds" and vigorously attracting foreign investment to make the economic development enter the fast track and the average GDP growth increase by about 8%. According to statistics, Laos's GDP of 2014 was USD billion, with a year-on-year growth of 7.8% and per capita GDP was about USD 1,670. With abundant hydropower resources in Laos and according to relevant planning result of Laos Power Department, its available hydropower resources will amount to more than 23,000 MW, including 18,000 MW of current available hydropower resources (excluding hydropower resources of the main stream of Mekong River) and 5 planning HPPs at Pak Beng, Louangprabang, Xaignabouli, Paklay and Sanakham along the main stream of Mekong River. In recent years, with more investment on the hydropower of Laos from China, Japan, Thailand and other countries, the hydropower development of Laos has entered an unprecedented stage. In ten years, hydropower installed capacity anticipated to operation in Laos will amount to several million kilowatts, while domestic power demand cannot consume such abundant power energy. Therefore, the power of Laos will be mainly exported to neighboring countries such as China, Thailand, Vietnam and other countries with relatively developed economy. Located in the middle of countries in Southeast Asia and bordering China, Myanmar, Thailand, Cambodia and Vietnam, Laos enjoys a good geographic position for power export. According to relevant planning result, Lao Government plans to export power to Thailand, China, Vietnam and other neighboring countries in In December 2007, Lao Government signed a memorandum of understanding on power cooperation with Thai 4-15

18 Government. Both parties agreed that 3,000 MW ~ 5,000 MW of power shall be supplied from Laos to Thailand before 2015, and 5,000 MW ~ 7,000 MW of power after Besides, according to relevant planning, Laos also planned to export 2,000 MW to Vietnam and 5,000 MW to China Southern Power Grid. The Paklay Hydroelectric Station (HPP) lies on the junction of Xaignabouli Province and Vientiane Province in Laos, about 50 km away from the border of Thailand. Based on the geographic position and the installed capacity of the HPP as well as the relevant power export planning of Lao Government, power of Paklay HPP will be partially supplied to Laos and partially exported to Thailand. Therefore, the power supply target of the Paklay HPP at this stage is mainly focused on Thailand. According to work progress in earlier phase of the project and designed construction period, design target year of the Paklay HPP is considered as the year of Analysis of Power Market potential in Power Supply Areas a) Laos Lao Power System composes of 3 power supply areas: power supply in the north, south and central areas respectively. As load center of Lao Power Grid, the central area, including Vientiane City, Vientiane Province, Louangprabang Province, Xaignabouli Province, Xieng Khuang Province, Bolikhamxai Province, etc., accounts for over half of the national electricity consumption and load. According to statistics, the total electricity consumption of Laos in 2009 was billion kw h and the maximum load was MW; the total installed power capacities of the whole nation were 2,558 MW and the total energy output was billion kw h of which 0.23 billion kw h was exported to other countries. Besides, Laos also imported billion kw h electricity for domestic demands. A preliminary analysis has been made on the profit and loss of national power in Laos in 2020 target years according to relevant forecasted power demands and power supply development plan in the Lao Power Development Plan prepared by the Lao Power Department. The analysis results are shown in the Table Table Preliminary Analysis Results of Profit and Loss of Power in Each Target Year in Laos 4-16

19 Item Unit 2009 (actual) Total electricity consumption GW h Max. load MW Annual operating hours h Installed capacities required for the system Installed capacities of built power supplies and power supplies under construction MW MW Profit (+) and loss (-) of power Note: 20% standby capacities shall be reserved on the basis of the maximum load for installed capacities required for the system. According to official forecasting results of the Lao Power Department, the maximum national loads of Laos in 2020 target years will be 2,905.2 MW respectively and the domestic power demand is limited. According to results shown in the Table , in addition to large-scale installed hydropower capacities on the main stream of Mekong River, the installed capacities of hydropower stations built and under construction in Laos have been up to 3,508 MW. Laos will have a little surplus of power in b) Thailand Thailand is located in the south central Indo-China Peninsula of Asia, bordering the Pacific Ocean in the southeast, the Indian Ocean in the southwest, Myanmar in the west and northwest, Laos in the northeast and Cambodia in the southeast. It covers 513,000 km 2, about 30% of which are plains and 70% are mountains, hills and plateaus. Its current population is about 68 million. The climate of Thailand is hot and humid, and with abundant rainfall and fertile land, Thailand enjoys abundant biological resources. It abounds in rice, rubber, various tropical and subtropical fruits. Its arable area is 207,000 km 2, taking up 40% of the national land area. As world-famous rice producer and exporter, Thailand contributes 1/3 of rice trade in the world market by exporting. Thailand is also one of the countries with largest seafood production in Asia, third to Japan and China, and the country with largest shrimp production in the world. Thailand has abundant mineral resources. Its reserves of tin, tungsten and tantalum ranks high in the world, and abounds in fluorspar, barite, iron, copper, zinc and other various minerals. Thailand is relatively shortage of energy resources. Its proved gas reserve is trillion m 3, lignite reserve is 4-17

20 1.8 billion t, oil reserve is 2.3 billion barrels and exploitable and available hydropower resource is 10,620 MW. The energy self-sufficient rate of Thailand is only about 50%, half of energy demand is supplied by export. Thailand is one of the most developed countries in Southeast Asia. During after Asian financial crisis, Thai economy has always enjoyed steady growth with annual average rate of 4.7%. Affected by international financial crisis and domestic political unrest in 2009, Thailand endured economic downturn. At that time, the GDP was USD billion, dropping by 3.1% compared with that in 2008, and the GDP per capita was USD 3,939. By the end of December, 2009, the total installed capacities for power generation of Thailand have been 29,212 MW, including 14,328.1 MW, accounting for 49.0%, from power plants owned by Electricity Generating Authority of Thailand (EGAT), 14,243.9 MW, accounting for 48.8%, from independent and private power plants, and 640 MW, accounting for 2.2% from foreign countries. By the end of December, 2009, the total length of transmission line of 69 kv and above in Thailand have been 30,446 m, of which 500 kv line is 3,722 km, 230 kv line is 13,393 km, 132 kv line is 9 km, 115 kv line is 13,280 km and 69 kv line is 19 km. There are 209 substations with power transformation capacities of 72,787 MVA. In 2011, the total power consumption of Thailand was 160,706GWh, the maximum load 24,070MW, and the maximum load utilization hours 6677h. According to Report on Thailand s Power Development Plan prepared by EGAT in 2012, forecasted national power demands in target year 2020 are shown in the Table Item Table Forecasted Power Demands in Each Target year in Thailand Installed Determined Profit and Annual Capacities Domestic Loss of Total Electricity Consumption Max. Load Operating Required Installed Installed Hours for the Capacities Capacities System (10 9 kw h) (MW) h MW MW MW 4-18

21 2008 (actual) (actual) (actual) (actual) Note 1: "+" for capacity profit and "-" for vacancy; Note2: 20% standby capacities shall be reserved on the basis of the maximum load for installed capacities required for the system. According to statistics, by the end of December, 2011, the total installed capacities for power generation of Thailand have been 32,395 MW. According to the power supply planning result in the Report on Thailand's Power Development Plan, with the installed capacity at the end of 2011 as basis, in consideration of domestic small thermal power generating units out of service in 2012~2015, and the planned newly installed capacities as the determined installed capacities of the system, the installed power capacities determined in Thailand in 2020 will be about 38,332 MW. With growth of national power demands and limited by domestic energy resources reserves, Thailand needs to import about 6,500 MW power from foreign countries (like Laos and Myanmar) in 2020 target year to meet domestic power demands. The linear distance between the Paklay HPP and Thailand's boundary is around 50 km, so the geographical condition for power supply to Thailand is favorable. The analysis of Thailand power market indicates huge power demands in 2020, so power supplied by Paklay HPP can be completely consumed. Therefore, the power supply target of the Paklay HPP at this stage is mainly considered as Thailand. Thailand: The Paklay HPP might adopt the following two methods to supply power for Method I: direct point-to-grid power supply. That is to say, new transmission lines will be built from Laos to Thailand. Power is directly supplied by the HPP to Thailand Power Grid and then directly bought by EGAT. According to power procurement policy of EGAT, price of electricity bought by this way varies according to different periods for power generation, i.e. the firm energy is purchased according to agreed electricity price, 4-19

22 secondary energy is purchased by 60% of the agreed electricity price, and procurement of excess energy cannot be guaranteed. Certain regulating storage is reserved for the reservoir under this power supply method which can transfer the water used for the periods when excess energy and secondary energy are generated to the period for generating firm energy. This can greatly help to enhance equivalent energy of the hydropower station and the power generation benefit. Method II: gird-to-grid power supply. That is to say, all power generated by the hydropower station is sold to Electricite Du Laos (EDL) and then sold to EGAT by EDL. Price of electricity bought by this way is single price. The HPP can obtain the maximum profit by maintaining high water level and adopting run-of-river power generation. Considering the above two power supply methods that might be adopted, design of the project scale at this stage (mainly involving minimum operating level) is carried out on the basis of method I. If method II is adopted when hydropower station is built up, only the operation mode of the reservoir needs to be changed (i.e. water level drawdown of the reservoir doesn't appear in day time and run-of-river power generation is adopted for the HPP). 4.3 Calculation of Water Resources and Energy Economy Analysis on Influence of Upstream Reservoirs on Runoff at Paklay Damsite Analysis on Influence of Reservoirs of Lancang River Main Stream on Runoff at Paklay Damsite a) Hydropower Planning and Development Overview for Middle-lower Reaches of Lancang River The development plan of "two reservoirs and eight cascades" is adopted for hydropower planning of middle-lower reaches of Lancang River, i.e. the development plan for two regulating reservoirs (Xiaowan and Nuozhadu) and eight cascades of hydropower stations including Gongguoqiao, Xiaowan, Manwan, Dachaoshan, Nuozhadu, Jinghong, Ganlanba and Mengsong. The regulating capacity and total installed capacity of these eight cascade projects are 22,150 million m 3 and 16395MW, respectively. According to the latest results, main parameters of cascade hydropower stations in middle-lower reaches of 4-20

23 Lancang River are shown in the Table Table Main Parameters of Cascade Hydropower Stations in Middle-lower Reaches of Lancang River Item Rain collection area at damsite Average annual flow Annual average runoff volume Unit Gongguoqiao Xioawan Manwan Dachaoshan Nuozhadu Jinghong Ganlanba Mengsong 10 3 km m 3 /s m Normal pool level m Minimum pool level Regulating storage Regulation capability Installed capacity Average annual energy Current development status Year of completion m m Daily regulation Multi-year Weekly Weekly Multi-year Weekly Daily regulation regulation regulation regulation regulation regulation Run-of-river MW kwh Completed Completed Completed Completed Completed Completed Feasibility study Planning At present, construction of all the cascade hydropower stations except Ganlanba and Mengsong in the middle-lower reaches of Lancang River is completed. In the above eight-cascade development plan, Xiaowan and Nuozhadu Reservoirs are of multi-year regulation type and their total regulation capacity is billion m³, playing a major role in regulating and storing the downstream cascade runoff into reservoir. The control catchment areas at Xiaowan and Nuozhadu damsites are 113,300 km 2 and 144,700 km 2 respectively, accounting for 40.4% and 51.6% of the control catchment area (280,500 km 2 ) of Paklay HPP; the annual average runoff volumes of the damsites are billion m 3 and billion m 3, accounting for 30% and 43.1% of the annual average runoff volume (128 billion m 3 ) of Paklay HPP, playing a major role in regulating the downstream cascade runoff into reservoir. 4-21

24 Located at the middle reach of Lancang River, Xiaowan Hydropower Station is the second cascade in the hydropower planning of "two reservoirs and eight cascades" of middle-lower reaches of Lancang River with Gongguoqiao Hydropower Station in the upstream and Manwan Hydropower Station in the downstream. The control catchment area at the damsite is 113,300 km 2, with an annual average discharge of 1,220 m³/s. The Hydropower Station is mainly developed for power generation, but it is also used for such comprehensive purposes as flood control, irrigation, sediment retaining and shipping. With normal pool level of 1240m, minimum pool level of 1166m and regulation capacity of billion m 3, the Reservoir has a multi-year regulation capacity. The installed capacity of the Hydropower Station is 4200MW (6 700MW) and the design average annual energy is 19 billion kwh. Construction of main body of the Project began in January 2002; gate closing for impounding began in December 2008; all the units were put into operation in August Nuozhadu Hydropower Station is located in the lower reach of Lancang River and is the fifth cascade in the hydropower planning of "two reservoirs and eight cascades" of middle-lower reaches of Lancang River with Dachaoshan Hydropower Station in the upstream and Jinghong Hydropower Station in the downstream. The control catchment area at the damsite is 144,700 km 2, with an annual average discharge of 1,750 m³/s. The Hydropower Station is mainly developed for power generation, but it is also used for such comprehensive purposes as urban and rural flood control, navigation improvement and tourism development of Jinghong City. The Reservoir has multi-year regulation capacity with normal pool level of 812m, limiting level during flood season of 804m, minimum pool level of 765m and regulating capacity of billion m 3. The installed capacity of the Hydropower Station is 5850MW (9 650MW) and the design average annual energy is billion kwh. Construction of main body of the Project began in January 2006; gate closing for impounding began in November 2011; all the units were put into operation in June b) Analysis on Influence of Reservoirs of Middle-lower Reaches of Lancang River on Runoff at Paklay Damsite Long series of monthly runoff data of 46 years from January of 1960 to December of 2005 is used to analyze the influence on runoff at Paklay HPP damsite by the regulation and storage of reservoirs (mainly are Xiaowan and Nuozhadu) in the middle-lower reaches of the Lancang River. After considering the regulation and storage of reservoirs in the 4-22

25 middle-lower reaches of Lancang River, the statistical results for long series of monthly average discharge at Parlay Hydropower Station damsite are shown in Table , comparison of monthly average discharge is shown in Figure , and comparison of dependability curve of monthly average discharge is shown in Figure Month Table Statistical Results for Long Series of Monthly Average Discharge at PakLay Damsite Unit: m 3 /s Natural Condition Considering Reservoir Regulation and Storage in the Middle-lower Reaches of Lancang River Discharge Difference Value Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Mean

26 Figure Comparison of Monthly Average Discharge at Damsite of Paklay HPP Figure Comparison of Dependability Curve of Monthly Average Discharge at Damsite of Paklay HPP As shown in the Table , the average discharge at Paklay damsite is consistent with that under the natural conditions after considering the reservoir storage-regulation 4-24

27 influence in middle-lower reaches of Lancang River. However, the annual discharge distribution varies very much; the average discharge in the flood season (June to October) will decrease by about 14%, and the average discharge in the dry season (December to May of the next year) will increase by about 50%. This indicates that the Xiaowan Reservoir and Nuozhadu Reservoir play an obvious part in regulating the reservoir inflow of Paklay HPP Analysis on Influence of Reservoirs at Tributaries of Laos Mekong River on Runoff at Paklay Damsite There are 25 hydropower stations (including the already completed stations, the stations under construction, and the stations planned to be built (CA agreement already signed)) at the tributaries of the Mekong River in the upstream of Paklay according to the drawing of Hydropower Project Sites published by the Department of Energy Business of Ministry of Energy and Mines of Laos in January of Please refer to Table for the basic information of these 25 hydropower stations. Among the above 25 hydropower stations, three have yearly or overyear regulation performance and have a total regulation capacity of million m 3, i.e., the Nam tha1, Nam OU7 and Nam Khan2 Hydropower Stations. These reservoirs, after the completion, will play a certain role in regulating the reservoir inflow of Paklay HPP, decreasing the average discharge of Paklay HPP in the flood season (June to October), and increasing the average discharge in the dry season (December to May of the next year). We cannot evaluate the influence of these reservoirs on the runoff at the damsite of Paklay HPP quantitatively and in detail for we have not collected the detailed information on them. From our point of view, the discharge in the flood season at Paklay HPP will decrease and that in the dry season will increase after the reservoirs at the tributaries are completed on the basis of overall trend analysis. This will be beneficial to the increase of power generation benefit of the HPP. 4-25

28 Table Summary Sheet for Situations of Main Hydropower Stations at Tributaries of Upstream Mekong River of Paklay Project Name Damsite Minimum Control Damsite Average Normal Regulating Design Installed Pool Unit Construction Catchment Annual Flow Pool Level Storage Head Capacity Area (m 3 Level /s) (m) (10 6 m 3 Quantity Status ) (m) (MW) (km 2 (m) ) Nam Long Completed Nam pha CA signed Nam Ngon Completed Nam tha3 Completed Nam tha Under construction Nam Ngao CA signed Nam Beng Completed Hongsa litnite Completed Nam OU CA signed Nam OU Under construction Nam OU Under construction Nam OU CA signed Nam phak To be built before 2020 Nam phak To be built before

29 Project Name Damsite Minimum Control Damsite Average Normal Regulating Design Installed Pool Unit Construction Catchment Annual Flow Pool Level Storage Head Capacity Area (m 3 Level /s) (m) (10 6 m 3 Quantity Status ) (m) (MW) (km 2 (m) ) Nam phak To be built before 2020 Nam ko Completed Nam OU CA signed Nam OU Completed Nam Nga Under construction Nam Nga To be built before 2020 Nam OU CA signed Nam Khan Completed Nam Khan Under construction Nam dong Completed Nam houg1 Under construction Note: The data in the table are provided by the Ministry of Energy and Mines of Laos, and many data which should be filled in the blank are not provided. 4-27

30 4.3.2 Runoff Regulation Calculation Premises and Methods of Calculation The Paklay HPP is the 4 th cascade hydroelectric station on the mainstream of the Mekong River, planned from top to bottom. The Sayaboury HPP is the upstream connection cascade of the Paklay HPP and the Sanakham HPP is the downstream connection cascade of the Paklay HPP. According to results of Mekong River Mainstream Hydropower Planning, the Sayaboury HPP, the Luang Prabang HPP and the Pak Beng HPP planned at the upper reaches of the Paklay HPP are all non-regulating or daily regulation run-of-river hydroelectric stations, nearly free from regulation performance. At the middle and lower reaches of Lancang River in China, there are 8 cascades of hydroelectric stations, including the Gongguoqiao HPP, Xiaowan HPP, Manwan HPP, Dachaoshan HPP, Nuozhadu HPP, Jinghong HPP, Ganlanban HPP, and Mengsong HPP. The Xiaowan Reservoir and Nuozhadu Reservoir are of the overyear regulating reservoir, with a total effective storage of about x 10 9 m 3. At present, both of them have been completed and put into operation. The Xiaowan dam site and Nuozhadu dam site respectively have a controlled drainage area of x 10 3 km 2 and x 10 3 km 2, accounting for 40.4% and 51.6% of the controlled drainage area (280.5 x 10 3 km 2 ) of the Paklay HPP. The dam sites respectively have a mean annual runoff of x 10 8 m 3 and x 10 9 m 3, accounting for 30% and 43.1% of the mean annual runoff (128 x 10 9 m 3 ) of the Paklay HPP. The above two dam sites have relatively strong regulating function on runoff into the reservoir of the Paklay HPP. Therefore, runoff regulation calculation for the Paklay HPP in this stage shall take impact of regulation and storage of the Xiaowan Reservoir and Nuozhadu Reservoir at the upper reaches into consideration. The Sayaboury HPP is the upstream connection cascade of the Paklay HPP and the Sanakham HPP is the downstream connection cascade of the Paklay HPP. Construction of the Sayaboury HPP commenced in 2012, and the Pak Beng HPP, Luang Prabang HPP, Paklay HPP and Sanakham HPP are all under preliminary works at present. Feasibility study reports (FSR) of the Pak Beng HPP and Sanakham HPP have been finished and assessed and approved by Lao Government. According to current analysis of preliminary 4-28

31 works, the Sanakham HPP will be completed and put into operation prior to those of the Paklay HPP. Therefore, runoff regulation calculation for the Paklay HPP shall take jacking impact from the Sanakham reservoir backwater on the tail water level of the Paklay HPP into consideration. Because the Paklay HPP is a daily regulation hydroelectric station, in principle, long series of daily runoff data shall be used for runoff regulation calculation. However, due to limitation of data, runoff regulation calculation in this stage shall be based on long series of monthly runoff data. Energy output difference shall be corrected based on the calculation results of monthly and daily runoff regulation in 5 representative years. Specific calculation method is as follows: 1) Based on the long series of monthly runoff data of the HPP Dam Site, runoff regulation calculation is carried out to obtain the average annual energy output of the HPP. 2) Based on daily and monthly average discharge data in 5 representative years of the HPP Dam Site, including a wet year (P=10%), relatively wet year (P=25%), normal year (P=50%), relatively dry year (P=75%) and dry year (P=90%), runoff regulation calculation is respectively carried out to obtain the weighted average energy output of 5 representative years corresponding to the daily runoff data and that corresponding to the monthly runoff data. 3) Based on the weighted average annual energy output obtained as per the daily and monthly runoff data in 5 representative years, the energy output correction factor is obtained via calculation. 4) The above energy output correction factor is used for correcting the average annual energy output obtained based on the long series of monthly runoff data in step 1. And the corrected calculation results will be the final design result of the average annual energy output of the HPP Basic data and calculating parameter a) Runoff The long series of monthly runoff data of the HPP Dam Site shall use the runoff date from January 1960 to December 2005, 46 years in total. Average annual discharge of the 4-29

32 natural runoff is 4,090 m 3 /s. The daily and monthly average discharge in representative years shall use the runoff data in the following 5 years: Wet year (P=10%): January 1, 2000 ~ December 31, 2000; Relatively wet year (P=25%): January 1, 1980 ~ December 31, 1980; Normal year (P=50%): January 1, 1990 ~ December 31, 1990; Relatively dry year (P=75%): January 1, 1986 ~ December 31, 1986; Dry year (P=90%): from January 1, 1989 to December 31, See Table for statistical results of each monthly average discharge in 5 representative years and long series of each monthly average discharge in many years of the Paklay HPP Dam Site. Month Table Results of Monthly Average Discharge in Representative Years and Long Series of Monthly Average Discharge of the Paklay Dam Site Unit: m 3 /s Considering Regulation and Storage of Natural Condition Discharge Difference Xiaowan and Nuozhadu Reservoirs Long Series 5 Representati ve Years Long Series 5 Representative Years Long Series 5 Representati ve Years Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Annual average As shown in Table , the average annual discharge of 5 representative years in the natural conditions column is 4,050 m 3 /s that is basically in conformity with the average annual discharge (4,090 m 3 /s) of long series in the same column. After impact from 4-30

33 regulation and storage of the Xiaowan Reservoir and Nuozhadu Reservoir is considered, average discharge of the Paklay Dam Site in flood season will reduce by about 15% while average discharge in dry season (December to Next May) may increase by about 50%. This means that the Xiaowan Reservoir and Nuozhadu Reservoir have obvious regulation function for reservoir inflow of the Paklay HPP. See Figure for dependability curve contrast of the monthly average discharge under natural conditions and the monthly average discharge under consideration of impact of regulation and storage at the Paklay Dam Site. Figure Dependability Curve Contrast for Monthly Average Discharge at the Paklay Dam Site b) Curve of reservoir level - area - storage In this stage, according to measured profile data of mainstream and tributary of the reservoir area, curve of reservoir level - area - storage shall be calculated as per method of section. See Figure for corresponding results. 4-31

34 Figure Curve Graph of Reservoir Level - Storage - Area of Paklay HPP c) Stage-Discharge Relation Curve of Downstream Side of Dam Site The Paklay HPP is of a powerhouse at dam-toe; therefore, stage-discharge relation of the powerhouse site is equal to that of lower dam site. Feasibility study design of the Sanakham HPP, downstream connection cascade of the Paklay HPP, has been finished by HYDROCHINA Northwest Engineering Co., Ltd. (hereinafter referred to as "Northwest Institute"). Based on results of feasibility study design, the reservoir has no regulation performance and has a normal pool level of m a.s.l. Preliminary works of the Sanakham HPP are ahead of those of the Paklay HPP, so it will be completed and put into operation prior to those of the Paklay HPP. During feasibility study period, results of jacking impact from the Sanakham reservoir backwater (water level in front of dam is m a.s.l.) provided by the Northwest Institute shall be applied to the stage-discharge relation curve of lower Paklay Dam Site. Comparison of the above curve with the stage-discharge relation curve under natural conditions at Paklay HPP is shown in Figure

35 Figure Curve Contrast Graph of Stage-Discharge Relation of Lower Paklay Dam Site d) Non-generating water consumption and water loss The Paklay HPP is provided with facilities such as navigation lock and fishway; therefore, some water needs to be discharged during operation. The Paklay Reservoir is designed to be navigable for ships with a tonnage of 500 t. Corresponding effective sizes of a navigation lock are 120 m x 12 m x 4 m (length x width x sill water depth). A navigation lock is considered to operate 21 h a day, its lockage time is considered to be 39.2 min every time and it has a water consumption discharge of about 7.94 m 3 /s under consideration of water loss. Water consumption for a fishway is about 3.23 m 3 /s by reference to similar engineering experience. In addition, water loss, such as reservoir evaporation and leakage, and results of feasibility study design of the Sayaboury HPP at the upper reaches shall be considered. In this way, the non-generating water consumption and water loss for runoff regulation calculation in this stage shall be considered as 15 m 3 /s. e) Other calculating parameters 1) The Paklay HPP is a low-head hydroelectric station, with a powerhouse at dam-toe, short passage and slight head loss. According to design results in this stage, its 4-33

36 average head loss shall be 0.5 m. considered. 2) For runoff regulation calculation, expected output limit of units shall be 3) The HPP is preliminarily proposed to adopt bulb through flow turbines, characterized by relatively wide high efficiency area and relatively high unit efficiency; therefore, the HPP has a comprehensive output factor of Calculation method for equivalent energy In this stage, it is considered that the Paklay HPP will supply power to Thailand in accordance with the method stated in Section According to relevant provisions stipulated by Electricity Generating Authority of Thailand (EGAT), various power purchase policies will be issued based on different power generation durations, including primary energy, secondary energy and excess energy. Power generation duration and electricity price policy of each type of energy are listed in Table Table Power Generation Duration and Electricity Price Policy of Primary Energy, Secondary Energy and Excess Energy Item Duration Purchase Policy Electricity Price Primary energy (PE) Secondary energy (SE) Excess energy (EE) 16 h/day (6 days/week) 5.35 h/day (7 days/week) Plus 16 h/day (1 day/week) Other duration except that of PE and SE 4-34 Guarantee to purchase 100% energy Guarantee to purchase 100% energy No guarantees Pay 100% of agreed electricity price Pay 60% of PE electricity price Pay 55% of PE electricity price According to the electricity price policies in Table , the energy that EGAT guarantees to purchase as per the agreed price is primary energy x secondary energy (PE x SE), which is the equivalent energy ensuring the Paklay HPP can obtain its economic benefits. In this stage, during calculation of daily runoff regulation in 5 representative years, impounding and discharging process of reservoir daily regulation is stimulated, with the maximum equivalent energy as the target. Priority of reservoir impounding and discharging reflects relative values of the PE, SE and EE. Sequence of power generation is that PE shall be the first one, followed by the SE and then the EE. According to calculation results of operation stimulation of daily power generation in

37 5 representative years, percentages of the PE, SE and EE to the total energy output in 5 representative years can be respectively obtained. The obtained statistical results are multiplied by the long series of average annual energy output obtained as per the calculation method stated in Section , in order to obtain the average annual PE, SE, EE and equivalent energy of the Paklay HPP Runoff regulation calculation results According to the above calculation premises and methods, basic data and calculating parameters, runoff regulation calculation is respectively carried out for the option of normal pool level, the option of minimum pool level, and the option of installed capacity of the Paklay HPP. See relevant sections for details of the calculation results Flood Regulation Calculation Flood design standard Paklay HPP, with a total storage capacity of 904 million m 3 /s and installed capacity of 770MW, is designed with such main structures as water retaining dams, powerhouses, ship locks and other grade 2 structures as well as grade 3 secondary structures. The effective dimension of lock chamber is m m 4.00 m, which is similar to that of China's Grade IV navigation lock; the lower lock head and lock chamber are grade 2 structures; the guide structure and berthing structure are designed as grade 4 structures. For structures such as water retaining structures, water release structures and run-of-river powerhouses, the design standard of flood control for normal application is based on a 2000-year return period and that for special application is based on a year return period. For the energy dissipation and anti-scour structures, the design standard of flood control for normal application is designed as per 100-year return period flood. The flood control standard for downstream guide wall and retaining wall shall be consistent with that for the energy dissipation and anti-scour structures Design Flood and Flood Releasing Structures Carry out flood regulating calculation based on flood at the damsite. According to the hydrological analysis and calculation at this stage, results of peak discharge of design flood 4-35

38 at Paklay damsite are shown in Table The design flood process is described in hydrological chapters of the report and the flood is the typical flood of September Table Results of Peak Discharge of Design Flood at Paklay Damsite Qm: m 3 /s Item P(%) Qm At the flood discharge dam section, 11 open-type high-level surface bays, 3 low-level surface bays and 2 sediment releasing bottom outlets are provided. The dimension of the high-level surface bay is 16m 20m (width x height). The weir is of WES practical type with top elevation of m. The dimension of the low-level surface bay is 16m 28m (width x height) and the base plate elevation is 212m. The dimension of the sediment releasing bottom outlet is 10m 10m (width x height) and the base plate elevation is 205m. Discharge capacity curve of the pivotal Paklay HPP is shown in Table Upper water level (m) Table Discharge Capacity Curve of Pivotal Paklay HPP Discharge by Discharge by Discharge by high-level surface low-level surface bottom outlets bays bays (m3/s) (m3/s) (m3/s) Total discharge (m3/s)

39 Water Level (m) Discha rge Flow (m 3 /s) Water Level (m) Discha rge Flow (m 3 /s) Flood Regulation Principles and Calculation Results a) Flood Regulation Principles The Paklay HPP is a low-head runoff type hydropower station. To lower the impact of reservoir inundation and to facilitate reservoir scouring, natural flow conditions shall be resumed as much as possible during flood season, and the water level of reservoir shall be close to the natural water level as much as possible. We propose the following operation mode of the reservoir during the flood period according to this principle and taking the characteristics of the water and sediment inflow of Paklay HPP into consideration: When the predicted water inflow is greater than the discharge 6,100m 3 /s under the full power of the generating unit and less than 16,700m 3 /s, the discharge can be controlled according to the condition that the outflow is equal to the inflow, the generating set generates the electricity as per flow under full power, the redundant flow can be discharged via opening the flood releasing facilities, and the water level of the reservoir keeps at the normal pool level 240m.When the water inflow is greater than 16,700m 3 /s and the predicted subsequent water inflow will continue to increase, the flood releasing facilities shall be opened cascade by cascade until all of them are opened fully. The hydroproject shall discharge fully as per discharge capacity, the water level of the reservoir goes down naturally, and when the net head is lower than the minimum power generation head of the units, the HPP shuts down. In the flood recession limb, when the water inflow is less than 16,700 m 3 /s and the predicted subsequent water inflow will continue to decrease, the flood releasing facilities shall be closed cascade by cascade, and the water level of the reservoir will restore to the normal pool level 240m. When the net head is higher than the minimum power generation head of the units, the generation of the power station restores. 4-37

40 In the flood season, when the water inflow is greater than 16,700m 3 /s and the predicted subsequent water inflow will continue to increase, the flood releasing facilities shall be opened cascade by cascade until all of them are opened. The water level of the reservoir will drop gradually from 240m. During this process, the opening speed and the opening degree of the flood gates should be adjusted reasonably according to the flood prediction and the discharge change rate of the hydroproject should be controlled. Similarly, at the flood recession limb, when the water inflow is less than 16,700 m 3 /s and the predicted subsequent water inflow will continue to decrease, the flood releasing facilities shall be closed cascade by cascade until the water level of the reservoir reaches the normal pool level 240m. The discharge change rate of the hydroproject should also be controlled during this process. The principles for outflow discharge control during the process of emptying out and restoring the reservoir in the flood season are as follows: 1) Ensure that the variation speed of the reservoir water level is not so fast as to affect the stability of reservoir bank; 2) Ensure that the variation amplitude of the downstream water level caused by the unsteady flow is not so large as to affect the stability of downstream embankment, shipping and water for other purposes; 3) In addition, it is necessary to avoid the inundation of downstream banks due to the increase of outflow discharge, and especially avoid the effect on Paklay County. At this stage, taking the characteristics of both the reservoir and water inflow of the Paklay HPP into consideration, according to the control principles mentioned above and taking the maximum daily variation range of 3m/d as the control condition, it is proposed preliminarily that the outflow discharge should be controlled with a speed which is 1,600m 3 /s greater than the inflow until complete discharge with full opening of the gates is realized; that the outflow discharge should be controlled with a speed 1600m 3 /s lower than the inflow until the water level of the reservoir restores to the normal pool level of 240m during the restoring process. The outflow discharge shall be controlled in this mode according to the flood regulating calculation on the design flood of various frequencies; the maximum daily variation amplitude of the reservoir water level can be controlled within 3m/d, and the corresponding maximum daily variation amplitude of the downstream water level will be within 2.2m/d. b) Flood Regulation Calculation Results 4-38

41 Carry out flood regulation calculation on design flood at damsites of various frequencies of Paklay HPP according to the abovementioned flood regulation principles, basic data and the typical flood process of September The regulation results for floods of 100-year return and above are shown in Table while the flood regulation process is shown in Figure ~ Figure Table Results of Flood Regulation Calculation for Paklay HPP Item Unit P=0.01% P=0.02% P=0.05% P=0.1% P=0.2% P=0.5% P=1% Maximum reservoir inflow Maximum water level in front of dam Maximum reservoir storage Maximum outflow discharge Maximum downstream water level m 3 /s m m m 3 /s m According to the Table , when the flood regulation calculation is conducted based on the typical flood process of September 2000, the maximum water level in front of the dam for design flood of Paklay HPP (P=0.05%) is m and the maximum water level downstream the dam is m; the maximum water level in front of the dam for check flood (P=0.01%) is m and the maximum water level downstream the dam is m. Paklay reservoir has relatively small storage and limited regulation performance, and the actual flood process has uncertainty and may be different from the typical design flood to a certain degree. Therefore, in dam safety design, both the design flood level and check flood level of the dam are derived from discharge capacity curve based on peak discharge. The derived design flood level of the dam is m (P=0.05%, 34700m3/s) and check flood level of the dam m (P=0.01%, 38800m3/s). 4-39

42 Figure Flood Regulating Process Chart for Frequency at P=0.01% (Typical Example in September 2000) Figure Flood Regulating Process Chart for Frequency at P=0.02% (Typical Example in September 2000) 4-40

43 Figure Flood Regulating Process Chart for Frequency at P=0.05% (Typical Example in September 2000) Figure Flood Regulating Process Chart for Frequency at P=0.1% (Typical Example in September 2000) 4-41

44 Figure Flood Regulating Process Chart for Frequency at P=0.2% (Typical Example in September 2000) Figure Flood Regulating Process Chart for Frequency at P=0.5% (Typical Example in September 2000) 4-42

45 Figure Flood Regulating Process Chart for Frequency at P=1% (Typical Example in September 2000) 4.4 Selection of Normal Pool Level Preparation of Scheme The normal pool level of the Paklay HPP is a crucial parameter for project scale and benefits. Therefore, factors such as power generation benefits of the HPP, reservoir inundation, navigation requirements, and rational cascade connection shall be taken into consideration for its options. The Sayaboury HPP is the upstream connection cascade of the Paklay HPP. According to the results of feasibility study design of the Sayaboury HPP, the normal pool level at the lower dam site is about m a.s.l. and the downstream water level corresponding to full-capacity power generation discharge is about m a.s.l. According to the 1994 Planning, the proposed reservoir normal pool level of the Paklay HPP is m a.s.l., which overlaps with the head of the Sayaboury HPP for about 6 m. This scheme has a large impacted population related to reservoir inundation. In terms of rational cascade connection and reservoir area inundation, the original water level is too high; therefore, this scheme is impracticable. In September 2009, CNR submitted results of optimization study on cascade water 4-43

46 level, which recommended that the Paklay HPP shall have a normal pool level of m a.s.l. ~ m a.s.l. In terms of cascade connection, the normal pool level ( m a.s.l.) is equal to the normal pool level at lower dam site of the Sayaboury HPP, which can not only rationally and fully take advantage of water power resources of the whole river reach, but also meet the navigation connection requirements under consideration of backwater of the Paklay reservoir area. Therefore, this normal pool level is relatively acceptable. In addition, when the normal pool level of the Paklay Reservoir lowers to m a.s.l., the corresponding reservoir inundation impact will be slighter than that of original proposed normal pool level ( m a.s.l.); when the normal pool level lowers to m a.s.l., the corresponding inundation index will be of no essential distinction with that of normal pool level ( m a.s.l.). In conclusion, rising of the normal pool level to be m a.s.l. is a better choice in terms of technology. However, due to many reasons, Ministry of Energy and Mineral Resources of Laos officially inform the Paklay HPP Employer that the normal pool level of the Paklay Reservoir shall not be greater than m a.s.l. in The informed water level is equal to the average water level at the lower dam site of the Sayaboury HPP in dry season. In terms of power generation connection or navigation connection, the informed water level is low. Due to compulsive demand of Laos Government, in this stage, the Paklay HPP is designed as per the normal pool level of m a.s.l. Upon technical analysis, rising of the normal pool level to be m a.s.l. will be in favor of the energy index of the Paklay HPP. To objectively reflect the impact on the energy and economic indexes of the Paklay HPP from rising of the normal pool level, in this stage, in addition to calculation and analysis of the normal pool level of m a.s.l., another two normal pool levels ( m a.s.l. and m a.s.l.) will be used for comparison, in order to objectively reflect advantages and disadvantages of the three options in terms of technology and economic benefit Other Matching Parameters Preliminarily Proposed a) Minimum pool level Minimum pool level of each scheme is proposed as per principle of maximum energy benefits (namely, maximum equivalent energy). Upon analysis and calculation, when the reservoir drop in level of the Paklay HPP is 1 m, its energy benefits will be the maximum value. Therefore, in consideration of the drop in level of 1 m, minimum pool levels corresponding to the scheme involving the normal pool level of m a.s.l. (the

47 m scheme), the scheme involving the normal pool level of m a.s.l. (the m scheme) and the scheme involving the normal pool level of m a.s.l. (the scheme) will respectively be m a.s.l., m a.s.l. and m a.s.l. b) Installed capacity The Paklay HPP is proposed to supply power to Thailand. According to the results listed in Table , the annual operating hours of the maximum load of Thailand's power system in recent years are above 6,500 h, which indicates that the electrical load of Thailand is relatively balanced. Power demands of the power grid are focused on electric energy. The Paklay HPP is a daily regulation hydroelectric station. It is subject to daily peak regulation operation only in dry season. At most times, it is subject to base load operation. In view of power demand characteristics in Thailand, the annual operating hours of installed capacity should not be too low. In terms of design results of each cascade HPP at the upper and lower reaches, the annual operating hours of installed capacity shall be about 5,500 h. Therefore, the m scheme, the m scheme and the m scheme will be proposed to have installed capacities of 770 MW, 860 MW and 950 MW respectively based on the annual operating hours of installed capacity of about 5,300 h ~ 5,500 h. c) Unit type, quantity, rated head The m scheme, the m scheme and the m scheme respectively have the maximum head of 20 m, 22 m and 24 m, based on bulb through flow turbines. According to current design and manufacturing level of this unit type, the unit capacity shall not be greater than 550 MW and quantity of units shall respectively be 14, 16 and 18. Under the premise that power generation at the full installed capacity will not be disabled at the normal pool level, a rated head shall be preliminarily proposed as per a head dependability of 85%. Therefore, the m scheme, the m scheme and the m scheme respectively have a rated head of 14.5 m, 16.5 m and 18.5 m Analysis of Impact on Scale of Waterway at Reservoir Head from 240 m Scheme According to provisions of Preliminary Design Guidance for Proposed Mainstream Dams in the Lower Mekong Basin developed by Mekong River Commission (MRC), after 5 HPPs along the Mekong River Mainstream in Laos are completed, the corresponding waterway will be channelized, so as to promote development of waterway of Lancang 4-45

48 River - Mekong River. The normal pool level (240 m a.s.l.) of the Paklay Reservoir is not properly connected with the normal pool level at lower dam site of the Sayaboury HPP, which is the upstream connection cascade. The river reach from the Paklay reservoir upstream end to lower dam site of the Sayaboury HPP is not completely channelized. Therefore, analysis shall be performed to the 240 m scheme to determine whether its waterway scale meets requirements of Preliminary Design Guidance for Proposed Mainstream Dams in the Lower Mekong Basin. According to requirements of Preliminary Design Guidance for Proposed Mainstream Dams in the Lower Mekong Basin, 5 HPPs along the Mekong River Mainstream in Laos shall all be provided with navigation locks so that ships can pass through their dams. It is recommended to design the navigation locks as per Grade-IV waterway standard in China. It is recommended to adopt a design representative ship form of 2 x 500t-ship fleet (109 m x 10.8 m x 2 m, length x width x design draft). According to the dimension of the fleet and by reference to provisions in Navigation Standard of Inland Waterway (GB ) of China, the dimension of the waterway for the fleet to navigate safely is considered to be 2.5m 50m 330m (depth of water x width of two-way waterway x bending radius). According to the results of feasibility study design of the Sayaboury HPP, its minimum navigation discharge at lower reaches shall be 1,000 m 3 /s. Therefore, the Report mainly involves calculation and analysis of water surface profiles of the river reach from reservoir upstream end of the Paklay HPP to lower dam site of the Sayaboury HPP under the condition that discharge flow of the Sayaboury HPP is 1,000 m 3 /s. The water surface profiles consist of a water surface profile under natural condition and a water surface profile under the condition that the Paklay HPP has a normal pool level of 240 m a.s.l. and a minimum pool level of 239 m a.s.l. Based on the above date, analysis is performed to determine whether the water depth and width of the river reach meet requirements of the above navigation scale. Results of water surface profiles from the Paklay HPP to lower dam site of the Sayaboury HPP under the condition that discharge flow of the Sayaboury HPP is 1,000 m 3 /s are listed in Table

49 Table Results of Water Surface Profiles from Paklay HPP to Sayaboury HPP S/N No. of Cross Section Accumulated Space Natural thalweg Q=1000m³/s Value Added in Comparison with Natural Water Level Natural Condition Water Level Water Level of Water Level of 239 m a.s.l. in Water Level of 240 m of m a.s.l. front of Paklay a.s.l. in m a.s.l. in front of Dam front of in front Paklay Paklay Dam of Paklay Dam Dam km m m m m m m 1 Paklay dam CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS

50 S/N No. of Cross Section Accumulated Space Natural thalweg Q=1000m³/s Natural Condition Water Level of 239 m a.s.l. in front of Paklay Dam Water Level of 240 m a.s.l. in front of Paklay Dam Value Added in Comparison with Natural Water Level Water Level of Water Level 239 m a.s.l. in of 240 m front of Paklay a.s.l. in Dam front of Paklay Dam km m m m m m m 36 CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS1-74 (Sayaboury dam site) As shown in Table , after Paklay Reservoir impounding, water level and depth 4-48

51 No. of Cross Section at the reservoir area will increase. In case the minimum navigation discharge flow of the Sayaboury HPP is 1,000 m 3 /s, when the water level in front of the Paklay Dam is 239 m a.s.l., water levels of each cross section in the reservoir area shall have the value added in comparison with natural water level of 4.16 m a.s.l.~ m a.s.l; when the water level in front of the Paklay Dam is 240 m a.s.l., water levels of each cross section in the reservoir area shall have the value added in comparison with natural water level of 4.93 m a.s.l.~ m a.s.l. According to backwater calculation results in this stage, the Paklay Dam Site ~ CS1-60 river reach is a perennial backwater area. After reservoir impounding, the river reach has a wide water surface, relatively deep water depth, slow water velocity, and waterway in good condition, which meets navigation requirements. CS1-60 ~ CS1-74 river reach (Sayaboury Dam Site) is a fluctuating backwater area with relatively narrow cross sections in some positions. Therefore, analysis of water depth and width of the cross sections shall be performed to determine whether the river reach meets requirements of waterway scale. According to calculation results of the water surface profile under natural condition and the water surface profile under the condition that the Paklay HPP has a normal pool level of 240 m a.s.l. and a minimum pool level of 239 m a.s.l., analysis results of maximum water depth and water body width corresponding to a water depth of 2.5 m of cross sections in CS1-60 ~ CS1-74 are listed in Table See Figures ~ for analysis results of water depth and water body width of narrow cross sections. Table Accumulated Space Natural thalweg Analysis Results of Water Depth and Water Body Width from Paklay HPP to Sayaboury HPP Water Body Width Corresponding to Water Maximum Water Depth (Q=1,000 m³/s) Depth of 2.5 m (Q=1,000 m³/s) Natural Conditio n Water Level of 239 m a.s.l. in front of Paklay Dam Water Level of 240 m a.s.l. in front of Paklay Dam 4-49 Natural Condition Water Level of 239 m a.s.l. in front of Paklay Dam Water Level of 240 m a.s.l. in front of Paklay Dam km m m m m m m m CS CS CS

52 CS CS CS CS CS CS CS CS CS CS CS CS As shown in Table , the following information can be obtained: a) In case the minimum navigation discharge flow of the Sayaboury HPP is 1,000 m 3 /s, under the natural condition the maximum water depth of each cross section (CS1-60 ~ CS1-74) at the Paklay reservoir upstream end is m ~ m; when the water level in front of the Paklay Dam is 239 m a.s.l., the maximum water depth of each cross section at the reservoir upstream end is m ~ m; when the water level in front of the Paklay Dam is 240 m a.s.l., the maximum water depth of each cross section at the reservoir upstream end is m ~ m. b) In case the minimum navigation discharge flow of the Sayaboury HPP is 1,000 m 3 /s, under the natural condition the water body width corresponding to a water depth of 2.5 m of each cross section at the Paklay reservoir upstream end is m ~ m, with some narrow river reaches which cannot meet the navigation width requirement (50 m); when the water level in front of the Paklay Dam is 239 m a.s.l., the water body width corresponding to a water depth of 2.5 m of each cross section at the reservoir upstream end is m ~ m; when the water level in front of the Paklay Dam is 240 m a.s.l., the water body width corresponding to a water depth of 2.5 m of each cross section at the reservoir upstream end is m ~ m; the latter two water body widths both meet the navigation width requirement (50 m). In conclusion, after Paklay Reservoir impounding, its water level rises and water surface widens, which will improve navigation conditions of river course in the reservoir area. For the 240 m scheme with the minimum pool level of 239 m a.s.l., the water depth 4-50

53 and width of the reservoir area both can meet the waterway scale requirements for 2 x 500t-ship fleet. Figure Cross Section (CS1-60) of Flow Graph of Paklay Dam Under Natural Condition Figure Cross Section (CS1-60) of Flow Graph Under Condition That Water Level in Front of Paklay Dam Is 239 m a.s.l. 4-51

54 Figure Cross Section (CS1-60) of Flow Graph Under Condition That Water Level in Front of Paklay Dam Is 240 m a.s.l. Figure Cross Section (CS1-63) of Flow Graph of Paklay Dam Under Natural Condition 4-52

55 Figure Cross Section (CS1-63) of Flow Graph Under Condition That Water Level in Front of Paklay Dam Is 239 m a.s.l. Figure Cross Section (CS1-63) of Flow Graph Under Condition That Water Level in Front of Paklay Dam Is 240 m a.s.l. 4-53

56 Figure Cross Section (CS1-64) of Flow Graph of Paklay Dam Under Natural Condition Figure Cross Section (CS1-64) of Flow Graph Under Condition That Water Level in Front of Paklay Dam Is 239 m a.s.l. 4-54

57 Figure Cross Section (CS1-64) of Flow Graph Under Condition That Water Level in Front of Paklay Dam Is 240 m a.s.l. Figure Cross Section (CS1-69) of Flow Graph of Paklay Dam Under Natural Condition 4-55

58 Figure Cross Section (CS1-69) of Flow Graph Under Condition That Water Level in Front of Paklay Dam Is 239 m a.s.l. Figure Cross Section (CS1-69) of Flow Graph Under Condition That Water Level in Front of Paklay Dam Is 240 m a.s.l Technological and Economic Comparison of the Schemes See Table for technological and economic comparison indexes for the m scheme, the m scheme and the m scheme. 4-56

59 Table Technological and Economic Indexes for Alternative Schemes of Normal Pool Level for Paklay HPP Item Unit Normal Pool Level Scheme 240m 242m 244m Normal pool level m Minimum pool level m Storage capacity at normal pool level 10 6 m Storage capacity at minimum pool level 10 6 m Effective storage 10 6 m Installed capacity MW Maximum head m Minimum head m Weighted average head m Rated head m Average annual energy output GW.h Primary energy (PE) GW.h Secondary energy (SE) GW.h HPP energy index Excess energy (EE) GW.h Equivalent energy (PE x SE) GW.h Annual operating hours of installed capacity h Total construction period Month Construction period for power generation of the first unit Month Project cost in hydroproject 4-57 million yuan Project cost per kilowatt yuan/kw Project cost per kilowatt hour (HPP itself) yuan/kw.h Average annual energy output (HPP itself) GW.h Impact on Sayaboury energy GW.h Average annual energy output (under consideration of impact GW.h on Sayaboury) Difference between schemes Equivalent energy GW.h Project cost in hydroproject Additional project cost per kilowatt Additional project cost per kilowatt hour (HPP itself) Additional Project cost per kilowatt hour (under million yuan yuan/kw yuan/kw.h yuan/kw.h

60 consideration of impact on Sayaboury) Note: The Project cost in hydroproject is obtained in the comparison and selection stage of options. As shown in Table 4.4.4, in terms of HPP energy indexes, as the normal pool level increases by every 2 m starting from 240 m a.s.l., the installed capacity of the HPP will increase by 90 MW, the average annual energy outputs will increase by GW h and GW h respectively, which are converted into equivalent energy of GW h and GW h respectively. Under consideration of impact on energy output of the Sayaboury HPP at the upper reaches, increase of average annual energy outputs shall be GW h and GW h respectively. Therefore, in terms of rational utilization of waterpower resources of river reaches, the schemes involving a higher normal pool level have obvious benefits. Upon investigation, the 240 m scheme of the Paklay HPP would inundate 789 households with a population of 3,545 and 127 hectares of farmlands and impact 448 people; when normal pool level fluctuates within 240 m a.s.l. ~ 244 m a.s.l., as the normal pool level increases, material index of reservoir inundation is slightly increased, but the increased number of impacted people would not exceed 1,192, and increased inundated farmland would not exceed 16 hectares. That is to say, these two schemes have no substantial differences. Difference between reservoir inundation impacts in each scheme has slight impact on selection of pool level. Impacts on environment by these two schemes are nearly the same. Upon navigation analysis, the normal pool level of 240 m a.s.l. is equal to the average water level of the lower dam site of the Sayaboury HPP in dry season, so the waterway is not fully connected. According to analysis made in Section 4.4.3, after reservoir impounding, water level, depth and width at the reservoir area will increase and water velocity will slow down, which can improve navigation conditions of river course. Therefore, in case the minimum navigation discharge flow of the Sayaboury HPP is 1,000 m 3 /s, for the 240 m scheme with the minimum pool level of 239 m a.s.l., the water depth and width at the reservoir area both can meet the waterway scale requirements for 2 x 4-58

61 500t-ship fleet. The higher the normal pool level is, the deeper the water is, the wider the water surface is, and the slower the water velocity is at the reservoir area. This is in favor of improving navigation conditions at the reservoir area. In terms of project construction conditions, both schemes have nearly the same topographical and geological conditions, hydroproject layout modes, dam types and construction layouts, free from obvious difference. The only difference is in the quantities, which has no restrictions on selection of normal pool level. In terms of construction period, construction period for power generation of the first unit is mainly subject to powerhouse concrete placing progress, while the total construction period is subject to unit installation progress. Because difference in powerhouse concrete placing quantities of each scheme is not obvious, and weir can be used for power generation during construction, difference in construction period of each scheme is not obvious. Construction period for power generation of the first unit shall be 36 months and total construction period shall be 78 months for all schemes. In terms of project cost and economic benefit, Project costs on hydroproject in three schemes involving different normal pool levels are respectively RMB x 10 9, RMB x 10 9, and RMB x 10 9 ; Project costs per kilowatt are respectively RMB 12,955/kW, RMB 12,132/kW and RMB 11,410/kW; Project costs per kilowatt hour (HPP itself) are respectively RMB 2.42/kW h, RMB 2.26/kW h and RMB 2.12/kW h. As the normal pool level gradually increases from 240 m a.s.l. to 244 m a.s.l., Project costs on hydroproject respectively increase by RMB 0.46 x 10 9 and RMB 0.41 x 10 9 ; additional Project costs per kilowatt are respectively RMB 5083/kW and RMB 4,511/kW; additional Project costs per kilowatt hour (HPP itself) are respectively RMB 0.91/kW h and RMB 0.81/kW h. Under consideration of impact on Sayaboury, the additional Project costs per kilowatt hour shall respectively be RMB 1.41/kW h and RMB 1.465/kW h, which are both lower than the Project costs per kilowatt and Project costs per kilowatt hour of the scheme. Therefore, in terms of economic investments, the scheme involving the normal pool level of 244 m a.s.l. would be a better choice. Nevertheless, only Project cost in the hydroproject 4-59

62 is involved in Table 4.4.3, free from differences of investment in compensation for reservoir inundation. In conclusion, as the normal pool level of the reservoir of the Paklay HPP gradually increases from 240 m a.s.l. to 244 m a.s.l., the project construction conditions do not change much, the environmental impact is basically the same, the people and farmlands impacted by reservoir inundation slightly increase, free from substantial difference. In terms of navigation condition, HPP energy index and economic investment, high normal pool level scheme has the advantage of improving navigation condition within the reservoir area with outstanding increase of power generation benefit and favorable economic benefit of investment. Therefore, in consideration of the comprehensive technological and economic comparison, the 244 m scheme is better than the 242 m scheme and the 242 m scheme is better than the 240 m scheme. However, in 2009, as Ministry of Energy and Mineral Resources of Laos requires that the normal pool level of the reservoir of the Paklay HPP shall not exceed m a.s.l., the m scheme will be adopted for design at this phase. 4.5 Selection of Minimum Pool Level According to electricity price policies of EGAT, electricity prices vary based on different power generation period; namely, the PE shall be purchased according to agreed electricity price, the SE shall be purchased by 60% of the agreed electricity price, and EE would not be guaranteed to purchase. Therefore, certain effective storage will be provided for the Paklay HPP so as to transfer the water consumed during the EE and SE periods to the PE period for power generation. This can greatly help to enhance equivalent energy and the power generation benefit of the hydroelectric station. However, the Paklay HPP is a low-head hydroelectric station with the maximum head of only 20 m. If the effective storage is too large, the energy output of the hydroelectric station would reduce greatly due to reduction of power generation head. According to initial analysis, the effective storage of the Paklay HPP should not be too large which would be appropriate if daily regulation performance of the hydroelectric station can be satisfied. The drop in level should not 4-60

63 exceed 2 m. Therefore, m a.s.l. would be the lower limit for scheme in this stage. Five schemes including m a.s.l., m a.s.l., m a.s.l., m a.s.l. and m a.s.l. with gradation of 0.5 m a.s.l. are proposed for comparison of minimum pool level. According to calculation results of sediment accumulation in reservoir in this stage, silt elevation in front of dam will not affect the comparison of minimum pool level. In addition, schemes involving all of the above minimum pool levels can meet requirements of layout of hydroproject according to topographical and geological conditions of the project dam site. If the difference between schemes involving various minimum pool levels is within 2 m, hydroproject layout scheme will be the same, and the project quantities and investment will basically be the same as well. Therefore, minimum pool level shall be mainly selected based on energy indexes of the project. See Table 4.5 for energy indexes of schemes involving various minimum pool levels. Table 4.5 Results of Energy Indexes of Schemes Involving Various Minimum Pool Levels Item Unit Minimum Pool Level Scheme m m m m m Normal pool level m Minimum pool level m Installed capacity MW Weighted average head m Average annual energy output GW h Primary energy (PE) GW h Secondary energy (SE) GW h Excess energy (EE) GW h Equivalent energy (PE x SE) GW h As a low-head hydroelectric station with a high discharge, regulation performance of the Paklay HPP is relatively poor. Its average annual energy output is mainly controlled by the power generation head. According to Table 4.5, as the minimum pool level rises, the weighted average head of the hydroelectric station increases, and the corresponding average annual energy output of the hydroelectric station increases progressively. The average annual energy output of the hydroelectric station increases by 39 GW h ~

64 GW h as the minimum pool level rises by every 0.5 m. However, on the other hand, after the minimum pool level rises, the effective storage of the reservoir will reduce, so the effective storage drops and the PE will decrease progressively. Impacted by both power generation head and effective storage, the scheme involving the minimum pool level of m a.s.l. has the maximum equivalent energy and better electric energy value. Therefore, it is recommended to select the minimum pool level of m a.s.l. for the Paklay HPP in this stage. 4.6 Selection of Installed Capacity Preparation of Installed Capacity Schemes The Paklay HPP is proposed to supply power to Thailand. According to the results listed in Table , the annual operating hours of the maximum load of Thailand's power system in recent years are above 6,500 h, which indicates that the electrical load of Thailand is relatively balanced. Power demands of the power grid are focused on electric energy. The Paklay HPP is a daily regulation hydroelectric station. It is subject to daily peak regulation operation only in dry season. At most times, it is subject to base load operation. In view of power demand characteristics in Thailand, the annual operating hours of installed capacity of the Paklay HPP should not be less than 5,000h. In addition, in terms of design results of each cascade hydroelectric station at the upper and lower reaches, the connection cascade hydroelectric stations at the upper and lower reaches are all run-of-river hydroelectric stations with annual operating hours of installed capacity of about 5,500h. In terms of cascade overflow capacity coordination and rational utilization of waterpower resources, the appropriate annual operating hours of installed capacity of the Paklay HPP shall be about 5,100 h ~ 5,700 h. Therefore, options of installed capacity shall be prepared respectively based on 5,100 h, 5,400 h and 5,700 h annual operating hours of installed capacity in this stage. The Paklay HPP has a maximum head of m, minimum head of 7.50 m, and weighted average head of about m. Corresponding to the above heads, a bulb through flow unit has the characteristics of high efficiency, large unit discharge, high unit 4-62

65 speed, small dimension, light weight, etc. In addition, it has advantages of economic investment in civil works, short construction period, good flexibility, ripe technology and wide application. Therefore, the bulb through flow unit is recommended for the HPP. Based on current design and manufacturing level of bulb through flow unit and combined with conditions of hydroproject layout, the unit capacity shall be 55 MW. Based on comprehensive consideration of the annual operating hours of installed capacity, unit capacity, condition of hydroproject layout, three installed capacity schemes, i.e. 715 MW (13 x 55 MW), 770 MW (14 x 55 MW) and 825 MW (15 x 55 MW), are proposed in this stage for technological and economic comparison. See Table for main parameters of units in each scheme. Table Main Parameters of Units in Each Installed Capacity Scheme Item Unit Installed Capacity Scheme 715MW 770MW 825MW Unit quantity Set Unit capacity MW Rated head m Rated discharge of single unit m 3 /s Rated total discharge m 3 /s Rated speed r/min Runner diameter m Unit speed r/min Technological and Economic Comparison of the Schemes See Table for results of technological and economic indexes in each installed capacity scheme. 4-63

66 Table Technological and Economic Indexes in Each Installed Capacity Scheme Installed Capacity Scheme Item Unit MW 825MW MW Waterpower index Economic indexes Normal pool level m Minimum pool level m Average annual energy output GW h Primary energy (PE) GW h Secondary energy (SE) GW h Excess energy (EE) GW h Equivalent energy (PE x SE) GW h Maximum head m Minimum head m Rated head m Weighted average head m Utilization ratio of water resource % annual operating hours of installed capacity h Difference of installed capacity MW Differenc e Average annual energy output GW h Primary energy (PE) GW h Secondary energy (SE) GW h Excess energy (EE) GW h Equivalent energy GW h Additional annual operating hours of installed capacity h Project cost in hydroproject 10 9 RMB Project cost per kilowatt Yuan/kW Project cost per kilowatt hour Yuan/kW h Project cost per kilowatt hour for equivalent energy Yuan/kW h Total project cost difference Million yuan Additional Project cost per kilowatt Yuan/kW Additional Project cost per kilowatt hour Yuan/kW h Additional Project cost per kilowatt hour for equivalent energy Yuan/kW h Note: The Project cost in hydroproject is obtained in the comparison and selection stage of options. In terms of HPP energy index, as the installed capacity gradually increases from 715 MW to 825 MW, the average annual energy output of the hydroelectric station respectively increases by 91.6 GW h and 70.3 GW h, with the amplification of 2.27% and 1.70%; the annual equivalent energy of the hydroelectric station respectively increases by 95.9 GW h 4-64

67 and 78.2 GW h, with the amplification of 2.82% and 2.24%; in addition, the additional annual operating hours of installed capacity are respectively 1,665 h and 1,277 h. As the installed capacity increases, power generation benefits of the hydroelectric station increases. In case the installed capacity increases from 715 MW to 770 MW, a relatively large annual increasing amplification of energy will be obtained. In terms of project cost, as the installed capacity increases, the Project cost per kilowatt of each installed capacity scheme decreases, but the Project cost per kilowatt hour increases. The 715 MW scheme has a relatively small Project cost per kilowatt hour and the 825 MW scheme has a relatively large Project cost per kilowatt hour. As the installed capacity increases from 715 MW to 770 MW, the additional Project cost per kilowatt hour shall be RMB 2.60/kW h that is slightly higher than the index of the scheme, but the additional Project cost per kilowatt hour for equivalent energy shall be RMB 2.48/kW h that is nearly equivalent to the index of the scheme; therefore, this installed capacity scheme has relatively good economic benefit. As the installed capacity increases from 770 MW to 825 MW, the additional Project cost per kilowatt hour shall be RMB 5.67/kW h that is higher than the index of the scheme, and the additional Project cost per kilowatt hour for equivalent energy shall be RMB 5.10/kW h that is higher than the index of the scheme; therefore, this installed capacity scheme has relatively bad economic benefit. In conclusion, in case installed capacity increases from 715 MW to 770 MW, the increase of energy benefit is obvious, and the additional Project cost per kilowatt hour is nearly equivalent to the index of the scheme; therefore, increase of installed capacity has favorable economic benefit. In case the installed capacity increases from 770 MW to 825 MW, the additional Project cost per kilowatt hour is relatively large; therefore, increase of installed capacity has poor economic benefit. For the cascade Sayaboury HPP connected at the upper reaches of the Paklay HPP, the installed capacity is 1,260 MW, the annual operating hours of installed capacity is 6,074 h, and the total rated discharge of the hydroelectric station is 5,000 m 3 /s. For the cascade Sanakham HPP connected at the lower reaches, the installed capacity is 660 MW, the annual operating hours of installed capacity 4-65

68 is 5,672 h, and the total rated discharge of the hydroelectric station is 5,500 m 3 /s. In view of long-distance power supply and overflow capacity regulation of the upstream and downstream connection cascade hydroelectric stations, adaptability of the 825 MW installed capacity scheme of the three proposed installed capacity schemes is relatively poor. The 770 MW installed capacity scheme is of relatively moderate indexes, with good adaptability. Therefore, 770 MW is the recommended installed capacity of the Paklay HPP in this stage. 4.7 Selection of Rated Head Maximum/Minimum Heads According to calculation result of daily runoff regulation for 5 representative years and considering about influence of backwater jacking of Sanakham at downstream, maximum and minimum heads of the Paklay HPP are m and 8.97 m respectively. As calculation of the runoff regulation cannot reflect extreme working conditions of the HPP, the calculated maximum and minimum heads cannot cover all possible operation scope of head. The maximum and minimum heads are determined as base for model selection and design of hydraulic turbine according to characteristics and possible operation modes of the Paklay HPP. Maximum head: normal pool level of the reservoir downstream water level corresponding to discharge of minimum technical output (i.e. output of half unit) of the unit corresponding head loss. The maximum head is taken as 20 m as the calculation result is approximate to 20 m. Minimum water head: For the Paklay HPP, the bulb type throughflow turbine is adopted with unit rated capacity of 55MW. According to the turbine characteristics and the water head of the hydropower station and through consultation with the unit manufacturer, 7.5m is taken as the minimum water head from the perspective of ensuring safe and stable operation of the unit. 4-66

69 4.7.2 Preparation of Scheme for Rated Head The Paklay HPP has the low head and large discharge, with a reservoir drawdown depth of only 1 m and relatively small change in reservoir water level. The power generation head of the HPP is closely related to the change of downstream water level. The Sanakham HPP is the downstream connection cascade of the Paklay HPP, with a normal pool level of m a.s.l., connecting with the normal pool level of the Paklay HPP. In view of impact from backwater jacking of the Sanakham HPP, change of the downstream water level of the Paklay HPP dramatically reduces. By calculation, the natural water level is raised by 7.67 m when discharge of dam site of Paklay increases from 920m 3 /s to 5,500m 3 /s under natural condition. Water level at downstream of the dam site is raised by 3.35 m when considering about influence of Sanakham backwater jacking. As variation of the downstream water level is relatively stable with change of the discharge, head scope of the Paklay HPP is centralized. Refer to Table and Fig for statistic of corresponding head of each dependability and curve of head dependability. Table Statistic of Corresponding Head of Each Dependability Head dependability 10% 20% 30% 40% 50% 60% 70% 80% 85% 90% Corresponding Head (m)

70 Figure Curve of Head Dependability of the Paklay HPP It can be inferred from Table and Fig that head scope of the Paklay HPP is mainly between m and m. The above head has duration of about 84% of the total duration, while head more than m and less than m composes 7% and 9% respectively. The Paklay HPP is a low-head hydroelectric station with a relatively poor regulating performance. The low head generally occurs in the flood period. Therefore, if the rated head is too high, the rated capacity will fail to be generated in the flood period. According to simulation results of Based on the power generation operation conditions at NPL and at full capacity of the HPP, in flood season, the reservoir water level of the Paklay HPP is basically kept at the normal pool level, with a the head corresponding to power generation at NPL and at full installed capacity is about m. Therefore, m is selected for the upper limit scheme at this stage. Three rated head schemes of m, m, and m are prepared to be compared. Refer to Table for main parameters of units of different schemes for rated head. 4-68

71 Table Main Parameters of Units of Different Schemes for Rated Head Scheme for Rated Head Item Unit 15.5 m 14.5 m 13.5 m Installed capacity MW Unit quantity Set Unit capacity MW Runner diameter m Rated discharge of single unit m 3 /s Rated total discharge m 3 /s 5,708 6,101 6,553 Rated speed r/min Unit speed r/min Output corresponding to minimum head of 7.5 m MW Technological and Economic Comparison of the Schemes Refer to Table for technological and economic indexes of each scheme for rated head. Table Technological and Economic Indexes of Each Scheme for Rated Head Scheme for Rated Head Item Unit 15.5 m 14.5 m 13.5 m Normal pool level m Minimum pool level m Installed capacity MW Parameters of the HPP Unit capacity MW Maximum head m Minimum head m Rated head m Energy index Weighted average head m Dependability of rated head Average annual energy output % GW h

72 Primary energy (PE) GW h Secondary energy (SE) GW h Economic indexes Excess energy (EE) GW h Equivalent energy (PE SE) Utilization ratio of water resource Annual operating hours of installed capacity Project cost in hydroproject GW h % h Million RMB Project cost per kilowatt Yuan/kw Project cost per kilowatt hour Project cost per kilowatt hour for equivalent energy Total project cost difference Yuan/kw h Yuan/kw h Million RMB By analyzing of energy indexes, installed capacity, unit quantity, and unit capacity under each rated head are the same. As the rated head reduces, diameter of turbine runner and rated discharge of single unit increase, and disabled generation capacity and probability of the unit reduce. When the rated head is reduced from 15.5 m to 14.5 m, use ratio of water yield of the HPP increases by 1.81% and annual generating capacity increases by 70.6 GWh; when the rated head is reduced from 14.5 m to 13.5 m, use ratio of water yield of the HPP increases by 1.45% and annual generating capacity increases by 62.6 GWh. Therefore, it can be inferred that as the rated head reduces, use ratio of water yield and annual generating capacity both increase, but with reducing growing rate. Judging from the project cost, as the rated head reduces, Project cost per kilowatt of each rated head scheme increases with an increasing growing rate, while Project costs per kilowatt hour of each rated head scheme are nearly the same, and investment of the scheme with rated head of 14.5 m is minimum. Project costs per KWH for equivalent energy of the schemes with rated heads of 15.5 m and 14.5 m are nearly the same and both are less than investment of the scheme with rated heads of 13.5 m. From the perspective of Project cost per kilowatt hour for equivalent energy, although reducing the rated head can increase 4-70

73 generating capacity of unit, economical efficiency of rated head that reduces from 14.5 m to 13.5 m is relatively poor. Judging from difficulty in unit manufacturing, unit capacities of each rated head scheme are all 55 MW. As the rated head reduces, diameter of unit runner increases. Judging from level of unit manufacturing, under same unit capacity, the rated head reduces more, the runner diameter and manufacturing difficulty increase more. Therefore, the rated head should not be too low. By comprehensive comparison, rated head of Paklay HPP at this stage is recommended as 14.5 m. 4.8 Selection of Type and Number of Units Selection of Unit Type The maximum head, minimum head, rated head, and weighted average head of Paklay HPP are m, 7.50 m, m, and about m. Head scope of the hydroelectric station is 7.5 m~20.0 m. Hydraulic turbine suitable for the head section includes axial flow type and through-flow type. The through-flow turbine consists of shaft-extension through-flow turbine, pit turbine, bulb through-flow turbine and rim-generator turbine. The shaft-extension through-flow turbine is available for the HPP with a runner diameter less than 3 m. The pit turbine is only available for conditions of low head and small capacity, with a maximum unit capacity of 3,000 kw and runner diameter of 3 m. The rim-generator turbine has an extra high requirement for the sealing technology; therefore, it is only applied to the small HPPs. The HPP has a medium unit capacity, with a runner diameter about of 6.90 m; therefore, the bulb through-flow turbine and axial flow turbine are selected for comparison. According to the installed capacity of the HPP, it is preliminarily proposed to use fourteen 55 MW bulb through-flow turbines and eight MW adjustable blade propeller turbines for comparison. Refer to Table for main parameters of the above two turbines. 4-71

74 Table Parameters for Comparison Schemes of Unit Type Description Bulb Through-flow Turbine Axial Flow Turbine Installed capacity (MW) Composition of installed capacity 14 55MW MW Turbine model GZ-WP-690 ZZ-LH-1020 Rated output of turbine (MW) Runner diameter (m) Rated speed (r/min) Rated discharge (m 3 /s) Unit discharge (m 3 /s) Efficiency at rated point (%) Weight of a single turbine (t) 756 1,550 Weight of a single generator (t) 460 1,150 Weight of a single unit (t) 1,216 2,700 Gross weight of unit in the whole plant (t) 17,024 21,600 Concluding from the above table and combining characteristics of the bulb through-flow turbine and axial flow turbine, generator set of bulb through-flow turbine used for the HPP has the following advantages: a) High efficiency. The bulb through-flow turbine has a straight and smooth passage, with relatively well-distributed flow fields; therefore, its hydraulic efficiency is relatively high and its high efficiency area is flat and wide. Optimum efficiency of a bulb through-flow turbine model is about over 1% higher than that of an axial flow turbine model, with HPP weighted average efficiency about over 2% ~ 3% higher. b) High unit parameter level of turbine. When the head is same, flow of bulb through-flow turbine is about 20%~40% higher than that of the axial flow turbine, that means the unit flow is 20%~40% higher as well. c) Because a bulb through-flow turbine has advantages of high parameter level, high rotate speed, small size, and light weight, total weight of units in the plant of this scheme is 4,576 t less than that of the scheme involving axial flow turbine. 4-72

75 d) Less investment on civil works. As level of parameters of the bulb through-flow turbine is high and dimension of the unit is small, space between units and length of the powerhouse are reduced, that is helpful for arrangement of the hydroproject. Although the installation elevation of a bulb through-flow turbine is less than that of an axial flow turbine, its draft tube is arranged horizontally and no elbow draft tube is provided, elevation of draft tube floor higher than that of an axial flow turbine. In this way, the scheme involving bulb through-flow turbines has dramatically less foundation excavation works. e) Short construction period. Because the scheme involving bulb through-flow turbines has no construction of curved passages such as a spiral case and elbow draft tube, its civil construction period can be shortened. In addition, after unit main shafts are installed, turbines and generators can be installed at the same time, which further reduces the construction period of the HPP. According to Electrical-Mechanical Design Code of Hydropower Plant (DL/T ), through-flow turbines should be preferably selected for a run-of-river hydroelectric plant with a maximum head less than 20 m. In conclusion, the bulb through-flow turbine is recommended for its advantages of easy arrangement of hydroproject, less investment, and high level of energy indexes Selection of Unit Numbers Preparation of Scheme Installed capacity of the Paklay HPP is 770 MW and head scope of the hydroelectric station is 7.50 m~20.0 m. The generator set of bulb through-flow turbine is recommended. Because the HPP has a relatively large installed capacity, to reduce quantity of the units, it should increase the unit capacity as far as possible. Considering about design and manufacturing limitation of the unit manufacturer and economic factors, unit capacity of the HPP at this stage is proposed as 55 MW~60 MW. Comparison is carried out between the scheme of 13 unit turbines with capacity of MW for each and the scheme of 14 unit turbines with capacity of 55 MW for each. Refer to Table for main parameters of units under different schemes. 4-73

76 Table Item Main Indexes of Units under Different Schemes for Unit Quantity Unit Scheme of Unit Quantity Unit capacity MW Rated head m Rated discharge of single unit m 3 /s Rated total discharge m 3 /s 6,103 6,101 Rated speed r/min Runner diameter m Unit speed r/min Technological and Economic Comparison of the Schemes quantity. Refer to Table for technological and economic indexes of each scheme for unit Table Parameters of the HPP Energy index Technical and Economic Indexes Corresponding to Schemes of Unit Quantity Item Unit Scheme of Unit Quantity Normal pool level m Minimum pool level m Installed capacity MW Unit capacity MW Maximum head m Minimum head m Rated head m Weighted average head m Average annual energy output GW h Primary energy (PE) GW h Secondary energy (SE) GW h Excess energy (EE) GW h Equivalent energy (PE SE) Utilization ratio of water resource Annual operating hours of installed capacity GW h % h

77 Project cost in hydroproject Million RMB Economic indexes Project cost per kilowatt Yuan/kw Project cost per kilowatt hour Yuan/kw h Project cost per kilowatt hour for equivalent energy Yuan/kw h Total project cost difference Million yuan Judging from energy indexes, installed capacity, rated head, and rated discharge of the whole plant under all schemes are almost the same. The units of HPP are of a relatively large quantity and flexible combination and operation methods. Comprehensive efficiencies of the plant and the energy indexes under all schemes are almost the same. Judging from the project cost, excavation works of the powerhouse increases a little and total weight of the unit reduces when the unit quantity increases from 13 to 14. Judging from total Project cost, the scheme with 14 units is economically better than the scheme with 13 units as the former saves RMB 8,490,000. Judging from manufacturing level and operation status of the unit, installed capacity of the Jirau HPP (Brazil) is 3,750 MW, with 50 bulb through-flow hydraulic turbine-generator units with unit capacity of 75 MW, and the runner diameter is 7.9 m. These units are the bulb through-flow hydraulic turbine-generator units with the largest unit capacity at present. Twenty-two units at left bank of the HPP are all designed and manufactured by Dongfang Electric Machinery Co., Ltd. The first generator unit was put into operation on August 31, The Guangxi Qiaogong HPP (China) has 8 bulb through-flow hydraulic turbine-generator units with unit capacity of 57 MW, they are the units with the largest unit capacity in China and the second largest in the world at present. Diameters of runners in the scheme involving 13 units are 7.2 m and the unit capacity is MW, which is the second largest capacity in the world, and the manufacturing is difficult. Diameters of runners in the scheme involving 14 units are 6.90 m and the unit capacity is 55 MW, and this unit has already manufactured and operated. Therefore, from perspective of the design and manufacturing level, the scheme involving 14 units is more advantageous. Based on the comprehensive comparison, in this stage, it is recommended to adopt the 4-75

78 scheme involving 14 units with the unit capacity of 55 MW for the Paklay HPP. 4.9 Navigation Scale a) Grade of Navigation Structure According to the current navigation capacity of the main stream of the Mekong River upstream of the Paklay dam site, the reaches upstream of Houayxay have a annual navigation capacity of 200 t ~ 300 t ships after waterway regulation, basically meeting the requirements of Grade V waterway. The Houayxay ~ Luang Prabang ~ Vientiane reaches without waterway regulation are available for navigation of small ships with the tonnage being 15t ~ 30 t in dry season and for ships with the tonnage being 60t ~ 80 t in flood season. The Paklay HPP is located on the Luang Prabang ~ Vientiane reaches of the Mekong River. Although the reaches have relatively low navigation capacity at present, they are the middle reaches of the upper Mekong River reaches, connecting two large cities Luang Prabang and Vientiane in Laos and being the only waterway for the economic trade among China, Myanmar, Laos, and Thailand. The regional economic development and gradual implementation of economic cooperation policies in the CAFTA will create new development opportunities for trade contacts and shipping business on the Lantsang River Mekong River. Along the development and construction of Sanakham, Paklay, Sayaboury, Luang Prabang, Pak Beng and other HPPs on the reaches in Laos of the main stream of the Mekong River, the reaches will be canalized, and the navigation capacity of which will also be greatly improved. According to the Overall Layout Planning for Development of Water Transport in Nine Provinces in the North of Laos, before 2020, it is planned to improve the about 1,117km long waterway from the No. 244 boundary monument at the Border among China, Laos and Myanmar to Nong Khai (40 km downstream of Vientiane) by waterway regulation and construction of cascade reservoirs, such that the waterway is available for navigation of 500t ships. According to the Preliminary Design Guidance for Proposed Mainstream Dams in the Lower Mekong Basin issued by MRC, hydroelectric projects 4-76

79 along the Mekong River must be set with navigation facilities to ensure smooth navigation of the reach and promote development of Lantsang River Mekong River. According to uniform requirement of MRC, the dimension of navigation lock of Paklay HPP should be m m 4.00 m (effective length effective width water depth at sill), which is basically close to the Grade IV navigation lock in China and can be passable for such one-pusher two-barge 500 t fleet (111.0 m m 1.60 m (length width design draft)) and 1000 t single ship or one-pusher one-barge fleet as specified in Chinese navigation standard of the inland waterway. b) Maximum and minimum stage of waterway of upstream The designed maximum stage of waterway of upstream of the Paklay HPP is the normal pool level of reservoir. Designed minimum stage of waterway is usually the minimum pool level. As it is stated above, maximum stage of waterway of upstream of the Paklay HPP is m a.s.l. (the normal pool level of reservoir) and minimum stage of waterway is m a.s.l. (the minimum pool level). c) Maximum and minimum stage of waterway of downstream The designed maximum stage of waterway of downstream of the Paklay HPP is the higher one between the water level corresponding to the open discharge flow of 16,700m 3 /s and maximum stage of waterway of the Sanakham Reservoir downstream. Thus, the designed maximum stage of waterway of downstream is m a.s.l. (the water level corresponding to the open discharge flow of 16,700m 3 /s). According to related stipulations of Navigation Standard of Inland Waterway (GB ), the designed minimum stage of waterway of downstream of the Paklay HPP is the minimum pool level of the Sanakham Reservoir. According to design achievement of the Sanakham HPP at feasibility study stage, operating water level for desilting during flood season of the reservoir is m a.s.l. Low water level at downstream of the Paklay dam site is m a.s.l. more or less. Therefore, the designed minimum stage of waterway of downstream of the Paklay HPP is m a.s.l. and designed elevation of base plate of corresponding approach channel is m a.s.l. 4-77

80 During construction of the Paklay HPP, the Sanakham HPP may have not been built completely for storage, so the navigation lock of Paklay HPP needs to be rechecked to see if it meets the navigation requirement before the Sanakham HPP is built completely. According to navigation status of the reach at present, navigation capacity of ships passing the dam is usually less than 100 t, during construction of Paklay HPP. Depth of the approach channel is between 1.0 m and 1.2 m and corresponding downstream water level is between m a.s.l. and m a.s.l. Upon reviewing of natural stage-discharge relation curve at downstream of Paklay HPP dam, when the discharge of dam site reaches 1200 m 3 /s ~ 1260 m 3 /s, the downstream water level is m ~ m a.s.l. According to statistics of average discharge of natural days of the Paklay HPP dam site, duration dependability corresponding to 1200 m 3 /s ~ 1260 m 3 /s is 71% ~ 73% (natural duration dependability). If considering about influence from regulation and storage of the Xiaowan Reservoir, Nuozhadu Reservoir, etc. (discharge during dry season will increase), duration dependability corresponding to the discharge can reach up to over 95%, which can totally meet the navigation requirement during construction Calculation and Analysis of Sedimentation by Mathematical Model River Morphology and Characteristics of Water and Sediment a) River morphology of the reservoir area The Paklay HPP is located on the upper reaches of the Mekong River and can be divided into three parts according to the morphology and characteristics of the river channel. In the upper part of the proposed reservoir, from proposed Xayaburi dam to Ban Pak Toung, the Mekong River flows towards South, corresponding approximately to a major geological fault. The river flows on rock through a set of near-straight channel bounded at the downstream end by a large bend. The channel slope is ranging from 3 to 3.5. The river exhibits a deeply rock incised channel. Small rapids occur also steadily through narrow openings of rocks. Locally, the flow is sometimes divided in multiple channels around in-channel outcrops. These outcrops and rock protrusions often lead to impressive 4-78

81 sand deposits that form in-channel bars during the falling stage of the wet season. The river is confined in a narrow valley flanked by steep hills. The low flow channel width is comprised between 50 m and 100 m while during the wet season, the Mekong flows through a m wide channel. Two tributaries join the mainstream in that part, the so-called Nam Houng and Nam Pouy. Many other small tributaries likely to experience torrential floods and debris flow events contribute also to the sediment supply of the Mekong River in that stretch. In the intermediate stretch, from Ban Pak Toung to Houay Khi, the Mekong River flows through a straight channel incised in rock. The channel slope is around For low flow conditions the river flow divides frequently around in-channel rocky outcrops that are usually submerged during the wet season. Numerous rocky protrusions and isolated rock piles are also regularly visible. Sometimes, these outcrops lead to sediment accumulations that can locally form inchannel islands. The largest one by far is located at Don Son. On the left side, the river is dominated by a mountainous range rising up to 1200 m asl, while low elevation hills (below 500 m) are present on the right side. For low flows, the river width doubles compared to previous reach and is comprised between 100 m and 200 m. It extends up to m during the wet season. From Houay Khi to proposed Pak Lay dam, in this short stretch, the river course is globally straight, even if a large meander resulting from the tectonic history is visible at the very beginning of the reach. The Mekong River valley is quite opened and surrounded by a landscape of hills. Some emerging limestone peaks are also visible in the upper part. The river channel is continuously incised in the bedrock. This important feature explains the regular presence of rocky banks (some of them being quite steep) and the existence of wide rock benches possibly covered by thick sand deposits. A significant change in the channel size has to be noted depending on the flow season. While the channel width ranges from 50 to 200 meters during the dry season, it is likely to extend up to 700 meters at the peak of the wet season. The channel slope is comprised between 1.5 ~2. b) Characteristics of water and sediment 4-79

82 The Paklay HPP is at upstream reach of Mekong River. This reach is of subtropical climate, low terrain, high temperature, developed river system, plentiful precipitation, centralized and heavy rainstorm during flood season, remarkable human activities, and severe water and soil loss. It is the main sediment yield area of Mekong River basin. This basin is of uneven annual rainfall, affected by southwest monsoon of the ocean and northeast monsoon the continent. The rainfall of rainy season (June ~ November) is plentiful and heavy, while rainfall of dry season (December ~ May) is little. Runoff of the basin ground is mainly supplied by rainfall, of which the inter-annual and annual distribution is uneven. According to statistics of runoff of natural months from 1960 to 2015 (56 years) of Paklay dam site, annual average flow of dam site is 4060 m 3 /s, annual runoff volume is m 3, of which the average flows of the most dry year (1992) and the most rainy year (1966) are 2,630 m 3 /s and 5,720 m 3 /s, and the wet-dry ratio is 2.2. Annual average flow of the dam site during flood season (June ~ November) is 6,524 m 3 /s, which is 80.6% of the annual runoff volume; annual average flow of the dam site during dry season (December ~ May) is 1,582 m 3 /s, which is only 19.4% of the annual runoff volume. According to statistics of monthly average suspended sediment concentration from 1960 to 2015 (56 years), annual average suspended load of Paklay dam site is kg/m 3 and sediment discharge of the annual average suspended load is million tons (considering the influence of sediment trapping in the cascade reservoirs of the upstream of Lancang River), of which the average sediment discharge of suspended load during flood season (June ~ November) and dry season (December ~ May) are million tons (about 93.5% of yearly sediment discharge) and 1.08 million tons (only 6.5% of yearly sediment discharge). Judging from annual dam site runoff and characteristics of sediment distribution, the inflow sediment mainly derives from surface erosion by storms in flood season. Characteristic of coarse sands brought by inundation is prominent. Paklay Reservoir has a storage of 890 million m 3 at NPL 240m, the mean annual suspended sediment runoff is million tons at the damsite, and the ratio of reservoir 4-80

83 storage to sediment runoff is about 71. When the power station is completed, the backwater in the reservoir area is not high, and sedimentation is not a prominent problem. In this stage, in addition to the reservoir sedimentation calculations, the impact of sedimentation in the project area on the operation of the power station shall be the stressed Basic Data and Parameters for Calculation a) Section Data The reach of the trunk river in Paklay Reservoir area for calculation is from Paklay damsite to upstream connecting cascade Sainyabuli Hydropower Station damsite which is about 109.9km long with 68 cross sections measured in total. The average distance between cross sections is 1616m. The control catchment area from Paklay to Sainyabuli is about 11,000 km 2, accounting for only 3.9% of the control catchment area of Paklay damsite. There are many branch drains in the area which are not the subject to be protected against inundation. Therefore, sediment calculation is only carried out for the trunk river section. The calculation results of the measured longitudinal sections of the reach are shown in Table Table Calculation Results of Reach Longitudinal Sections of Paklay Reservoir Cumulative Thalweg Cumulative Thalweg Section Spacing Distance Elevation Section Spacing Distance Elevation No. No. m km m m km m CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS

84 CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS b) Data on Reservoir Water and Sediment Inflow According to series statistics of natural monthly runoff and sediment discharge in 56 years from 1960 to 2015 at Paklay damsite, the average annual flow at the damsite is 4060m 3 /s while the average annual suspended load discharge is million tons. Considering the characteristics of runoff and sediment and through comprehensive calculation and analysis, daily average flow and sediment concentration in suspended load of 5 representative years are selected at this stage: January 1-December 31, 2000; January 1-December 31, 1980; January 1-December 31, 1990; January 1-December 31, 1986; January 1-December 31, 1989; The series average annual flow of 5 representative years is 4054m³/s, a difference of about 0.15% compared with average annual flow. The series average annual suspended load discharge of 5 representative years is 16.9 million tons, a difference of about 2.38% compared with the average annual suspended load discharge. In general, the selected series is very representative. During calculation, flow and sediment discharge of the 5 representative years are modified to be consistent with the average annual values. For the reservoir bed load discharge inflow, only the bed load sediment in the section from Xaignabouli damsite to Paklay damsite is considered. 3% is taken as the ratio of bed load discharge to suspended load discharge by reference to the design results of cascade hydropower stations in middle-lower reaches of Lancang River and the Pak Beng 4-82

85 Hydropower Station. c) Sediment Grouping and Gradation In this stage, the Water Regime and Reservoir Scheduling Engineering Company samples sediments based on gradations in the Paklay Reservoir area. The analysis (see Section for details) shows that the suspended load sediment gradations are divided into three groups: average gradation, inner gradation envelope and outer gradation envelope as shown in Table and Figure The gradations of bed load are shown in Table Table Gradations of Sediments in Suspended Load in Paklay Reservoir Area Outer Gradation Envelope Average Gradation Inner Gradation Envelope Grain size Percentage Grain size Percentage Grain size Percentage mm % mm % mm %

86 Fig Gradation Curves of Suspended Sediments in Paklay Reservoir Area Table Gradations of Bed Load in Paklay Reservoir Area Separation Grain Size mm Percentage % d) Stage-Discharge Relation at Damsite The natural stage-discharge relations at Paklay and Xaignabouli damsites are shown in Figure

87 Fig Natural Stage-Discharge Relation Curves at Paklay and Xaignabouli Damsites e) Discharge Curve Discharge capacity curve of the pivotal Paklay HPP is shown in Table f) Sediment Calculation Parameters 1) Coefficient k and Index m for Sediment Carrying Capacity of Flow Coefficient k and index m for sediment carrying capacity of flow: By reference to the results of upstream Nuozhadu, Jinghong, Pak Beng and other hydropower stations, the coefficient k and index m for sediment carrying capacity of flow are: k=0.18, m=1.0. Calculate for sediment scouring and deposition under natural conditions of riverway in the Paklay Reservoir area and the result shows basically no scouring or deposition of the river bed. This means that the k and m values basically apply for the riverway in the Paklay Reservoir area. 2) Recovery Saturation Coefficient Based on previous engineering experience, 1 is taken as the coefficient in case of scouring and 0.25 is taken as the coefficient in case of deposition. 3) Water level in Front of Dam Paklay HPP is a typical low-head channel reservoir with only daily regulation 4-85

88 capacity. According to the reservoir operation mode planned for this stage, the water level of the Paklay Reservoir shall be maintained at the normal pool level as much as possible to increase the generated energy. When the flow at the damsite is greater than 16700m 3 /s, open all the flood gates to discharge at the maximum discharge capacity. As a result, during sediment calculation this time, when the flow at the damsite is less than 16700m 3 /s, normal pool level of m should conservatively be taken as the water level in front of the dam. In this case, the water level in front of the dam is obtained according to the discharge capacity curve. Accordingly, the 5-representative-year discharge, reservoir water level and sediment concentration processes are show in Fig and Fig

89 Discharge Water level Discharge Reservoir level 10% representative year 25% representative year 50% representative year 75% representative year 90% representative year Time (day) Fig representative-year discharge and reservoir water level process diagram 4-87

90 Discharge Sediment content Discharge Sediment content 10% representative year 10% representative year 25% representative year 50% representative year 75% representative year 90% representative year Time (day) Fig representative-year discharge and sediment concentration process diagram 4-88

91 4) Ratio of Bed Load Discharge to Suspended Load Discharge Normally there are three methods to determine the bed load. The first is field testing, the second is flume testing, and the third is estimation based on experience and ratio of bed load discharge to suspended load discharge. Measured bed load data for the reservoir area of Paklay HPP is not available, and bed load measurement is a long-time and multi-frequency activity and is difficult and uncertain to some extent due to the influence of measuring instrument and method. As for flume testing, it s difficult to accurately simulate the transport rule of bed load due to the constraints of test conditions and similarity, and the accuracy of results is relatively low. Consequently, for Paklay HPP, ratio of bed load discharge to suspended load discharge is adopted to estimate the bed load amount. According to the comprehensive considerations of the channel characteristics, precipitation, vegetation, human activities and other factor of the river reaches upstream of Paklay and referring to the experiences from large rivers such as the lower reaches of the Jinsha River and of the Lancang River in China, the ratio of bed load discharge to suspended load discharge is taken at 3%. 3% is taken as the ratio of bed load discharge to suspended load discharge by reference to design results of cascade hydropower stations in the middle-lower reaches of Lancang River and the Pak Beng Hydropower Station. 5) Other Calculation Parameters 2650kg/m 3 is taken as the sediment dry density and 0.5 is taken as the porosity Roughness Calculation and Analysis The following 3 methods are mainly used for roughness calculation: a) Method 1: Calculate roughness in the reservoir area according to the measured section water levels (discharge in the reservoir area is about 1150m 3 /s) of April The calculation results are shown in Table Table Calculated Roughness Results Based on Measured Section Water Levels of April 2008 Thalweg Measured S/N Section No. Spacing Cumulative Distance Roughness Elevation Water Level 4-89

92 m km m m 1 CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS

93 S/N Section No. Thalweg Measured Spacing Cumulative Distance Elevation Water Level m km m m 44 CS CS CS CS Roughness 48 CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS Comprehensive average roughness in the reservoir area As shown in Table , when the discharge in Paklay Reservoir area reaches 1150m 3 /s, roughness of each section of the riverway is in the range of ~ and the comprehensive average roughness is b) Method 2: Calculate the comprehensive roughness of reaches for different discharges planned according to the natural stage-discharge relation at the Xaignabouli and Paklay damsites. The calculation results are shown in Table and Figure Table Calculation Results of Comprehensive Roughness of Riverway with Different Discharges in Paklay Reservoir Area Discharge Water Level of Xaignabouli Reservoir Water Level of Paklay Reservoir m³/s m m Roughness

94 Discharge Water Level of Xaignabouli Reservoir Water Level of Paklay Reservoir m³/s m m Roughness

95 Fig Comprehensive Roughness Curve for Riverway with Different Discharges in Paklay Reservoir Area According to Table and Figure , when the discharge in the Paklay Reservoir Area is less than 3000m 3 /s, the riverway comprehensive roughness is in the range of ~ and basically follows the rule of the greater the discharge, the smaller the roughness. When the discharge in the Paklay Reservoir Area is 3000m 3 /s~6000m 3 /s, the riverway comprehensive roughness is in the range of ~ and basically follows the rule of the greater the discharge, the greater the roughness. When the discharge in the Paklay Reservoir Area is greater than 6000m 3 /s~39000m 3 /s, the riverway comprehensive roughness is in the range of ~ c) Method 3: The roughness is calculated based on the water levels measured on August 26 and 27 of From August 26 to 27 of 2016, we surveyed the flood surface profile in the river reach of the reservoir. Altogether 6 points were measured for the water level. For the measuring points and measured water level, see Table See Fig for survey site. 4-93

96 Table Calculation Results of Comprehensive Roughness of the River Reach of the Reservoir under Different Flows Measured water No Measuring Measuring Location level. Point time m 1 S7 15:23, Aug.27 13m upstream of dam site S22 9:25 Aug.27 52m upstream of CS S41 16:10, Aug m upstream of CS S54 14:46, Aug.26 57m downstream of CS S64 13:02, Aug m downstream of CS S72 10:02, Aug.26 49m downstream of CS Fig Water Level Survey Site of Paklay Reservoir Area Based on the data of hydrological station, the average flow in the river reach of the reservoir during the survey ranged from m³/s to 11940m³/s, which is relatively stable. According to the discharge in the reservoir area and the measured water levels in front of the dam, the water levels of various sections are derived from roughness of various river sections by trial calculations and compared with the measured water levels, and finally the roughness of various sections is obtained by trial calculation. The calculation process and 4-94

97 results are presented in the tables from to and Fig Table Trial calculation results of roughness in Paklay reservoir area (1 st group) No. Measuring point Location Measured water level Calculated roughness (1 st group) Calculated water level Difference between measured and calculated levels m m m 1 S7 13m upstream of dam site S22 52m upstream of CS S41 210m upstream of CS S54 57m downstream of CS S64 300m downstream of CS S72 49m downstream of CS Table Trial calculation results of roughness in Paklay reservoir area (2nd group) Difference Calculated between Calculated Measured roughness measured water No. Measuring point Location water level (2nd and level group) calculated levels m m m 1 S7 13m upstream of dam site S22 52m upstream of CS S41 210m upstream of CS S54 57m downstream of CS S64 300m downstream of CS S72 49m downstream of CS Table Trial calculation results of roughness in Paklay reservoir area (3rd group) No. Measuring point Location Measured water level Calculated roughness (3rd group) Calculated water level Difference between measured and calculated levels m m m 1 S7 13m upstream of dam site S22 52m upstream of CS S41 210m upstream of CS S54 57m downstream of CS S64 300m downstream of CS S72 49m downstream of CS

98 Water level (m) Measured From 1st group roughness From 2nd group roughness From 3rd group roughness Distance from dam (km) Fig Comparison of water levels derived from roughness and the measured The analysis of the tables from to and Fig indicates that the water levels derived from the first group roughness are lower than the measured, and those derived from the second group roughness are almost the same as the measured. Therefore, the second group roughness is relatively appropriate, and the roughness of various reaches ranges from to basically, which is reasonable. In the three methods above-mentioned, Method 1 uses the measured water surface profile of 2008 for roughness calibration, corresponding to a flow of 1150m 3 /s, which belongs to low-water flow. When Paklay HPP is completed, the water level in the river channel in the reservoir area will rise, and the roughness calibrated by low-water flow differs from that with the water level rise after reservoir impoundment, so it should not be adopted. Method 2 uses the rating curves of Paklay damsite and Xayabury damsite for roughness calibration. The roughness calibrated is the comprehensive average roughness of the whole reach of the reservoir area and cannot reflect the characteristics of various river sections, so it should not be adopted too. Method 3 uses the measured water surface profile of August 2016 for roughness calibration, corresponding to a flow of 11000m 3 /s with water 4-96

99 levels in the river channel in the reservoir area are relatively high. The measured water surface profile has 6 control points and can basically reflect the hydraulic characteristics of various river sections in the reservoir area at high water level, and the derived roughness result is reasonable. By comprehensive analysis of sectional form of the river bed, river morphology and vegetations on both banks in the reservoir area, the roughness results derived from measured water levels of August 2016 (refer to Table ) are adopted as the natural roughness of river channel in Paklay reservoir area for reservoir sedimentation calculation. To be conservative, the natural roughness is taken as the roughness after reservoir establishment and in sediment deposition process Calculation of Reservoir One-dimensional Sediment Deposition For calculation of one-dimensional sediment deposition in Paklay Reservoir, the SUSBED-2 model (one-dimensional steady non-uniform non-equilibrium full sediment mathematical model) co-developed by POWERCHINA ZhongNan Engineering Corporation Limited and College of Water Resources and Hydropower Engineering of Wuhan University. The calculation results are shown below: Analog Calculation for Sediment Deposition in Natural River Channel Under natural conditions, the sediment deposition in the river channel should be basically balanced during the long-term evolution process. To verify the rationality of the calculation model and parameters, an analog calculation for sediment deposition in natural river channel has be conducted. In the analog calculation for sediment deposition in natural river channel, the average gradation is employed, and the water level process at Paklay damsite is derived from the discharge and the rating curve of the damsite. The sediment deposition in the river channel of the reservoir area under natural conditions is adjusted to a balanced status by adjusting the calculation parameters of the model ( k and m mainly). The results of analog calculation for sediment deposition in natural river channel for Paklay HPP are presented in Table , and the deposition variation at longitudinal section of river channel is shown in Fig Table Results of Analog Calculation for Sediment Deposition in Natural River 4-97

100 Channel for Paklay HPP Item Unit Years of Deposition 20 years 40 years 60 years 80 years 100 years Reservoir sediment inflow 10 6 t Reservoir sediment outflow 10 6 t Deposition quantity 10 3 m³ Sediment delivery ratio % The analysis of Table and Fig indicates that the sediment deposition in Paklay river channel is basically balanced during the long-term evolution process, and the corresponding calculation parameters k and m are taken at 0.18 and 1.0, respectively. 4-98

101 El. (m) Natural thalweg 20 years 40 years 60 years 80 years 100 years Distance to dam (km) Fig Sediment deposition variation at longitudinal section of Paklay river channel 4-99

102 Calculation of Reservoir One-dimensional Sediment Deposition after reservoir establishment a) Sediment Deposition Quantity and Sediment Delivery Ratio See Table for calculation results for sediment deposition of Paklay HPP reservoir with different operating years. Table Calculation Results for Sediment Deposition of Paklay Reservoir with Different Operating Years Different Years of Deposition Sediment Gradation Item Unit Scheme 20 years 40 years 60 years 80 years 100 years Reservoir sediment inflow 10 6 t Outer Gradation Reservoir sediment outflow 10 6 t Envelope Deposition 10 3 quantity m³ Sediment delivery ratio % Reservoir sediment inflow 10 6 t Average Gradation Reservoir sediment 10 6 t outflow Deposition quantity m³ Sediment delivery ratio % Reservoir sediment inflow 10 6 t Inner Gradation Reservoir sediment outflow 10 6 t Envelope Deposition 10 6 quantity m³ Sediment delivery ratio % Note: 1. The reservoir sediment inflow, reservoir sediment outflow and deposition quantity are all cumulative values of suspended sediments, the same below. 2. For the deposition quantity, porosity of 0.5 is considered, the same below. Based on the analysis according to Table , with the extension of reservoir operating years, the sediment delivery ratio increases, the deposition quantity shows a trend of gradual decrease and the deposition speed also slows down gradually. According to comparison and analysis of three groups of sediment calculation results, the smaller the suspended sediment gradation, the greater the reservoir sediment outflow and the sediment delivery ratio in the same time period. According to calculation based on average gradation curve and outer gradation envelope, scouring and deposition of the reservoir basically 4-100

103 balance with each other for 20 years of operation. According to calculation based on inner gradation envelope, the sediment delivery ratio of the reservoir is 82.38% for 100 years of operation. b) Longitudinal Sediment Deposition Form See Figure ~ for variation of deposition thalweg elevation of the Paklay HPP reservoir with different operating years. Based on analysis according to the abovementioned figures, if calculation is done according to the average gradation curve and the outer gradation envelope and based on 100 years of operation of the reservoir, the sediment deposition and the variation of riverway form in the reservoir area are small. If calculation is done according to the inner gradation curve and fine gradation envelope, then almost all the sediments are deposited in the river reach within 75km from the dam. This river reach is basically in belt form of deposition

104 Fig Comparison of Sediment Deposition Thalweg Elevation of Paklay HPP Reservoir for Different Years of Operation (Outer Gradation Envelope) 4-102

105 Fig Comparison of Sediment Deposition Thalweg Elevation of Paklay HPP Reservoir for Different Years of Operation (Average Gradation Curve) 4-103

106 Figure Comparison of Sediment Deposition Thalweg Elevation of Paklay HPP Reservoir for Different Years of Operation (Inner Gradation Envelope) 4-104

107 c) Analysis of Regulating Storage See Table for variation of regulating storage of Paklay Reservoir for different years of operation. Table Regulating Storage Loss of Paklay Reservoir due to Sedimentation Sediment Different Years of Sedimentation Gradation Scheme Item Unit Initial value 20 years 40 years 60 years 80 years Outer Gradation Envelope Average Gradation Inner Gradation Envelope Storage capacity at normal pool level 100 years 10 6 m³ Dead storage 10 6 m³ Regulating storage 10 6 m³ Percentage of regulating storage loss by deposition % Storage capacity at normal pool level 10 6 m³ Dead storage 10 6 m³ Regulating storage 10 6 m³ Percentage of regulating storage loss by deposition % Storage capacity at normal pool 10 6 m³ level Dead storage 10 6 m³ Regulating storage 10 6 m³ Percentage of regulating storage loss by % deposition According to Table , with the extension of operating years of the reservoir, the reservoir regulating storage decreases somewhat and the regulating storage loss ratio shows a trend of gradual increase. Within the same period of deposition, the greater the sediment gradation, the greater the deposition quantity and the higher the regulating storage loss ratio

108 If the reservoir is to operate for 100 years, based on calculation according to the average gradation curve and theouter gradation envelope, the regulating storage loss ratios are within 3%; based on calculation according to the inner gradation envelope, the regulating storage loss ratio is 12.0% Calculation of Sensitivity Schemes The basic scheme for the calculation is based on a mean annual reservoir suspended sediment inflow of 1.65 million tons and ratio of bed load discharge to suspended load discharge of 3%. The sensitivity analysis is mainly to consider the unfavorable condition of increase of reservoir sediment inflow, and 2 sensitivity schemes have been analyzed: one is to increase the reservoir suspended sediment inflow by 10% and 20%, the other is to take the ratio of bed load discharge to suspended load discharge at 5% and 10%. Mean gradation is adopted in both sensitivity schemes, and the calculation results are presented below: a) Scheme to increase the reservoir suspended sediment inflow Paklay reservoir has a mean annual suspended sediment inflow of 1.65 million tons, and in the sensitivity scheme, the sediment amount is increased by 10% and 20% to million tons and million tons, respectively. The results of sedimentation calculation are listed in Table , and the changes of regulating capacity are listed in Table Table Results of Sedimentation Calculation for Paklay Reservoir for Various Operation Years Years of Deposition Sediment gradation Item Unit scheme Sediment gradation scheme Basic scheme (16.50 million tons) Suspended sediment rise by 10% years 40 years 60 years 80 years 100 years Reservoir sediment inflow 10 6 t Reservoir sediment outflow 10 6 t Deposition 10 6 quantity m³ Sediment delivery ratio % Reservoir sediment inflow 10 6 t Reservoir 10 6 t

109 (18.15 million tons) sediment outflow Deposition quantity Sediment delivery ratio Reservoir sediment inflow Reservoir sediment outflow Deposition quantity Sediment delivery ratio Basic scheme (16.50 million tons) 10 6 m³ % t t m³ % Table Calculation Results of Regulating Storage Loss due to Sedimentation for Paklay Reservoir Years of Deposition Sediment Item Unit gradation scheme Initial years years years years years Storage at NPL 10 6 m³ Dead storage 10 6 m³ Regulating storage 10 6 m³ Loss rate of Suspended sediment rise by 10% (18.15 million tons) Suspended sediment rise by 20% (19.80 million tons) regulating storage due to sedimentation % Storage at NPL 10 6 m³ Dead storage 10 6 m³ Regulating storage 10 6 m³ Loss rate of regulating storage due to sedimentation % Storage at NPL 10 6 m³ Dead storage 10 6 m³ Regulating storage 10 6 m³ Loss rate of regulating storage due to sedimentation % Table and Table indicate that when the reservoir suspended sediment inflow is higher, the deposition quantity and the loss rate of regulating storage due to sedimentation of the same period will be higher. However, the overall difference among the schemes is small. The reservoir can basically reach relative sediment balance state within 20 operation years for all the schemes.

110 b) Scheme to increase ratio of bed load discharge to suspended load discharge The ratio of bed load discharge to suspended load discharge is taken at 3% in the basic scheme of this calculation and is increased to 5% and 10% in sensitivity analysis. The changes of regulating capacity of the schemes are presented in Table Table Calculation Results of Regulating Storage Loss due to Sedimentation for Paklay Reservoir Years of Deposition Sediment gradation Item Unit scheme Initial years years years years years Storage at NPL 10 6 m³ Dead storage 10 6 m³ Regulating Basic scheme (ratio of bed load discharge to suspended load discharge 3%) Scheme with ratio of bed load discharge to suspended load discharge 5% Scheme with ratio of bed load discharge to suspended load discharge 10% storage Loss rate of regulating storage due to sedimentation 10 6 m³ % Storage at NPL 10 6 m³ Dead storage 10 6 m³ Regulating storage 10 6 m³ Loss rate of regulating storage due to sedimentation % Storage at NPL 10 6 m³ Dead storage 10 6 m³ Regulating storage 10 6 m³ Loss rate of regulating storage due to sedimentation % Table indicates that the higher the ratio of bed load discharge to suspended load discharge is, the higher the loss rate of regulating storage due to sedimentation of the same period will be. However, the overall difference among the schemes is small. After 100 years of operation, the loss rate of regulating storage will range from 2.9% to 7.4%, and its impact to the reservoir normal operation is small Integral Two-dimensional Sedimentation Calculation of Hydroproject Calculation Scope a) Upstream the dam site As for the integrated two-dimensional water and sediment mathematical model at the 4-108

111 river reaches in the hydroproject area of the Paklay HPP, the riverway about 2.1km long upstream the dam site (from the dam site to Section CS1-8) is involved in calculation. The inlet control section is Section CS1-8, and the outlet control section is the section at the dam site. b) Downstream the dam site As for the integrated two-dimensional water and sediment mathematical model at the river reaches in the hydroproject area of the Paklay HPP, the riverway about 1.85 km long downstream the dam siteis involved in calculation. The inlet control section is the section at the dam site, and the outlet control section is the section 1.85km downstream of the dam site Fundamental equations of 2D sediment mathematical model a) Fundamental equations for Cartesian coordinate system In consideration of the impact of lateral inflows, the fundamental equations for the 2D water-sediment simulation under Cartesian coordinate system are as below: Continuity equation of flow: Z M t x N y 0 Motion equation of flow along x direction: (4-1) M t um x vm y 2 Z M gh D 2 x x Motion equation of flow along y direction: 2 M gn 2 y 2 M h u v 2 (4-2) N t un x vn y Z gh y 2 N D 2 x 2 N gn 2 y 2 N h u v 2 (4-3) Continuity equation of sediment: HS MS NS t x y Equation of unbalanced transport of bed load: g x bx g y Equation of riverbed deformation: by 2 2 HS HS S S* 2 2 x y (4-4) b b* g g (4-5) 4-109

112 Z t g x g b bxk byk K SK S* K (4-6) y where, H is water depth in meter; u and v are flow velocity respectively along x and y directions in m/s, M=uh, N=vh; Z is water level in meter; n is Manning roughness coefficient; D is turbulent viscosity coefficient; is water density in g/cm 3 ; S is sediment concentration; S * is sediment carrying capacity; is sediment settling velocity in m/s; ' is dry density of sediment in kg/m 3 ; is recovery saturation coefficient of suspended load; is sediment recovery saturation coefficient of bed load (dimensional); is sediment diffusion coefficient; K, S K and S * K are sediment settling velocity, sediment concentration and sediment carrying capacity respectively; g b g b* are unit-width transport rate and effective transport rate of bed load respectively; g bxk and g byk are transport rates of bed load along x and y directions respectively, with expression as below: u v g bxk, g byk g bk, g bk u v u v (4-7) b) Fundamental equations for generalized curvilinear coordinate system Under generalized curvilinear coordinate system, given J x y x y (4-8) y x, J y x, J x y, J x y (4-9) J If FM and FN are the components of unit-width discharge at and directions under generalized curvilinear coordinate system, then: FM y M x N J x M y N (4-10) FN y M x N J x M y N (4-11) If U and V are the components of flow velocity at and directions under generalized curvilinear coordinate system, then: J v U y u x v J x u y v (4-12) V y u x v x u y (4-13) According to general curvilinear transformation relation, the above fundamental 4-110

113 equations for Cartesian coordinate system can be transformed to: Z FM FN Continuity equation of flow: J 0 (4-14) t Motion equation of flow along direction: M J t MU MV Z Z ghj x x DJ q gn M u v DJ q M q M J h 4 3 Motion equation of flow along direction: N NU NV Z Z J ghj y y DJ q t gn N u v DJq N q N J 12 Continuity equation of sediment: HS UHS VHS J J t 22 h 4 3 J q HS q HS JW S S q 11 HS q Equation of unbalanced transport of bed load: Equation of riverbed deformation: Z t g * 12 HS gb g b J g g g b g 11 b* N 11 M q 12 q N 12 M (4-15) (4-16) (4-17) (4-18) b bxk byk bxk byk x y x y K S K S* K (4-19) g The above equation set is the fundamental equations for the 2D water-sediment mathematical model under generalized curvilinear coordinate system, where, q ; x y q 12 x x y y ; q ; M, M, N, N are partial derivative, for x y instance M M ; and the meaning of other symbols are the same as above. c) Model discrete The above control equations can be expressed by a uniform convection diffusion equation (see Table ): 4-111

114 J t H HU HV Jq H Jq H S U S P (4-20) Non-staggered grid arrangement is adopted for the computing physical quantities of model, i.e., arranged at central point P of the control body (see Fig ). Generalized discrete form of the control equation can be obtained by integrating the control equation to the intended control volume along time and space by control volumetric method: Where, a a E N a P P a E E a W W a N N a D A P ) C,0 ; a D A P ) C,0 e ( e e w w S ; ( w w D A P ) C,0 ; a D A P ) C,0 n ( n n S ; s ( s s S a b S U. a P P ; a P a E aw a N a S a P S P. ; 0 P 0 P a b 0 P 0 H p t (4-21) Where, = J, the quantities with superscript 0 represents the values of the upper time level, P C / D is Peclet number of grid, C e, C w, C n and C s are convection coefficients of control volume surface, and D e, diffusion coefficients of control volume surface, the expressions are: D w, C HU ; C HU w ; C HU n ; HU e e w n C ; s s D n and D s are D e 1 H J 1 H D s J s e 1 H 1 H ; D w ; Dn J ; J A P = 0,1 0.5 P ; w n 4-112

115 N n W w v P H u e E s S Fig Schematic Diagram of Control Body Table Variables, Diffusion Coefficients and Source Items in Generalized Equations of Model Equation SU Continuity equation Momentum equation along x direction Momentum equation along y direction Continuity equation of sediment u v S D D Z Z ghj x x DJq12 M DJq DJq 12 M Z Z ghj x x DJq12 N 12 Jq 12 N Jq JWS * HS 12 HS gn gn 2 2 H H SP H H u 4 3 u JW In the process of solution, to avoid water level fluctuation, the flow velocity at control body interface is subject to momentum interpolation. To avoid occurrence of overrun in v v 2 2 J J 4-113

116 calculation and iterative process, under-relaxation technology proposed by Patankar and Spalding is adopted, i.e., introducing under-relaxation factor in discrete equation to improve diagonal dominance of coefficient in discrete equation Division of Computing Grid a) Computing grid for area upstream of damsite A curvilinear grid in the computing area is generated from elliptic differential equation, totaling cells, of which 226 at direction (mainstream direction of river channel), 141 at direction. Additionally, the grid is intensified (about 4m 4m) at high-level surface bays, low-level surface bays, sediment releasing outlets, sand traps and other structures. The computing grid for the area upstream of the damsite is shown in Fig Fig Schematic Diagram of Computing Grid for Area Upstream of Damsite b) Computing grid for area downstream of damsite A curvilinear grid in the computing area is generated from elliptic differential equation, totaling cells, of which 121 at direction (mainstream direction of river channel), 121 at direction. Additionally, the grid is intensified (about 4m 4m) at high-level surface bays, low-level surface bays, sediment releasing outlets, sand traps and 4-114

117 other structures. The computing grid for the area upstream of the damsite is shown in Fig Fig Schematic Diagram of Computing Grid for Area Downstream of Damsite Computing boundary conditions In 2D sediment mathematical model, boundary conditions normally include river channel inlet and outlet boundary, bank boundary and moving boundary treatment. In this model: a) Inlet boundary: Based on the known full-section discharge at the inlet, the transverse distribution of unit-width discharge of inflow along the section is given, and the sediment concentration of each grid of inlet section is given. The discharge and sediment concentration process of the inlet section is provided by the 1D sedimentation computations for reservoir. b) Outlet boundary: The water level at the outlet section is given. The computing outlet water level for the upstream area of the damsite is the reservoir water level, and that for the downstream area of the damsite is derived from the discharge at the outlet and the corresponding rating curve. c) Bank boundary: It is of no-slip boundary, and its flow velocity is given as zero. d) Moving boundary: Freezing method is adopted for moving boundary treatment for this model, i.e., the river bottom elevation at water level node is used to judge the emersion of the grid cell. If not emerged, a normal value is taken for the roughness, otherwise, a 4-115

118 positive number close to infinity is taken. Meanwhile, in order not to affect the solution of flow control equation, a thin water layer needs to be given at the emerged node, and its thickness normally is given at 0.5cm Calculation Scheme and Contents a) Upstream the dam: the reservoir sedimentation (especially the front of power intake, front edge of sediment sill, sediment releasing bottom outlet and upper approach channel), sediment concentration passing through the turbine and gradation within 40 years of reservoir operation shall be calculated and analyzed; Downstream the dam: the sediment scouring and deposition (especially the riverbed downstream the dam and the inlet of the lower approach channel) within 5 years of reservoir operation shall be calculated and analyzed Calculation Results and Analysis Upstream the dam a) Analysis of integral sediment scouring and deposition in river reaches upstream of the dam For the sediment scouring and deposition in the river reach upstream of the dam after 20 and 40 years of operation of the reservoir, see Fig and Fig Fig Sediment scouring and deposition in the river reach upstream of the dam after 20 years of operation of the reservoir 4-116

119 Fig Sediment scouring and deposition in the river reach upstream of the dam after 40 years of operation of the reservoir As shown from Fig and Fig , sediment deposition prevails in the river reach upstream of the dam. The sediment deposition is low in the main river channel and high on the side shoals. b) Analysis of sediment scouring and deposition of local areas of main structures See Table for the sedimentation in the main structure areas upstream of the dam after different operation years. Table Sedimentation Elevations in the main structure areas upstream of the dam after different operation years Service Year Sedimentation Elevation at Upstream End of Sediment Barrier Sedimentation Elevation ahead of Power Intake Sedimentation Elevation ahead of the surface bays Sedimentation Elevation at Entrance Area of Upper Approach Channel End of 10 th year El m Unit 3: El m ; Unit 11: El m. El m El m 4-117

120 End of 20 th year El m Unit 3: El m ; Unit 11: El m. El m El m End of 30 th year El m Unit 3: El m ; Unit 11: El m. El m El m End of 40 th year El m Units 3 and 11: flush with the power intake invert El m El m 1) Analysis of sediment scouring and deposition of local areas of main structures after 20 years of operation of the reservoir For the local sedimentation thickness ahead of the powerhouse after 20 years of operation of the reservoir, see Fig For profiles of funnels ahead of power intakes of Unit 3 and Unit 11, and ahead of the bottom outlet, low-level surface bay and high-level surface bay of the overflow section after 20 years of operation of the reservoir, see Fig through Fig espectively. Fig Local sedimentation thickness ahead of the powerhouse after 20 years of operation of the reservoir 4-118

121 Elevation 高程 (m) 初始 20 年末 距进水口距离 (m) Distance from the power intake (m) Fig Profile of funnel ahead of power intake of Unit 3 after 20 years of operation of the reservoir Elevation 高程 (m) 初始 Initial 20 年末 Distance from 距进水口距离 the power intake (m)(m) Fig Profile of funnel ahead of power intake of Unit 11 after 20 years of operation of the reservoir 4-119

122 初始 20 年末 Elevation 高程 (m) 距进水口距离 (m) Distance from the power intake (m) Fig Profile of funnel ahead of bottom outlet after 20 years of operation of the reservoir Elevation 高程 (m) 初始 20 年末 Distance from 距进水口距离 the power intake (m)(m) Fig Profile of funnel ahead of low-level surface bay after 20 years of operation of the reservoir 4-120

123 Elevation 高程 (m) 初始 20 年末 Distance from 距进水口距离 the power intake (m)(m) Fig Profile of funnel ahead of high-level surface bay after 20 years of operation of the reservoir As shown from Fig through Fig , after 20 years of operation of the reservoir, the sedimentation elevation ahead of the power intake of Unit 3 will be m, almost no sedimentation will occur at the excavated slopes and a sedimentation thickness of 1.5 to 2m will occur upstream of the ramp; the sedimentation ahead of the power intake of Unit 11 will be identical to that of Unit 3; the max. sedimentation thickness around the gate of bottom outlet will be m, and the funnel profile has a gradient of 1:9.8; the max. sedimentation thickness around the gate of low-level surface bay will be m, and the funnel profile has a gradient of 1:8.4; the max. sedimentation thickness around the gate of high-level surface bay will be m, and the funnel profile has a gradient of 1: ) Analysis of sediment scouring and deposition of local areas of main structures after 40 years of operation of the reservoir For the local sedimentation thickness ahead of the powerhouse after 40 years of operation of the reservoir, see Fig For profiles of funnels ahead of power intakes of Unit 3 and Unit 11, and ahead of the bottom outlet, low-level surface bay and high-level surface bay of the overflow section after 40 years of operation of the reservoir, 4-121

124 see Fig through Fig respectively. Fig Local sedimentation thickness ahead of the powerhouse after 40 years of operation of the reservoir Elevation 高程 (m) 初始 40 年末 Distance from 距进水口距离 the power intake (m)(m) Fig Profile of funnel ahead of power intake of Unit 3 after 40 years of operation of the reservoir 4-122

125 Elevation 高程 (m) 初始 40 年末 Distance from 距进水口距离 the power (m) intake (m) Fig Profile of funnel ahead of power intake of Unit 11 after 40 years of operation of the reservoir 初始 40 年末 Elevation 高程 (m) Distance from 距进水口距离 the power intake (m)(m) Fig Profile of funnel ahead of bottom outlet after 40 years of operation of the reservoir 4-123

126 Elevation 高程 (m) 初始 40 年末 Distance from 距进水口距离 the power intake (m) (m) Fig Profile of funnel ahead of low-level surface bays after 40 years of 230 operation of the reservoir 225 Elevation 高程 (m) 初始 40 年末 Distance from 距进水口距离 the power intake (m) (m) Fig Profile of funnel ahead of high-level surface bays after 40 years of operation of the reservoir As shown from Fig through Fig , after 40 years of operation of the reservoir, the sedimentation elevation ahead of the power intake of Unit 3 will be 201m, almost no sedimentation will occur at the excavated slopes and a sedimentation thickness of 2.2 to 4.3m will occur upstream of the ramp; the sedimentation ahead of the power intake of Unit 11 will be identical to that of Unit 3; the max. sedimentation thickness around the gate of bottom outlet will be m, and the funnel profile has a gradient of 4-124

127 1:50.0; the max. sedimentation thickness around the gate of low-level surface bay will be m, and the funnel profile has a gradient of 1:6.8; the max. sedimentation thickness around the gate of high-level surface bay will be m, and the funnel profile has a gradient of 1:6.0. c) Sediment concentration in turbine flow For the sediment concentration in turbine flow for different operation years, see Table As shown from the table, with the increase of operation years of the reservoir, the average annual sediment concentration in turbine flow increases. In the 40th year of operation, the average annual sediment concentration in turbine flow is kg/m 3. Table Sediment concentrations in turbine flow for different operation years Year of 0peration Unit 10 years 20 years 30 years 40 years Sediment concentration in turbine flow kg/m Among the sediment in turbine flow, the percentage of grain larger than 0.05mm by weight is shown in Table As shown from the table, after 40 years of operation of the reservoir, the percentage of grain larger than 0.05mm by weight ranges from 42% to 43%. Table Percentage of sediment grain larger than 0.05mm by weight Year of 0peration 10 years 20 years 30 years 40 years Percentage of sediment grain larger than 0.05mm by weight (%) Downstream the dam a) Analysis of integral sediment scouring and deposition in the river reach downstream the dam The sediment scouring and deposition in the river reach downstream the dam after 5 years of operation of the reservoir is shown in Fig

128 Fig Sediment scouring and deposition in the river reach downstream the dam after 5 years of operation of the reservoir As shown from Fig , the sediment upstream the dam will be intercepted after the dam is built, and the sediment concentration in the outflow will decrease, which will result in scouring in the river reach downstream the dam. The scouring will mainly occur in the existing main channel, with a max. depth of 2.71m, and part of the side shoals will be subject to slight sedimentation. b) Analysis of local sediment scouring and deposition in the downstream approach channel The sediment scouring and deposition in the downstream approach channel after 5 years of operation of the reservoir is shown in Fig

129 Fig Sediment scouring and deposition in the downstream approach channel after 5 years of operation of the reservoir As shown from Fig , the sediment will mainly deposit at the entrance area of the downstream approach channel. The sedimentation thickness in the downstream approach channel will decrease with the increase of distance from the entrance area, and the max. sedimentation thickness will be about 1.3m Three-dimensional Sediment Calculation for Local Areas of Main Structures Scope and contents of the calculation The scope and contents of the 3-D sediment calculation for local areas of main structures are as below: a) Upstream the dam: sedimentation ahead of the powerhouse after 40 years of operation of the reservoir. b) Downstream the dam: sedimentation in the downstream approach channel after 5 years of operation of the reservoir Fundamental equations of 3D sediment mathematical model SSIIM software is adopted for the mathematical simulation of the project. The 4-127

130 software is 3D computational fluid mechanics software developed to simulate sediment movement in river channel and reservoir. SSIIM model is software developed specifically to study computational fluid mechanics for water resources works and can be used to simulate reservoir sediment movement during water level fluctuation, to simulate sediment deposition and reservoir sediment discharging, and to study sediment deposition for multi-intake cases. This model was developed to simulate sediment movement initially and has been applied to other field recently. SSIIM solves N-S equation based on 3D unstructured grid and solves convection diffusion equation including sediment and other parameters by apply k-ε turbulence model and adopting SIMPLE algorithm for pressure term. Compared to other CFD software, the advantage of SSIIM is that it can simulate sediment movement of movable bed. Meanwhile, it can simulate movement of several groups of sediment grain sizes and handle the variation of dry-wet grid caused by water level fluctuation. Therefore, this model is suitable for sediment simulation for the project. SSIIM has two versions, SSIIM1 and SSIIM2, the difference is that SSIIM1 is based on structured grid and SSIIM2 is based on unstructured grid. SSIIM1 is relatively convenient to use but cannot handle dry-wet grid. The discharge of this hydropower project varies from day to day, and dry-wet boundary must be considered, so SSIIM2 is employed. a) Flow calculations SSIIM calculates flow velocity by solving 3D turbulence N-S equation and solves turbulent shear stress with k-ε turbulence model. N-S equation of incompressible fluid can be expressed by: U t i U i U x j i 1 x j ( P ij u u i j ) (4-22) On the left side of the equation the first term is time-varying term and the second is convective term, and on the right side of the equation the first term is pressure term and the second is Reynolds stress term. Turbulence model needs to be introduced to determine Reynolds stress term

131 The equation uses finite volume method for dispersing and implicit scheme for solving, and the default method for pressure correction is SIMPLE algorithm. For convective term, exponential scheme and second-order upwind scheme are adopted for dispersing. Exponential scheme is the function of Pechlet number, and this scheme can reduce diffusion flux while second-order upwind scheme cannot. In SSIIM computations, time-varying term is ignored by default. In canonical algorithm, gravity term is exclusive and is only involved in some calculations with free surface such as simulation of spillway and flood wave with steep forward. In the computations, gravity term can be introduced by Command F36. b) Sediment movement calculations Non-uniform sediment transport is calculated with given sediment gradation in SSIIM. In sediment calculations, in Control file, the percentage of each size group, sediment size and sediment settling velocity are given by Command S, and the number of sediment size groups is given by Command G1. In Control file, there are two methods to give sediment inflow: one is give sediment inflow (in kg/s) by Command I. The distribution of sediment concentration at vertical is derived by Hunter-Rouse calculations. The sediment inflow given by this method is distributed throughout the whole intake section (i=1). The other method is give sediment inflow by Command G 5, and the sediment inflow is distributed only at the specific positions of grid boundary and in volume facture of sediment. Similarly, sediment inflow can be accumulated with the sediment inflows of several places given by Commands I and G5. Initial gradation of bed load is realized by Commands N and B in Control file. A series of bed load gradations are given by Command N, and the distribution of bed load gradation on bed surface is given by Command B. Sediment movement includes bed load movement and suspended load movement usually, and suspended load movement can be simulated by convection diffusion equation of sediment concentration c: 4-129

132 c U t j c x j c w z x j T c x j (4-23) Where, c is sediment concentration and calculated in volume fraction in SSIIM, w is the sediment settling velocity, Γ is diffusion coefficient and derived by k-ε model: T (4-24) S c Sc is Schmidt number and is taken at 1 by default. It can be adjusted by Command F12 in Control file. For suspended load movement, an expression to calculate sediment concentration close to the bed c bed was proposed by van Rijn in 1987: d 0.3 c c bed (4-25) a 0.1 g c Where, d is sediment size; a is the reference bed surface, equal to roughness height; τ is the shear strength on bed surface; τc is critical incipient shear stress derived from Shield curve; ρ w and ρ s are sizes of water and sediment; ν is the coefficient of kinematic viscosity of water; and g is gravitational acceleration. The empirical parameters in the equation (0.015, 1.5 and 0.3) can be adjusted by Command F6 in Control file. For unsteady calculations, the sediment concentration in the equation can be calculated by converting it to incipient sediment, i.e., giving Command F372 in Control file. The attenuation coefficient of sediment critical incipient shear stress is the function of bed gradient, and the functional relation between them can be expressed by the equation (Brooks, 1963) below: 2 2 sin sin sin sin 2 tan K cos 1 (4-26) tan tan tan s w w 2 1`.5 Where, α is the included angle between the flow direction and the direction vertical to bed surface; φ is the bed gradient; θ is the base slope parameter; K is the attenuation factor, 4-130

133 and the product of the attenuation factor and the critical incipient shear stress under horizontal bed surface condition is the effective critical bed incipient shear stress. q b of bed load is calculated by Van Rijn equation: q D b s g c (4-27) ( ) 50 s D 2 c The empirical parameters in the equation (0.053, 2.1, 0.3 and 1.5) can be adjusted by Command F83 in Control file. The bed form height Δ is calculated by van Rijn equation g 0.1 (1987). D 0.11 d d e c 2 c c 25 c 50 (4-28) Where, d is water depth. The effective roughness height is calculated by the equation below (van Rijn, 1987): 3D e 25 k s (4-29) Where, λ is the bed form length, taken as 7.3 times of the water depth. It should be noted that in van Rijn equation, the bed form roughness height is established under uniform sediment condition, and for non-uniform sediment, the bed form size is smaller than that for uniform sediment. The parameters in the equation can be given by relevant commands in Control file. If it s necessary to use different equations, programming computations can be conducted in File beddll.dll Division of Computing Grid In accordance with the topographic data of the computing area, an unstructured grid are generated by the grid generation module in SSIIM and are shown in Fig and Fig The SSIIM grid generation principle is as follows: firstly, select the plane area (i.e., underwater area) requiring grid generation and generate 2D grid in the selected area, then generate vertical grid by vertical layering technology, i.e., layering between the water surface and the bed surface at grid nodes (10 layers vertically for the model), and 4-131

134 thus generate 3D grid. In the actual computation process by SSIIM, before the start of each computing step, the grid is re-divided based on the topography calculated from the previous time step and the water level of the current time step. Since the study of this report involves unsteady flow process and riverbed deformation, this feature of SSIIM software is applicable. To better simulate the original terrain boundary by 3D grid, body-fitted grid technology is employed and can be realized by adding Command F in Control file in SSIIM. Fig Upstream Computing Grid 4-132

135 Fig Downstream Computing Grid Computing boundary conditions a) Inlet boundary: Based on the known full-section discharge at the inlet, the transverse distribution of unit-width discharge of inflow along the section is given, and the sediment concentration of each grid of inlet section is given. The discharge and sediment concentration process of the inlet section is provided by the overall 2D sediment computations for the main works. b) Outlet boundary: The water level at the outlet section is given. The computing outlet water level for the upstream area of the damsite is the reservoir water level, and that for the downstream area of the damsite is derived from the discharge at the outlet and the corresponding rating curve. c) Solid wall boundary: Solid wall no-slip condition is adopted for the model, and the flow velocity of solid wall boundary is given as zero. Moving boundary is subject to cyclic determination by the minimum water depth. d) Free surface boundary: The vertical gradient along water surface of flow variables of free surface is taken at zero, and the sediment concentration boundary is determined by 4-133

136 the equation below: sk ssk s z zz s 0 e) Bed surface boundary: A critical factor deciding success or failure of a sediment mathematical model is sediment exchange between riverbed and stream flow. In SSIIM program, the sediment exchange at bad surface is controlled by suspended sediment concentration close to the bed Calculation Results and Analysis a) Analysis of sediment scouring and deposition ahead of the powerhouse For the sedimentation thickness ahead of the powerhouse for different operation years, see Fig through Fig As shown from the figures, the sediment will mainly deposit upstream of the sediment barrier and the area ahead of the powerhouse where the flow pattern is relatively steady. Fig Sediment scouring and deposition ahead of the powerhouse after 10 years of operation 4-134

137 Fig Sediment scouring and deposition ahead of the powerhouse after 20 years of operation Fig Sediment scouring and deposition ahead of the powerhouse after 30 years of operation 4-135

138 Fig Sediment scouring and deposition ahead of the powerhouse after 40 years of operation In order to analyze the sedimentation along the longitudinal direction ahead of the powerhouse, Units 1, 4, 7, 10 and 14 are selected for the analysis. For the locations of the units, see Fig For the longitudinal sections of sedimentation ahead of the units, see Fig through Fig

139 Unit 14 Unit 10 Unit 7 Unit 4 Unit 1 Fig Location of units in the powerhouse Elevation Distance from the power intake (m) Fig Longitudinal section of sedimentation ahead of Unit

140 Elevation 高程 (m) 年末 30 年末 40 年末 Distance from 距坝前距离 the power (m) intake (m) 初始 10 年末 Fig Longitudinal section of sedimentation ahead of Unit 4 Elevation 高程 (m) 年末 30 年末 40 年末 Distance from 距坝前距离 the power (m) intake (m) 初始 10 年末 Fig Longitudinal section of sedimentation ahead of Unit 7 Elevation 高程 (m) 年末 30 年末 40 年末 Distance from 距坝前距离 the power (m) intake (m) 初始 10 年末 Fig Longitudinal section of sedimentation ahead of Unit

141 Elevation 高程 (m) 年末 30 年末 40 年末 Distance from the 距坝前距离 power intake (m) (m) 初始 10 年末 Fig Longitudinal section of sedimentation ahead of Unit 14 As shown from Fig through Fig , after the power station is put into operation, all the longitudinal sections present sedimentation trend. The sedimentation will mainly concentrate at the front edge of the power intake and the area upstream of the excavated slope. The sedimentation thickness ahead of all the power intakes has no big difference. At the end of the 10th year of operation, the average sedimentation thickness will be 1.18m, and the sedimentation elevation will reach 199.2m; At the end of the 20th year of operation, the average sedimentation thickness will be 2.02m, and the sedimentation elevation will reach m; At the end of the 30th year of operation, the average sedimentation thickness will be 2.56m, and the sedimentation elevation will reach m; At the end of the 40th year of operation, the sedimentation elevation will reach m. b) Analysis of sediment scouring and deposition in the downstream approach channel In order to analyze the sediment scouring and deposition in the downstream approach channel, 4 typical sections are selected. The locations of the sections are shown in Fig For the sediment scouring and deposition of each section, see Fig through Fig

142 Fig Locations of typical sections 3 Sedimentation thickness (m) 淤积厚度 (m) 2 1 第一年末第二年末第三年末第四年末第五年末 Relative 相对河宽 river width Fig Sedimentation at Section

143 3 Sedimentation thickness (m) 淤积厚度 (m) Sedimentation 淤积厚度 thickness (m) (m) Relative 相对河宽 river width Fig Sedimentation at Section 2 第一年末第二年末第三年末第四年末第五年末第一年末第二年末第三年末第四年末第五年末 Relative 相对河宽 river width Fig Sedimentation at Section

144 2 Sedimentation thickness (m) 淤积厚度 (m) 1 第一年末第二年末第三年末第四年末第五年末 Relative 相对宽度 river width Fig Sedimentation at Section 4 As shown from Fig through Fig , after the power plant is put into operation, all the sections present sedimentation trend. Among them, the sedimentation at Sections 1 and 2 which are close to the entrance are relatively high, and that at Sections 3 and 4 which are far from the entrance are relatively low. After one year of operation of the power plant, the average sedimentation thickness will be 0.28m, 0.31m, 0.23m and 0.14m for Sections 1, 2, 3 and 4 respectively. After five years of operation of the power plant, the average sedimentation thickness will be 1.26m, 1.43m, 1.04m and 0.65m for Sections 1, 2, 3 and 4 respectively Calculation of Reservoir Backwater Calculation Scheme According to the opinions proposed by French CNR, the natural water surface profile and reservoir backwater line of the flood at various frequencies (such as 20%, 10%, 5%m 4%, 2%, 1%, 0.5%, 0.2%, 0.1%, 0.05%, 0.02% and 0.01%) shall be calculated. In addition, the natural water surface profile and reservoir backwater line at frequent flood with a return period less than 5 years and various small discharges (full load discharge of units 6100m 3 /s, 10000m 3 /s, and open discharge of 16,700m 3 /s)

145 Basic Data for Calculation a) Section data Measured natural section is adopted for calculation of natural water surface profile, while that subjected to 20-year sedimentation is adopted for calculation of reservoir backwater line. b) Roughness According to the calculation results and comprehensive analysis on roughness at this phase, in combination with the comprehensive analysis on section shape of river bed in the reservoir area, riverway pattern and the vegetation developed on both banks, and in reference to engineering experience of other projects in this region, the sectional roughness results (see Table ) derived from the water level measured in August 2016 has been adopted to calculate the reservoir sedimentation. Conservatively, the natural roughness will be employed as the roughness after the reservoir establishment and in the process of sedimentation.. c) Initial water level and discharge Since there are no large tributaries in the Paklay reservoir area, the water-collecting area between the dam site of Paklay and that of Xayabury only accounts for 3.9% of that at the dam site of Paklay. Since the change of discharge in the reservoir area along the elevation is small, to guarantee safety, the discharge at the dam site of Paklay is taken as the discharge at each section while calculating the backwater. The initial water level in front of the dam for calculation of natural water surface profile at each discharge can be obtained from the rating curve at the dam site; for backwater calculation at a flood with a return period of 5 years or more, the calculation results for flood regulation is taken as the initial water level in front of the dam; and for backwater calculation at frequent flood with a return period less than 5 years and various small discharges, NPL (240m) and the maximum water level at open discharge (obtained from discharge capacity curve) are taken as the 4-143

146 water level in front of the dam under routine dispatching mode and ecologically friendly sediment flushing mode, respectively. See Table and Table for the initial water level in front of the dam and discharge calculated

147 Table Initial water levels in front of the dam and discharges (at a flood with a return period of 5 years or more) Discharge Initial water level in front of the Initial water level in front Item at Dam Dam Calculated for Natural Water of the Dam Calculated for Site Surface Profile Backwater m 3 /s m m 0.01% % % % % % Flood 1% Frequency 2% % % % % % Open discharge Table Initial water levels in front of the dam and discharges (at frequent flood with a return period less than 5 years and various small discharges) Initial water level in front of the Dam Initial water level in front of the Dam Discharge at Calculated for Backwater Calculated for Natural Water Surface Dam Site Maximum water level in front Profile NPL of the dam at open discharge m 3 /s m m m Result of Backwater Calculation Reservoir backwater is calculated according to the model of constant gradual flow of open channel. Refer to Table to Table for backwater calculation results. Table Backwater Calculation Results for Paklay Reservoir (P=0.01%, Q=38800m 3 /s) Water level Mean velocity at section Accumulated Section Thalweg S/N distance Natural Backwater After reservoir Natural Difference No. level level building km m m m m/s m/s m/s 1 Upper damsite CS CS

148 4 CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS

149 53 CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS Table Backwater Calculation Results for Paklay Reservoir (P=0.02%, Q=37000m 3 /s) Water level Mean velocity at section Accumulated Section Thalweg S/N distance Natural Backwater Natural Backwater Difference No. level level level level km m m m m/s m/s m/s 1 Upper damsite CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS

150 27 CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS Table Backwater Calculation Results for Paklay Reservoir (P=0.05%, Q=34700m 3 /s) Water level Mean velocity at section Accumulated Section Thalweg S/N distance Natural Backwater After reservoir Natural Difference No. level level building km m m m m/s m/s m/s 1 Upper

151 damsite 2 CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS

152 50 CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS Table Backwater Calculation Results for Paklay Reservoir (P=0.1%, Q=33000m 3 /s) Water level Mean velocity at section Accumulated Section Thalweg S/N distance Natural Backwater After reservoir Natural Difference No. level level building km m m m m/s m/s m/s 1 Upper damsite CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS

153 24 CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS Table Backwater Calculation Results for Paklay Reservoir (P=0.2%, Q=31200m 3 /s) 4-151

154 Water level Mean velocity at section Accumulated Section Thalweg S/N distance Natural Backwater After reservoir Natural Difference No. level level building km m m m m/s m/s m/s 1 Upper damsite CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS

155 45 CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS Table Backwater Calculation Results for Paklay Reservoir (P=0.5%, Q=29000m 3 /s) Water level Mean velocity at section Accumulated Section Thalweg S/N distance Natural Backwater After reservoir Natural Difference No. level level building km m m m m/s m/s m/s 1 Upper damsite CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS

156 19 CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS

157 68 CS Table Backwater Calculation Results for Paklay Reservoir (P=1%, Q=27200m 3 /s) Water level Mean velocity at section Accumulated Section Thalweg S/N distance Natural Backwater After reservoir Natural Difference No. level level building km m m m m/s m/s m/s 1 Upper damsite CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS

158 42 CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS Table Backwater Calculation Results for Paklay Reservoir (P=2%, Q=25500m 3 /s) Water level Mean velocity at section Accumulated Section Thalweg S/N distance Natural Backwater After reservoir Natural Difference No. level level building km m m m m/s m/s m/s 1 Upper damsite CS CS CS CS CS CS CS CS CS CS CS CS CS CS

159 16 CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS

160 65 CS CS CS CS Table Backwater Calculation Results for Paklay Reservoir (P=3.33%, Q=24000m 3 /s) Water level Mean velocity at section Accumulated Section Thalweg S/N distance Natural Backwater After reservoir Natural Difference No. level level building km m m m m/s m/s m/s 1 Upper damsite CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS

161 39 CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS Table Backwater Calculation Results for Paklay Reservoir (P=4%, Q=23700m 3 /s) Water level Mean velocity at section Accumulated Section Thalweg S/N distance Natural Backwater After reservoir Natural Difference No. level level building km m m m m/s m/s m/s 1 Upper damsite CS CS CS CS CS CS CS CS CS CS CS

162 13 CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS

163 62 CS CS CS CS CS CS CS Table Backwater Calculation Results for Paklay Reservoir (P=5%, Q=23000m 3 /s) Water level Mean velocity at section Accumulated Section Thalweg S/N distance Natural Backwater After reservoir Natural Difference No. level level building km m m m m/s m/s m/s 1 Upper damsite CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS

164 36 CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS Table Backwater Calculation Results for Paklay Reservoir (P=10%, Q=21100m 3 /s) Water level Mean velocity at section Accumulated Section Thalweg S/N distance Natural Backwater After reservoir Natural Difference No. level level building km m m m m/s m/s m/s 1 Upper damsite CS CS CS CS CS CS CS CS

165 10 CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS

166 59 CS CS CS CS CS CS CS CS CS CS Table Backwater Calculation Results for Paklay Reservoir (P=20%, Q=19000m 3 /s) Water level Mean velocity at section Accumulated Section Thalweg S/N distance Natural Backwater After reservoir Natural Difference No. level level building km m m m m/s m/s m/s 1 Upper damsite CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS

167 33 CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS Table Backwater Calculation Results for Paklay Reservoir (Q=16700m 3 /s) Water level Mean velocity at section S/N Section No. Accumulated distance Thalweg Natural level Backwater lever before open discharge Backwater lever after open discharge Natural After reservoir building (before open discharge) Difference After reservoir building (after open discharge) Difference km m m m m m/s m/s m/s m/s m/s 1 Upper damsite CS CS

168 4 CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS

169 53 CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS Note: NPL is adopted as the initial water level for water surface profile before open discharge, and the maximum water level in front of the dam obtained from flood regulation calculation as the initial water level for water surface profile after open discharge. The same is applied below. Table Backwater Calculation Results for Paklay Reservoir (Q=10000m 3 /s) Water level Mean velocity at section S/N Section No. Accumulated distance Thalweg Natural level Backwater lever before open discharge Backwater lever after open discharge Natural After reservoir building (before open discharge) Difference After reservoir building (after open discharge) Difference km m m m m m/s m/s m/s m/s m/s 1 Upper damsite CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS

170 20 CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS

171 Table Backwater Calculation Results for Paklay Reservoir (Q=6100m 3 /s) Water level Mean velocity at section S/N Section No. Accumulated distance Thalweg Natural level Backwater lever before open discharge Backwater lever after open discharge Natural After reservoir building (before open discharge) Difference After reservoir building (after open discharge) Difference km m m m m m/s m/s m/s m/s m/s 1 Upper damsite CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS

172 39 CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS The tables to show that after Paklay reservoir is established, the reservoir water level will be higher than that in the natural conditions, and the flow velocity in the river channel in the reservoir area will be slower. Under open discharge or ecologically friendly sediment flushing scheduling modes, the water level in the reservoir area will be lowered, and the velocity will be increased and gradually approach the velocity under natural conditions. After Paklay reservoir is established, the area with large velocity change is mainly the 20km-long stretch in front of the dam, and the velocity change at the upper and intermediate parts will be small and within 0.1m/s basically. Therefore, by reasonable and effective scheduling of Paklay reservoir, the impact on the stream flow in reservoir area can be mitigated to a certain extent

173 Section No Upper damsite Natur al water level Table Calculation Results for Backwater of Paklay Reservoir Unit: m 0.01% 0.02% 0.05% 0.1% 0.2% 0.5% 1% 2% 3.33% 4% 5% 10% 20% Backwa ter level Natura l water level Backwat er level Natura l water level Backwat er level Natur al Backwate water r level level Natural water level Backwa ter level Natural water level Backwa ter level Natura l water level Backwat er level Natura l water level Natural Backwat water er level level Backwa ter level Natural water level Backwa ter level Natural water level Backwa ter level Natura l water level Backwat er level Natura l water level Backwat er level Open discharge (16700) Natura l Backwater water level level CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS

174 Section No Natur al water level 0.01% 0.02% 0.05% 0.1% 0.2% 0.5% 1% 2% 3.33% 4% 5% 10% 20% Backwa ter level Natura l water level Backwat er level Natura l water level Backwat er level Natur al Backwate water r level level Natural water level Backwa ter level Natural water level Backwa ter level Natura l water level Backwat er level Natura l water level Natural Backwat water er level level Backwa ter level Natural water level Backwa ter level Natural water level Backwa ter level Natura l water level Backwat er level Natura l water level Backwat er level Open discharge (16700) Natura l Backwater water level level CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS

175 Section No Natur al water level 0.01% 0.02% 0.05% 0.1% 0.2% 0.5% 1% 2% 3.33% 4% 5% 10% 20% Backwa ter level Natura l water level Backwat er level Natura l water level Backwat er level Natur al Backwate water r level level Natural water level Backwa ter level Natural water level Backwa ter level Natura l water level Backwat er level Natura l water level Natural Backwat water er level level Backwa ter level Natural water level Backwa ter level Natural water level Backwa ter level Natura l water level Backwat er level Natura l water level Backwat er level Open discharge (16700) Natura l Backwater water level level CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS CS

176 4.12 Operation Mode of Reservoir and Power Station Main Characteristic Parameters of Reservoir and Power Station The Paklay HPP has a normal pool level of m a.s.l. with a corresponding storage of x 10 6 m 3 and a minimum pool level of m a.s.l. with a regulating storage of 58.4 x 10 6 m 3. The HPP has a design installed capacity of 770 MW, an average annual energy output of GW h, and an annual operating hours of installed capacity being 5357 h. Based on the power procurement policy of EGAT, the HPP has an average annual PE of GW h, SE of GW h, EE of GW h, and an average annual equivalent energy of GW h Reservoir Operation and Dispatching Mode The Paklay HPP is a low-head runoff type hydropower station. To lower the impact of reservoir inundation and to facilitate reservoir scouring, natural flow conditions shall be resumed as much as possible during flood season, and the water level of reservoir shall be close to the natural water level as much as possible. We propose the following operation mode of the reservoir according to this principle and taking the characteristics of the inflow of Paklay HPP into consideration: a) Power generation dispatching When the predicted inflow is less than the discharge 6,100m 3 /s under the full power of the generating unit, the power station operates according to the normal generation mode, and the necessary intraday adjustment can be carried out according to the change of the intraday electric load, and the water level of the reservoir can vary between the minimum pool level 239m and the normal pool level 240m. The minimum operation level of the reservoir shall not be lower than 239m. If the Paklay HPP directly supplies power to Thailand in method I specified in 4.2.2, according to EGAT's power procurement policy, its reservoir should operate with the maximum annual energy value (i.e., equivalent energy) as the target. On condition that the minimum discharge requirement is satisfied, the highest priority shall be given to the PE, followed by the SE and then the EE. As the reservoir of the Paklay HPP is a typical 4-174

177 low-head river channel type reservoir, restricted by the reservoir storage, the run-of-river power generation is adopted during flood season with high discharges, and the reservoir maintains the normal pool level to obtain a high head for power generation, reduce blocked generation capacity and increase power generation benefits. During dry season with low discharges, limited regulating storage can be utilized to regulate and store the daily discharge, and during the periods of EE and SE, priority is given to water storage and the stored water is used for power generation during the period of PE to increase the equivalent energy and power generation benefits of the HPP. If the Paklay HPP sells power to EDL and EDL then sells power to EGAT in method II specified in 4.2.2, as EDL purchases power at a single price, the reservoir should operate with the maximum annual energy output as the target and the normal pool level maintained as much as possible, without daily regulation, and the run-of-river power generation should be adopted. b) Flood dispatching When the predicted inflow is greater than the discharge 6,100m 3 /s under the full power of the generating unit and less than 16,700m 3 /s, the discharge can be controlled according to the condition that the outflow is equal to the inflow, the generating set generates the electricity as per flow under full power, the redundant flow can be discharged via opening the flood releasing facilities, and the water level of the reservoir keeps at the normal pool level 240m.When the inflow is greater than 16,700m 3 /s and the predicted subsequent inflow will continue to increase, the flood releasing facilities shall be opened cascade by cascade until all of them are opened fully. The hydroproject shall discharge openly as per discharge capacity, and the water level of the reservoir goes down naturally, and the HPP shuts down when the net head is lower than the minimum power head of the units. At the flood recession limb, when the inflow is less than 16,700m 3 /s and the predicted subsequent inflow will continue to decrease, the flood releasing facilities shall be opened cascade by cascade, the water level of the reservoir gradually reaches the normal pool level 240m, and the power generation of the HPP restores when the net head is higher than the minimum power head of the units

178 In the flood season, when the inflow is greater than 16,700m 3 /s and the predicted subsequent inflow will continue to increase, the flood releasing facilities shall be opened cascade by cascade until all of them are opened fully. The water level of the reservoir will drop gradually from 240m. During this process, the opening speed and the opening degree of the sluice gate shall be adjusted reasonably according to the flood prediction and the rate of change in the outflow discharge of the hydroproject shall be controlled. Similarly, at the flood recession limb, when the inflow is less than 16,700m 3 /s and the predicted subsequent inflow will continue to decrease, the flood releasing facilities shall be opened cascade by cascade until the water level of the reservoir reaches the normal pool level 240m. The rate of change of the outflow discharge of the hydroproject shall also be controlled during this process. The control principle of the outflow discharge during the process of emptying out and restoring the reservoir in the flood season is as follows: 1) Ensure that the variation amplitude of the reservoir water level is not so fast as to affect the stability of reservoir bank; 2) Ensure that the variation amplitude of the downstream water level caused by the unsteady flow is not so large as to affect the stability of downstream embankment, the shipping and other water; 3) In addition, it is necessary to avoid the inundation of downstream banks due to the increase of outflow discharge, and especially avoid the effect on Paklay County. At this stage, taking the characteristics of both of the reservoir and inflow of the Paklay HPP into consideration, according to the control principle mentioned above and with the maximum daily variation range of reservoir water level controlled at 3m/d, it is proposed preliminarily that the outflow discharge should be controlled with a speed which is greater than the inflow by 1,600m 3 /s till the complete discharge under the full opening of the gates; it is proposed preliminarily that the outflow discharge should be controlled with a speed which is less than the inflow by 1,600m 3 /s till the water level of the reservoir restores to the normal pool level 240m during the restoring process. The outflow discharge shall be controlled under the mode obtained from the flood regulating calculation on the 4-176

179 design flood of various frequencies; the maximum daily variation amplitude of the reservoir water level can be controlled within 3m/d, and the corresponding maximum daily variation amplitude of the downstream water level is within 2.2m/d. Water level (m) NPL Min. operating level Natural water level Reservoir operating curve Discharge Fig Schematic Diagram on Reservoir Operation Mode Dispatching and Management of Reservoir Sediment After the Paklay HPP is built, the water level in the reservoir area will be raised and the flow conditions along the riverway will be consequently changed, thus exerting certain impact on the transport of river sediment. To reduce the impact of reservoir construction on the transport of river sediment and river morphology, at this phase, according to the inflow and sediment conditions of the Paklay reservoir, the proposed sediment dispatching mode and management measures of the reservoir are as follows: 1) When the inflow is greater than 16,700m 3 /s during the flood season and the predicted subsequent inflow will continue to increase, the flood releasing facilities shall be opened cascade by cascade until all of them are opened fully. The hydroproject shall discharge openly as per discharge capacity, and the water level of the reservoir goes down naturally. The water level of riverway under natural conditions shall be realized as much as 4-177

180 possible, to facilitate reservoir scouring. According to the mean flow velocity of river channel sections in the reservoir area at various discharges (see the tables from to ), when the gates are fully opened and the reservoir water level is lowered, the mean velocity of river channel sections in the reservoir area is close to that under the natural conditions. That indicates the mode of operation at lowered water level can effectively discharge the sediment from the reservoir area. 2) In case of large sediment concentration and sediment discharge through monitoring, even though the inflow during flood season is less than 16,700m 3 /s, the sediment can be discharged by opening the sluice gate or lowering the reservoir water level as appropriate. 3) To scour and discharge the coarse bed material deposited inside the reservoir effectively, it is recommended that the reservoir water level be lowered to the lowest level for ecologically friendly sediment scouring every 2~5 years and the specific frequency can be determined as per the monitoring results of hydrology and sediment. The sediment discharge should synchronize with that at the upstream/downstream cascade HPPs. 4) The sediment releasing bottom outlet shall be subject to irregular opening/closing operations as appropriate, to prevent direct deposit of sediments behind the gate of such outlet, posing threats to the stability of structure. Besides, the operations above can prevent potential equipment rusting and aging due to long-term idling and can ensure that such gate can be opened in case of emergency. 5) Considering that the effect of sediment scouring and discharge may be unfavorable for some area of the reservoir through the sediment scouring and discharge methods above, the sediment in such area can be removed through sand basin and mechanical desilting. 6) Proceeding from the features concerning inflow and sediment and operation of the Paklay reservoir, an observation and monitoring plan for hydrology and sediment of the reservoir shall be formulated and the work concerning such observation and monitoring shall be carried out, including the tests on water and sediment in and out from the reservoir, observation on fixed sections in the reservoir area, observation on section beneath dam, 4-178

181 observation on water level in the reservoir area, sampling on sedimentation in the reservoir area and tests on grain gradation. 7) During the sediment flushing period, monitoring over the reservoir sediment inflow and outflow shall be more frequent. 8) The data concerning observation and monitoring on hydrology and sediment of the reservoir shall be collected regularly, and such data shall be analyzed in combination with the operation and dispatching features of the reservoir. The sediment dispatching mode of reservoir shall be optimized and adjusted as per the analysis results. 9) During sediment scouring, the sediment concentration of the outflow discharge shall be monitored and controlled, to prevent adverse impact on the ecology at the downstream. According to the operation and dispatching of the reservoir, the maximum allowable downstream sediment concentration shall be proposed to serve as the controlling index for ecological regulation of sediment through evaluation on the ecology at the downstream. At this stage, the preliminary index of maximum allowable downstream sediment concentration can be determined by analysis based on the measured data from the adjacent hydrometric stations. In the future, sediment monitoring at the damsite shall be continued to accumulate more monitoring data and adjust the index based on the monitoring results Overyear Operation Characteristic Indices a) Discharge After influence from regulation and storage of the Xiaowan Reservoir and Nuozhadu Reservoir is considered, the HPP has an average annual reservoir inflow of 4,090 m 3 /s, an average annual power discharge of 3,500 m 3 /s, an abandon water discharge of 570 m 3 /s, a utilization ratio of water resource of 86.03%, and a maximum quotative discharge for power generation of 6,101 m 3 /s. The Paklay HPP's daily average reservoir inflow and power discharge dependability curves are shown in Fig

182 Fig Paklay HPP's Daily average Reservoir Inflow and Power Discharge Dependability Curves b) Reservoir water level The Paklay HPP has a normal pool level of m a.s.l. and a minimum pool level of m a.s.l. The daily average water level dependability curve of the reservoir is shown in Fig Statistics indicates that the duration when the reservoir operate with daily average water level at the normal pool level of m a.s.l. accounts for about 20.0% of its total operation duration. The daily average minimum pool level of the reservoir is m a.s.l

183 Fig Daily average Reservoir Water Level Dependability Curve of Paklay HPP The overyear monthly average reservoir water level is shown in Fig The figure indicates that the reservoir inflow is high and the drop in level is small in the main flood season from July to October, with an average reservoir water level of above m a.s.l. The reservoir water level is close to the normal pool level of m a.s.l. in August and September, about m a.s.l. in June before the flood season and November after the flood season, and about m~239.60m a.s.l. in the dry season from December to next May

184 Fig Overyear Monthly Average Reservoir Water Level of Paklay HPP c) Head The maximum head, minimum head, weighted average head, and rated head of the Paklay HPP are m, 7.50 m, m, and m respectively, with a corresponding head dependability of 89%. The head dependability curve of the Paklay HPP is shown in Fig Fig Head Dependability Curve of Paklay HPP 4-182

185 d) Output The Paklay HPP has a duration dependability of 10% for power generation at the full installed capacity, and the daily average output with dependability of 90% is 260 MW. The daily average output dependability curve and energy accumulation curve of the HPP are shown in Fig and the overyear monthly average output is shown in Fig Fig Daily Average Output Dependability Curve and Energy Accumulation Curve of Paklay HPP 4-183

186 Fig Overyear Monthly Average Output of Paklay HPP 4.13 Analysis on Impact of Paklay Reservoir on Upstream and Downstream Reaches The Paklay HPP is a low-head runoff type hydropower station with small regulating storage, and therefore it is incapable of storing and transferring the inflow during flood season for power generation during dry season. As a whole, the outflow discharge of reservoir is identical to the inflow. The operation of reservoir will not change the discharge at the downstream basically, exerting no impact on the hydrological conditions of the Mekong River. However, the outflow discharge of reservoir is different from the inflow under the following conditions: 1) Intraday peak load operation of the HPP; 2) Flood regulation during flood of reservoir; 3) Sediment scouring of reservoir. The impact of Paklay reservoir operation on the upstream and downstream will be analyzed below directing at the three conditions above