COMPARATIVE SALIENT FEATURES

Transcription

1 COMPARATIVE SALIENT FEATURES Raigam HEP 126 MW 195 MW LOCATION OF THE PROJECT State Arunachal Pradesh Arunachal Pradesh District Anjaw Anjaw Tehsil Hayuliang (100 km from Tezu) Brahmaputra, Sub-basin Lohit Nearest Airport Dibrugarh (Assam) Dibrugarh (Assam) Nearest Railhead (Broad gauge) Tinsukia (Assam) Tinsukia (Assam) Nearest National Highway NH 52 (Tezu) NH 52 (Tezu) Name of the river/tributary River Basin/sub-basin Dalai (tributary to Lohit) Brahmaputra, Sub-basin Lohit Dalai (tributary to Lohit) Brahmaputra, Sub-basin Lohit Barrage Latitude N N Longitude E E Power House Latitude N N Longitude E E HYDROLOGY & CLIMATE 126 MW 195 MW Catchment area up to barrage km² Rainfed Catchment area km² Snowfed catchment area km² Average annual yield DIVERSION FLOOD(S) River diversion flood for 25 year return period Mcu m m³/s Design flood (SPF) for barrage height m³/s Design flood adopted for design of Barrage m³/s RESERVOIR FRL m MDDL m River Bed Level at barrage axis m Submergence area at FRL ha

2 DIVERSION STRUCTURE 126 MW 195 MW Type of structure Barrage Barrage Average river bed level at axis m Deepest foundation level m Length of barrage at top m Barrage top m Maximum height (above deepest foundation) m COFFER DAM & RIVER DIVERSION Diversion channel location Through river bed Diversion Tunnel 6.0m Long, Type of coffer dam Earthen Earthen Top elevation Coffer Dam m INTAKE Number of openings no 3 3 Size m x m 4.0 (w) x (w) x 3.5 (h) (h) Design discharge m³/s HEAD RACE TUNNEL 126 MW 195 MW Location Left Bank Left Bank Finished shape Modified Modified Horse Horse Shoe Shoe Length m Finished diameter m 7 7 Design discharge m3/s Velocity m/s Adit- 1: Shape, Size & Length D-Shape, 6.0 m & 238m Adit- 2: Shape, Size & Length D-Shape, 6.0 m & 223m Adit- 3: Shape, Size & Length D-Shape, 6.0 m & 196m SURGE SHAFT D-Shape, 6.0 m & 238m D-Shape, 6.0 m & 223m D-Shape, 6.0 m & 196m Type Restricted Restricted orifice orifice Diameter m Height m Top elevation (up to crown) m

3 PRESSURE SHAFT Type Circular Steel Circular Steel Lined Lined Discharge m3/s Internal diameter m Maximum velocity m/s Length of pressure shaft (up to trifurcation) m POWERHOUSE 126 MW 195 MW Type Underground Surface Power House Installed capacity MW 126 (3x42) 195 (3x65) Number of units no 3 3 Gross head (maximum) m Rated head m Type of turbine ENERGY Vertical Francis Vertical Francis Design energy in 90% dependable year MU Plant Load Factor in 90% dependable year % Energy in a 50% dependable year MU Plant Load Factor in 50% dependable year % Average annual energy MU 666, Average Plant Load Factor % Size of machine hall cavern (Incl. service bay) mxmxm 89.6x18x m (L) x 18.0m (W) x 38m (H) TAILRACE TUNNEL 126 MW 195 MW Diameter m 7 7 Shape Modified Open Channel Horse Shoe Length m m Wide, 75 m long, 8 m High Maximum TWL ( SPF Flow) m Tail water level Normal (all units running) m Minimum tail water (one machine running) m CONSTRUCTION PERIOD Year 4 5 PROJECT ESTIMATED COST Total Hard cost Crore Cr.

4 Escalation during construction (ESC) Crore Cr. Interest during construction (IDC) Crore Cr. Financial charges Crore Cr. Total estimated cost (including ESC, IDC & FC) Crore Cr. Cost per MW of installed capacity Crore TARIFF Tariff during 1st year of operation Rs Levelized Tariff (for 40 years of lease) Rs No. Project Component/ Item of works Land requirement Total Area(ha) 1 Barrage Complex (barrage, intake & coffer dams) Reservoir Submergence area (up to FRL 700m) Headrace tunnel 7m dia Adit 1, 2, 3-5m dia strip & portals (50m x 50m) Surface power house complex (surge shaft, pressure shaft, power house, Transformer Yard, tailrace) 6 Pot head yard & DG room N/A 7 Area for approach roads fro Barrage complex and Contractors camp Area for Permanent colony, Office, Quality control lab,workshop, Storage facilities (E & M equipment, Cement & Steel)& Fuelling area 9 Crusher, Batching & Mixing Plant Muck Disposal area 1, Magazine Area (in two places) Total 83.23

5 RELEVANT SECTIONS OF DETAILED PROJECT REPORT 3 x 65 MW Raigam HEP RAIGAM HEP (195 MW) RELEVANT SECTIONS OF DPR FOR THE PURPOSE OF SCOPING CLEARANCE SECTION I : INTRODUCTION SECTION II: EXECUTIVE SUMMARY SECTION III: SALIENT FEATURES SECTION IV: HYDROLOGY SECTION V: POWER POTENTIAL 11010A-H D01 A 1 of Mar-13

6 SECTION I INTRODUCTION

7 3 x 47 MW Raigam HEP TABLE OF CONTENTS LIST OF FIGURES... 2 CHAPTER 1 INTRODUCTION General Arunachal Pradesh Power Scenario Need for the Project Approach to the Project Area Project Proposal Major Components Preparation of Detailed Project Report Objectives of the Study Scope of Study Targeted Output Contents of Detailed Project Report A-H D01 A Chapter 1: Introduction 1 of Mar-13

8 3 x 47 MW Raigam HEP LIST OF FIGURES FIGURE NO. Fig. 1.0 TITLE Districts and Major Rivers Flowing in Arunachal Pradesh 11010A-H D01 A Chapter 1: Introduction 2 of Mar-13

9 3 x 47 MW Raigam HEP CHAPTER 1 INTRODUCTION 1.1 General M/s Sai Krishnodaya Industries (P) Ltd (SKIL) has signed a Memorandum of Agreement (MOA) with the Government of Arunachal Pradesh on 26 th February, 2009 to develop the proposed Raigam Hydro Electric Project ( 96 MW) on river Dalai, a major right bank tributary of Lohit river in on Build, Own, Operate and Transfer (BOOT) basis. As per MOA, the allotted FRL &TWL are 725 m & 520 m respectively. Based on detailed Surveys & Investigations carried out by the Project Company and keeping in view the upstream submergence of the villages at the proposed Barrage site, the FRL of the project has been kept at EL.725 m. As per finalized Project features, the Project will generate 195 MW by utilizing a design discharge of m 3 /s and net head of m. Raigam Hydro Electric project is located in the state of Arunachal Pradesh, India (Drawing No A-H X01) on river Dalai with its Barrage at latitude N and longitude E. and Surface Powerhouse at latitude 28 05' 43.60" N and longitude 96 32' 11.93" E. The project envisages utilization of water of Dalai, which is a right bank tributary of river Lohit. The river Brahmaputra is one of the biggest rivers in the world. The total length of Brahmaputra River in India is 885 km and its drainage basin in India is 1, 95,000 sq. km. There are 25 principal north bank tributaries of this river. The major ones are Subansiri, Siang, the Manas, the Dibang, the Dhansiri, the Torsa, and the Teesta etc. The Kameng is one of these 25 principal north tributaries of this river. The state of Arunachal Pradesh is enriched with tributaries like Tawang Chu, Kameng, Subansiri, Dihang etc. which originates from the mighty Himalayas. These are perennial in nature and carry floods almost every year during monsoon and as such have huge hydro potential. On completion, the project will provide 195 MW of power with generation of GWh of Design Energy. The project will provide benefits of free to Arunachal Pradesh as provided in the MoA signed with them. The development of the project will enhance the quality of life of the people living in and around the project by way of development of roads & communications, availability of reliable, dependable, uninterrupted power for development of small/medium industries, employment generation, development of tourism etc A-H D01 A Chapter 1: Introduction 3 of Mar-13

10 3 x 47 MW Raigam HEP 1.2 Arunachal Pradesh Arunachal Pradesh the Land of the Rising Sun with an area of 83,743 sq. km. is the largest State in the North Eastern region sharing international boundaries with Bhutan in the West, China in the North and Myanmar in the East. The States of Assam and Nagaland flank it s Southern and South Eastern borders. Forest covers about 82% area of the State and numerous turbulent streams, roaring rivers, deep gorges, lofty mountains, snow clad peaks and rich diversity of flora and fauna characterize the landscape. The climate varies from sub-tropical in the South to temperate and alpine in the North, with large areas experiencing snowfalls during winter. The heights of the mountain peaks vary, the highest peak being Kangte (7090 m above MSL) in West Kameng District. The major rivers that drain the area with their numerous tributaries are Siang, Kameng, Subansiri, Kamlang, Lohit, Dibang, Noa - Dihing and Tirap. The State is administratively divided into 16 districts. The state capital is at Itanagar at an altitude of 530 m above MSL. A wide variety of altitudinal gradients and climatic conditions have given rise to varied eco-systems which form the habitat of diverse plant wealth and wild life in the State. Due to its high species diversity, the region has been identified as a global hot spot for biodiversity conservation. The pre-dominant forest types occurring in the State are Tropical Semi Evergreen, Tropical Wet Evergreen, Sub-tropical, Pine, Temperate and Sub-Alpine / Alpine Forests. There are also degraded forests and grass lands. The State harbours a rich variety of wildlife which includes four major cats namely tiger, leopard, clouded leopard and snow leopard. The region is home to seven species of primates, large mammals like elephants, gaur and wild buffalo. High altitude animals include musk deer, bharal, Himalayan black bear, red panda etc. The State animal is Mithun (Bos Frontails) existing both in wild and semi-domesticated form. This animal has religious significance and intimate relation with socio-cultural life of the people. The bird fauna of the State include many species. This is the rich State for pheasants with various species found at different altitudes. The rivers contain many species of fishes. The State also abounds in a variety of reptiles and amphibians. The forests of the State cover about 82% of the State s geographical area of which 960 sq. km have been set aside as protected area comprising two national parks (Namdapa and Mouling) and nine wildlife sanctuaries A-H D01 A Chapter 1: Introduction 4 of Mar-13

11 3 x 47 MW Raigam HEP The population of Arunachal Pradesh is 1.09 Millions (2001 estimate). The people are of Mongoloid stock with heritage of arts and crafts, enchanting folk songs with their own distinct and diverse culture, dialects and lifestyles. There are 82 tribes and sub tribes in the State. Major tribes are Adi, Nyishi, Apatani, Bugun, Galo, Hrusso, Koro, Meyor, Monpa, Tagin, Mishmi, Sajolang, Sartang, Tai Khamti, Yobin, Singpho, Sherduken, Khamba, Tangshang and Memba. The State has a literacy rate of 54.74%. A map showing all the districts and major rivers flowing in Arunachal Pradesh is given in Fig.1.0. Fig. 1.0: Districts and Major Rivers Flowing in Arunachal Pradesh The State has been developing steadily through Five Year Plans with emphasis on development of infrastructure such as roads and bridges, buildings, educational institutions, hospitals and health care units etc. The economy of the State is largely agrarian. Other areas important to the economy of the state are horticulture, forest and small and medium scale industries. The state of Arunachal Pradesh is bestowed with rich natural resources which include rich forest area, mineral resources and mighty rivers etc. Development of hydro projects will give ample scope for development of agro-based industries. Other socio-economic benefits to the people, from these projects will include employment to workers, development of communications, markets and other benefits consequent to large scale construction activity. Arunachal Pradesh is largely rural with 94 percent of its population living in villages scattered all over the State. The indigenous people are tribes with rich and glorious 11010A-H D01 A Chapter 1: Introduction 5 of Mar-13

12 3 x 47 MW Raigam HEP heritage of arts and crafts. The State has 20 major tribes and a number of sub-tribes having their own ethos, dialects and cultural identities, which present a unique scenario of unity in diversity. Most of the tribal communities are ethnically similar having derived from an original common stock, but their geographical isolation from each other has brought amongst them certain distinctive characteristics in language, dress and customs. 1.3 Power Scenario The per capita power consumption of Arunachal Pradesh is below 100 kwh as compared to the national average of 373 kwh. The State plans to harness its enormous natural resources like forests and hydro power and exploit its natural wealth to usher in an era of economic development and raise the per capita electricity consumption to 500 kwh by the end of Eleventh Five Year Plan period i.e The State s generating capacity was only MW hydro and MW diesel till now, which has increased substantially with the completion of 405 MW Ranganadi hydro power project. The capacity will further enhance with the commissioning of ongoing 600 MW Kameng H.E. Project and 2000 MW Lower Subansiri Projects. These projects will provide electricity not only to Arunachal Pradesh and other States in the North-Eastern region but also to other power starved regions of the country. Most of the regions of the country are suffering from power shortages leading to irregular and unreliable supply. The problem becomes acute during peak hours. Based on the projections made in the 16th Electric Power Survey, an additional generating capacity of over 100,000 MW needs to be added to ensure Power on Demand by This, in effect, means doubling the existing capacity, which has been created in the last half a century in the next ten years. Not only the capacity to be added but also the present hydro-thermal imbalance of 25:75 has to be corrected and brought to 40:60 to meet the peak load requirements, achieve frequency and voltage stability and provide system operating flexibility under changing seasonal and diurnal load pattern. For achieving a 40:60 hydro thermal ratio in an installed capacity of around 200,000 MW, the total requirement of hydro capacity will be 80,000 MW, which means that 53,000 MW additional hydro capacities have to be created in the next 10 years. 1.4 Need for the Project Raigam HE Project has been planned as a run-of-the-river scheme A-H D01 A Chapter 1: Introduction 6 of Mar-13

13 3 x 47 MW Raigam HEP Region wise projections of Availability, Demand and Deficit/Surplus of power during peak period (winter peak) at the end of 11th five year plan as determined by the Central Electricity Authority and indicated in the National Electricity Plan is as given below: Peak Power Availability and Demand scenarios at the end of 11 th Plan ( ) Region Peak Power (MW) Availability Demand Surplus(+)/ Deficit(-) Northern (-) Western (-) 4747 Southern (-) 1749 Eastern North-Eastern It may be seen from the above table that at the end of 11th Plan, Eastern and North- Eastern Regions would be surplus in power during peak period, whereas huge shortage is projected in the Northern and Western Regions. The same conditions are expected to continue even beyond 11 th plan period. 1.5 Approach to the Project Area The project is located near Hayuliang town in the and is about 250 km. from Tinsukhia. The project site is about 300 km from Dibrugarh. The project is approachable by National Highway No. 52 from Dibrugarh to Tinsukhia and Tinsukhia to Hayuliang. The broad gauge main railway station is at Tinsukia station which is about 265 km from the Barrage site. The location map of the project and its approaches is attached in drawing no A-H X Project Proposal Raigam H.E Project is a run- of- the river project located on the Dalai River, a major right bank tributary of Lohit River in the Anjaw district of Arunachal Pradesh. The run- of-the river plant with a design head of m has three units with unit capacity of 65 MW each giving a total installed capacity of 195 MW. From the intake on the left bank of the river, a km long headrace tunnel leads to an Underground 11010A-H D01 A Chapter 1: Introduction 7 of Mar-13

14 3 x 47 MW Raigam HEP powerhouse on the left bank of the river Dalai. The full reservoir level (FRL)/ Minimum drawdown level (MDDL) is at an elevation of EL m. The General layout of the Project is presented in drawing no: 11010A-H A Major Components A concrete Barrage 172 m long & 22 m high above deepest foundation level, with 11 nos. of bays each 10.5m(W) x 14m(H) including one bay as inoperative, with crest level at EL m (at river bed level). A Power Intake on the left bank aligned 90 0 to the river flow with invert level at EL m. 7 m dia finished modified horse shoe-shaped head race tunnel km long. A 22 m dia, m high restricted orifice type Underground Surge shaft. A 5.4 m dia, 675 m long steel lined pressure shaft with three 3.20 m dia steel lined Unit Pressure shaft of length 45m/58m/72m will be taking from it for feeding the turbines; 89.6 m (l) x 18 m (w) x 38 (h) Surface Powerhouse with three vertical Francis type units of 65 MW each; 56.6 m (l) x 65 m (w) GIS Switchyard. A 40m Wide and 75 m long tail race channel connected to the river, and Pothead yard The design energy shall be million units (MU) in a 90% dependable year at 95% plant availability. The Power generated would be taken through a 220kV Double Circuit line having zebra ACSR or equivalent AAAC conductor from 220kV switchyard of Raigam HE Project to proposed pooling station at Tezu with line length of approx. 50 km. Double circuit line is proposed for redundancy. The total cost of the project is estimated to Rs Crores at March 2013 price level. The construction period of the project is 5 years, including infrastructure and mobilization work A-H D01 A Chapter 1: Introduction 8 of Mar-13

15 3 x 47 MW Raigam HEP 1.8 Preparation of Detailed Project Report M/s SKIL has engaged the services of M/s Lahmeyer International India for preparation of detailed project report (DPR). The DPR of the project with an installed capacity of 195 MW having three units of 65 MW each has been prepared. 1.9 Objectives of the Study Studies for the DPR were conducted with the objective of preparing a bankable report capable of forming the basis for project financing by national and/or international agencies. In specific terms, the studies were aimed at attaining the following objectives: a) Establishing the main technical parameters of the project. b) Determining the optimum project layout. c) Preparing a feasibility-level cost estimate of the project. d) Determining the economic and financial indicators of the project Scope of Study Preparation of the DPR for the Project included the following activities: a) Collection and review of available data and information pertaining to the project. b) Field investigations, including topographic survey and mapping of project area, including access road and tunnel alignment. c) Assessment of the power potential of the project site. d) Optimization of the project installed capacity. e) Layout and preliminary design of project components, including the civil works, electromechanical equipment and hydraulic structures. f) Construction planning. g) Quantity and cost estimation for the entire project. h) Economic and financial evaluation of the project. i) Preparation of reports, including DPR level drawings. The DPR was prepared in accordance with the requirements of various guidelines published by the Central Electricity Authority, Ministry of Power A-H D01 A Chapter 1: Introduction 9 of Mar-13

16 3 x 47 MW Raigam HEP 1.11 Targeted Output The DPR of the Project was prepared to attain the following: Establishment of the main technical parameters of the project. Preparation of a DPR level cost estimate of the project. Determination of the economic and financial indicators of the project. Establishment of a strong basis for further studies and implementation of the project Contents of Detailed Project Report The DPR describes the findings, results and conclusions of various investigations, analyses, design and evaluations conducted during the present study spread across the following volumes, namely: Volume I A Main Report Volume I B Main Report (Design Notes) Volume II Volume III Volume IV Project Geology Cost Estimate Drawings 11010A-H D01 A Chapter 1: Introduction 10 of Mar-13

17 SECTION II EXECUTIVE SUMMARY

18 3 x 47 MW Raigam HEP EXECUTIVE SUMMARY 1.0 Introduction The state of Arunachal Pradesh is located in eastern most part of the country and is popularly known as the land of the rising sun. It is one of the eight North eastern states with an area of 83, 743 sq.km; thus the biggest in terms of geographical area among the NE states. The entire state falls under seismic zone-v and the geology is fragile due to young mountain formation system. The state has the highest forest cover in the country. The state shares international borders with Bhutan in the West, China in the North and Myanmar in the East. The topography of the state provides for very ideal conditions for development of hydro-electric power projects. There are five major river basins in the state, namely Kameng River basin, Subansiri River basin, Siang River basin, Dibang River basin and Lohit River basin. There are many smaller river systems in the state which also offer very conducive sites for hydro power projects. Almost all the major river system flows in the North-South direction and ultimately drains into the Brahmaputra. There are many tributaries and distributaries of the said major rivers which also offer suitable sites for the development of hydro-electric power projects. As per the preliminary ranking study done by the Central Electricity Authority (CEA), the total potential from 89 major projects is estimated to be about 49,126 MW. If the available potential can be harnessed, the state would be floating in Hydro Dollars as popularly said that the Arab countries are floating in Petro Dollars, In the National Electricity Policy formulated by the Government of India in February, 2005, maximum emphasis is laid on the full development of the feasible hydropower potential in the country and the state governments have been advised to review procedures for land acquisition and other clearances for speedy implementation of hydroelectric projects. Under the Prime Minister s 50,000 MW Hydro-electric Initiatives, the Ministry of Power, Government of India has identified 89 projects in Arunachal Pradesh. Out of these, the preliminary feasibility reports (PFRs) in respect of 42 projects having installed capacity totalling 27,293 MW have already been prepared. Thus the state of Arunachal Pradesh is privileged to share more than 50% of the PM s MW Hydro initiative. The Department of Hydro power Development, Government of Arunachal Pradesh, has been declared as the state Nodal agency in order to oversee, co-ordinate and monitor the activities of hydropower development in the state. All the approvals/consents of the state 11010A-H D01 A Executive Summary 1 of Mar-13

19 3 x 47 MW Raigam HEP government relating to development of power projects are conveyed by the Secretary (Power). Government of Arunachal Pradesh has earmarked certain projects for allocation to private developers for the development of hydropower projects in the state, which will generate economic activity in the state leading to its growth and will also serve as an engine to achieve the objective of promoting all round development of the state and the country. As such the following policy decision applies for developing any project: i) The hydro power projects in the state would be developed as run-off-the river projects. As far as possible, storage projects involving high dams would be avoided. ii) DPR of the project must be got approved by the state Govt. also prior to implementation by the developers. The central Government has envisaged a hydropower capacity addition of about 30,000 MW during the 12 th Plan (2013 to 2017). Government of Arunachal Pradesh approved the engagement of M/s Sai Krishnodaya Industries (P) Ltd., a company incorporated under the Companies Act 1956 and having its Registered office at & 334, Near HUDA office, Opp. Begumpet Police Lines, Secunderabad to execute the 96 MW, Raigam Hydro-electric Project on Dalai River (a major right bank tributary of Lohit river) in Anjaw district of Arunachal Pradesh between FRL 725m and TWL 520m including complete hydroelectric power generating facility covering all components such as dam, intake works, water conductor system, power station, generating units, project roads, bridges, offices, residential facilities, stores, guest houses, security office and other connected facilities including the interconnection facilities on build, own, operate and transfer (BOOT) basis for a lease period of 40 years from the commercial operation date (COD). MoA was signed between the company and GoAP on 26 th, February, The pre-feasibility report (PFR December 2008) of Raigam HEP was envisaged a 2 x 48 MW run-off-the river project consisting of a concrete gravity dam with breast wall sluice spillway having FRL 725 m, length of the dam at top 220 m and crest elevation at 690 m provided with 6 nos of spillway radial gates to pass the design flood of 5580 cumec (SPF) and 4.5 m horse shoe shape headrace tunnel of 9483 m on the left bank of the river and a surface power house with 2 generating unit of 48 MW each. The proposed surface power house is located on the left bank of the river Dalai on a available river terrace at the bottom of hill slope near the village Hayugam, which is about 1.5 km upstream from the confluence of Dalai river with Lohit river. Approximate elevation near river bank at the 11010A-H D01 A Executive Summary 2 of Mar-13

20 3 x 47 MW Raigam HEP proposed PH site is ± 520 m. A design flood of 5100 cumec for 100 year return period and 6180 cumec for SPF was computed. A diversion flood of 450 cumec was recommended through a diversion tunnel of 6 m dia x 450 m. SKIL engaged M/s Lahmeyer International India Pvt Ltd (LII) as a consultant during February 2011 for preparation of Detailed Project Report. LII suggested the developer for survey and investigation plan and EIA study for the project area to prepare bankable DPR. 2.0 Hydrology The total catchment area up to the proposed barrage site ( N, E) is km², out of which km² falls in Tibet and km² (59.5%) lies in India. Moreover, the area above an elevation of 4500 m has been identified as under permanent snow cover and the corresponding area is 59.8 km². These hypsometric features have been duly considered in the establishment of project hydrology. An integrated Lohit basin development has been studied and indicated in Chapter 3 of the DPR. 2.1 Long-Term Water Availability The project company has started observation of daily gauge and discharge near Hayuliang Bridge, about 14 km downstream of the proposed barrage site since September Flow series observed at bridge site on Dalai River since October 2008 to July 2011 which is not sufficient to arrive at the water availability series for the project. Hence, the water availability series for Raigam HEP has been worked out on the basis of approved water availability series of Kalai-I HEP proposed on Lohit river and approved by CWC (Ref: CWC U.O. No.4/334/2010-Hyd(NE)/136 dated , described in Pre Feasibility Report of Kalai-I -2011). The average annual flow and average annual yield of the series thus obtained at Raigam HEP site is 4034 MCM and 2368 mm respectively and generally is in order. 2.2 Design Flood Discharge For computation of the design flood discharge for designing the spillway, Standard Project Storm (SPS) value for 1 day is obtained (326 mm) from IMD. The unit hydrograph has been worked out as per FER-subzone-2(a). The contribution has been computed as per WMO formula. The SPF thus obtained is cumec and the same is adopted as design flood for planning of the project and approved by CWC on For designing 11010A-H D01 A Executive Summary 3 of Mar-13

21 3 x 47 MW Raigam HEP the free board of a barrage, a minimum of 500 year frequency flood is desirable and design of items other than free board, a design flood of 50 year frequency may normally suffice. The hydraulic head of proposed barrage at Raigam site is 15 m and FRL is fixed at 725m and the crest is kept at 691 m. As per IS: (1985), the inflow design flood for the barrage structure should be 100 years frequency flood; hence the same is adopted. For deciding the free board, standard project flood have been adopted. The flood discharge corresponding to 100 years return period has been computed as 7480m³/s. 2.3 Environmental Release Out of the established long-term flow series for power generation, 20% of the average 10- daily flow in four consecutive leanest months in the 90 per cent dependable year has been set aside as the mandatory environmental release in compliance with the recommendations of MOEF for similar projects Diversion Flood Considering the construction period from October to April, the design diversion flood of 5370 m 3 /s for 25 years return period non-monsoon flood as approved by CWC is adopted. 2.5 Sedimentation Studies CWC pointed out that as the project is a run-of river scheme; the reservoir is likely to get filled up to the spillway crest in a short span of time. The deepest river bed is at m and the crest of the barrage main gates are kept at 710 m; hence most of the deposited silt in the reservoir in front of intake and main barrage gates will be washed away during monsoon flood. 3.0 Survey and Investigation 3.1 Topography The detailed topographical survey undertaken in the project area for planning and detailing in the DPR level are as under: Sl. No Title Scale Contour interval in m 1 Diversion site-barrage (including submergence) & intake 1: A-H D01 A Executive Summary 4 of Mar-13

22 3 x 47 MW Raigam HEP 2 HRT alignment (left bank), surge shaft, pressure shaft, Powerhouse complex and TRT 1: The map generated in the project area is adequate for preparation of the DPR and further survey of barrage area including submergence and powerhouse complex along with tailrace tunnel alignment in the scale of 1:1000 with a contour interval of 1 m is in progress. 3.2 Geology Mapping of the surface geology has been completed for the entire project area covering the entire project area. The left bank of the river is accessible along the existing road (from Hayuliang to Chipru) and rock is exposed along the road cut. The project area lies within the lithological assemblage of Tidding formation. The bedrock within the project area are fine medium grained, moderately strong, hard, compact, and light to medium gray Schistose quartzite and granitic gneiss. The bedrock is well exposed on the left abutment of the barrage axis. Sporadic exposures of bedrock are available around the area adjoining the surge shaft underground powerhouse Tailrace tunnel alignment. The headrace tunnel (HRT) alignment is mostly covered with the slope wash / scree material with thick vegetation. The bedrock exposures available all along the existing road level confirms the availability of sufficient rock cover for headrace tunnel. Three major nala crossings are present across the HRT alignment. These HRT stretches needs to be excavated with adequate support measures. A total of 16 (sixteen) drill holes and one exploratory drift for PH Cavern have been planned for the project components, out of which 7 drill holes have been completed at barrage site and used in the preparation of DPR. The remaining 9 drill holes are in progress and shall be completed in due course of time. The work of drift is being taken up. 4.0 Alternate Studies At PFR level, Raigam HEP is planned as a run-of-the river scheme with a 73 m high (above deepest foundation level and 220 m long at the top) concrete gravity dam and a surface powerhouse. It was planned to divert river through diversion tunnel of 6 m dia x 450 m on the right bank of the Dalai river, with u/s & d/s coffer dams. The proposed diversion site is located near Gomin village (on the right bank) which is about 2.5 km 11010A-H D01 A Executive Summary 5 of Mar-13

23 3 x 47 MW Raigam HEP upstream of Chipru village. At this location, the river has developed a deep gorge section; both the banks expose steep slopes with rock vegetation cover. The depth of overburden at the dam site is approximately 10 m below river bed level. Therefore, the dam has to be constructed on the fresh rock available at that depth. The foundation level is at EL 655 m. the top of dam is at EL 728 m. The river bed level is at EL 665 m. Therefore the height of dam above river bed level is 63 m. 6 nos of river sluices are provided in the dam. The size of each sluice is 9m x 9m. The invert level of the sluice is 690 m. The sluices are designed to pass flood discharge of 8350 cumec (PMF) at MWL. The invert level of power intakes are kept at 20 m above the invert level of dam sluices on the left bank side of the river. The sluices are provided with radial gates which will allow partial opening of gate to pass required discharge and also to maintain water level in the reservoir between MDDL and FRL. A surface power house is located downstream of Chipru village on the left bank of the Dalai River on a terrace at the bottom of hill slopes. The minimum tail water level is assumed at 519 m. 4.1 Observation of PFR level study a) Geological features reveal that there is no rock available up to 50 m in the deepest river bed and also the valley is very wide; hence construction of concrete dam at the PFR proposed location is not desirable. a. There is a perennial nala in the downstream of proposed surface power house and comprises of the river terrace and alluvial material deposit. The thickness of the terrace material/alluvial and scree material may vary up to 10 m. In addition, it was noted that the FRL of upper Demwe project was fixed at 525 m. 4.2 Selected Alternative The diversion site is located about 1.5 km upstream of Tee Pani Village (almost PFR location) and the selected barrage axis is located at Latitude 28º N, Longitude 96º E and the deepest river bed level is m and FRL is fixed at 700 m. Alternatively, underground powerhouse (Latitude 28º N, Longitude 96º E) which is approximately 1 km upstream of the PFR proposed surface power house is selected due to well exposed rock at this location and suitable for the surge shaft, pressure shaft and underground power house complex A-H D01 A Executive Summary 6 of Mar-13

24 3 x 47 MW Raigam HEP 5.0 Power Potential The proposed Raigam hydro-electric Project is a run-of-the-river scheme. Based on studies for installed capacity 195 MW, 3 units of 65 MW each, has been selected. The unit size (65MW) is small enough to utilize the lowest river discharge (during lean flows) of 7.77 m 3 /s in the 90% dependable year. The Project will generate 195 MW by utilising a design discharge of m 3 /s and net head of m. The design energy in a 90% dependable year with Installed capacity of 195 MW is MU at 44.59% load factor. In addition to the design energy, the project is estimated to generate secondary energy of MU. The details of energy generation are as given below. Sl. No Parameters Unit Value 1 Installed capacity MW Number of units no 3 3 Gross head (maximum) m Head loss (three units running) m Net head m Design discharge m³/s Design energy MU Plant Load Factor (90% dependable year) % Permissible overload % Works 6.1 Barrage A Barrage of 22 m height from the deepest foundation level and top length of 172 m is proposed across the river upstream of Teepani village. 11 bays of size 10.5 m X14 m is provided with a discharging capacity of m 3 /s (SPF) including one bay as inoperative m floor length with 4.0 m deep upstream cut-off and 6.0 m downstream cut-off has been proposed for a design discharge of 7480 m 3 /s (Design flood) considering the crest at EL.710.0m. A stilling basin of 85 m length at the Floor level 11010A-H D01 A Executive Summary 7 of Mar-13

25 3 x 47 MW Raigam HEP of m and end sill at m has been provided to dissipate the energy at downstream during flood. 6.2 Water Conductor System The power intake and the water conductor system are located on the left bank. In order to ensure proper hydraulics of the system, the intake is aligned in such a way that the front face of the intake wall is almost parallel to the general bank line. Three feeder tunnels of 4 m (w) x 3.5m (h) D-shaped tunnel off-take from the intake well. The water conductor system has been designed for a total design discharge of cumec. The three feeder tunnels join to form a single head race tunnel (HRT) of 7.0m diameter 10375m Long. The size of the HRT has been finalized through an optimization study. An orifice type, all underground surge shaft of dia 22.0m is provided and 5.4 m dia pressure shaft emanate from the circumference of the surge shaft. 6.3 Power Plant Civil Works The Surface power house of size 56.6m (L) x 18.0m (W) x 38m (H). Units are spaced at 16 m c/c. The 21m long service bay is located at the right end and the 12m long Control Block is located at the left end of the machine hall. The centreline of machines is set at El m. An open tail race channel 40m Wide x 75m Long will discharge back to the river. 6.4 Power Plant and Electro-Mechanical System Raigam powerhouse envisages installation of 3 units of 65 MW, vertical axis Francis turbines with unit auxiliaries, three hydro generators and 3 phase generator step-up transformers, 220 kv GIS & 220 kv XLPE cables and 220 kv Transmission line. The scope of work and supply shall include all engineering, detailed design, manufacture, testing, transport, installation, painting, commissioning and trial operation of the equipment, training of the Employer's personnel, spare parts, tools and guarantees to be supplied in accordance with the standard provisions of the hydro generating units. 7.0 Power Evacuation The proposed Raigam HEP is near to the proposed pooling station at Tezu which is around 50km. The proposed pooling station is the nearest pooling station which is considered to be convenient and cost effective evacuation system for Raigam HEP as well as Gimliang HEP A-H D01 A Executive Summary 8 of Mar-13

26 3 x 47 MW Raigam HEP After reviewing the capacity and location of these hydro projects, it is proposed to evacuate power of 195MW Raigam (along with power from 88.5 MW Gimliang HEP in LILO at Raigam substation) in a same transmission line to proposed pooling station at Tezu. The power from Tidding-I HEP and Tidding- II HEP shall also be transmitted through proposed double circuit transmission line from Raigam HEP to Tezu pooling substation. The transmission line coming out from switchyards of Tidding-I HEP and Tidding II HEP shall be Liloed into the above said DC transmission lines (Raigam HEP to Tezu pooling station). It is proposed the following evacuation system for the project. 220kV Double Circuit line having zebra ACSR or other suitable conductor from 220kV switchyard of Raigam HE Project to proposed pooling station at Tezu with line length of approximately 50 km. Double circuit line is proposed for redundancy. The transmission line coming out from switchyards of Tidding-I HEP and Tidding II HEP shall be Liloed into the above said DC transmission lines (Raigam HEP to Tezu pooling station). The above 220kV double circuit line will originate from Gimliang HEP and one circuit will be made LILO at Raigam 220kV GIS. As per CERC grid connectivity regulation, grant of connectivity is made for a hydro project capacity 50MW and above. As such, based on the same connectivity and long term open access can be applied for Raigam HEP. 8.0 Environmental Aspects The proposed project does not involve any major diversion structure causing huge impoundment of water. There is no seasonal or diurnal storage and there is no displacement of population due reservoir submergence at FRL. The impact of project on various social and environmental factors has been considered during site selection and project alignment. No significant adverse impact on the physical, chemical and biological environment is anticipated. The Raigam HEP is proposed as a-run-of-the river scheme without any storage. Therefore, this project is not expected to have any impact on the flow volume or the flow 11010A-H D01 A Executive Summary 9 of Mar-13

27 3 x 47 MW Raigam HEP pattern of the river. No adverse impact on the land use pattern, seismicity and groundwater recharge is anticipated. The exact nature of impact on the flora and fauna in the project area shall be known upon completion of the EIA Study. In order to mitigate the threat to aquatic life in the reach between the barrage site and the powerhouse area, provisions have been made for a minimum environmental flow to be released downstream of the diversion site. The proposed diversion structure will not worsen the flood situation on upstream or downstream side. There are no buildings or infrastructures which are likely to be lost due to flooding. There are no monuments or sites of cultural or historical importance in the area. Detailed EIA/EMP studies shall be carried out for the project by an independent agency in accordance with MOEF (Ministry of Environment & Forest) guidelines. A report of the same will be available in due course of time. 9.0 Construction Planning and Schedule It is proposed to construct the project within a period of 5 years including infrastructure development which is proposed to be completed within 6 months. Therefore the main works of the project will have to be completed within 3 years 6 months time. Suitable construction methodology and requirement of plant and machinery has been worked out and given in the report. A bar chart showing the construction program is also included in Chapter 12 of this report Estimated Project Cost The estimate of cost has been prepared as per Guidelines for Formulation of Detailed Project Reports for Hydro-electric Schemes issued by Central Electricity Authority in April 2011 to arrive at the hard cost of the project at March 2013 price level. The total cost of the Project works out as given below: A-H D01 A Executive Summary 10 of Mar-13

28 3 x 47 MW Raigam HEP Data Base on Equipment Cost Power Plant & E-M System and Hydro-mechanical Estimate of BoQ Civil Works (C & J) Unit Rate Analysis Cost of Equipment- E-M (S) and HM (C & J) Cost of Civil Structures and other Expenses (excluding works) Hard Cost (Works & Other Expenses) at the Start of the Project Phasing of Cost Escalation during Construction Financing Arrangement Interest During Construction Add Financing Charges Completed Cost of Project FLOW CHART FOR PROJECT COST ESTIMATE The quantities have been worked out on the basis of DPR level design and drawings of different components of works. Unit Rate analysis has been done as per Guidelines for the preparation of Detailed Project Report of Irrigation and Multipurpose Projects (issued by Ministry of Irrigation in 1980) and Guidelines for the preparation of Project Estimates for River Valley Projects (issued by Central Water Commission in 1997). The basic labour wages have been taken from Schedule of Rates- Arunachal Pradesh PWD 2010 read with other applicable provisions. The Carriage Charges including loading, unloading & stacking charges from Schedule of Rates Arunachal Pradesh PWD 2010 with appropriate escalation have also been considered. The quantities and ratings of various Hydro-mechanical and Electro-Mechanical equipments have been worked out on the basis of system design and 11010A-H D01 A Executive Summary 11 of Mar-13

29 3 x 47 MW Raigam HEP equipment sizing calculation. Unit rates and costs have been worked out based on in-house data base on similar projects. The total project cost works out as given below: Sr. No. Description of Item Cost (in Crores) 1 Cost of Civil works including HM equipment Cost of Power plant & Electro-mechanical equipment Other direct & Indirect Cost (Preliminary works, Land, buildings, plantation, communication etc.) Total Hard Cost Escalation during construction (ESC) Interest during construction (IDC) Financial Charges (FC) Total Cost including Escalation, IDC & FC Cost per MW of Installed Capacity Financial Aspects The economic evaluation of the Raigam Hydro Electric Project as described has been made in accordance with the latest 2009 recommendations of CERC. The basic methodology for carrying out the economic evaluation is to find out energy cost taking into account the total project cost with an assured net after tax return of 15.5% throughout the life of the project. Debt: Equity ratio of 2.33: 1(70:30) i.e., loan and equity components of 70% and 30% respectively of the total capital project cost has been considered. A period of repayment of 12 years has, therefore, been considered in fixation of tariff. 13 % (which is equal to the latest State Bank of India, Prime Lending Rate) on working capital has been considered. Escalation in civil, HM, and E-M has been computed by averaging out the sum of inflation rates i.e. 60% of the wholesale price index and 40% of consumer price index. The tariff has been worked out on the basis of the latest CERC guidelines. Details of calculations of tariff during 40 years of plant operation are presented in Chapter 17 of this report. Summary of the tariff is given below: 11010A-H D01 A Executive Summary 12 of Mar-13

30 3 x 47 MW Raigam HEP Sl. No. Summary of the Tariff 1st year Tariff (Rs. per Unit) 40 years Levelized Tariff (Rs. Per Unit) Conclusion The DPR conclusively establishes that the project as envisaged techno-economically attractive and therefore worth taking up for construction. The construction of this project will also result in obtaining substantial socio economic benefits. Power availability from this project will improve the balance between hydro and thermal power generation in the state and the region as a whole A-H D01 A Executive Summary 13 of Mar-13

31 SECTION III SALIENT FEATURES

32

33 Raigam HEP- 195 MW (3x65MW) Salient features 1. Location State District District Head Quarter River/Stream Location of Intake Structure Arunachal Pradesh Anjaw Tezu Brahmaputra, Sub-basin Lohit N E 2. Geographical Co-ordinates of Project Area Latitude N Longitude E Altitude m (At barrage Location) Access to the Project Site 250 Km from Tinsukia rail head and 300 km from Dibrugarh Airport and approchable by NH-52 from Dibrugarh to Tinsukia and than Hualiang. Nearest Rail head Tinsukia, ASSAM Nearest Airport Dibrugarh

34 Salient features contd. 3. Hydrology Catchment area km 2 Annual Average Rainfall mm Average annual yield 4034 Mcum 90% Dependable yield Mcm Flood corresponding to 100-year return period at diversion site of u/s 7480 Cumecs project SPF at diversion site of u/s project m3/s 4. Power Intake No. Of Openings 3Nos. Size & Shape 4.0 (W) x 3.5 (H), Rectangular Bellmouth Invert Level of Intake m Type of Gates Vertical Lift Gates, Rope Drum Hoist Arrangement Intake Stop Log 3Nos. 4.0 (w) x 3.5 (h) Intake Service Gate 3Nos. 4.0 (w) x 3.5 (h)

35 Salient features contd. 5. Head Race Tunnel Type Modified Horse Shoe Diameter 7 m finished Total Plan Length km Slope 1 in 200 Design Discharge m 3 /s Velocity 3.4 m/s 6. Surge Shaft Type Restricted Orifice Size 22 m Height m Orifice size 3.6 Level of Intersection with HRT m Top Level m Maximum Up Surge level m Minimum Down Surge level m Adit-1 (Lenght/Size/Shape) m, 6.0 m Dia., D-Shape Adit-2 (Lenght/Size/Shape) m, 6.0 m Dia., D-Shape, Adit-3 (Lenght/Size/Shape) m, 6.0 m Dia., D-Shape,

36 Salient features contd. 7. Pressure Shaft Type Nos. 1 Diameter Length Length of Unit Pressure Shafts after trifurcation Circular Steel Lined m m UPS-1 = 32.9 m, UPS-2 = 26.92, UPS-3 = Dia. Of Unit Pressure Shaft 3.20 m

37 Salient features contd. 8. Power House Complex Type of Power House Installed Capacity Normal Tail Water Level Rated Head Design Discharge Size of Power House (including Service Bay) Surface power house 195 (3x65) MW m m m3/s 89.6 (L )x 18 (W) 38 (H) m. Surface structures. Size of Switchyard Switchyard (56.6 x 65 m) 9. Tail Race tunnel Shape Open channel Size & Shape 40 m Wide, 75 m long, 8 m High Min. Tail Water Level m

38 Salient features contd. 11. E&M Equipment Turbines 3 Type Vertical Fransis No. & Capacity 3 x 65 MW Rated head m Rated Discharge Cumecs Over loading 10% Generators No. & Capacity 3Nos. Generators, 71.5 MVA, 11 kv Power factor 0.9 Overloading 10% continuous overloading Transformer Type and Numbers 3Nos MVA, 11/220 kv, 3Φ phase generator step-up (GSU) transformers.

39 Salient features contd. 12. Power Generation Installed Capacity Design Energy (in 90% dependable year with 95% M/c availability) 13. Estimated Cost (at January 2014 price level) Civil Work E & M Works excluding Transmission Line Other Direct & Indirect Charges Total Cost 14. Estimated Cost- For Tariff Calculations Escalation on Civil Works Escalation on E&M Works Interest During Construction Financing Charges Project Cost Including escalation, IDC & FC 15. Financial Aspects Levellized Tariff 6.09 Tariff For Block of 1st Five Years Construction Period Construction period excluding infrastructure work MW MU Cr Cr Cr Cr Cr Cr Cr Cr Cr.

40 SECTION IV HYDROLOGY

41 TABLE OF CONTENTS LIST OF APPENDIX... 3 LIST OF ANNEXURES... 3 LIST OF FIGURES... 4 LIST OF TABLES... 5 LIST OF ABBREVIATIONS... 6 LIST OF REFERENCES... 7 CHAPTER 6 HYDROLOGY Introduction General Information River System and Basin Characteristics River Characteristics Catchment Area Hypsometric Curve Soil type Land use / Land cover Climate Demography Water Availability Study Data Availability Estimation of Snow Melt Runoff Methodology of Long Term Runoff Computation at Raigam Barrage site Flow Pattern Dependable Flow Analysis Environmental Release Design Flood Studies General Design Approaches Empirical Approach Deterministic Approach Unit Hydrograph Daily Rainfall Values Temporal Distribution of Rainfall A-H D01 B Chapter 6: Hydrology 1 of 60 3-Jul-14

42 6.4.8 Design Base Flow Design Peak Snow Melt Runoff Flood Hydrograph GLOF Design Flood Value Construction Diversion Flood Flood Frequency Analysis Maximum Observed Flow Maximum Observed Non-monsoon Flow Maximum Observed Monsoon Flow Choice of Working Period for Construction Design Construction Diversion Flood Value Stage-Discharge Curve General Tail water level at downstream of barrage site Powerhouse-Tailrace Outfall Reservoir Storage Volume Maximum Water Level Sedimentation Study Conclusion A-H D01 B Chapter 6: Hydrology 2 of 60 3-Jul-14

43 LIST OF APPENDIX ANNEXURE NO. TITLE 6.1 GLOF study 6.2 CWC approved letter for GLOF study dated LIST OF ANNEXURES ANNEXURE NO. TITLE 6.1 Raigam Hydrology CWC Approval letter dated Computation of Stream Slope for Dalai River 6.3 Observed Daily Rainfall at Mitiliang Village, District: Anjaw in Arunanchal Pradesh 6.4 Monthly Rainfall Data of Surrounding Stations 6.5 Monthly Rainfall Data Graph of Surrounding Stations 6.6 Observed Ten Daily Discharge Series at Raigam Barrage Site on Dalai River, Arunachal Pradesh ( to ) 6.7 CWC Provided Ten Daily Discharge of Lohit River at Kalai - I site 6.8 Ten Daily Discharge of Lohit River at Kalai - I site (May 1985 to April 2004) 6.9 Estimation of Monthly Snowmelt Runoff at Kalai I HEP 6.10 Snowmelt Calculation for Raigam Barrage 6.11 Ten Daily Rain-Fed Discharge of Lohit River at Kalai - I site (May 1985 to April 2004) 6.12 Ten Daily Rain-Fed Discharge of Dalai River at Raigam Barrage site (May 1985 to April 2004) 6.13 Ten Daily Discharge of Dalai River at Raigam Barrage site (May 1985 to April 2004) 6.14 Ten Daily Discharge of Dalai River at Raigam Barrage site from observed discharge at Dalai Bridge (May 2008 to April 2011) 6.15 SPS Value & Time distribution of 24-hour storm rainfall values from IMD 6.16 Synthetic Unit Hydrograph for Raigam HEP 6.17 Flood Hydrograph for 100 Years Return Period Flood (2-1 sequence) 6.18 Flood Hydrograph for SPF sequence) 6.19 Flood Hydrograph for 50 Years Return Period Flood (2-1 sequence) 6.20 Flood Hydrograph for 25 Years Return Period Flood (2-1 sequence) 6.21 Check for Outliers in the Annual Peak Monsoon Flood Values at Mompani Site 6.22 Check for Outliers in the Annual Peak Non-monsoon Flood Values, Mompani Site 6.23 Derivation of Design Flood Discharge by Gumbel's Method 6.24 Estimation of Tail water level at barrage site 6.25 Estimation of Tail water level at Tail Race Out Fall 11010A-H D01 B Chapter 6: Hydrology 3 of 60 3-Jul-14

44 LIST OF FIGURES FIGURE NO. TITLE 6.1 Index Map of Raigam HEP 6.2 Catchment Area Map 6.3 Hypsometric Curve 6.4 Slope Map of the Catchment Area 6.5 Aspect Map of the Catchment Area 6.6 Stream Segments of the Main Stream up to the Barrage Site of Dalai River 6.7 Landsat (Nov 05) TM False Colour Composite of the Catchment Area 6.8 Average Monthly & Maximum Daily Rainfall at Mitiliang Village 6.9 Monthly Mean Rainfall & Evaporation at Pasighat 6.10 Monthly Mean Maximum & Minimum Temperature at Pasighat 6.11 Cross-section of Dalai River at Near Dalai Bridge Site 6.12 View of the Dalai River Near the Barrage Site 6.13 Diagram Showing Sub-section for Current Method 6.14 Monthly Mean Discharge at Barrage Site (Derived and Observed) 6.15 Annual Flow Volume based on Derived and Observed 10-Daily Series 6.16 Ten-Daily Flow Duration Curve (Period to ) 6.17 Flow Duration Curve for 90% Dependable Year: Flow Duration Curve for 50% Dependable Year: Stream to the Centre of Gravity of Raigam Catchment 6.20 Synthetic Unit Hydrograph of 1 cm Rainfall Excess 6.21 Interpolated and Adjusted Temporal Distribution of Rainfall 6.22 SPF Hydrograph 6.23 Rating Curve at Barrage Site 6.24 Rating Curve at Tail Race Out fall near Power House Site 6.25 Elevation-Area-Capacity Curve 11010A-H D01 B Chapter 6: Hydrology 4 of 60 3-Jul-14

45 TABLE NO. LIST OF TABLES TITLE 6.1 Distribution of Catchment Area in Different Elevation zones 6.2 Equivalent Stream Slope (S) and Length of the Main Stream (L) of Dalai River 6.3 Available Rainfall Data 6.4 Monthly Mean Maximum & Minimum Temperatures at Pasighat 6.5 Summary of Snowmelt for each Month for Lohit River up to Kalai-I HEP 6.6 Summary of Snowmelt for each Month at Raigam Barrage Site 6.7 Flow Pattern of Dalai River at Raigam Project Site based on Derived Data 6.8 Flow Pattern of Dalai River at Raigam Project Site based on Observed Data 6.9 Dependability of Annual Flow Volumes 6.10 Dependable Year Flow Volumes 6.11 Classification of Dams for Design Flood 6.12 Flood Discharges for Different Return Periods using Empirical Approach 6.13 Parameters of Synthetic Unit Hydrograph for Raigam Barrage Site 6.14 Adjusted 1 Hour Synthetic Unit Hydrograph 6.15 Rainfall Values Corresponding to Different Return Periods 6.16 Temporal Distribution of Rainfall following IMD 6.17 Hourly Distribution of Rainfall 6.18 Rainfall Distribution for Different Return Periods in 2 Bells 6.19 Cumulative Distribution of Hourly Rainfall for Each Bell 6.20 Temporal Distribution of Hourly Rainfall for Each Bell 6.21 Hourly Distribution of Effective Rainfall for Each Bell 6.22 Critical Sequence of Effective Rainfall for Each Bell 6.23 Reverse Critical Sequence of Effective Rainfall for Each Bell 6.24 Flood Discharges for different Return Periods using Deterministic Approach 6.25 Annual Peak Discharges during Monsoon and Non-Monsoon at Mompani Site 6.26 Flood Values at Raigam site for different Return Period 6.27 Observed Maximum Flood near Dalai Bridge on Dalai River Maximum Flood for Different Working Periods 6.29 Water Levels at Barrage Site for Different Flood Frequencies 6.30 Water Levels at TRT Outfall near Powerhouse Site for Different Flood Frequencies 6.31 Elevation Area Capacity at Raigam Barrage Site 6.32 Number of Days with Heavy Silt Load (Jan 2011 to Jul 2011) 11010A-H D01 B Chapter 6: Hydrology 5 of 60 3-Jul-14

46 LIST OF ABBREVIATIONS ABBREVIATIONS EXPANDED FORM BIS CA CWC d/s EL. Bureau of Indian Standards Catchment Area Central Water Commission, India Downstream Elevation ha Hectare = 10 4 m 2 HEP IMD M Hydroelectric Project India Meteorological Department Snowmelt in mm/day MCM Million Cubic Meter = 10 6 m 3 MDDL MU No. P PMF PMP Q RL SPF SPS Sta. T u/s WMO Minimum Drawdown Level Million Units of Energy = GWhr Number Precipitation in mm/day Probable Maximum Flood Probable Maximum Precipitation Discharge Reduced Level (refers to Elevation above mean sea level) Standard Probable Flood Standard Project Storm Station Average Ambient Temperature Upstream World Meteorological Organization 11010A-H D01 B Chapter 6: Hydrology 6 of 60 3-Jul-14

47 LIST OF REFERENCES REFERENCE NO. TITLE 1 CWC (1991). Flood Estimation Report for North Brahmaputra Basin (Subzone- 2a), Hydrology (Small Catchments) Directorate, Central Water Commission, New Delhi. 2 CWC (2001). Manual on Estimation of Design Flood, Central Water Commission, New Delhi. 3 IS: 6966 (Part 1):1989. Indian Standard Hydraulic Design of Barrage and Weirs- Guidelines 4 IS: (1987). (Reaffirmed 1992). Indian Standard Guidelines for Determination of Effects of Sedimentation in Planning and Performance of Reservoirs, Bureau of Indian Standards, New Delhi. 5 IS: (2000) Design Flood for River Diversion Works Guidelines, Bureau of Indian Standards, New Delhi. 6 MOEF (2011). Report of the Committee Constituted for Development of Criteria and Formulation of Guidelines for Categorization of Non Compliances into the Category of Serious and Not So Serious, Ministry of Environment & Forests, New Delhi. 7 Mutreja, K.N. (1986). Applied Hydrology, Tata McGraw Hill Publishing Company Limited, New Delhi A-H D01 B Chapter 6: Hydrology 7 of 60 3-Jul-14

48 CHAPTER 6 HYDROLOGY 6.1 Introduction The SKIL Group has planned to develop 96 MW Raigam Hydro Electric Project as a Run of River scheme by utilizing water from the streams River Dalai, tributary of the River Lohit in Arunachal Pradesh. The Dalai River, a right bank tributary of the Lohit, originates from Tibet at an elevation of about 3866m flows southwards and meet the main river near Hayuliang township in Anjaw district of Arunachal Pradesh. The River Lohit is a major right bank tributary of the River Bhahmaputra. The proposed barrage site (Latitude North and Longitude East) is located upstream of Teepani Power House (2X500KW) while Power House (Latitude North and Longitude East) is located on the left flank terrace of the Dalai River at about 4km upstream of the confluence of Dalai River with Lohit River. An index map showing Latidude, Logitude, rain gauge stations and Guage & Discharge (G & D) sites in and around the catchment along with other existing/proposed hydro-electric power projects in the basin has been presented in Figure 6.1. This analysis deals with the study of hydro meteorological characteristics of the basin and the assessment of different hydrological parameters required for the project design. Hydrological studies for Raigam Hydroelectric Project (HEP) aims to: Assess the availability of water for power generation from a long-term series of average 10 daily discharge for the project site Estimate the design flood for the main structure i.e. the barrage Assess diversion flood for diversion discharge during construction Assess maximum water level upstream of barrage during passage of flood Prepare Reservoir Elevation-Area-Capacity curve for determining the capacity of the reservoir and the area of submergence Sedimentation study 11010A-H D01 B Chapter 6: Hydrology 8 of 60 3-Jul-14

49 96 MW Raigam HEP Hydrological Chapter has been submitted to Central Water Commission (Ref: Lr.No.SKIL/Raigam/2012/201/146 dated ). In response, we have received preliminary comments from Directorate (PAC) vide letter dated 20th April 12 (Ref: Directorate (PAC) letter no.2/arp/50/cea/12-pac/ dated 20th, April 2012) and clarified vide Lr.No.SKIL/Raigam/2012/122/159 dated and requested to approve 100 year Design Flood. Director (PAC), CWC examined the hydrological studies of the project and observations have been communicated vide Letter- Director PA(S), CWC UO.No.4/382/2012-Hyd (NE)/160 dated On receipt of the observations, we have submitted the compliance report as desired to accord approval of design flood vide Lr.No.SKIL/Raigam/Hydro/2012/204/166 dated Finally, Directorate PA(C), CWC Lr.No.4/382/2012-Hyd(NE)/41-42 dated vide which it was communicated that SPF of m 3 /s may be adopted as design flood as per BIS criteria for planning purpose of the project. Directorate also provided the 10-daily water availability series for Raigam HEP for the period to with average annual flow of 4034 MCM as Annexure A-H D01 B Chapter 6: Hydrology 9 of 60 3-Jul-14

50 Figure 6.1: Index Map of Raigam HEP 11010A-H D01 B Chapter 6: Hydrology 10 of 60 3-Jul-14

51 6.2 General Information River System and Basin Characteristics Lohit River, a Major left bank tributary of Bhramputra River, originates at an elevation of 6190m from the snow clad peaks of Nimbout Chcumbouri Nechai Gongra Tirap Phasi ranges (approximate elevation of 6000m) in the eastern Tibet, constituting part of Kangrigarpo range, and flows down as Kangrigarpo Qu (also called Zayal Nga Chu and Rongtu Chu), forming the eastern-most river basin of India. The River flows into India near its eastern most inhabited tip Kibithoo and surges through Arunachal Pradesh for two hundred kilometres before emptying itself in the plains of Assam. Its flow is uncontrolled and turbulent and the river is therefore is known as the river of the blood in the local language. The river flows through Mishmi hills to meet the Siang at the head of the Brahmaputra valley. The catchment area of the Dalai River up to the proposed barrage site is sq.km. More than 80% of the area is covered with dense forest and the rest by open forest. Shifting (jhum) cultivation in the hills and permanent cultivation in the foot hills and plains are practised ( accessed on ). Cultivable waste lands usually situated in the low lying areas along the intermontane valleys which have been developed for permanent cultivation. The agriculture mainly depends on monsoon rainfall River Characteristics Dalai is a major right bank tributary of Lohit River, originating at an elevation of about 3866m and passes near Tajobum, Plongllang and Minutang town, reaching an elevation of 691m at the proposed barrage site. It is snow fed and lackfed streams which flows mainly southwards till the proposed Barrage site. Tributary of Lohit originates from morainic landform and passes through dense pine forests in its higher reaches. Both the left and right bank slopes of Dalai River are covered with settlement and cultivable terraces below 1000 m elevation. It is fed by streams Tasha Nala, Rai/Raigam Nala, Bom Nala, Pajai Nala, Talai Nala, Bazi Nala, Kha Nala, Zu Nala and Hemang Nala from the right and Teepani Nala, Ching Nala 11010A-H D01 B Chapter 6: Hydrology 11 of Jul-14

52 and Tallo Nala from the left. The river network is dendritic to sub-parallel in nature and flows the geomorphological trends of the hills and mountains. In the hilly terrain, the river have deep gorge along their courses, with an average basin slope of about 1:31. The total length of the river up to the Barrage site is 72km and the mean slope is 33.47m/km. The bed level of Dalai River at proposed Barrage site of Raigam Hydroelectric Project is 691 m Catchment Area The catchment of Dalai River in upper reach extends over an area of km² in Tibet (China). The Indian part of this catchment up to the proposed Raigam Barrage site is km². The total catchment area up to the proposed Barrage site ( N, E) of the Raigam HEP is km² out of which snowfed catchment area above permanent snow line of 4500 m above mean sea level (a.m.s.l.) is about 59.8 km² (3.5%). The catchment is more or less Leafshaped having a length of 58.12km and a width of 52.14km and spread between Latitudes and North and Longitudes and East. Indian toposheet are not available for the catchment in upper reach contributing from Tibet region, hence the catchment map has been prepared using SRTM-Version 4 Digital Elevation Model (90m spatial resolution), Tile No -56_07 ( accessed on ). It gives accuracy information for the regional study and hence sufficient for the present Hydrology study. The highest elevation in the catchment is 5046m. Catchment area map showing Latitude, Longitude, rain gauge and G & D sites inside and around the catchment has been furnished in Figure 6.2, which also shows the distribution of catchment area under different elevation zones A-H D01 B Chapter 6: Hydrology 12 of Jul-14

53 Figure 6.2: Catchment Area Map 11010A-H D01 B Chapter 6: Hydrology 13 of Jul-14

54 6.2.4 Hypsometric Curve A hypsometric curve is an empirical cumulative distribution function of elevations in a catchment. The hypsometric curve for the proposed project was prepared using SRTM-Version 4 Digital Elevation Model (90m spatial resolution), Tile No -56_07. The distribution of catchment area in different elevation zones is given in Table 6.1 Table 6.1: Distribution of Catchment Area in Different Elevation zones Incremental Area Area Area Elevation % of below above (m) (Km 2 ) (Km 2 Km ) Total Area The Hypsometric curve for the project is plotted in Figure 6.3. Assuming the elevation of Permanent Snowline as 4500 m Above Mean Sea Level (a.m.s.l), the hypsometric curve shows that 59.8 km² of Dalai catchment lies above this level A-H D01 B Chapter 6: Hydrology 14 of Jul-14

55 The highest elevation in the catchment is 5046 m, as obtained from SRTM DEM. Figure 6.4 portrays the slope over the catchment; which brings out that leaving aside very small patches near the river channel, the entire catchment area is under extremely steep slopes exceeding of 50% or larger. Figure 6.5 presents the aspects of the terrain. Figure 6.3: Hypsometric Curve 11010A-H D01 B Chapter 6: Hydrology 15 of Jul-14

56 Figure 6.4: Slope Map of the Catchment Area Figure 6.5: Aspect Map of the Catchment Area 11010A-H D01 B Chapter 6: Hydrology 16 of Jul-14

57 In general for determining physiographic parameters L(Length of longest main stream along the river course in km), Lc and Equivalent Stream Slope (S) only rainfed portion of catchment has been considered. Considering elevation above EL4500m as permanent snowline, Raigam CA has only 3.5% under permanent snow area. Therefore longest main stream has been considered upto EL4500m. Segmental length and elevations of the main stream has been calculated using SRTM and its values are given in Table 6.2 and shown in Figure 6.6. Computations of Equivalent Stream Slope for the catchment have been given in Table 6.2. Computations of Statistical Mean Stream Slope for the catchment have been given in Annexure 6.2. It is seen that the longest stream considered up to the ridge originates from a point with lower elevation, rather than the highest peak in the catchment. Length of longest main stream (L) along the river up to EL 4500 m has been calculated as km. Equivalent Stream Slope (ESS) and Statistical Mean Slope of the river based on SRTM DEM have been calculated as m/km m/km respectively. Table 6.2: Equivalent Stream Slope (S) and Length of the Main Stream (L) of Dalai River Seg.Length Height above Di-1 + Sl Chainage R.L. Li * (Di-1 Li datum, Di Di No. m m + Di) Km. m m L21= L20= L19= L18= L17= L16= L15= L14= L13= L12= L11= L10= L9= L8= L7= L6= L5= L4= L3= L2= A-H D01 B Chapter 6: Hydrology 17 of Jul-14

58 Σ L= S=( m/km m/m 1 in 26 / 71.74^2) = Figure 6.6: Stream Segments of the Main Stream up to the Barrage Site of Dalai River Soil type Primary information regarding soil type in the catchment area is not available. In general, the nature and properties of soil vary according to the topography and elevation of the area. Soil in greater part of the Anjaw district is red sandy soils and skeletal soils. In hilly regions, Soil generally contains high humus and nitrogen due to presence of extensive forest cover. The soils of the foothills are generally alluvial, loamy or sandy loam mixed with gravel and pebbles. In the valleys, it is clayey in nature and rich in organic matter ( accessed on ) A-H D01 B Chapter 6: Hydrology 18 of Jul-14

59 The main characteristic of the soil is sandy and progressively clayey in nature. The mountain soils are red to brown in colour and are good for cultivation of dry paddy, maize etc Land use / Land cover Major part (more than two-third) of the Anjaw district is under forest cover which ranges from very dense forest to open forest. Land use pattern in this district are Forest, Jhum (slash and burn) agriculture and Horticulture ( accessed on ). The catchment area for Raigam Barrage project is mostly under forest cover. Landsat TM Standard False Colour Composite Image of the catchment area ( accessed on ) for November 2005 indicates that most of the area is under dense forest (appearing as Dark Red), while some portion near the ridges is under snow cover (appearing as white) (Figure 6.7). Figure 6.7: Landsat (Nov 05) TM False Colour Composite of the Catchment Area 11010A-H D01 B Chapter 6: Hydrology 19 of Jul-14

60 6.2.7 Climate A. Precipitation As substantial portion of the catchment lies in China/Tibet, hydro-meteorological data for this area of the basin is not available. The rainfall in the Raigam catchment is predominantly influenced by the mountain system and occurs due to South-West monsoon and cyclonic rainfall, which generally sets in May and continues till October (CWC- 2a, 1991). A lot of rainfall takes place due to premonsoon thunderstorm activity in the months of March and April. The rainfall intensity usually decreases after October. Generally November, December and January are the dry months, with occasional scattered rainfall. The project company has provided daily rainfall data recorded at Mitiliang village which is within the catchment for 1 st January 2008 to 30 th June 2011 (Annexure 6.3). Average monthly and maximum daily rainfall in each month is shown in Figure 6.8. Figure 6.8: Average Monthly & Maximum Daily Rainfall at Mitiliang Village From observed data, it is found that on 22 April, 2010 a maximum of 108mm rainfall occurred. The annual rainfall of basin varies from 2500 mm to 5000 mm. There are several rain gauge stations in the Lohit Basin maintained by India Meteorological Department (IMD) as well as by the State Government with data available for varying periods. However, no station has long-term record of the 11010A-H D01 B Chapter 6: Hydrology 20 of Jul-14

61 rainfall. The nearest rainfall station having somewhat longer data series is at Passighat, in East Siang district. Distribution of mean monthly rainfall ( hrome=true assessed on ) and evaporation over 35 years on observations at Pasighat are shown in Figure 6.9. Figure 6.9: Monthly Mean Rainfall & Evaporation at Pasighat The average annual rainfall recorded in the catchment area region at Chaglongam station is 2554 mm, 2165mm at Hawai (towards south east), 3790mm at Hayuliang (towards south from the barrage site), 1204mm at Kibithoo (towards north east), 4654mm at Salangam, 4230mm at Tidding (towards south west) and 1167mm at Walong (towards south east) are available as summarized in Table 6.3. The available rainfall data has been put under Annexure to Annexure The monthly mean, maximum and minimum rainfall of all the above mentioned stations have been plotted in Annexure to Annexure Table 6.3: Available Rainfall Data Sr. No. 1 2 Rainfall Stations Chaglongam ( N, E, Elev m) Hawai ( N, E, Elev m) Data Availability Period May 1972 to February1991 (with some intermittent gap data) May 1972 to March 1991 (with some intermittent gap 11010A-H D01 B Chapter 6: Hydrology 21 of Jul-14

62 Sr. No. Rainfall Stations Data Availability Period Hayuliang ( N, E, Elev m) Kibithoo ( N, E) Salangam ( N, E) Tidding ( N, E) Walong ( N, E, Elev m) data) May 1972 to March 1988 (with some intermittent gap data) May 1972 to May 1988 (with some intermittent gap data) May 1972 to March 1985 (with some intermittent gap data) May 1979 to March 1991 (with some intermittent gap data) May 1972 to March 1985, Oct 1988 to March 1989 (with some intermittent gap data) Occasional snowfall takes place on the peaks in winter. Contribution from snowmelt has been considered for the present report as some catchment lies above the permanent snow line. Though some portion of the catchment area within Indian border has some snow bound area, information regarding the snow gauge with sufficient long-term data of the snow depth is not available for inclusion in the report as well as in the study. The catchment area is covered with dense forest and without any significant agricultural activity. B. Temperature Depending on the elevation, the high hills belong to temperate zone while lower hills and valleys are in the sub tropical agro climate zone. The region experiences four seasons viz., the winter (starting from late November and continuing up to March), the Pre-Monsoon (April to beginning of May), South-West Monsoon (May to September) and Post Monsoon (October to beginning of November). The temperature in the region varies generally from a maximum of 25 C to 35 C in summer to a minimum of 1 to 10 C in winter. Further, monthly mean minimum and maximum temperatures recorded at Pasighat stations reported by IMD based on data for 35 years ( ) have been furnished in Table 6.4 and shown in Figure A-H D01 B Chapter 6: Hydrology 22 of Jul-14

63 Table 6.4: Monthly Mean Maximum & Minimum Temperatures at Pasighat Month Maximum Temperature ( C) Minimum Temperature ( C) May Jun July Aug Sep Oct Nov Dec Jan Feb Mar Apr Figure 6.10: Monthly Mean Maximum & Minimum Temperature at Pasighat Demography The state of Arunachal Pradesh with a geographical area of 83,743km 2, has a population of 13,82,611 (7,20,232 males and 6,62,379 females)and a population density of only per square kilometre, compared to a national average of 382 per square kilometre as per census records of The Anjaw district has a population of 21, 089 (M & F 9403) and has sex ratio of 805 females for every 1000 males having population density of 3 per square kilometre and literacy rate of 59.4% (M-69.54% and F46.39%) (source: B Chapter 6: Hydrology 23 of Jul-14

64 prov-results/prov_data_products_arunachal.html, assessed on ). The decadal growth rate of population over has been 13.77% which is lower than the national growth rate of 17.64%. The major tribes inhabiting the district of Lohit are the Mishmis and Zakhring (Meyor). 6.3 Water Availability Study The water availability study is the most important aspect for assessing the hydro power potential of a project. Correct estimate of the annual flow in the river based on historical flow data can optimize a project by generating power to the maximum possible extent. However, this inherently assumes the condition of stationarity in runoff behaviour. Considering the location and topography of the catchment and distribution of settlements near the catchment, major change in land use is not envisaged in near future. On the other hand, projections of future climate due to global climatic change are highly uncertain for consideration of water availability assessment at a catchment scale of km 2. Under the circumstances, assumption of stationarity in runoff behaviour in future might not be imprudent. The studies on water availability at various levels of dependability and variations of flow over considerably long period has been carried out and described in the following paragraphs Data Availability The project company has started observation of daily gauge and discharge near Dalai Bridge, about 14 km downstream of the proposed barrage site since September At the gauge site, discharge measurement was done using by float method and current method. A relatively straight river reach of 60m was chosen for the purpose. Discharge is the volume of water moving down a stream or river per unit of time, commonly expressed in cubic meter per second. In general, river discharge is computed by multiplying the area of water in a channel cross section by the average velocity of the water in that cross section. Float method 11010A-H D01 B Chapter 6: Hydrology 24 of Jul-14

65 A neutral buoyancy object has been used to float in the river and time differences of travel of floats for each of the chosen 4 to 5 sub-sections across the width of the river measured using accurate stop watch. Cross section of the river at the gauge site has been shown in Figure A photographic view of the Dalai River near the proposed barrage site is portrayed in Figure Dividing the distance with float time gives velocities of floats for each sub-section. Objects float close to the river surface, which is faster than the average velocity of the water profile and must, therefore, be reduced by a coefficient. Consider a factor of 0.85 to convert surface velocity into average velocity of flow across the depth profile. Average velocity for each sub section of floats was multiplied with the river cross section gives discharges. The average of discharges corresponding to different velocities through sub-sections was considered as river discharge for the day. Q = n ( Α) n avg vi i= 1 Where A is cross-section of the river. Figure 6.11: Cross-section of Dalai River at Near Dalai Bridge Site 11010A-H D01 B Chapter 6: Hydrology 25 of Jul-14

66 Figure 6.12: View of the Dalai River Near the Barrage Site Current method In this method, the stream channel cross section is divided into numerous vertical subsections. In each subsection, the area is obtained by measuring the width and depth of the subsection, and the water velocity is determined using a current meter. With current metering the rotation of a current meter's impeller for a period of time gives the local water velocity. For average velocity for the profile two depths are used for measurement, and then an average of 0.2D and 0.8D gives a good representation of the profile velocity, or 0.6D if only one depth is used. The discharge in each subsection is computed by multiplying the subsection area by the measured velocity. The total discharge is then computed by summing the discharge of each subsection. Schematic diagram for current method measurement is shown is Figure n ( Α ) i Q avg = vi i= A-H D01 B Chapter 6: Hydrology 26 of Jul-14

67 Figure 6.13: Diagram Showing Sub-section for Current Method Flow series observed at Dalai bridge site on Dalai River having catchment area km² since September 2008 to July 2011 is reproduced under Annexure 6.6. However, the length of observed data at the location is not sufficient to establish water availability for a project of the size conceived. Based on observed flow series at Hayuliang and Mompani G & D sites (shown in Figure 6.1), discharge series approved by CWC (Ref: CWC U.O. No.4/334/2010-Hyd(NE)/136 dated , described in Pre Feasibility Report of Kalai-I -2011) for Kalai I HEP in the near vicinity are also available, and furnished under Annexure 6.7. Annexure 6.8 shows the different flow parameters like maximum, minimum, average annual flow at Kalai-I site. In the region heavy rainfall starts generally from mid April to May. Hence, hydrological analysis considers a year starting from May and ending in April Estimation of Snow Melt Runoff Estimation of snowmelt has been carried out using equation adapted from the U.S. Army Corps of Engineers for open or partially covered areas (Equation 31.10, Page 438, WMO 168, 1994). The formula is M = ( P) x (T) + 1; Where, M = snowmelt in mm / day, P = Precipitation in mm / day and T = Average ambient temperature A-H D01 B Chapter 6: Hydrology 27 of Jul-14

68 For transferring the Passighat temperature to the required mean elevation of the vertical bands, a lapse rate of 7 degrees per km has been used uniformly and temperature for each elevation zone computed accordingly for each month. Elevation of snowline has been considered as 4500 m, the recorded elevation of permanent snowline in the region, to arrive at a conservative estimate. Since Kalai-I catchment (14168 km²) contains 4444 km² area above permanent snowline, snowmelt runoff assumes a significant proportion of the discharge. For estimating snowmelt runoff at Kalai I, monthly average rainfall measured at Pasighat. The computations for each month have been shown in Annexure 6.9 and the summary of results is given in Table 6.5. Table 6.5: Summary of Snowmelt for each Month for Lohit River up to Kalai-I HEP Area Area Avg. daily Avg. Month Assumed below above temperature daily snowmelt snowmelt snowline snowline snowline in the slice rainfall in (m 3 /s) (10 6 m 3 ) (km 2 ) (km 2 ) ( o C) (mm) Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Calculation of snowmelt runoff for Raigam Barrage catchment in each month has been done based on the methodology discussed above. Catchment area up to Raigam barrage ( km²) contains 59.8 km² area above permanent snowline. Calculations of snow melt for each month at Raigam Barrage site are given in Annexure Such calculations have been done for all 12 months and the abstract of results for catchment area for Dalai River up to Raigam Barrage site is given in Table A-H D01 B Chapter 6: Hydrology 28 of Jul-14

69 Month Table 6.6: Summary of Snowmelt for each Month at Raigam Barrage Site Area Area Avg. daily Avg. daily Assumed below above temperatur snowmelt rainfall snowline snowline snowline e in the in (m (mm) 3 /s) (km 2 ) (km 2 ) slice ( o C) snowmelt (10 6 m 3 ) Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Methodology of Long Term Runoff Computation at Raigam Barrage site As mentioned above CWC has made its own estimation following the above methodology and provided the flow series at Kalai-I site given in Annexure 6.7. This flow series is used for finding the flow series at Raigam Barrage site. As a fair approximation, the catchment area is assumed as only the rain-fed area of the total catchment for deriving the catchment area proportion. Methodology for transferring data from Kalai-I to Raigam Barrage Site Step-1: Separate snow-fed and rain-fed catchment areas for Kalai-I and Raigam barrage Site. The total catchment of Kalai-I and Raigam site are km² and km² respectively. Since the snow-fed area of Kalai-I and Raigam site are 4444 km² and 59.8 km², the rain-fed catchment areas for Kalai-I and Raigam are 9724 km² and km² respectively. Step-2: Deduct snowmelt contribution from Kalai-I discharge. Snowmelt contribution for each month as given in Table 6.5 is deducted to get rain-fed discharge at Kalai I site. Discharge at Kalai-I after deduction of snowmelt runoff from total discharge has been presented in Annexure Step-3: The rain-fed contribution has been transferred from Kalai I to Raigam site by rain-fed catchment area proportionality A-H D01 B Chapter 6: Hydrology 29 of Jul-14

70 Rain-fed discharge data at Raigam HEP site has been derived by considering the runoff obtained by deducting snowmelt runoff from total discharge at Kalai-I and multiplying with rain-fed catchment area factor {( )/ ( ) =1643.6/9724=0.169}. Rain-fed discharge at Raigam Barrage location has been presented in Annexure Step-4: Add the snowmelt for Raigam catchment contribution for each month as given in Table 6.6 to the rain-fed discharge to get the flow series at Raigam site. Ten daily discharges for different years along with the different flow parameters (maximum, minimum, average annual flow) at Raigam Barrage site is furnished under in Annexure The 10 daily discharge series for Raigam HEP has been approved from CWC, the same has been given in Annexure 6.1 (Ref: CWC U.O. No. 4/382/2012-Hyd (NE)/41-42 dated ). Approved series has been used for energy calculation. Observed data for to at Bridge on Dalai River (provided by project company), downstream of project transferred at Raigam Barrage site (using catchment area proportionality factor, / =0.942) has also been presented in Annexure Gap data from 1 st May 2008 to 20 th September 2008 has been filled by taking average of respective available months from succeeding years. Mean monthly discharge from derived data and observed data at Barrage site are presented in Figure 6.14 for the purpose of comparison A-H D01 B Chapter 6: Hydrology 30 of Jul-14

71 Figure 6.14: Monthly Mean Discharge at Barrage Site (Derived and Observed) This brings out that observed discharge has higher values compared to the derived series for most of the time. However, the short duration of observed data (about 3 years) is insufficient for proper assessment of water availability. Appreciating the fact that the computations are based on once daily observations at site, which might have errors of observation involved and actual flood peaks might have been missed due to fixed time of observation. Annual flow volumes computed on the basis of derived and observed 10-daily flow series are portrayed in Figure 6.15, which also show higher flow volume as compared with Derived series. Therefore, use of derived data series for water availability analysis is supposed to provide a safer picture. Hereafter, hydrologic computations are based on derived data, unless mentioned otherwise A-H D01 B Chapter 6: Hydrology 31 of Jul-14

72 6.3.4 Flow Pattern Figure 6.15: Annual Flow Volume based on Derived and Observed 10-Daily Series The stream flow consists of the contribution from rain, snow and glaciers and the respective contribution of each component varies with time of the year. Generally, the snowmelt contribution starts from March and lasts until June/July, depending upon the snowpack water equivalent accumulated in the preceding winter season and the prevailing temperature in the summer season. As the summer season progresses, the snow melt contribution increases continuously and exceeds the rainfall component. Thus, in the pre-monsoon season (March-April), a major part of the stream flow is generated from seasonal snow melt. During the monsoon season (May- September), the flow is augmented by monsoon rains, producing higher discharges in the river. Generally, high discharges and floods are observed in the months of July and August and these are essentially due to the heavy rain in the lower part of the basin. Usually, seasonal snow accumulated on glaciers during the winter season is almost exhausted by the end of May/June and glaciers start contributing to the flow thereafter. Glaciers share maximum contribution of runoff in the months of July and August. As such, contribution of glaciers to runoff lasts till September/October. In the post monsoon season, stream flow is partly from glaciers and partly from rainfall. Minimum stream flow is observed during winter because no melting takes place due to low temperatures. The base-flow 11010A-H D01 B Chapter 6: Hydrology 32 of Jul-14

73 contribution sustains the flow in the river during this period. In the Dalai River catchment, significant rainfall occurs in the month of May and June due to thunderstorm activity. Characteristics of the flow pattern of the river at the project site for hydrologic year (May to April) based on derived and observed data are given in Table 6.7 and Table 6.8 respectively. It shows that the observed data is on the higher side. It may also be reiterated that the time duration (3 years) of observed data is insufficient to arrive at a firm conclusion, and hence not considered for design of Hydropower Projects with capacity greater than 25MW. Table 6.7: Flow Pattern of Dalai River at Raigam Project Site based on Derived Data Sr. No. Characteristics Flow Values 1 Average Annual Flow (MCM) Maximum Annual Flow (MCM) Minimum Annual Flow (MCM) Average monsoon Flow (May -Sept.) (MCM) Average non-monsoon Flow (Oct.-Apr.) (MCM) Maximum 10-daily discharge ( m 3 /s) Minimum 10-daily discharge ( m 3 /s) 20 Table 6.8: Flow Pattern of Dalai River at Raigam Project Site based on Observed Data Sr. No. Characteristics Flow Values 1 Average Annual Flow (MCM) Maximum Annual Flow (MCM) Minimum Annual Flow (MCM) Average monsoon Flow (May -Sept.) (MCM) Average non-monsoon Flow (Oct.-Apr.) (MCM) Maximum 10-daily discharge ( m 3 /s) Minimum 10-daily discharge ( m 3 /s) Dependable Flow Analysis Estimates of annual flow volumes for the period to have been used to arrive at the 90% and 50% dependable hydrologic year based on Weibull Plotting position formula, as shown in Table A-H D01 B Chapter 6: Hydrology 33 of Jul-14

74 Year Table 6.9: Dependability of Annual Flow Volumes Annual Yield Sorted Rank Probability of Exceedance (%) (MCM) Year Yield , , , , , , , , , , , , , , , , , , , The summary results of dependable flow analysis for 90%, 50% dependable year are shown in Table Table 6.10: Dependable Year Flow Volumes Dependability Dependable Water Year (Apr Mar) Annual Flow Volume (MCM) 90% % The flow duration curve based on all 10-daily discharge data is presented in Figure Flow Duration Curve for 90% and 50% dependable year has been portrayed in Figure 6.17 and Figure 6.18 respectively. Flow duration curves after deduction of environmental release have been presented under Chapter 8: Power Potential & Installed Capacities A-H D01 B Chapter 6: Hydrology 34 of Jul-14

75 Figure 6.16: Ten-Daily Flow Duration Curve (Period to ) Figure 6.17: Flow Duration Curve for 90% Dependable Year: A-H D01 B Chapter 6: Hydrology 35 of Jul-14

76 Figure 6.18: Flow Duration Curve for 50% Dependable Year: Environmental Release Environment and ecological considerations require that a certain minimum flow must be released at the barrage toe to meet the requirement between the barrage and the main powerhouse tailrace outfall. As per the recent recommendations of MOEF for river valley hydropower projects, 20% of the average flow of four consecutive leanest months in a 90% dependable year should be maintained as environmental flow during the lean season (December to March). During the monsoon period (considered as June to September for this purpose, in tune with other projects in the country), 30% of average discharge computed on the basis of 90% dependable year has to be released. During the non-lean non-monsoon period (October November and April May) release of about 25% of the average discharge estimated on the basis of 90% dependable year is required. The year was identified as the 90% dependable year. The four leanest consecutive months in the 90% dependable year of happens to be from December 2002 to March 2003, with monthly average discharges computed as 41.4 m 3 /s, 36.6 m 3 /s, 37.6 m 3 /s and 39.7 m 3 /s cumecs respectively. The average flow during the period is m 3 /s, and 20% of that comes out to be 7.77 m 3 /s. Accordingly, environmental releases for the lean season, monsoon season, and non-lean non-monsoon season have been computed as 7.77 m 3 /s, m 3 /s and 11010A-H D01 B Chapter 6: Hydrology 36 of Jul-14

77 13.65 m 3 /s respectively. However, following the international practice, as also the basic principle behind the regulatory guidelines of the MoEF, the pulse of river flow is required to be maintained for sustenance of the riverine ecology. Therefore, it is proposed that the environmental release during the monsoon season and the nonlean non monsoon season be considered as a variable amounting to 20% of the actual inflow or at most 30% and 25% of the actual inflow during the periods respectively. This will help to prevent loss of significant amount of energy generation. 6.4 Design Flood Studies General Design flood studies are essential and important for proper planning and design of water resource projects. Other than empirical estimation of design flood, the conventional design flood estimation involves the computation of a set of design floods of various return periods either using the frequency analysis of flood series (stochastic approach) or carrying of hydro-meteorological analysis using storm rainfall parameters obtained from meteorological data (deterministic approach) and flood discharge records from river gauging sites. The return period selected for design depends upon the importance of the structure as well as economic and safety considerations. The return period of design flood to be adopted for different category of dams as specified by Central Water Commission (CWC) vide their manual on Manual on Estimation of Design Flood is given in Table Table 6.11: Classification of Dams for Design Flood Dam Type Gross Storage (mcm) Hydraulic Head (m) Probability of Design Flood (years) Small 0.5 to to Year Intermediate 10.0 to to 30.0 Standard Project Flood (SPF) Large More than 60.0 More than 30.0 Probable Maximum Flood (PMF) The above classification of dam based on the gross storage behind the dam and hydraulic head (from normal or annual average flood level on the downstream side 11010A-H D01 B Chapter 6: Hydrology 37 of Jul-14

78 to the maximum water level) as per Clause of IS: (1985): Guidelines for Fixing Spillway Capacity. But in all cases, flood of larger and smaller magnitude may be used if the hazard involved in the eventuality of a failure is particularly high or low. The parameters considered are I. distance to and location of the human habitations on the downstream after considering the likely future developments. II. maximum hydraulic capacity of the downstream channel at a level at which catastrophic damage is not expected. According to this classification, the proposed barrage on River Dalai, with envisaged storage height of 15 m is of Intermediate category. Hence as per the same code, the inflow design flood for the barrage structure should be SPF. For upstream submergence condition, adoption of 25 year flood for land acquisition and 50 year flood for built up property acquisition has been suggested (vide Para 2.3.3, Page 9, CWC, 2001) Design Approaches Flood estimation has been done following (i) Empirical approach and (ii) Deterministic approach. Finally, design flood value has been chosen judiciously Empirical Approach Dicken s formula has been commonly used for flood estimation in Central and Northern India. It is expressed as Q = CA 3/4 Where, Q = peak flow rate in m 3 /s A = Catchment area in sq.km C = Dicken s constant Dicken s constant has been estimated following UPIARI formula cited in page 682, Mutreja (1986) as C = log (0.6T) x log (1185/P) + 4 Where, P = [(a + 6) / (A + a)] 11010A-H D01 B Chapter 6: Hydrology 38 of Jul-14

79 a = perpetual snow area (km 2 ) = 59.8 A = total catchment area (km 2 ) = T = return period in years Therefore, P = Dicken s Coefficient and flood discharges corresponding to different return periods have been furnished underneath under Table Table 6.12: Flood Discharges for Different Return Periods using Empirical Approach Return Dicken's Discharge Period Coeff. C Q ( m 3 /s) T Deterministic Approach The maximum floods for 100 years frequency and SPF for free board calculation have been estimated using the hydro-meteorological approach. The computations involve derivation of design storm hyetograph based on 24 hrs rainfall for 100 years return period and Standard Project Storm (SPS) rainfall and derivation of the lumped catchment response function i.e., the flood hydrograph based on synthetic unit hydrograph approach. Rainfall for 100 years has been obtained from CWC Sub Zone -2a (1991). while India Meteorological Department (IMD) has recommended the Standard Project Storm (SPS) value for the catchment, viz., 32.6 cm for 1 day storm and derivation of the lumped catchment response function i.e., the flood hydrograph based on synthetic unit hydrograph approach. (Ref: Annexure 6.15, Letter No. HS-32/18/2011 dated ). The same technique was applied to estimate peak flood for different return periods, using 24-hours rainfall corresponding to the same return period. It is worthy to mention that SPS values provided by IMD are catchment area averaged, and does not require catchment area adjustment for conversion into catchment averaged rainfall; while the point rainfall values read from CWC (1991) require the same Unit Hydrograph The unit hydrograph of the catchment for one hour Unit duration has been prepared following the CWC Report on Flood Estimation for Subzone-2a (CWC, 1991) 11010A-H D01 B Chapter 6: Hydrology 39 of Jul-14

80 applicable for the specific zone 2a, i.e., the North Brahmaputra Basin. The stream segment (Lc), extending from the outlet to the centre of gravity of the catchment required for estimation of synthetic unit hydrograph following CWC (1991), has been portrayed in Figure Catchment area for calculation of centroid is considered up to Permanent snow line of elevation 4500m. Centroid of the catchment has been identified using SRTM and Lc measured is 33.4 km. The parameters of Unit Hydrograph have been mentioned under Table 6.13 following standard notations. Figure 6.19: Stream to the Centre of Gravity of Raigam Catchment 11010A-H D01 B Chapter 6: Hydrology 40 of Jul-14

81 Table 6.13: Parameters of Synthetic Unit Hydrograph for Raigam Barrage Site Parameter Expression Value Unit qp 2.272(LxLc/S) m³/s Qp qpxa 691 m³/s tp 2.164(qp) , say 4.5 hrs W (qp) hrs W (qp) hrs WR (qp) hrs WR (qp) hrs TB 5.428(tp) , say 20 hrs Tm tp + tr/ hrs TD 1.1 tp (or = TB) 19.55, say 20 hrs Time of concentration has also been computed using other approaches in order to have a cross check. Kirpich Equation: t c = L S Where, tc = time of concentration in minutes L = length of the watershed along longest stream in metres = m S = slope of the watershed = difference in elevation between the highest and the lowest point in the watershed I watershed length L = ( ) / = tc = 330 minutes = 5.5 hours 5 hours, say Also, following computations in Table 6.13, 1.1tp=4.95 hours, 5 hours, say. It can be seen that these equations yield reasonably similar results. However, for the purpose of this study, time of rainfall duration TD has been adopted as 20 hours, as adoption of TD = TB has been reported to yield higher discharges for most of the cases (Clause 3.1.1, page -23, CWC, 1991). The synthetic unit hydrograph prepared in accordance has been given in Annexure Based on above parameters, the falling limb has been modified slightly to match the volume of discharge over the catchment with 1 cm of effective rainfall depth. The ordinates and graphs of the adjusted Synthetic Unit Hydrograph have been presented under Table 6.14 and shown in Figure A-H D01 B Chapter 6: Hydrology 41 of Jul-14

82 Table 6.14: Adjusted 1 Hour Synthetic Unit Hydrograph Time (hr) Discharge (m 3 /s) Time (hr) Discharge (m 3 /s) Figure 6.20: Synthetic Unit Hydrograph of 1 cm Rainfall Excess Daily Rainfall Values Catchment averaged 1-day storm rainfall values corresponding to SPS have been obtained from IMD. Point rainfall values corresponding to return period of 25 years, 50 years and 100, years return period have been read from Plates 8, 9 and 10 of CWC Flood estimation Report for subzone 2a (CWC, 1991) A-H D01 B Chapter 6: Hydrology 42 of Jul-14

83 One-day storm rainfall values Rainfall Values for different return periods have been summarized under Table Values for 24 hour storm rainfalls corresponding to SPS were obtained by multiplying the 1-day rainfall with clock hour correction factor of The rainfall values for 100 years, 50 years and 25 years return period have been obtained from CWC (1991), and are 24 hour storm rainfalls. Table 6.15: Rainfall Values Corresponding to Different Return Periods Sr. 1-day Rainfall 24 Hour Rainfall Areal Rainfall Return period No. Values (mm) Values (mm) (mm) 1 SPS years years years Design storm duration for the catchment area has been considered as 20 hours. For deriving areal rainfall for a catchment area of km², it was modified using areal reduction factor of (Ref. Table 6, CWC, 1991). It might be mentioned that areal reduction factor is not applicable for SPS values provided by IMD, which are catchment area averaged, but required for point rainfall values from CWC Flood Estimation Report or observed rainfall at site Temporal Distribution of Rainfall Since the design storm duration is longer than 12 hours, the rainfall increments have been arranged in the form of two bell shaped spells per day following suggestion of CWC(Ref: CWC U.O 4/382/2012-Hyd (NE)/160 dated 13/06/12). Base of unit hydrograph is 20 hours, therefore 24 hour design storm rainfalls in two bell have been considered for design flood studies. Hourly distribution of storm rainfalls for this project has been obtained following time distribution coefficients provided by IMD (Annexure 6.15) as shown in Table It has been normalized to obtain distribution over 12 hour period. Thereafter, it has been adjusted slightly to arrive at a smooth hourly distribution as shown in Figure 6.21 and Table Table 6.16: Temporal Distribution of Rainfall following IMD Time (Hours) % of 24- hour Storm Rainfall Normalized Rainfall for 12 Hours A-H D01 B Chapter 6: Hydrology 43 of Jul-14

84 Time (Hours) % of 24- hour Storm Rainfall Normalized Rainfall for 12 Hours Figure 6.21: Interpolated and Adjusted Temporal Distribution of Rainfall Table 6.17: Hourly Distribution of Rainfall Cumulative Time Rainfall (Hrs) Fraction (Adjusted) A-H D01 B Chapter 6: Hydrology 44 of Jul-14

85 From Table 6.15, the 24 hour 100 years Precipitation is cm. From Table 6.16, the fraction of 24 hour rainfall received in 12 hours is The first bell, therefore, considers 74% of the storm rainfall, which is cm. The remainder of the oneday rainfall has been attributed to the second bell, which is 6.56 cm. In a similar way, distribution of rainfalls in 2 bells was carried out for the SPS and rainfalls with other return periods, i.e., 50 years and 25 years and is shown in Table 6.18 below. Table 6.18: Rainfall Distribution for Different Return Periods in 2 Bells Bell 1st Bell (cm) 2nd Bell (cm) SPS 100 Years 50 Years 25 Years The cumulative hourly distribution of storm rainfall corresponding to different return periods for the two bells following the distribution pattern shown in Table 6.17 has been provided under Table Duration (Hours) Table 6.19: Cumulative Distribution of Hourly Rainfall for Each Bell Rainfall (cm) SPS 100Y 50Y 25Y Bell-1 Bell-2 Bell-1 Bell-2 Bell-1 Bell-2 Bell-1 Bell Incremental rainfall in each hour has been computed from the cumulative rainfall (Table 6.19), and furnished under Table A-H D01 B Chapter 6: Hydrology 45 of Jul-14

86 Duration (Hours) Table 6.20: Temporal Distribution of Hourly Rainfall for Each Bell Rainfall (cm) SPS 100Y 50Y 25Y Bell-1 Bell-2 Bell-1 Bell-2 Bell-1 Bell-2 Bell-1 Bell Design loss rate of 0.24cm/hr as per Flood Estimation Zone - 2a, Report of Central Water Commission, India (CWC-1991, Para 2.3.0) has been adopted. The hourly distribution of effective rainfall corresponding to different return period have been derived by subtracting the loss rate from hourly rainfall furnished under Table 6.20, which is shown under Table Duration (Hours) Table 6.21: Hourly Distribution of Effective Rainfall for Each Bell Rainfall (cm) SPS 100Y 50Y 25Y Bell-1 Bell-2 Bell-1 Bell-2 Bell-1 Bell-2 Bell-1 Bell Hourly effective rainfalls for different return periods have been arranged in critical sequence in Table 6.22, placing the largest rainfall value against the largest UH ordinate and following the same order for the remaining ordinates. The corresponding 11010A-H D01 B Chapter 6: Hydrology 46 of Jul-14

87 ordinates of the design unit hydrograph have also been provided under the same table. Time (Hrs) UH Ord (m 3 /s) Table 6.22: Critical Sequence of Effective Rainfall for Each Bell Rainfall (cm) SPS 100Y 50Y 25Y Bell-1 Bell-2 Bell-1 Bell-2 Bell-1 Bell-2 Bell-1 Bell Hourly effective rainfall arranged in reverse critical sequence has been given in Table 6.23, which are used for estimating the peak flood corresponding to different return periods, following CWC (1991). Time (Hrs) Table 6.23: Reverse Critical Sequence of Effective Rainfall for Each Bell UH Ord (m 3 /s) Rainfall (cm) SPS 100Y 50Y 25Y Bell-1 Bell-2 Bell-1 Bell-2 Bell-1 Bell-2 Bell-1 Bell A-H D01 B Chapter 6: Hydrology 47 of Jul-14

88 6.4.8 Design Base Flow A design base flow of 0.05 m 3 /s per km² has been considered for analysis as per as per Flood Estimation Zone - 2a, Report of CWC-1991, Para 2.4. Considering base flow from Rainfed catchment area of , the base flow rate turns out to be m 3 /s Design Peak Snow Melt Runoff Design snowmelt rate has been estimated using equation adapted from the U.S. Army Corps of Engineers for open or partially covered areas (Equation 31.10, Page 438, WMO 168, 1994). The formula is M = ( P) θ Where, M = snowmelt in mm / day, P = rainfall in mm / day, θ = mean daily temperature in C For the Raigam catchment, snowbound catchment area = 59.8 km 2 P = 200 mm (Assumed rainfall in area above 3000 EL) Mean daily temperature = 4 C. Melt rate = ( ) =8.17 mm Snowmelt discharge for Raigam catchment = /( )=8.17 m 3 /s Flood Hydrograph The critical sequence of the bells has been chosen in a way that the storm hydrograph ordinates are maximised. The flood hydrographs corresponding to different return periods have been computed by summing up the runoff due to rainfall, base flow and snowmelt. The flood discharge corresponding to 100 Years return period has been obtained as 7480 m³/s when the bells are arranged in the sequence 2,1. The details of computation have been furnished under Annexure Arrangement of bells in reverse order yields lower peak rate of runoff. The standard project flood discharge has been computed as m³/s, as detailed under Annexure 6.18 and shown in (Figure 6.22). SPF of m³/s have been approved from CWC ( Ref: CWC U.O. No. 4/382/2012-Hyd (NE)/41-42 dated ). Computations for peak flood for return periods of 50 and 25 years have been 11010A-H D01 B Chapter 6: Hydrology 48 of Jul-14

89 presented under Annexure 6.19 and Annexure 6.20 respectively. The rounded flood discharges corresponding to different return periods have been summarized in Table 6.24 underneath. Time(hr) Discharge (m 3 /s) Discharge (m3/s) Time (hour) Figure 6.22: SPF Hydrograph 11010A-H D01 B Chapter 6: Hydrology 49 of Jul-14

90 Table 6.24: Flood Discharges for different Return Periods using Deterministic Approach Sl. No. Return period Flood Discharge (m 3 /s) 1 SPF years years years GLOF A glacial lake outburst flood (GLOF) is a type of outburst flood that occurs when the structure containing a glacial lake fails. The Himalayan regions have suffered many GLOF events. Detailed GLOF study has been enclosed in Annexure 6.1. The peak discharge estimated at barrage site due to GLOF event has been estimated as 889 m 3 /s. This study has been approved from CWC (Ref: CWC U.O. No. 4/382/2012-Hyd (NE)/41-42 dated ), Annexure Design Flood Value Flood magnitudes estimated using the empirical approach appears to be smaller in magnitude. Frequency analysis conducted using Gumbel distribution considering annual peak flood data (refer to Annexure 6.23) shows that the 100 year return period flood has a magnitude of 2605 m 3 /s, which is less than the design flood calculated by deterministic approach. The rounded design flood values for different return periods (modified from the results of hydro meteorological analysis for subzone 2a) have been summarized in Table 6.24 above. The peak discharge for Raigam catchment at the Barrage Site for a return period of 100 years has been chosen as the design flood value obtained following hydrometeorological approach suggested by CWC for zone 2a (CWC, 1991), which is 7480 m 3 /s. GLOF value has been estimated as 889 m³/s. Sum of 100 year flood and GLOF is 8369 m³/s. SPF of m 3 /s, which is higher than the sum of 100 years flood and GLOF value has been considered as design flood for the project. Therefore, SPF of m 3 /s, which has been approved from CWC has been adopted as design flood for the project A-H D01 B Chapter 6: Hydrology 50 of Jul-14

91 Construction Diversion Flood According to IS 14815: 2000 Design Flood for River Diversion Works Guidelines (vide Clause 4.1, Page 2) the following should be considered while deciding the diversion flood capacity for concrete dams and barrages: I. Maximum non-monsoon flow observed at the Barrage site or II. Frequency analysis based on Gumbel s Method The highest of the above should be taken as the capacity of the design flood for diversion construction. Computation of diversion flood for 25 years and 100yrs return period have been calculated using frequency analysis by Gumbel method. Analysis has been done based on observed maximum annual peak discharges during monsoon (May to September) and non-monsoon (October to April) at Mompani site for the period of 1987 to 2004, excluding the year 1994 and 1995 for which the flow data is not available. The maximum values at Mompani site has been increased by 15% to account for any missing peaks in a 24-hour period as the observation was made only once in a day as given in Table Table 6.25: Annual Peak Discharges during Monsoon and Non-Monsoon at Mompani Site Monsoon Period (May to September) Non - Monsoon Period (October to April) Increased Increased Year Year Maximum Maximum Flow maximum flow maximum Flow (m 3 /s) by 15% flow by 15% (m 3 /s) (m 3 /s) (m 3 /s) , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , A-H D01 B Chapter 6: Hydrology 51 of Jul-14

92 Flood Frequency Analysis The annual peak flow series of Mompani data as shown in the above table has been checked for any outliers. Outliers are data points that depart significantly from the trend of the remaining data. The retention or deletion of these outliers can significantly affect the magnitude of statistical parameters computed from the data, especially for small samples. High outlier check in the Mompani base data for monsoon peak values for flood frequency analysis has been given in Annexure Series has one higher outlier of discharge 11,729 m 3 /s. However, m 3 /s is an observed flood; therefore it is considered for the frequency analysis. Low outlier check in the Mompani base data for non-monsoon peak values for flood frequency analysis has been given in Annexure Series has one lower outlier of discharge 776 m 3 /s. However, 776 m 3 /s is an observed flood; therefore it is considered for the frequency analysis. Therefore all 16 years value are considered for the frequency analysis. The flood contribution from rainfed catchments of Mompani to the same of Raigam have been taken using Dicken s approach based on ratio of rainfed catchment area method instead of direct area proportion (14503 km² and km², respectively). Steps for finding Flood values at Raigam from Mompani has been given in steps below: Methodology for transferring Flood value from Mompani to Raigam Step-1: Separate snow-fed and rain-fed catchment areas for Mompani and Raigam. Step-2: Deduct average snowmelt from the Mompani flood values during monsoon (May- September) period to get rainfed flood for monsoon period. Step-3: Deduct average snowmelt from the Mompani flood values during nonmonsoon (October- April) period to get rainfed flood for non-monsoon period. Step-4: Rainfed flood during monsoon and non-monsoon at Raigam have been transferred by rainfed catchment area proportion using Dicken s approach method A-H D01 B Chapter 6: Hydrology 52 of Jul-14

93 Step-5: Add Raigam average monsoon snowmelt to the calculated Raigam rainfed flood values to get flood at Raigam for monsoon period. Step-6: Add average non-monsoon snowmelt to the calculated Raigam rainfed flood values to get flood at Raigam for non-monsoon period. The flood frequency analysis for different period considering monsoon and non monsoon period by Gumbel (Extreme Value, EV I) method is included in Annexure The result of the frequency analysis is tabulated in the Table Table 6.26: Flood Values at Raigam site for different Return Period Predicted Non-monsoon Flood in m 3 /s for different Return Periods Years Predicted Monsoon Flood in m 3 /s for different Return Periods Years Maximum Observed Flow Based on the observed discharge from September, 2008 to July 2011, the observed maximum flow for every month near Dalai Bridge on Dalai River is given in Table 6.27 below. Table 6.27: Observed Maximum Flood near Dalai Bridge on Dalai River. Month Peak Flood Date (cumecs) Jan th Jan 2009 Feb th Feb 2009 Mar th Mar 2010 Apr th Apr 2010 May th May 2010 Jun th Jun 2010 Jul th Jul 2011 Aug th Aug 2010 Sep th Sep 2010 Oct th Oct 2008 Nov st Nov 2008 Dec st Dec Maximum Observed Non-monsoon Flow I. Maximum non-monsoon flow observed at downstream Mompani HEP site 11010A-H D01 B Chapter 6: Hydrology 53 of Jul-14

94 Based on the data available, the observed maximum Non-monsoon flow at downstream Mompani HEP site is m 3 /s. The flood value when transferred to Raigam diversion site is 989 m 3 /s, which is less than the 25 year non-monsoon flood at Raigam site. II. Maximum non-monsoon flow observed at the Barrage site on Dalai River Based on the observed discharge from September, 2008 to July 2011, the observed maximum Non-monsoon (October to April) flow near Dalai bridge on Dalai river is m 3 /s on dated 24 th April, The flood value when transferred to Raigam diversion site is 1375 m 3 /s, which is more than the 25 year non-monsoon flood at Raigam site. If the construction period is considered from October to March month, the observed maximum flow near Dalai Bridge on Dalai River is m 3 /s on dated 30 th October, The flood value when transferred to Raigam diversion site is 751m 3 /s, which is less than the 25 year non-monsoon flood at Raigam site Maximum Observed Monsoon Flow Based on the observed discharge from September, 2008 to July 2011, the observed maximum Monsoon (May to September) flow near Dalai bridge on Dalai river is m 3 /s on dated 20 th May, The flood value when transferred to Raigam diversion site is 1350 m 3 /s, which is less than the 250 year monsoon flood at Raigam site. It is remarkable that maximum observed flood during nonmonsoon is higher than the maximum observed flood during monsoon. This may be due to the flush flood comes during the month of April Choice of Working Period for Construction It is seen that the magnitude of maximum transferred flood varies based on the months chosen as working period, as shown under Table 6.28, which are also approved from CWC (Ref: CWC U.O. No. 4/382/2012-Hyd (NE)/41-42-dated A-H D01 B Chapter 6: Hydrology 54 of Jul-14

95 Table 6.28: Maximum Flood for Different Working Periods Working Period Flood Discharge (m³/s) October to March 1185 October to April 1375 Considering Monsoon Period 2148 While consideration of working period from October to March will require minimum expenditure for the cofferdam embankment and diversion tunnel, restricting construction at barrage site to 6 months will lead to increased construction time and as a result, increased project expenditure. On the other hand, adoption of working period from October to April, though allows working at barrage site for 7 months together, will require larger expenditure for diversion arrangements. Therefore, optimizing on both counts, it is suggested that working period be limited to 7 months between October and April Design Construction Diversion Flood Value The study suggests the flood values may be adopted depending upon the type of structure and construction season. Considering construction period from October to April the diversion flood may be adopted as 1375 m 3 /s as approved by CWC (Ref Annexure 6.1). 6.5 Stage-Discharge Curve General The rating curve for stage discharge at downstream of barrage and at powerhouse tailrace outfall is required to study the different flow elevation Tail water level at downstream of barrage site Computations for estimating tail water level downstream of the barrage site have been done using Flow MasterV8i Software. Manning s n has been assumed as 0.05, as the bed material comprises of boulders with vegetation near the upper levels. Average river slope at barrage location is taken as m/m. The details are furnished under Annexure 6.24; the rating curve has been shown in Figure A-H D01 B Chapter 6: Hydrology 55 of Jul-14

96 Figure 6.23: Rating Curve at Barrage Site From the figure, it is seen that the maximum water level attained during passage of SPF is m. The water levels which would be attained during passage of floods of different frequencies have been furnished under Table Table 6.29: Water Levels at Barrage Site for Different Flood Frequencies Water Frequency Level (m) 1 in 25 Years (working period, Oct-April) in 25 Years in 50 Years in 100 Years SPF Powerhouse-Tailrace Outfall The water level at SPF will cause the maximum water level at the powerhouse site. The rating curve at the power house site obtained using HEC RAS using local survey observations has been furnished in Figure A-H D01 B Chapter 6: Hydrology 56 of Jul-14

97 W.S. Elev (m) Legend W.S. Elev Q Total (m3/s) Figure 6.24: Rating Curve at Tail Race Out fall near Power House Site For SPF, m 3 /s, the maximum water level at tailrace location will be m, as detailed under Annexure Water surface elevations corresponding to flood magnitude of different return periods have been estimated from the stagedischarge rating curve at the power house location and have been summarized under Table Table 6.30: Water Levels at TRT Outfall near Powerhouse Site for Different Flood Frequencies 6.6 Reservoir Storage Volume Frequency Water Level (m) 1 in 25 Years (working period, Oct-April) in 25 Years in 50 Years in 100 Years SPF Area-elevation-capacity computations have been done for the barrage site based on surveyed data collected at site, and the results have been presented in Table 6.31 and shown in Figure The reservoir of Raigam Hydroelectric Project is formed by the construction of 15m high barrage and covers an area of km² and has a capacity of MCM at FRL of 725m A-H D01 B Chapter 6: Hydrology 57 of Jul-14

98 Table 6.31: Elevation Area Capacity at Raigam Barrage Site Elevation Area capacity m Km 2 M m A-H D01 B Chapter 6: Hydrology 58 of Jul-14

99 Figure 6.25: Elevation-Area-Capacity Curve 6.7 Maximum Water Level It has been decided that Maximum Water Level upstream of the barrage will be restricted to 726 m, i.e., 1 m above the Full Reservoir Level. Computations and dimensions of gates to establish adequacy for safe passage of the SPF Flood will be furnished under the chapter on Civil Design. 6.8 Sedimentation Study Computations based on observed silt data from Hayuliang in Anjaw district, Arunachal Pradesh (available for Jan 2011 to July 2011) has been furnished in Table It is generally observed that the sediment volume and concentration during monsoon are high. Sedimentation studies have been not been carried out as compared to the annual average inflow, the storage behind the barrage is limited. Also, opening of barrage gates will ensure effective flushing out of silt during monsoon A-H D01 B Chapter 6: Hydrology 59 of Jul-14

100 Sediment Conc. (PPM) Table 6.32: Number of Days with Heavy Silt Load (Jan 2011 to Jul 2011) Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Annual 0 < X <= < X <= < X <= < X <= X > Conclusion This chapter established the water availability for the Raigam Reservoir. It also sets the design flood value as SPF of m³/s has been considered. construction diversion flood has been computed as 1375 m³/s. The FRL is at 725 m, having water spread surface of km². At the power house site, the maximum water level attained under this condition is m. Reservoir sedimentation is not envisaged to pose a major problem. The 11010A-H D01 B Chapter 6: Hydrology 60 of Jul-14

101 ANNEXURE 6.1 RAIGAM HYDROLOGY CWC APPROVAL LETTER DT

102 Government of India Central Water Commission Hydrology (NE) Directorate Sub: Hydrological studies for Raigam HE Project, Arunachal Pradesh Ref: CWC U.O. No. 32/85/12-PA(S)A3 date (S), Sewa Bhawan R.K.Puram, New Delhi-66 Raigam HE project is a run off the river scheme proposed on Dalai river, a right bank tributary of Lohit river in Anjaw district of Arunachal Pradesh. The total catchment area at the diversion site is about sq.km out of which snowfed catchment area above permanent snow line of 4500 m is about 59.8 sq.km. The project envisages construction of a diversion structure. The latitude and longitude of diversion site is 28 10'01"N and 96 31'12/'E respectively. The Compliance of hydrological study report received by this Directorate vide CWC U.O. No. 32/85/12-PA(S)/13 date have been examined and observations are as follows: Water availability The discharge data at Raigam bridge site is available for the period October 2008 to July 2011 only, which is not sufficient to arrive at the water availability series for the project. Hence, the water availability series for Raigam HE Project has been worked out on the basis of approved water avialability series of Kalai-I HE Project proposed on Lohit river. The total catchment area at Kalai-I HE Project is sq.km out of which snow fed catchment area is about 4444 sq.km for permanent snow line at EL 4500 m. The snow melt contribution of Kalai-I catchment has been deducted from approved series of Kalai-I and series thus obtained at Kalai-I has been transferred to Raigam HE Project site in rainfed catchment area proportion. The snow melt contribution of Raigam catchment has been added in the above series to get the 19 years 10- daily water availability series for the Raigam HE Project for the period to The average annual flow and average annual yield of the series thus obtained at Raigam HE Project site is about 4034 MCM and 2368 mm respectively. Observations: 10-daily water availability series for Raigam HE Project for the period to2dd3-04 with average annual flow of 4034 MCM (2368 mm) is generally in order. The same enclosed at Annexure-I can be adopted for planning purpose of the project. Design flood The design flood study has been carried out using hydro-meteorological approach. The 1-day SPS value as supplied by IMD has been taken as 326 mm. The clock hour correction has been considered as 15%. The unit hydrograph has been worked out as per FER-subzone-2(a). The loss rate of 2.4 mm/hr and base flow of 0.05 cumec/km2 have been adopted. The snowmelt contribution has been computed as per VVMO formula. The study recommends a design flood (SPF) value of cumec.

103 Observations: The unit hydrograph ordinates were not properly adjusted. The unit hydrograph has been worked out in this Directorate. The same has been convoluted with hourly effective rainfall taking the bells of 12 hours each. The SPF thus obtained is cumec and the same may be adopted as design flood for planning purpose of the project. Diversion Food For diversion flood study of the project the observed flood peaks at Mompani G&D site (total catchment area km2 and rainfed catchment area sq.km) for the period 1987 to 2004 have been used. The observed flood peaks have been increased by 15% to convert those into instantaneous peaks. Flood frequency analysis have been carried out fitting Gumbel distribution to the instantaneous annual peak series. The snowmelt contribution has been deducted from the flood peak of different return periods calculated at Mompani and resulting flood peak has been transferred to Raigam HE Project site using Dickens formula taking rainfed catchment. The snowmelt of Raigam catchment has been added to get the flood peaks of different return periods. The study suggests the following flood at Raigam HE Project site: SI. Particular Value (cumec) No year return period non-monsoon flood for construction 1185 season October-March 2 25 year return period non-monsoon flood for construction 1375 season October-April (on the basis of maximum observed flood near Dalai bridge) 3 25 year return period monsoon/annual flood year return period monsoon/annual flood 2605 Observation The monsoon and non-monsoon flood peaks of different years as obtained from flood frequency analysis are generally in order. The calculated flood of different return periods as mentioned above may be adopted as diversion flood as per BIS criteria depending upon the type of structure and construction season. Sedimentation Studies of the Reservoir As the project is a ROR scheme, the reservoir is likely to get filled up upto the spillway crest in a short span of time. Hence, adequate sediment management practice needs to be adopted by project authorities in consultation with the concerned design Directorate.

104 The project authorities should also improve the rain gauge network and continue observation of G&D data so that the future review of hydrological studies could be carried out based on project specific representative rainfall and runoff data. Director PA(C),CEA CWC U.O. No.4/382/2012-Hyd(NE)/4/-4Z dated: i-^^/j o j c (N.tt.Rai) ' Director Copt to: Director, PA(S), CWC

105 Annexi're-I 10-daily discharge series for Raigam HEP (CA sq.km) Unit: i^.iiec I May II III I June II III I July II III I August II III I September II III I October II III I November II ' III I December II III I January II III I February II III I March II III I April II III

106 APPENDIX 6.2 CEA LETTER DT GLOF STUDIES

107

108

109 SECTION V POWER POTENTIAL

110 TABLE OF CONTENTS LIST OF APPENDICES... 2 LIST OF ANNEXURE... 2 LIST OF FIGURES... 3 LIST OF TABLES... 3 LIST OF ABBREVIATIONS... 4 CHAPTER 8 POWER POTENTIAL & INSTALLED CAPACITY Introduction Water Availability Discharge Data Dependable Years (90% and 50%) Environmental Release Operating levels Turbo-Generating Equipment - Type & Parameters Head Loss Computation Storage and Head Available For Power Generation Installed Capacity and Number of Units Power Potential Choice of Plant Capacity and Unit Size Incremental Energy Potential Harnessed Firm Power Plant Load Factor Lean Period Plant Load Factor Plant Capacity Utilization over the Year Plant Capacity Utilization over the Monsoon months Design Energy Monthly Energy Estimates Peaking Energy Conclusion A H D01 C Chapter 8: Power Potential & Installed Capacity 1 of Mar-14

111 Annexure No. Title LIST OF APPENDICES 8.1 Memo. No. CWC U.O. No. 4/382/2012-Hyd(NE)/41-42 dated 1 st February, 2013 of the Central Water Commission 8.2 Minutes of the 67th Meeting of the Expert Appraisal Committee for River Valley and Hydroelectric Projects constituted under the provisions of EIA Notification 2006, held on 6th June, 2013 at SCOPE Complex, New Delhi. 8.3 CEA Memo. No. 2/ARP/50/CEA/12-PAC/ dated 20 th June, CEA Memo. No. 2/ARP/50/CEA/2012-PAC/ dated 26 th July, Revised Level Approval Letter - Memo. No CE(M)/HPD/W- 101/ / dated 18 th November 2013, 8.6 CEA (PAC) Memo. No. 18/74/2012/HPA/2154 dated 27 th December, Annexure No. Title LIST OF ANNEXURE 8.1 Ten-Daily Pristine Discharge for Raigam HEP in Arunachal Pradesh 8.2 Dependability of Annual Unrestricted energy for Raigam HEP in Arunachal Pradesh 8.3 Ten Daily Discharge for Power Generation at Raigam HEP in Arunachal Pradesh after Compulsory Deductions 8.4a Head Loss in Water Conductor System for Raigam HEP in Arunachal Pradesh With All Units Running (Full Loading_3-Units) 8.4b Head Loss in Water Conductor System for Raigam HEP in Arunachal Pradesh With 1-Unit Running (at full load) 8.5 Ten-Daily Energy for Raigam HEP in Arunachal Pradesh 8.6 Design Energy computation for 90% and 50% Dependable Year 11010A H D01 C Chapter 8: Power Potential & Installed Capacity 2 of Mar-14

112 LIST OF FIGURES Figure No. Title 8.1 Layout of the Raigam HEP 8.2 Incremental Design Energy (MU) per MW increase in I.C. 8.3 Potential Harnessed with increasing I.C. 8.4 Plant Load Factors for Different I.C. 8.5 Lean Period Plant Load Factors for Different I.C 8.6 Capacity Utilization over the Year for Different I.C 8.7 Capacity Utilization in Monsoon for Different I.C 8.8 Fraction of Annual Energy Generated per Month LIST OF TABLES Table No. Title 8.1 Important Project Features of Raigam HEP 8.2 Dependable Energy Years 8.3 Environmental Release 8.4 Turbine and Generator Parameters 8.5 Important Water Levels and Storage 8.6 Maximum and Minimum Power Potential 8.7 Design Energy for a Range of Installed Capacities for the 90% Dependable Year (at 100% plant availability) 8.8 Annual Energy Generation for different I.C. (at 100% Plant Availability) 8.9 Energy Generation Estimates 8.10 Monthly Energy Generation in the 90 and 50% Dependable Years 11010A H D01 C Chapter 8: Power Potential & Installed Capacity 3 of Mar-14

113 LIST OF ABBREVIATIONS Abbreviations Expanded Form CWC Central Water Commission, India d/s Downstream EL. Elevation ha Hectare = 10⁴ m² HEP Hydro Electric Project HRT Head Race Tunnel I.C. Installed Capacity MCM Million Cubic Metre = 10 6 m³ MDDL Minimum Drawdown Level MOEF Ministry of Environment and Forests, Govt. of India MU Million Units of Energy = GWhr MW Mega Watt =10 6 Watt No. Number PLF Plant Load Factor Q Discharge SPF Standard Project Flood u/s Upstream 11010A H D01 C Chapter 8: Power Potential & Installed Capacity 4 of Mar-14

114 CHAPTER 8 POWER POTENTIAL & INSTALLED CAPACITY 8.1 Introduction Raigam Hydro-Electric Project is a pure run-of-the-river scheme on the Dalai River. The scheme has been contemplated to run at full capacity in monsoon season and at part load in non-monsoon season. The discharge from the River Dalai will be diverted by Raigam barrage near Village Teepani in District Anjaw of Arunachal Pradesh at Latitude North and Longitude East through tunnels. The proposed surface power house is located on the left bank of the River Dalai at Latitude North and Longitude East, approximately 2 km upstream of its confluence with River Lohit, about 9.7 km downstream of the barrage site. The outflow from the powerhouse will be discharged into the Dalai River. The purpose of this study for Raigam Hydroelectric Project (HEP) is to estimate the available flow for generation and corresponding power potential, and to find out plant and unit size and estimate energy generation A few important project features related to power potential study have been listed in Table 8.1. The layout of the project components have been shown in Figure 8.1. Table 8.1: Important Project Features of Raigam HEP Sl. No. Description Unit Value 1 Full Reservoir Level, FRL m Min. Draw Down Level, MDDL m Normal Tail Water Level m Length of Head Race Tunnel (Modified Horse Shoe shaped) m Length of Penstock m Diameter of Head Race Tunnel m Diameter of Penstock m A H D01 C Chapter 8: Power Potential & Installed Capacity 5 of Mar-14

115 FRL 725 Figure 8.1: Layout of the Raigam HEP 11010A H D01 C Chapter 8: Power Potential & Installed Capacity 6 of Mar-14

116 8.2 Water Availability The 10-daily discharge series for Raigam HEP has been worked out on the basis of approved discharge series of proposed Kalai-I HEP on River Lohit (vide CWC U.O. No.4/334/2010-Hyd(NE)/136 dated ) as described in Chapter 6 (Hydrology) of this DPR Discharge Data The catchment area up to the Raigam barrage site is km², which includes 59.8 km² area above the permanent snow line considered at 4500 m amsl. The catchment area at Kalai HEP is km², with about 4444 km² lying above the permanent snow line. The rainfed discharge of Raigam HEP has been obtained from the rainfed discharge at Kalai HEP using catchment area proportion. Snowmelt discharge has been added thereafter, to arrive at the total discharge. The series thus derived, spans over 19 years from May 1985 to April 2004 and has received concurrence of the CWC (vide CWC U.O. No. 4/382/2012-Hyd(NE)/41-42 dated 1 st February, 2013, Appendix 8.1). The details are presented under Chapter 6: Hydrology. The series has been presented again under Annexure 8.1. It is seen that the annual minimum 10-daily average flow varies between and m³/s whereas the maximum flow ranges from to m³/s. The average of 10-daily flows is around m³/s Dependable Years (90% and 50%) Arranging the series in descending order of annual unrestricted energy, the dependability of different years has been found using Weibull s plotting position formula, as shown in Annexure 8.2. From Annexure 8.2, it can be seen that the year has 90% dependability, while the year has 50% dependability. This has also been presented in Table 8.2. Table 8.2: Dependable Energy Years Annual Sl. Dependability Year Unrestricted No. Energy (MU) 1 90% % A H D01 C Chapter 8: Power Potential & Installed Capacity 7 of Mar-14

117 8.2.3 Environmental Release As per the Minutes of the 67 th Meeting of the Expert Appraisal Committee for River Valley and Hydroelectric Projects (Appendix 8.2, extract for Raigam HEP), 20% of the average flow of four consecutive leanest months in a 90% dependable year has been maintained as environmental flow during the lean season (December to March). During the monsoon period (considered as June to September for this purpose, in tune with other projects in the country), 30% of average discharge computed on the basis of 90% dependable year has to be released. During the non-lean non-monsoon period (October November and April May) release of about 25% of the average discharge estimated on the basis of 90% dependable year is required. The year was identified as the 90% dependable year. Accordingly, environmental releases for the lean season, monsoon season, and non-lean non-monsoon season have been computed as 7.75 m³/s, m³/s and m³/s respectively. The ten-daily average discharge available for power generation has been prepared after deduction of environmental release from the series presented in Annexure 8.1, and has been furnished under Annexure 8.3. The abstract of environmental release considered for the power potential study is given in Table 8.3. Table 8.3: Environmental Release Sl. No. Period Units Value 1 December to March m³/s June to September m³/s October-November, April-May m³/s Operating levels The Full Reservoir Level for the project has been fixed at 725 m by the CEA (vide Memo. No. 2/ARP/50/CEA/12-PAC/ dated and Memo. No. 2/ARP/50/CEA/2012-PAC/ dated , enclosed as Appendix- 8.3, 3 HPA and Appendix 8.4, respectively). With an assumed trifurcated intake of height 3.5 m and width 6.0 m, the Minimum Draw Down Level has been fixed at 723 m A H D01 C Chapter 8: Power Potential & Installed Capacity 8 of Mar-14

118 As per the suggestion from CEA mentioned in above memo, the Full Reservoir Level for the project has been fixed at 725 m, following the revised levels sanctioned by the Department of Power, Government of Arunachal Pradesh, Department of Power (vide Memo. No. CE(M)/HPD/W-101/ / dated 18 th November 2013, Appendix 8.5). Since the bed level is 710 m, the required submergence depth will be available if the invert is placed 1.5 m above the bed level. The maximum Tail Water Level will be m, attained during the passage of the Standard Project Flood having magnitude of m³/s. However, the power house is assumed to be shut down during the passage of such extreme flood. The crest of the tail race weir has been considered at m, the TWL allotted to the project (as per Appendix 8.5). Assuming a width of 40 m for the tail race channel, the normal Tail Water Level has been considered as m. The minimum tail water level obtained during operation of one machine at 50% load is m. For the purpose of energy estimation, average gross head has been considered as the difference between 2/3 of the difference between FRL and MDDL added to the MDDL, and the TWL [725+2 ( )/ = m]. 8.4 Turbo-Generating Equipment - Type & Parameters Sl. No. The available head indicates that a Francis turbine is suitable. A Francis turbine allows a negative setting yielding a higher head for generation. The minimum load at which a Francis turbine may be operated is about 50%. It is envisaged that the plant will act as a base plant operating at full capacity throughout the day during the monsoon period. Due to limited pondage of MCM (from Chapter 6: Hydrology) available to the project, it is apprehended that operation as a peaking plant might not be possible during the lean season. So, during the lean season the project has to operate on part load in run-of-the-river mode. The turbine and generator parameters are mentioned in Table 8.4 below. Table 8.4: Turbine and Generator Parameters Description Units Value 1 Type of Turbine Francis, vertical setting 2 Turbine Efficiency % A H D01 C Chapter 8: Power Potential & Installed Capacity 9 of Mar-14

119 Sl. No. Description Units Value 3 Generator Efficiency % Combined Overall Efficiency % Minimum Operating Load % 50 6 Permitted Continuous Overloading % Head Loss Computation The head loss in the pressure flow system from the power intake to the turbine is calculated as; Head Loss, HL = flv 2 / 2gD Where, f = Coefficient of friction L V g D = Length of the conductor = Velocity in the conductor = Acceleration due to gravity = Diameter of the conductor Head Loss in the bends, valves and intake are to be calculated as; Head Loss, HL = NfV 2 / 2g Where, N = Number of valve / bends etc. The velocity depends on the discharge in the conductor, which in turn depends on the sizing of the generating units and the associated design discharge. To that extent, the computation of head loss becomes a reiterative procedure. The components for head loss calculations are: loss in the Power Intake, loss in straight reach of Head Race Tunnel (HRT), loss in bends of HRT, loss in straight reach of Pressure Shaft, loss in bends of Pressure Shaft, losses in Main Inlet Valve, Penstock after Wye Piece and Penstock Valve. The detailed estimation of head loss for all units running on full load is given in Annexure 8.4a. For one unit running on full load, head losses are given in Annexure 8.4b. A contingency of 5% has been considered in the computations, to take care of slight modifications at later stage. The design head loss for all units with full load is 12.4 m, while that for two and one unit with full load are 6.2 and 2.5 respectively. For one unit operating on 50% of the load (the minimum loading considered for Francis machines) the head loss works out as A H D01 C Chapter 8: Power Potential & Installed Capacity 10 of Mar-14

120 8.6 Storage and Head Available For Power Generation The proposed Raigam Project consists of a very small pondage behind a concrete barrage with a water storage height of 15 m up to the FRL. The Weighted Average Head for plant operation has been obtained as Net Head = Gross Head Head Loss Gross Head = {MDDL + 2/3 (FRL-MDDL)} Normal Tail Water Level. Considering the 19 year available series for energy generation, average discharge during monsoon (June to September), non lean non monsoon (April, May, October and November) and lean (December to March) period are m 3 /s, m 3 /s, m 3 /s respectively. Therefore, head losses have been computed on seasonal basis. During monsoon period head loss works out as 12.4m considering all machines running at full load. During non lean non monsoon period head loss works out as 6.2m considering two machines running at full load. Similarly, during lean period head loss works out as 2.5m considering one machines running at full load. Important head water levels at the barrage and tail water levels at the power house and head available for power generation are given in Table 8.5 below: Table 8.5: Important Water Levels and Storage Sl. No. Description Units Value 1 Full Reservoir Level (FRL) m Maximum Water Level (MWL) m Minimum Draw Down Level (MDDL) m Normal Tail Water Level (TWL) at powerhouse m Maximum Tail Water Level at powerhouse under SPF m Minimum Tail Water Level at powerhouse m Gross Head m Head Loss under Full Plant Load m Head Loss with only 2 unit running at full load m Head Loss with only 1 unit running at full load m Head Loss with only 1 unit running at 50% load m Net Head in monsoon (June-September) m Net Head in non lean non monsoon (Apr-May, Oct-Nov) m Net Head in lean period (Dec-Mar) m Gross Storage Capacity at FRL MCM A H D01 C Chapter 8: Power Potential & Installed Capacity 11 of Mar-14

121 Sl. No. Description Units Value 16 Gross Storage Capacity at MDDL MCM Live Storage / Pondage MCM Since this project is a single purpose scheme, the entire live storage / pondage will be available for power generation. 8.7 Installed Capacity and Number of Units The installed capacity and the number of units are to be fixed with a view to maximize harnessing of available power potential at the optimum cost. The first step therefore is to establish the available power potential. In this regard, the basic formulae used are given below: Power, P (kw) = γηhq Where, γ = specific weight of water = ρg ρ g η = density of water = acceleration due to gravity = combined efficiency of turbine and generator = ηt x ηg ; ηt = eff. of turbine, ηg = eff. of generator H Q = Net head for generation = discharge passing through the turbine Energy, E(kWHr) = P x T Where, P = power as explained above T = time in hours. For a 10-day period T= 240 hours 8.8 Power Potential Sl. No. The unrestricted maximum and minimum power obtained from the 19 years of flow data with adopted project layout is given in Table 8.6 below: Table 8.6: Maximum and Minimum Power Potential Description Units Value 1 Maximum unrestricted power in 19 years MW Minimum unrestricted power in 19 years MW 20 # 3 Maximum power in 90% DY with water available for generation MW A H D01 C Chapter 8: Power Potential & Installed Capacity 12 of Mar-14

122 Sl. No. Description Units Value 4 Minimum power in 90% DY with water available for generation MW 45 5 Maximum unrestricted annual energy in 19 years with water available for generation MU Unrestricted annual energy in 90% DY MU 773 # During the last 10-daily period in September 1986 no water was available for power generation, which has been ignored as an exceptional case. 8.9 Choice of Plant Capacity and Unit Size The following may be observed from Table 8.6: 1. To fully utilize the power potential, the plant size must be 737 MW while the unit size must not be larger than 40 MW (to harness 20 MW at 50% plant loading), yielding the number of equally sized units as To fully utilize the power potential in a 90% dependable year, the plant size must be 215 MW while the unit size must not be larger than 90 MW (considering operation at 50% load), yielding the number of units as From experience on similar projects, it is inferred that a design discharge with a 33% probability of exceedance indicates a reasonable installed capacity, subject to acceptability of other parameters. The discharge available for power generation with 33% probability of exceedance is m 3 /s. This calls for an installed capacity of /1000= MW. It is clear that a unit and plant sizing for utilizing the maximum power potential as per point 1 above shall not be an economically optimum solution. An optimum sizing should be closer to what is indicated by point 2 and point 3. As recommended by CEA (vide Clause 1.2, Appendix-1, CEA, 2011), incremental benefit study has then been carried out for installed capacities at ± 5% intervals In order to examine other parameters like the Plant Load Factor (PLF), incremental energy per MW increase in the I.C., percentage harnessing of available potential etc., study has been carried out for estimation of design energy for 15 installed capacities considering plant capacities ranging from MW to MW at an interval of 9.5 MW. The estimated power and energy generation in each 10- daily period for all the capacities over all the 19 years is given in Annexure A H D01 C Chapter 8: Power Potential & Installed Capacity 13 of Mar-14

123 This also shows the unrestricted power and energy from the discharge available for generation for all the 10-daily periods. The summary of energy generation estimates for the 90% dependable year is given in Table 8.7. The plot of incremental design energy per MW increase in the installed capacity is shown in Figure 8.2. The plot shows drop in incremental design energy between 138 and 195 MW and again beyond MW indicating that the upper limit of installed capacity is near MW, indicating these as probable optimal choices. Figure 8.2: Incremental Design Energy (MU) per MW increase in I.C. The percentages of potential harnessed for each of these installed capacities are shown in Figure 8.3. The incremental rate of potential harnessed for every increase in plant capacity reduces with increasing capacity. Finally, there is no increase in harnessed potential beyond plant capacity of MW indicating this as the upper limit of plant capacity A H D01 C Chapter 8: Power Potential & Installed Capacity 14 of Mar-14

124 Table 8.7: Design Energy for a Range of Installed Capacities for the 90% Dependable Year (at 100% plant availability) 90% DY 2002 Month May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr 10- Daily Period Unrestricted Power with flow available for generation (MW) Unrestricted Energy with flow available for generation (MU) Power (MW) Energy (MU) Power (MW) Energy (MU) Power (MW) Energy (MU) Power (MW) Energy (MU) Power (MW) Energy (MU) Power (MW) Energy (MU) Power (MW) Energy (MU) Installed Capacity (MW) I II III I II III I II III I II III I II III I II III I II III I II III I II III I II III I II III I II III Power (MW) Energy (MU) Power (MW) Energy (MU) Power (MW) Energy (MU) Power (MW) Energy (MU) Power (MW) Energy (MU) Power (MW) Energy (MU) Power (MW) Energy (MU) Power (MW) Energy (MU) 11010A H D01 C Chapter 8: Power Potential & Installed Capacity 15 of Mar-14

125 90% DY 2002 Month 10- Daily Period Unrestricted Power with flow available for generation (MW) Unrestricted Energy with flow available for generation (MU) Power (MW) Energy (MU) Power (MW) Energy (MU) Power (MW) Energy (MU) Power (MW) Energy (MU) Power (MW) Energy (MU) Power (MW) Energy (MU) Power (MW) Energy (MU) Installed Capacity (MW) Max Power Annual Energy Incremental Energy PLF (%) Potential Harnessed (%) Lean Period Energy (MU) Lean Period PLF (%) Firm Power (MW) Capacity Utilization Annual (%) Capacity Utilization Monsoon (%) Power (MW) Energy (MU) Power (MW) Energy (MU) Power (MW) Energy (MU) Power (MW) Energy (MU) Power (MW) Energy (MU) Power (MW) Energy (MU) Power (MW) Energy (MU) Power (MW) Energy (MU) 11010A H D01 C Chapter 8: Power Potential & Installed Capacity 16 of Mar-14

126 Figure 8.3: Potential Harnessed with increasing I.C. The Plant Load Factors for different installed capacities are portrayed in Figure 8.4. The Plant Load Factor reduces gradually with increasing capacity. Figure 8.4: Plant Load Factors for Different I.C. The Lean Period Plant Load Factors for different installed capacities are given in Figure 8.5. The Lean Period Plant Load Factor reduces gradually with increasing capacity, but is greater than the minimum allowable limit of 12.5% for all the capacities under consideration A H D01 C Chapter 8: Power Potential & Installed Capacity 17 of Mar-14

127 Figure 8.5: Lean Period Plant Load Factors for Different I.C The utilization of plant capacity over the year, considering data for all the 19 years is shown in Figure 8.6. For all the plant capacities less than 252 MW, the plant capacity utilization is greater than the minimum allowable limit of 25%. Figure 8.6: Capacity Utilization over the Year for Different I.C The utilization of plant capacity during the monsoon months, considering data for all the 19 years is displayed in Figure 8.7. For all the plant capacities up to 11010A H D01 C Chapter 8: Power Potential & Installed Capacity 18 of Mar-14

128 252 MW, the plant capacity utilization is greater than the minimum allowable limit of 60%. Figure 8.7: Capacity Utilization in Monsoon for Different I.C From Table 8.7, with installed capacity of 195 MW, about 99.17% of the unrestricted energy available in the 90% dependable year gets harnessed. If harnessing of higher percentage is targeted, the PLF falls down, along with generation of additional energy. For instance, after 195 MW, for another 9.5 MW increase in the installed capacity (i.e. I.C. of MW), only about 0.47% additional potential gets harnessed. At the same time, the PLF drops by about 1.88%. This justifies the choice of not increasing the plant capacity any further beyond 195 MW. Also, the design discharge for the I.C. of 195 MW is m 3 /s. This has a probability of exceedance of 32% considering the flow available for power generation, which is acceptable. The summary of annual energy generation for different capacity for all 19 years has been given in Table 8.8. Average annual incremental energy per MW Increase based on entire 19 year flow series is 2.85 MU/MW, which is within the acceptable limit. Based on revised levels, CEA (ref Meno No PAC - 18/74/2012/HPA/2154 dated 27 th December, 2013, Appendix 8.6) also 11010A H D01 C Chapter 8: Power Potential & Installed Capacity 19 of Mar-14

129 recommended an installed capacity of 195 MW for Raigam HEP considering FRL, MDDL,TWL(N), and TWL (Min) as 725 m, 723 m, 538 m and 537 m respectively. Therefore, a plant capacity of 195 MW is selected. Considering the low discharges during the lean period and the limited pondage available, a unit size of 65 MW (with 3 units) is proposed, allowing harnessing of most of lean season flow during operation in run-of-the river mode, which is the worst case scenario. The minimum 10-daily average discharge available for power generation in the 90% dependable year of is m³/s. This allows generation of /1000=45.77 MW Considering generation to be possible at a minimum of 50% of load, with a machine capacity of 65 MW, generation is possible throughout the year for the 90% dependable year. If two units were planned instead, considering operation in run-of-the river mode, the worst scenario, the minimum discharge required to generate with a single machine at a minimum load of 50% would have been 29.2 m³/s, considering net head as during lean period. In that case, power generation has to be sacrificed for 50 days in the 90% dependable year, as the available discharge for power generation is lower than this value. When, considering the 2 (two) unit having each size of 97.5 MW, design energy works out to MU with PLF of 41.21% within the permitted lowest loading of 50% for the unit energy generated. In this case as comparing with three units, plant loosing energy of MU and the PLF falls much below 45%. This may not be acceptable A H D01 C Chapter 8: Power Potential & Installed Capacity 20 of Mar-14

130 Table 8.8: Annual Energy Generation for different I.C. (at 100% Plant Availability) Year Unrestricted Energy with flow available for generation Installed Capacity (MW) , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , Average Increm.(Avg) Increm.(90%DY) Max Min PLF-Avg PLF-90% Energy Harnessed (% of Max)* Energy Harnessed (% of 90%DY) Energy Harnessed (% of Max)** Energy Harnessed (% of 90%DY) A H D01 C Chapter 8: Power Potential & Installed Capacity 21 of Mar-14

131 Therefore, Plant size of 65 MW with three units optimally utilizes the lean flows. Having three units also provides necessary redundancy during operation and maintenance of the plant. Also, in view of the increasing uncertainty of rainfall, and, as a consequence, discharge, associated with growing impacts of climate change, it is sensible to go for larger number of units having smaller size. Provision of still larger number of units will be uneconomical due to increased cost of electromechanical equipments as well as requirement of additional area in the power house and consequentially, increased cost of civil structures. On the other hand, further reduction in number of units is not favorable to avoid loss of generation during the lean season as mentioned above, considering operation in true run-of-the-river mode. Provision of three units will also pose fewer difficulties for transportation of electromechanical equipments to the site located in difficult terrain Incremental Energy From Table 8.7, the incremental energy at the chosen capacity of 195 MW is 0.50 MU per MW increase of installed capacity. This is lower than the acceptable range of 1.2 MU per MW. An incremental energy generation rate of 1.49 MU/MW is obtained for an installed capacity of MW. However, the plant is able to harness only 95.1% of the unrestricted energy generation potential, indicating wastage of water resources. From Table 8.8, average annual incremental energy generation rate of 2.85 MU/MW is obtained for an installed capacity of 195 MW Therefore, the plant capacity of 195 MW is retained, and checked for other criteria for acceptance Potential Harnessed From Table 8.7, with the chosen plant capacity of 195 MW, 99.17% of the unrestricted potential in the 90% dependable year is harnessed. This is within acceptable limits as it is greater than 90% Firm Power Firm power is the power that is always available from the stream, even at the times of lowest flow. It has been calculated on the basis of average flow during 11010A H D01 C Chapter 8: Power Potential & Installed Capacity 22 of Mar-14

132 the 4 leanest months of December to March in the 90% dependable year of , which is m³/s. Therefore, the firm power is /1000= MW. This is the same as the firm power calculated in Table 8.7, by averaging power over the 10-daily periods of the lean months of the 90% dependable year Plant Load Factor From Table 8.7, the Plant Load Factor for the chosen capacity of 195 MW is MW. This is close to the acceptable range of 45% Lean Period Plant Load Factor From Table 8.7, for the chosen plant capacity of 195 MW, the energy generated during the lean months (December to march) of the 90% dependable year is MU. Thus, the Plant Load Factor for the lean period works out as 26.63%. This is greater than the minimum acceptable PLF of 12.5%, and therefore, acceptable Plant Capacity Utilization over the Year Over the 19 years, the plant capacity is utilized 32.75% of the time, considering all the months. This is greater than 25% and, therefore, acceptable Plant Capacity Utilization over the Monsoon months Over the monsoon months of June to September, the plant capacity is utilized 73.68% of the time. This is acceptable as it is greater than 60% Design Energy The design energy is defined as the energy generated in a 90% dependable year with 95% plant availability and without any overloading. Energy calculations for 90% dependable year and 50 % dependable year have been given in Annexure 8.6. A summary of energy generation estimates is given in Table A H D01 C Chapter 8: Power Potential & Installed Capacity 23 of Mar-14

133 Table 8.9: Energy Generation Estimates Sl. No. Description Units Value 1 Design Discharge m 3 /s Monsoon period Net Head m Non-Lean Non-Monsoon period Net Head m Lean period Net Head m Design Energy MU PLF in 90% Dependable Year MU Energy in 50% DY with 10% Overloading MU Average Annual Energy without Overloading MU Average Annual Energy with 10% Overloading MU Secondary energy is defined as energy generated over and above design energy. Here, secondary energy has been considered as the energy generated in the 50% dependable year with full plant availability and allowable overloading of 10%, less the design energy, amounting to MU Monthly Energy Estimates The monthly energy generation estimates for the 90% and 50% dependable years are given in Table A plot showing the fraction of annual design energy generated per month is given in Figure 8.8. This also shows the month wise fraction of average annual energy generation calculated over the 19 year period. As may be seen from the monthly generation data shown in Table 8.10, about % of the design energy is generated during the four monsoon months of June to September while the eight non-monsoon months generate the remaining % of the design energy. Table 8.10: Monthly Energy Generation in the 90 and 50% Dependable Years Energy in Energy in 50% DY Month 90% DY Without OL Without OL With OL May Jun Jul Aug Sep Oct Nov Dec Jan A H D01 C Chapter 8: Power Potential & Installed Capacity 24 of Mar-14

134 Energy in Month 90% DY Energy in 50% DY Without OL Without OL With OL Feb Mar Apr Total (MU) PLF (%) Figure 8.8: Fraction of Annual Energy Generated per Month 8.19 Peaking Energy In the 90% dependable year of , the minimum 10-daily average discharge available for power generation is m³/s. With a design discharge of m³/s, the minimum inflow required for operating the plant at full load in peaking mode for 3 hours is /24=15.43 m³/s Since the available discharge is greater than the minimum required discharge, the plant is able to support peaking operation for a minimum period of 3 hours throughout the lean season of the 90% dependable year, so far as availability of water is concerned. The storage required for 3 hours peaking operation is 11010A H D01 C Chapter 8: Power Potential & Installed Capacity 25 of Mar-14

135 ( ) / =1.037 MCM The available pondage of MCM is much smaller than this minimum storage required. Therefore, peaking operation of the plant cannot be supported Conclusion It is proposed to set up power house with a plant capacity of 195 MW comprising of 3 units of 65 MW each. A provision of continuous overloading of 10% has been envisaged for better utilization of monsoon inflows during the years with good monsoon discharge. The turbines are proposed to be of Francis type, with vertical axis. The plant may be operated as a base plant operating at full load throughout the day during the monsoon season; while it may be operated as a run-of-the-river plant on part load during the non-monsoon season. The design energy with 95% plant availability is MU, equating to a Plant Load Factor of 44.59%. The firm power from the plant is MW. The Plant Load Factor for the lean period is 26.63% A H D01 C Chapter 8: Power Potential & Installed Capacity 26 of Mar-14

136 APPENDIX 8.1 RAIGAM HYDROLOGY CWC APPROVAL LETTER

137 Government of India Central Water Commission Hydrology (NE) Directorate Sub: Hydrological studies for Raigam HE Project, Arunachal Pradesh Ref: CWC U.O. No. 32/85/12-PA(S)A3 date (S), Sewa Bhawan R.K.Puram, New Delhi-66 Raigam HE project is a run off the river scheme proposed on Dalai river, a right bank tributary of Lohit river in Anjaw district of Arunachal Pradesh. The total catchment area at the diversion site is about sq.km out of which snowfed catchment area above permanent snow line of 4500 m is about 59.8 sq.km. The project envisages construction of a diversion structure. The latitude and longitude of diversion site is 28 10'01"N and 96 31'12/'E respectively. The Compliance of hydrological study report received by this Directorate vide CWC U.O. No. 32/85/12-PA(S)/13 date have been examined and observations are as follows: Water availability The discharge data at Raigam bridge site is available for the period October 2008 to July 2011 only, which is not sufficient to arrive at the water availability series for the project. Hence, the water availability series for Raigam HE Project has been worked out on the basis of approved water avialability series of Kalai-I HE Project proposed on Lohit river. The total catchment area at Kalai-I HE Project is sq.km out of which snow fed catchment area is about 4444 sq.km for permanent snow line at EL 4500 m. The snow melt contribution of Kalai-I catchment has been deducted from approved series of Kalai-I and series thus obtained at Kalai-I has been transferred to Raigam HE Project site in rainfed catchment area proportion. The snow melt contribution of Raigam catchment has been added in the above series to get the 19 years 10- daily water availability series for the Raigam HE Project for the period to The average annual flow and average annual yield of the series thus obtained at Raigam HE Project site is about 4034 MCM and 2368 mm respectively. Observations: 10-daily water availability series for Raigam HE Project for the period to2dd3-04 with average annual flow of 4034 MCM (2368 mm) is generally in order. The same enclosed at Annexure-I can be adopted for planning purpose of the project. Design flood The design flood study has been carried out using hydro-meteorological approach. The 1-day SPS value as supplied by IMD has been taken as 326 mm. The clock hour correction has been considered as 15%. The unit hydrograph has been worked out as per FER-subzone-2(a). The loss rate of 2.4 mm/hr and base flow of 0.05 cumec/km2 have been adopted. The snowmelt contribution has been computed as per VVMO formula. The study recommends a design flood (SPF) value of cumec.

138 Observations: The unit hydrograph ordinates were not properly adjusted. The unit hydrograph has been worked out in this Directorate. The same has been convoluted with hourly effective rainfall taking the bells of 12 hours each. The SPF thus obtained is cumec and the same may be adopted as design flood for planning purpose of the project. Diversion Food For diversion flood study of the project the observed flood peaks at Mompani G&D site (total catchment area km2 and rainfed catchment area sq.km) for the period 1987 to 2004 have been used. The observed flood peaks have been increased by 15% to convert those into instantaneous peaks. Flood frequency analysis have been carried out fitting Gumbel distribution to the instantaneous annual peak series. The snowmelt contribution has been deducted from the flood peak of different return periods calculated at Mompani and resulting flood peak has been transferred to Raigam HE Project site using Dickens formula taking rainfed catchment. The snowmelt of Raigam catchment has been added to get the flood peaks of different return periods. The study suggests the following flood at Raigam HE Project site: SI. Particular Value (cumec) No year return period non-monsoon flood for construction 1185 season October-March 2 25 year return period non-monsoon flood for construction 1375 season October-April (on the basis of maximum observed flood near Dalai bridge) 3 25 year return period monsoon/annual flood year return period monsoon/annual flood 2605 Observation The monsoon and non-monsoon flood peaks of different years as obtained from flood frequency analysis are generally in order. The calculated flood of different return periods as mentioned above may be adopted as diversion flood as per BIS criteria depending upon the type of structure and construction season. Sedimentation Studies of the Reservoir As the project is a ROR scheme, the reservoir is likely to get filled up upto the spillway crest in a short span of time. Hence, adequate sediment management practice needs to be adopted by project authorities in consultation with the concerned design Directorate.

139 The project authorities should also improve the rain gauge network and continue observation of G&D data so that the future review of hydrological studies could be carried out based on project specific representative rainfall and runoff data. Director PA(C),CEA CWC U.O. No.4/382/2012-Hyd(NE)/4/-4Z dated: i-^^/j o j c (N.tt.Rai) ' Director Copt to: Director, PA(S), CWC

140 Annexi're-I 10-daily discharge series for Raigam HEP (CA sq.km) Unit: i^.iiec I May II III I June II III I July II III I August II III I September II III I October II III I November II ' III I December II III I January II III I February II III I March II III I April II III

141 APPENDIX 8.2 RAIGAM GIMLIANG EAC MINUTES

142 ! " # $ $ % & % # $ ' ( ) * % " +, -. / : ; 6 / 0 < = > 0? > >? A 7 B A C D : E E F D G ; :? H 7 I 0? J A C C 0 K A 8 L M K L? : > : N 0? O? : P 0 Q 6 B N A B / 0 C L L R? S R 8 0 T U V W X A 6 Y D Z O < D : 8 I : 8 D 0 8 6? 0 T Z > > : B S A N A / A? C A C [ 0 /? R Y 6 A L 7 R E T [ 0 N \ 0 C / 7 ]. / 0 E N A B Q / A 7? 0 L ^ K \? ] _ ] O ] \ A B T J 7 Q 0 ` D / A 7? E A 8 ] Y / ] Y /? 7 H A a 0 B / [ A 6 / T D / A 7? E A 8 T \? ] S ] b ] Y / A? E A T \? ] Y ] b ] 5 7 B /? A T \? ] Y ] _ / : N E 7 a T \? ] O? A I A 6 / R? T 5 0 E ^ 0? B T D Q : R C L 8 : 6 A L 6 / 0 E L R 0 6 : >? 0 ` : Q Q R > A 6 7 : 8 ]. / 0 C 7 B 6 : ; D 5 0 E ^ 0? B A 8 L : ; ; 7 Q 7 A C B A B B : Q 7 A 6 0 L N 7 6 / I A? 7 : R B >? : P 0 Q 6 B N / : A L 0 L 6 / 0 E B A = 0 L ] - - # $ ' (. / 0 ; : C C : N L A E B N 0? 0 6 A a 0 8 ` R > / A 6 :? L 0? ; :? L 7 B Q R B B 7 : 8 B c ` W ]! " - ' d e f -. / 0 D / A 7? E A 8 N 0 C Q : E 0 L 6 / 0 E 0 E ^ 0? B A 8 L 6 / 0 ; : C C : N A L A E B N 0? 0 6 A a 0 8 R > ; :? L 7 B Q R B B 7 : 8 ]. / R 6 0 B : ; 6 / D E N 0? 0 Q : 8 ; 7? E 0 L N 7 6 / 6 / 0 ; : C C : N A E 0 8 L E B c " - # - g h ( $ $ e i " ) j j, ) j j f - k - l m # n $ e ( $ $ e - H 7 I 0?. A C : 8 9 B / : R C L ^ 0? 0 A L A B. : C R 8 9 ]. / 0 > :? 6 7 : 8 o p q r s t u r v w p p s x y z { s s x w } ~ p s t p w } s z { q ƒ p p w p s v p q ^ 0 L 0 C L ] " - # - $ e e ), f - j + ˆ! f -. / 0 L A 6 A ; 7 9 R? 0 B B / : N 8 R 8 L 0? Q : C R E 8 X Š / A I 0 6 : ^ 0? 0 I 0? B 0 L A B? 0 >? : L R Q 0 L ^ 0 C : N c ) - " -! * W ] D A 6 Q / E A F b E Œ G X 1 X 1 1 U ] Ž ] H ] F E G < C ] U U U V < C ] U U X 1 X 0 A R 8 L 0? B R ^ E 0? Q 0 A 6 Ž H F M A G U ] U ] 2

143 ! " # $ % & & % # $ $ ' % # $ ( ) * )! " + ' ), -. & / 0 0 " 1 2 ( ' % ). 3 0 & 4 & ' % & & % 2 ) 3. 5 & 1 1 $ ) / & ) 5 0 & $ 8 ' 9 2! " ( ! # ' 2! # '. 0 0! ' : ; : < = >? A B C D E : F G H I J K L = M = > < > N O P > K Q K R = S L > T U P > V U W Q P X K = V Y = M C P = Z O T Y [ \ G ] T ; ^ = > _ P > T Y K J Z = \ = ` K Z X T U P > O T D C I a U Z b ^ V J c > K? d M O = P = K V O ) 8 ' " 1 8 " 2 1 $ 2 " + e $ ) ' )

144 f f f! 4 % g + 1 f h f h f h h / 5 & " i 9 j k l m n o p m n q m n r n s p o t u v w x y x w z { q k } ~ r n s p o v w y w t z ƒ } p o ~ k s } p k o ˆ k s o m n q m n r n s p o t u v x y t u z { q k } ~ r n s p o v t y t z ƒ $ ) / 3 0. ( & # ) Š, 5 7, 0. Š,!! %! / 6 ) 8 " 1 2 / - Š * / Š / / ', Š / f / & 8 ) ' Œ % /., &. 7 Š 4 7, Š Š & 6 Š, 9 / Š - 8 " # ' - 7! 5,, 9 /., * + % " ' ( 1 3 3, 7 '

145 / 7,! ' ) " & i e 9 ' 5 0 & 1 ' ' - Š 6,! Œ Š 0 ' ! Œ 5 0 ' " 1,, Ž 2 8 o o } k n l k j o n o r } n ˆ o r } r n y o l k p ƒ n n ˆ m n 1 / - /! ' " # ) f f + ' " # ) &. 0 Š 0 $ 7 5 Š 0 $ f 7 0 Š 0 $ Š. 3 ' ' Š 0 $ ' / 7,! ' / 7,! 2 ( ' 1 $ ) + ' 1 1 $ ) ) 8 " 1 % $ Œ 8 " $ Š 0 0 ). & $ Œ 1 ( g % ' 1 7 / & ) h ) # ' m o p s k } ˆ m r k } o n ˆ y l j m r r l m n r k } m } p } k n o o j m o p s k } š k o n

146 & " h ) + ' ' ' 1 2 " ' ' % ' ' ' ' 2 ( ' f 6 & ' % ' (! # % " % "! " ' e ' % ' ' ' ' & 9 ' & ' + + ) & 2 1 ' e 1 & & '

147 2 ' ' ' ' ' + ( ' + 2 ' 2 & ' f f 1 & & 2 ) 8 " ) / 2 ' ' f f f ) f ( f ' '! f f Š 0 '. 0 Š 0 ' 7 # ' ' ' ˆ m r k } o n ˆ y l j m r r l m n r k } m } p } k n o o j m o p s k } š k o n k œ r } ~ j m }. % ' ' ' - ' 5 ( '! "

148 , 1 $ " ) 3 " 6 * $ + 2 Š f ' ' ' e ' + + $ ' + # ) + $ / 0 $ f 1 / / 1 & ' E : ; ^ U X Z \ Q P O = ž Ÿ } l j s p o m o m o n o o } p k m m j k } ~ n ˆ o r o l k s o m } p p k k o k s o z ƒ # 2 ' % " ) & 7 8 ) & $! ' % j k l m n r k } m } p r } n o } r n š k o m j o { s o m } p r o k ª s m p m n m } p n ˆ o r o j r l m n r k } z «r } m s j m k m } p r } m m r } n s o } n o s r o } n '! 4 %! )! $! 2 ( $ ' f % ' ( ) ' ' % # ± ² ³ ± µ ¹ º» ¼ + ½ ¾ o } o m j o ~ o n m n r k } m n n o } r j j m j k r } l j s p o n o r p k ˆ n o k ˆ n o m } p q r l ˆ o } z m } o m k k ƒ r j p m } m } m À Á  ƒ «Ã l ˆ r p z " % )

149 2 } p o m s } m j o j o o } n z ˆ r r m } z r j j m j k o n s p r 2 + Œ ) " 2 % µ ¹ º» ± À ² º ¹ º» Ä ± ' " : ; Å Æ M > = K? A B C D Ç È G H I J K L = N < > N O P > K Q K R = S L > T U P > V U W Q P X K = V Y = M C P = Z O T Y [ \ G ] T ; ^ = > _ P > T Y K J Z = \ = ` K Z X T U P > O T D C I a U Z b ^ V J c > K? d M O = P = K V O 8 ' " 1 8 " 2 1 $ 2 " + e $ ) ' ) f f f! 4 % g + 1 f h f h f h h m r r j k l m n o p m n q m n r n s p o t u v x u y t É ƒ x É z { q k } ~ r n s p o v u y ƒ t z Œ m n q m n r n s p o t u v x É y Ê É ƒ É Ë z { q k } ~ r n s p o v Ê y u ƒ t É z ƒ $ ). 3 / -, ( & # ) / 0 -!. 7, 8 " * 7 0 / 0 5 ' Š " + & & Š 0 0 Š., $ f 3 /. 7 & 8 ) / 5 ' & - / &

150 APPENDIX 8.3 CEA OBSERVATIONS-RAIGAM

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