Progress of Irrigation and Drainage in Korean Paddy Field Chapter 7

Transcription

1 Progress of Irrigation and Drainage in Korean Paddy Field Chapter 7 is particularly high during transplanting period from late April to late May, when water resources are least available. The large seasonal variation in water demand has forced the development of integrated central water management systems. These systems are not only built with computers and tele-communication equipments, but runoff measurement and estimation from watershed, accurate reservoir storage measurement, short- and long-term storage prediction, water delivery efficiency, real-time monitoring devices, and equipments for water distribution are also needed. One of the prerequisite for setting up the integrated system is the canal modernization. In the beginning of irrigation system development, the uppermost priority was put on the expansion of irrigation facilities such as the construction of reservoirs and canals. These hydraulic structures aged and were damaged with time. Rural water has multifunctions to supply not only irrigation water but also domestic, livestock, industrial, and environmental water to the rural area. However, development of new water resources and supply system are very difficult. Not only is the construction of new dams and canals very costly, but land price is also very high and water right complicated. In addition environmental problems associated with new water resource development may cause serious civil disturbances and protests. Therefore, repair and reinforcement of existing irrigation systems are considered to be the best alternative to meet the increasing water demand. Maximization of water use and supply efficiency through repair and reinforcement of existing dams and canals, installation of TM/TC instrumentation systems, networking of water resources, and automation of water management have emerged as the major water management policies for large irrigation districts of 300 hectares or more. It is also believed that automated water management systems contribute to the conservation of natural resources and environment. Modernization Water supply in rural areas has changed as the conditions of living, agricultural, and industrial environments improved. Old irrigation systems were designed solely to supply water for irrigation, mostly for paddy field. However, the current irrigation systems convey water not only for irrigation but also for household, industry, and livestock breeding as well as environment. Furthermore, these systems also often supply water to streams to secure a minimum stream flow and water quality. Patterns of irrigation have changed from seasonal rice irrigation to year-round irrigation for the agricultural productions both in the paddy field and upland. Peak water supply span also have shortened due to the mechanization of transplanting processes in rice culture. These changes have increased both the peak and normal water demands of the irrigation system far higher than the originally assumed values. Therefore, modernization of irrigation structures, automatic control of water distribution and development of various income sources are necessary to operate an irrigation system. Rational water distribution based on real-time flow rate and water level monitoring can be achieved by installing TM/TC and central control system as an integrated central water management system. Successful installation and operation of the central water management system require the improvement of canal structures and water delivery efficiency. In addition, prospective income sources such as generation of hydro-power in agricultural reservoirs and tourist resorts in and around the reservoirs need to be developed to alleviate the operating cost of the central water management systems. 91

2 Rice Culture in Asia Modernization of an irrigation system equipped with an integrated central water management system in an irrigation district can increase agricultural production and farm earning by improving the efficiency of water use and timely water distribution. The modernization also helps prevent or reduce disasters such as flood, decreases management personnel, improves local environment, enables multiple use of water, and contributes to the advancement of water management techniques. An integrated central water management system must be a real-time system that can monitor, control, and adjust water intake at a water source, allow delivery through main and branch canals, and provide distribution at gates and regulators by adopting electricity, mechanics, electronics, telecommunication, and computer technologies. In an integrated system, dams, reservoirs, pumping stations, headworks in streams, irrigation and drainage canals, and other hydraulic structures are integrated into one operation system. In designing and building the system, the following requirements must be considered: - Minimizing water deficiency - Irrigation water must be supplied to where and when needed. - Maximizing irrigation efficiency - Effective irrigation must be achieved. - Maximizing system reliability - Rational supply and distribution must be achieved. - Maximizing safe irrigation or minimizing system failure - Irrigation system must be reliable and free from failure. - Maintaining a minimum stream flow - Stream flow must be maintained to support stream ecosystem and water quality. - Maximizing end-of-optimization-horizon reservoir stage - The reservoir after an irrigation season must maintain a certain water level. - Maximizing income sources - Development of income sources such as small hydropower generation and public resorts must be maximized. Seongju integrated central water management system completed in 1998 is a typical example. Seongju irrigation district covers 3,530 hectares of agricultural fields. Water is supplied from Seongju dam, 60 meters high and 430 meters long, with storage capacity of about 40 million m 3. Watershed area of the dam is about 14,960 hectares. Irrigation canals of 240 km was built, repaired or reinforced to improve water delivery efficiency and are tightly monitored. The dam also supplies domestic water of 8,800 m 3 per day through irrigation canals, and hydro-power electricity is generated during the irrigation season. The integrated central water management system was found to contribute to the improvement of agricultural productivity and saving of a large amount of water resources. The water saved is used to expand irrigation area and domestic water supply. Estimated profit from the expanded irrigation area and domestic water supply was assessed to be higher than the construction, maintenance, and operation costs of the integrated central water management system. Figures 7.9 and 7.10 show the graphic control panel at the control center and a gauging system of an irrigation canal, respectively. Hydro-power generation Rise in the international energy price, increase in the electricity demand in rural areas and adverse impacts of fossil fuel use on the environment have driven to generate more hydro-power electricity where possible. Currently, small hydro-power stations are installed in the Dae-a, Gangneung, Gyeongcheon, and Seongju dams. In Gyeongcheon dam, electricity generation capacity is 800 kw, and the annual amount of electricity generation and sale was 2.33 million kwh and US$ 130,000 in 92

3 Progress of Irrigation and Drainage in Korean Paddy Field Chapter , respectively. The income from electricity sale helps to maintain and operate the Gyeongcheon irrigation system. Beside these four dams, 21 agricultural dams were evaluated to have potential for commercial electricity generation. Estimated discharge rate and electricity generation capacities of these 21 dams during irrigation season ranged from 0.7 m 3 /s to 9.57 m 3 /s and from 100 kw to 1,640 kw, respectively. Total amount of electricity generation capacity of the dams was estimated to be 11,950 kw. It should be pointed out that the major role of agricultural reservoirs is to supply irrigation water mainly during irrigation season. Furthermore, electricity generation in agricultural reservoirs may not be possible or be very low during non-irrigation season. The minimum electricity generation capacity to meet economic break-even point was estimated to be 1,000 kw under condition of agricultural reservoirs. Benefit-cost ratio (B/C ratio) of electricity generation in agricultural reservoirs in 1996 was assessed to be 2.36, an indication that the electricity generation is profitable. It is also forecasted that if fuel price rises further, the marginal profit would also increase. Therefore, it is expected that electricity generation in agricultural reservoirs will be increased and help economically to maintain and operate the irrigation systems. Figure 7.9 Figure 7.10 Graphic control panel of the integrated central water management system in Seongju A TM/TC system in an irrigation canal of Seongju Raising dam crest An economic and effective way of increasing the reservoir capacity without the construction of new dams is to raise the normal water surface level and dam crest. This method has been applied at many dams, though only when the dam or the spillway of the reservoir is structurally and hydrologically safe. For example, dam crest and storage capacity in Wonseon reservoir located in Hampyeong-gun were raised by 2.5 meters and 56%, respectively. As a result, the irrigation area was expanded from 45 to 88 hectares. 93

4 Rice Culture in Asia Another method of expanding reservoir capacity is to build a new dam downstream of the existing one. Dae-a dam is an example of this method (Figure 7.5). This dam was originally constructed in 1922 as an irrigation dam. The dam thus could not meet the increasing demand of rural water during the early 1980 s. Therefore, a new dam was built 300 meters downstream of the existing one. The new dam with a height of 55 meters and a length of 255 meters has a storage and irrigation capacities of 55.3 million m 3 and 8,125 hectares of farmland. The old dam was partly removed and submerged. The reservoir supplies domestic, livestock, and industrial water and in-stream flow, in addition to irrigation water. Also a small hydro-power station was installed. Installing 0.5 to 1 meter high gates or a rubber dam on the existing spillway is a good alternative to raise reservoir water level and increase its storage capacity. It can be applied to reservoirs that have sufficient freeboard on crest and large surface area when it is full. For example, the storage capacity of Giheung reservoir was increased by 10% with the installation of gates on the spillway in 1998 (Figure 7.11). Dredging of sediment can be an alternative to increase reservoir capacity. Average sedimentation of reservoirs was surveyed to be about 8% of the total reservoir storage capacity. About 160 million m 3 of water storage could be increased if the sediments are dredged. However, dredging of sediments is not considered as a viable option because the dredged sediment may cause adverse effects on the environment and secondary pollution. Fishways Preservation of ecological environments and biodiversity has become an important issue during the 1990 s. The Fisheries Resources Protection Act, Article 12, Section 2 obligates the provision of fishways in all riverine hydraulic structures, which hinder the stream flows, and Article 31 of the Act has punitive clauses against the violation. Extensive scientific research on fishways had not been conducted until the act was passed although tens of fishways have been installed along the streams and rivers near the Eastern and Southern coasts. Studies on migrating aquatic animals have revealed that more than 23 fish species migrated through fishways. Various fishway models developed abroad were applied, tested, and modified to accommodate the uniqueness in flow mechanisms, tides, and fish species. By 2000, 193 fishways were constructed on 121 hydraulic structures in 42 rivers nationwide. Dominant types of fishways are fish ladder (Figure 7.12; 87 units, 45%) and baffled fishway (66 units, 34%). The average dimension of fishways is 3.2 meters wide, 2.5 meters high, and 20.2 meters long. As new fishways are installed, the height and length of typical fishway tend to increase, while the width remains similar. Large lock gate fishways (fish lock) were also established, where sea dike was constructed at the mouth of a river, to reclaim a large tideland for agricultural production and other land uses. It should be pointed out that many old fishways were not constructed friendly to fish migration and have not been managed properly because the fishway requirement was under local administrative regulations and fishways were constructed by unqualified contractors. As a result, many fishways have been seriously damaged with time and do not function properly. However, with the increase in civil awareness on natural resources and environmental protection, various fishways are expected to be installed in both small hydraulic structures in small streams and large dams in major rivers. 94

5 Progress of Irrigation and Drainage in Korean Paddy Field Chapter 7 Irrigation canal Irrigation water is delivered through irrigation canals to fields. Depending upon the type of the canals, water delivery efficiency and loss show large differences. The rate of water loss in earthen canals is estimated to be about 30~40% while that of concrete canals is estimated between 5~10%. Total length of the main irrigation canals is about 24,959 km, and concrete main irrigation canal is about 11,148 km. Water loss difference between the earthen and concrete canals may account for about 600 to 800 million m 3. National projects to convert earthen canals into concrete or other canals that can minimize water loss and maintenance cost are being carried out. Figure 7.11 Gates installed on an existing spillway of Giheung reservoir Earthen canals are widely distributed throughout the country. These canals are generally old and not well-maintained. Water loss in the canal is also very high. To minimize water loss and improve water delivery reliability, earthen canals are currently converted into lined channel, concrete canal, or pipeline where necessary. There are many other reasons to convert earthen canal into lined canal. Competition for water use and value of water resources increased as agricultural, industrial, and domestic water Figure 7.12 A ladder-type fishway installed in a Osip-cheon, demands increased. Replacement of Yeongdeok (3rd weir from estuary) the earthen canal with concrete or pipeline results in the reduction of the canal site area, which then can be utilized for agricultural production or other uses. This becomes more important where the land price is high. Water management in irrigation systems is being modernized by adopting TM/TC techniques. Minimization of water loss and maximization of water delivery reliability are prerequisite in setting up the TM/TC system. Rectangular-shaped cement concrete waterway and earthen canal lined with various materials mostly form the lined open channel structure. Large main canals are usually lined, but relatively small branch canals are converted into concrete canals. Lining meth- 95

6 Rice Culture in Asia ods of a canal are different depending on lining materials. Concrete, concrete block, asphalt and clay linings are typical examples. Lining methods are selected based on the conditions of site such as topography, soil texture, groundwater level, safety of canal, economic efficiency, and workability. Rectangular concrete canal is commonly used for medium to small branch canals (Figure 7.13) Prospects of rural water development Figure 7.13 An example of a rectangular-shaped and medium-sized Rice culture in the monsoon concrete irrigation canal. region of Asia has multi-functions, such as reliable food supply to meet ever-increasing demand, economic development, land and environment conservation, and the vitalization of rural community. These multi-functions of rice culture will continue to be effective for the sustainable development of agriculture and rural areas. The Ministry of Agriculture and Forestry (MAF) is executing the comprehensive rural development plan of Agricultural land and water 91% Agricultural land and water 91% On-going plan during US$ 10.3 billion Mid-&long-term plan during US$29.1 billion Off-farm income 1% Rural living standards 8% Off-farm income 3% Rural living standards 6% Figure 7.14 On-going and Mid- & long-term investment plan for comprehensive rural development 96

7 Progress of Irrigation and Drainage in Korean Paddy Field Chapter 7 The purposes of the plan are to insure: (1) stable food supply, (2) preservation of productive farm land, (3) environmentally sound agriculture, (4) reformation of agricultural marketing systems, and (5) improvement of rural living standards. The on-going plan aims to increase the ratio of irrigated paddy field from 76 to 88%, that of rural road pavement from 32 to 51%, and that of domestic water supply from 48 to 71%. National target for the maintenance of cultivated area is 1,850,000 hectares for agriculture use, with 1,100,000 hectares for paddy field and 750,000 hectares for upland. A total of US$ 10,349 million have been allocated to the on-going plan (Figure 7.14 left). In the mid- & long-term plan for , the MAF plans to achieve the national goal of attaining self-sufficiency in staple food and establish rural life amenities. A harmonious policy should be also considered in the agricultural sectors for the reunification of Korea. A total of US$ 29,143 million will be invested for this purpose (Figure 7.14 right) Challenges for rural water development The purposes of the on-going plan are the achievement of stable food supply and sustainable agriculture, the preservation of productive farmland, strengthened collaboration with North Korea and foreign countries in the agricultural sector, and the improvement of rural living standards. During the 21st century, rural areas will undergo urbanization through which urban and rural people will be mixed and space functions as supporting background to large metropolitan areas. The solutions to complicated problems related to rural water development such as cost, water quality, water pricing, sustainable agriculture, inter-korea and international cooperations would be major challenges in the future. The strategies for the future must involve the optimization of water usage and mitigation of harmful effects. Cost Agricultural land and water development projects need significant investments. The average construction costs of irrigation facilities as of 1999 are US$ 40,000, 17,500, 33,000, and 20,000/ha for a reservoir, a pumping station, a tube well, and a drainage pumping station, respectively. At these costs, investments in agricultural land and water are difficult to justify if benefits are projected on the basis of present prices. Improving or rehabilitating an existing system is less costly, ranging from US$ 2,000 to 5,000/ha. Rural water quality Pollutant from non-point sources in the agricultural system has deteriorated the quality of water. Therefore, pollutant sources should be regulated by prohibiting the discharge of pollutants into streams, rivers, and lakes. Chemical fertilizer of 421 kg per hectare and pesticide of 11 kg per hectare were applied in By 2004, the 97

8 Rice Culture in Asia Table 7.4 Present status and plans for rural development (unit : million US$) Name of project for comprehensive rural development Total Unit Present status in 1998 On-going plan during Mid- & long-term plan during No. Fund No. Fund No. Fund 22,434 10,349 29,143 Agricultural land and Water development Disaster prevention Drought countermeasure Drainage improvement Repair & Modernization Land & water development Rural water Large scale project Tidal land reclamation Paddy land consolidation Large block consolidation Upland consolidation Farm road pavement Regional infrastructure Rehabilitation Research and development Rural living standards Rural settlement area Advanced village Rural sewage treatment Rural domestic water Off-farm income Rural industrial complex Farm tourism 10 3 ha 10 3 ha Ea Ea 10 3 ha 10 3 km Ea 10 3 ha Ea Ea Ea , ,860 2, ,040 16,325 5,243 2,535 1,251 6, ,026 1, ,547 1, , ,468 2, ,147 1,478 6,593 1,590 1, (8) (4) , ,646 5, ,623 20,522 5,140 3,677 2,752 2,064 2,310 1,497 1, , , Source: MAF, Mid- & long-tern plan for the comprehensive rural development MAF, Yearbook of agricultural land and water development. government plans to reduce the use of chemical fertilizers and other agrochemicals by 50% of the current amount by promoting natural and organic fertilizer use. Water pricing Under the new policy, farmers are not required to pay costs for water use. All investment, operation, and maintenance costs are subsidized through the government budget from the year As a result, farmers and the operating organization have little interest in water pricing and saving. Nearly full cost recovery is achieved on domestic and industrial water supply, but not on agricultural water supply. Sustainable agriculture The promotion of sustainable agricultural systems is one of the top priorities of the government policies. The sustainable agriculture promotion act was established in 1997 to develop environment-friendly agriculture, which is classified as organic farming, farming without agrochemicals or low input farming. The environ- 98

9 Progress of Irrigation and Drainage in Korean Paddy Field Chapter 7 ment-friendly farming household and area are expected to increase rapidly. Overuse of agrochemicals has caused deteriorations in human health, ecosystems, and water quality, among others. Inter-Korea and international co-operations Since North Korea has been suffering from food shortages during the recent years, a harmonious policy should be considered in the agricultural sectors. The Republic of Korea shares several rivers with North Korea and proposed a joint-study for the watershed development and farmland restoration. Shortage of cereal food in North Korea reached 28% of total consumption in 1998 because floods had seriously deteriorated the cultivated land of 360,000 hectares (19%) in 1995 and 298,000 hectares (16%) in Recently, international cooperation in rural development is becoming more important and active than ever. The government is paying more attention to international cooperation. 7.3 Drainage improvement in paddy fields Sang-Ok Chung In Korea, irrigation of paddy fields has traditionally received more attention than drainage. Only after mid 1970 s did modern drainage projects begin in Korea. Surface drainage is more important than subsurface drainage for protecting farmland from flooding. Although flooding and sea water intrusion have been national concerns since the ancient dynasty, drainage improvement has a very short history in Korea. In Joseon dynasty the first river stream bank project was initiated at Susan-je, Milyang-si, Gyeongnam province to protect land areas from flooding (1489). During the Japanese occupation, small-scale mole drainage was practiced from 1920 s. Mole drain of 22,000 hectares was installed in 1940 as a part of the rice production-increasing plan in Korea, which lasted until 1954 after liberation (Ahn 1989). After the world food crisis in 1974, the Korean government planned a farmland drainage improvement project in order to increase double-cropping areas, namely barley after rice, to increase crop production. In 1975 the Korean government allocated budget to the drainage improvement sector for the first time. From 1975 to 1978 three sample drainage projects of 2,000 to 4,000 hectares including 20 to 50 hectares subsurface drainage were executed with the support of UNDP, through which new construction technologies on drainage facilities including subsurface tile drainage were introduced (RDC 1999). The Rural Development Corporation (1999) classified the modern farmland drainage in Korea into three stages: 99

10 Rice Culture in Asia (1) 1975 to 1979: Drainage improvement for double cropping, namely barley after rice, to increase crop production. Land consolidation projects completed during 1970 s separated irrigation and drainage canal systems, which raised problems of poor drainage in lower areas. (2) 1980 to 1989: Increased demand and expansion of drainage improvement. Drainage projects mostly dealt with surface drainage such as canals and pumping stations. (3) 1990 to 1998: Drainage improvement for the prevention of disaster. More farmlands suffered from flooding due to the urbanization and extreme regional rainfalls. Thus, to prevent frequent flooding of the farmland, surface drainage facilities were installed. During this period, several river rehabilitation projects improved the nearby paddy field drainage condition by reducing water table, which thus decreased land areas requiring subsurface drainage Objectives and effects of paddy field drainage The main objective of farmland drainage is the removal of excess surface and subsurface water. For this purpose, surface drainage facilities are installed in paddy fields to prevent the inundation of land during flood seasons, and subsurface drainage facilities are installed to improve soil water environment of plants in waterlogged areas. Direct effects of farmland drainage improvement include prevention of flooding, yield increase, rice quality improvement, increased land utilization, multi-purpose land use, and increased labor productivity. Some secondary effects are improved land bearing stress, improved trafficability of farm machineries, dried land, reduced maintenance cost, and improved rural community structure (RDC 1999). In addition, these effects can bring about economic and social benefits to the farmers. Based on studies conducted in Korea, some effects of the drainage improvement projects are described below. Land utilization rate increased from to 138.3%, due to the increased double-cropping areas achieved through the improved soil water condition. The drainage improvement projects increased the per hectare yield by reducing land submergence. On the average, rice yield per hectare increased from 3,967 to 4,717 kg, which is a 1.9% increase. The drainage improvement projects reduced labor requirement from 435 to 336 hours, showing a 23% decrease. Lastly, the drainage improvement projects improved farming environment through better water management, which reduced agrochemical application and water contamination downstream Causes of poor drainage To improve land drainage, the following causes of poor drainage must be eliminated (RDC 1999): 100

11 Progress of Irrigation and Drainage in Korean Paddy Field Chapter 71 1) Intrusion of stream or sea water into the farming area. 2) Stagnation of water inside the area because the incoming water is not removed on time. 3) Excess water in the plant root zone. These causes can be classified in more details. Table 7.5 shows main causes of poor land drainage in Korean paddy fields. The most detrimental causes of poor land drainage are the rise of river flood stage and inundation of low-lying land, followed by insufficient drainage canal conveyance. Countermeasures include installation of drainage facilities such as pumping stations, catch drains, canals, and gates, dredging of stream beds, and rearrangement of drainage streams. Table 7.5 Main causes of poor land drainage in Korea Number Causes Percentage (%) 1 Rise of river flood stage and inundation of low lying land 41 2 Insufficient drainage canal conveyance 26 3 Low main drainage stream bed and high flood stage at a relatively low rainfall intensity 18 4 High tidal river stage near shore 10 5 Insufficient drainage canal or pump capacity 3 6 Insufficient capacity and poor maintenance of lateral canals 2 Total 100 (Source: MAF 2000b) Needs of field drainage in Korea Yield reduction of rice due to submergence in Korea is shown in Table 7.6. In booting stage only 0.5 day-long submergence resulted in 27% yield reduction. More than five-day submergence should be avoided in order to achieve satisfactory rice yield. Table 7.6 Yield reduction of rice due to submergence (%) Submergence period (day) Growth stage Rooting Tillering Panicle forming Booting Heading (Source: MAF 1983) 101

12 Rice Culture in Asia Drainage improvement can be achieved as follows: by preventing the intrusion of outside water into the benefit area, by preventing the stagnation of inside water in the benefit area, and by controlling groundwater level and soil water contents. Stream banks and sea dikes prevent flood and seawater from coming into the benefit area. Catch drains, drainage canals, drainage gates, and pumping stations may prevent submergence of the benefit area. Subsurface pipe drainage removes excess soil water to keep the soil moisture optimum condition for the crop growth. A survey on the land drainage condition in Korea was performed in 1992 by the Rural Development Administration. Table 7.7 shows the results of the survey. Poor and bad conditions represent 62.0 percent of the total paddy field area. Table 7.7 Drainage condition of paddy fields in Korea Condition Acreage (ha) Percentage (%) Excellent 4, Good 13, Fair 423, Poor 572, Bad 148, Total 1,162, (Source: RDC 1999) A survey for the land drainage improvement began in 1975 with the support of UNDP. From 1975 to 1980, 80,000 hectares was surveyed by UNDP. The Korea Ministry of Agriculture and Forestry surveyed from 1996 to 1998 additional 180,000 hectares. Based on these studies, the paddy field area requiring land drainage was set at 235,000 hectares, among which drainage facilities for 84,300 hectares were completed by Drainage projects for the remaining 150,700 hectares were planned for the period of 1999 through Acreage and investment of drainage improvement projects are shown in Table 7.8. Drainage projects are mostly for surface drainage with only 23% of the total area allocated for subsurface drainage. Great emphasis was placed on the water supply system development than field drainage because the nation suffers more from droughts than from floods. However, whenever the nation suffers from floods, short-term investment to the drainage improvement greatly increases. There has been no sufficient longterm investment for the land drainage. Table 7.8 Type Acreage and investment of drainage improvement projects in Korea (Unit: thousand ha, million US$) Completed by 1998 Planned from 1999 Total Acreage (%) Investment Acreage (%) Investment Acreage (%) Investment Surface 82.7(46) (54) 1, (100) 2,648.3 Subsurface 1.6(3) (97) (100) Total 84.3(36) (64) 2, (100) 3,082.4 (Source: MAF 2000b) 102

13 Progress of Irrigation and Drainage in Korean Paddy Field Chapter Classification of field drainage methods in paddy fields Figure 7.15 shows a typical drainage system layout in Korea. The drainage area is divided into three main parts: out-of-boundary mountainous area, the upper part, and the lower part. A catch drain is installed to divert incoming water from higher area, and the upper part is drained through gravity and the lower part by pumps. Field drainage methods can be classified as normal and flood drainage, gravity and pump drainage, and surface and subsurface drainage. lower part catch drain upper part main canal Stream Watershed boundary Remark paddy field upland forest drainage gate pump station Field drainage facilities in Korea Figure 7.15 Schematic of a typical drainage system Field drainage facilities are determined for each specific drainage area based on the topography, soil, area size, and construction cost, among others. Table 7.9 Total surface drainage facilities required in the paddy field No. of sites Benefit area (ha) Facilities Drainage stations Canals Catch drain Gate 1, , site 3,458 km 245 km 864 site (Source: RDC 1999) Table 7.10 Surface drainage facilities completed by 1998 Item Up to Total No. of sites Area (ha) 1,558 15,428 32,654 33, Percent (%) (Source: RDC 1999) The paddy field area of 180,000 hectares requires surface drainage, of which 82,691 hectares were completed by 1998 (Tables 7.9 and 7.10). Drainage canals Table 7.11 shows number and length of drainage canals in paddy fields. Total length of drainage canals is 60,804 km, of which 51,305 km is composed of earth and 9,499 km of concrete structure. Earth canals represents 84.4% of the total drainage canal length. Figure 7.16 A main drainage canal with concrete block lining 103

14 Rice Culture in Asia Table 7.11 Number and length of drainage canals in paddy fields (1999) (unit: km) Kind Earth Structure Total Set Length Set Length Set Length Main 11,476 6,864 16,226 1,591 27,702 8,475 Sub-main 32,886 14,893 57,809 3,579 90,695 18,472 Lateral 90,261 29, ,688 4, ,949 33,877 Total 134,623 51, ,723 9, ,346 60,804 (Source: MAF 2000a) Recently, the importance of canals with regard to the environment and ecology came to light. Therefore, transition to the environment friendly design and management of the canals will be the general trend in the future. Design and management of canals will be toward the conservation of the environment and ecology. For this, canals and hydraulic structures should be constructed using natural materials such as earth, rock, and woods rather than concrete. Figure 7.17 An environment friendly main drainage canal constructed using rocks and grasses In particular, small streams acting as main drainage canals in plains should be conserved naturally through bank protection using rocks and woods. A project of 500 m environment friendly drainage canal has been recently completed in Songsam area using rocks and grasses (Figure 7.17), with a 150 meters long ecological site, a 100 meters long natural study area, and a 150 meters long rest area with a walk. Drainage gate The drain outlets are located at the lowest point of the project area. Occasionally, drainage gates are needed at the outlet to prevent reverse flow from the downstream into the upstream drainage area. Figure 7.18 An electrically operated drainage gate The drainage gate can be operated either manually or electrically. Figure 7.18 shows an electrically operated drainage gate. The drainage gates may be installed with a pumping station. Pumping station Pumping stations are required when the gravity drain is not applicable or insufficient. Prior to the introduction of the pumps, only gravity drainage was practiced in Korea. Until 1969 only small diameter pumps with diameters up to 1,000 mm were used, which include horizontal axis, single side suction, and single stage pumps. During 1970 s and 104

15 Progress of Irrigation and Drainage in Korean Paddy Field Chapter s large-size pumps of more than 2,000 mm diameter with vertical axis were introduced along with the large scale comprehensive agricultural development projects. In the case of paddy fields, surface ponding is allowed to some extent. In pumped drainage system, normal and flood drainages are processed separately. The drain flow rate per unit area in pumping stations ranges 0.6 to 1.0 m 3 /s/km 2, which is much lower than that of the gravity drainage. Drainage pumping stations are normally required to handle large capacities at low lifts. Therefore, centrifugal pumps are generally used in the drainage pumping stations. Table 7.12 shows the number of drainage pumping stations in paddy fields as of The drainage station is used only for drainage, while drainage & irrigation station for either drainage or irrigation use depending on the need. There are 446 drainage stations and 122 drainage & irrigation stations, totaling 568 stations. Figure 7.19 shows a pumping station with drainage gates. Pumping stations may require screening systems in order to prevent pumps from being clogged by solid wastes and debris. Screening can be performed using bar racks only or bar racks with rakes to automatically remove the debris (Figure 7.20). Table 7.12 Drainage pumping stations in paddy fields (1999) Types up to 100 hp 101 ~500 hp Number of stations 501 ~1,000 hp 1,001 ~3,000 hp above 3,000 hp Total Total power (hp) Drainage only ,466 Drainage & Irrigation ,946 Total ,412 (Source: MAF 2000a) Figure 7.19 A pump house with drainage gate Figure 7.20 A bar screen with an automatic rake. 105

16 Rice Culture in Asia Table 7.13 Recommended water table depths from the ground surface Land use Water table depth 2-3 days Water table depth 7 days after rainfall (cm) after rainfall (cm) Rice mono culture 30~40 40~50 Rice and upland crop rotation 40~50 50~60 Perennial crops 50~60 60~100 (Source: MAF 1988) Subsurface drainage Subsurface drainage is practiced to lower the water table and/or to control soil water content. Table 7.13 shows recommended water table depths for different land use in Korea. Subsurface drainage system can be either open ditch or subsurface pipe drain. Subsurface pipe drain is mostly used in paddy fields. Subsurface drainage plays a very important role in reclaimed tideland on removal of salt from the root zone. In Korea, many large-size tideland reclamation projects along the western coast have been completed or are under construction. For efficient land utilization, fast desalinization of the reclaimed tideland is very important. In these areas, dark gray swollen clay with very low hydraulic conductivity is dominant. Figure 7.21 A trencher installing drain pipes with a laser control About 55,000 hectares of the paddy fields require subsurface drainage in Korea (Table 7.14). However, only 1,605 hectares or 3% of the total fields were equipped with subsurface drainage facilities as of 1998 (Table 7.15). The most important subsurface drainage facility is lateral pipes, followed by mole drain and collectors. Table 7.14 No. of sites Total subsurface drainage facilities required in the paddy field Facilities Benefit area Canal Lateral Mole drain Catch drain Collector 1,347 54,560 ha 2,061 km 48,975 ha 5,304 ha 391 km 82,132 ea. Table 7.15 Subsurface drainage facilities completed by Item Total No. of sites Benefit area (ha) ,605 Percentage (%)

17 Progress of Irrigation and Drainage in Korean Paddy Field Chapter Land consolidation Nam-Ho Lee and Ju-Chang Kim Land consolidation is executed for the elimination of land fragmentation and improvement of the prevailing defective land ownership structure which is primarily characterized by small holding size, intense land fragmentation, mixed land ownership, lack of farm roads, and irregularly shaped plots. All these features constitute major structural and technical obstacles to the rational development of agriculture. Land consolidation provides paddy fields with irrigation and drainage canals, and proper farm road network, which changes irregularly shaped plots into large and rectangular-shaped plots. All these changes will lead to increases in the production, in capital and labor productivity, and the number of economically viable holdings, with consequent rise in the agricultural income Role of land consolidation Increase in land productivity In general, paddy fields selected for land consolidation are not properly equipped with canal systems. Land consolidation thus provides paddy fields with irrigation and drainage canal systems. Figure 7.22 Land consolidated area (Chogang scheme) Sufficient and stable water supply provides paddies with optimum condition for paddy crop growth. Maximum crop production can be achieved through the supply of irrigation water at an amount equivalent to the potential crop evapotranspiration. Water management involves the supply of water to crops at the right time and place and with right amount, which are guaranteed by properly equipped water supply systems. Proper management of water systems is effective for maximum crop production as well as water saving. Furthermore, qualified canal systems allow rotational or intermittent irrigation. Drainage systems prevent rice paddies from being inundated. In addition, they allow farmers to perform mid-season drainage exercise in rice paddies needed for crop growth with proper drainage systems. Increase in labor productivity At present rural regions are suffering from the shortage of young and qualified labors. One of the best solutions to this problem is the introduction of farm mechanization, 107

18 Rice Culture in Asia which can improve farming activities in rice cultivation such as puddling, transplanting, and harvesting, amomg others. Consolidated paddy field provides farm machinery with work space and accessibility. Introduction of large-sized machinery in the rice cultivation becomes possible through the enlargement of paddy plots. Since the surface of the paddy field is wet, which does not allow the use of heavy machines, immediate and solid drainage work can provide optimum working condition for farm machineries during the harvesting period Fundamental planning Planning activities for land consolidation include basic plan, parceling, computation of land acreage before and after project, land leveling, irrigation and drainage, and farm road plan. Basic plan - Decision of boundaries of the project area - Review of parceling size - Formulation of irrigation and drainage systems - Farm road plan - Considerations in decision of plots and acreage a) efficiency of the mechanized farming b) topographic conditions c) operation and maintenance of the irrigation and drainage canals d) management conditions e) shape and acreage of the typical plot Parceling - Basic conception of parceling - Decision on typical parcel and direction Computation of land acreage of the project area before and after project - Preparation of lists of land categories and land owners Land leveling - Computation of earth moving amount for leveling Irrigation plan - Planning of irrigation system - Criteria on computation of irrigation water - Computation of irrigation water requirement - Calculation of canal section Drainage plan - Planning of drainage system - Computation of unit drainage discharge 108

19 Progress of Irrigation and Drainage in Korean Paddy Field Chapter 7 - Calculation of canal section Farm road plan - Decision on typical cross section - Computation of profile on cross section and quantity Layout principles General considerations - Planning of land consolidation should be based on topographical conditions. - Land consolidation should be carried out on places where a dependable water source for irrigation is available. - Adequate drainage and flood control facilities should be in existence or under as part of the layout planning. - The land should be at an acceptable level. Cost of earth moving and structure will increase considerably with steeper slopes. - Due to the high investment required for land consolidation, only deep and fertile soils suitable for paddy rice should be considered. - Irrigation canals should be located on ridges and have command of the area to be irrigated (i.e. the water level of the canal must be above the maximum water level of the field). - Drainage canals must be located along the lowest areas and should be kept as straight as possible. - Length of the fields should be closely parallel to the contours such that the earth moving is reduced to a minimum. Thus, the field irrigation canals and drains should run at right angles to the contours to be of minimum length. Layout of irrigation canals, drainage canals and farm roads Individual paddy field must be kept along each irrigation and drainage canal without making depressions. Positioning of the irrigation canals, drains, and road should be as perpendicular to the contours as possible. Each field must have individual inlet and outlet from the irrigation canal and to the drain, respectively. It also must have a direct access to the road for better management, farm mechanization and easy axcess. The farm road should be high enough not to be flooded. However, highly elevated roads make it difficult to reach the field by farm machinery Parcellation Size of parcels Size of parcels depend on the following factors: - Topographic condition - Existing pattern of ownership - Efficient use of farm machinery - Convenience for operation and maintenance - Surface and subsurface drainage - Canal length giving minimum loss of water - Cost of providing such facilities as irrigation ditch, farm drain, and road, which is directly related to the length of parcel - Social and economic conditions 109

20 Rice Culture in Asia Recommended standard dimensions are: - Width: 15, 20, 25, 30, 40, 50, and 100 m - Length: 80 and 100 m Shape of parcels Existing topographical conditions should be the determining factors for the parcel shape. In areas flatter than 5% slope, rectangular- or parallelogram-shaped parcels of , or may be planned. For narrow strip paddy areas of slopes steeper than 10%, shapes requiring minimum cut and fill should be planned. For an effective use of farm machineries, each parcel should have the same ground surface elevation. Construction of multiple benches in one parcel to reduce earth moving should be avoided Land consolidation works in Korea Historically, land consolidation dates back to 1419 A.D., when the irrigation area of Nul-je, about 10,000 hectares, was rearranged in rectangular shape for the purpose of equitable taxation. During Japanese colonial period, 42,743 hectares was consolidated. However, land consolidation through Government-initiated projects began in 1965, and is being continued until now. Total consolidated area as of 1999 is 791,657 hectares, 69% of total paddy field area of 1,152,579 hectares. Table 7.16 shows the average area of land consolidation is a little above 20,000 ha/year during the last 3 decades. Size of plots and farm road width increased gradually and canal system was also improved depending on the introduction of farm machinery. Table 7.16 Development of land consolidation Period Before Area consolidated 42, , , , ,480 (ha) Size of plot (ha) 0.2~ ~0.3 Hilly area: Hilly area: Hilly area: 0.2~ ~ ~0.3 Plain area: Plain area: Plain area: 0.3~ ~ ~0.5 Reclaimed tideland: 0.5~2.0 Canal system Irrigation- Dual or irr. Irrigation Irrigation Irrigation drainage & drainage & drainage & drainage & drainage dual separated separated separated separated purpose and lined canal canal Farm road width 2.0~ ~ ~ ~ ~7.0 (m) paved Financing project More than 50:30:20 60~70:20:20~10 80:20:0 cost by 50% by (Government:Local farmers government:farmer) 110

21 Progress of Irrigation and Drainage in Korean Paddy Field Chapter 71 Figure 7.23 shows farmlands before and after land consolidation project of Juam scheme in Gyeonggi province of Korea. Road and canal systems are well arranged after consolidation. (a) Before project (a) After project Figure 7.23 Before and after land consolidation of Juam Scheme 111

22 Rice Culture in Asia 7.5 Water management organization Keun-Hoo Lee Korea Agricultural & Rural Infrastructure Corporation Provincial Office Figure 7.24 District Office Local Office General remarks The operation and management (O&M) of agricultural water in Korea is classified into two categories: management by Korea Agricultural and Rural Infrastructure Corporation (KARICO) and that by non-karico. In KARICO area agricultural water is operated and managed by KARICO, while non-karico area by city or county authorities. Some parts of non-karico area are operated and maintained by Irrigation Club (IC) through the support of city or county authorities. The present system for O & M of agricultural water system as of 2001 in Korea is shown in Figure KARICO manages large-size land area exceeding 50 hectares, while ICs and cities or counties under the authorization of their respective Provinces manage small-size lands of 5~50 hectares. KARICO, a government-run corporation, was founded in 2000 through the merging of three existing organizations, Rural Development Corporation, Farmland Improvement Associations and Federation of Farmland Improvement Associations. The notable features of water management in Korea are the integrated management of agricultural water system from tertiary to water sources in a package, and the exemption of irrigation fees in areas operated by KARICO Irrigation Club and Cities or Counties Historical backgrounds Before 2000, Irrigation Club (IC) was known as Farmland Improvement Club (FIC), a typical rural fraternity to manage irrigation facilities at the village level. ICs were born as mutually co-operative farmer groups Ministry of Agriculture & Forestry Integrated city & Province City & County Irrigation Club Administrative system for agricultural water management with long history and backgrounds. They played important roles in overcoming agricultural disasters such as droughts and floods, and helping each other in various agronomic activities. They also preserved local traditions and community spirit. ICs are now supported by city or county authority. Roles and functions IC is a type of water management club in rural villages, where it operated and maintained small-scale water sources such as small ponds, diversion weirs, and wells to supply 112

23 Rice Culture in Asia Chapter 7 water for the scattered small-scale lands. The operation of ICs and collection of operation costs are subjected to Province regulations legislated through the ministerial ordinance of the Ministry of Agriculture. Land areas and facilities operated and maintained Among the 878,489 hectares of total irrigated land area, KARICO manages 58% and city or county authorities together with ICs manage 42% of land. As of 1999, 169,325 hectares was operated by ICs and 196,738 hectares directly by city or county authorities. A total of 12,305 ICs with 12,839 water sources facilities were operated and maintained by 404,609 IC members. Reservoirs and pumping stations supplied irrigation water to 61% of the authorized area, while diversion weirs and others covered the rest Farmland Improvement Association (Irrigation Association) Historical backgrounds Farmland Improvement Association (FIA) played an important role as a typical water management organization before The origin of FIA goes back to 1908, with the birth of the first Irrigation Association (IA) in Jeonbuk Province, at which time the construction of reservoirs and large dams were included in the roles and functions of IA in addition to water management. In August 1945, the year of independence, the total number of IAs in the southern Korea was 429 benefiting 188,000 hectares of land. Since then, the number of IAs fluctuated depending on the social environment. In 1970, IA was renamed as FIA. In 1973 the number of FIAs was reduced to 127 for the efficient management. In 1989, democratic operational system such as election system for staff members and the governing body was introduced as a result of political democratization of the nation. At the end of 1999, 104 FIAs with 958,801 members operating 512,964 hectares were dissolved, and the staff and command areas were transferred to the newly born KARICO. Roles and functions The status of FIA was legalized. As a professional organization, it operated and maintained agricultural water systems from the tertiary up to the main level. The purpose of the FIA established by the authorization of the Minister of the Agriculture and Forestry was to promote the agricultural productivity and to contribute to the achievement of economical self-sufficiency of association members through effective operation and management of agricultural infrastructure. The highest decision-making body of the association was the general assembly, which was composed of representatives of the members. The basic functions of the FIAs were categorized into three parts, organizational, financial, and O & M functions for irrigation and drainage systems. Organizational functions refer to the establishment and appointment of the general assembly, the board of representatives, the board of trustees, the president and staffs, and the management of organization staff members and book-keeping. The financial functions refer to the assessment and collection of operational budget including special fees, and bond and refund of loans. 113

24 Rice Culture in Asia The O & M functions refer to the development and management of irrigation and drainage facilities. Other functions such as water quality conservation were later added to the existing functions. Land areas and facilities operated and maintained The FIA managed 512,426 hectares of paddy fields, 58% of total irrigated paddy fields in Korea as of Agricultural water systems such as 12,025 sites of water sources (reservoir 3,277, pumping station 2,952, others 5,796) and 94,938 km of irrigation and drainage canals (irrigation canals 62,239 km, drainage canals 32,699 km) were operated and maintained by an average of 4,042 staff members (administrative staffs 1,397, technicians 2,645) from 96 to 97. All staff members belonged to one of the 105 associations, and performed O & M works for irrigation systems of their respective association. The O&M fee paid by farmers was 28 kg/ha in polished rice until In 1988, the fee was reduced to 10 kg/ha to lighten the financial load of farmers, which was additionally reduced to 5 kg/ha in The deficit of maintenance costs was supported by the central government. Federation of Farmland Improvement Associations This organization was established in 1971 as a center organization representing FIAs under the name of the Society of Farmland Improvement Association. In 1973, the name was changed to Federation of Farmland Improvement Association (FFIA). The functions of FFIA include survey, study, and guidance for the benefit of FIAs, and the training of FIA staff members, in addition to rearrangement of farmlands, construction supervision for farmland consolidation projects, operation and management of the FIA Self-support Fund including implementation of projects commissioned by the government. All 104 FIAs were members of the FFIA, having one headquarters, 8 provincial offices, and one laboratory Korea Agricultural and Rural Infrastructure Corporation (KARICO) Historical backgrounds The beginning of KARICO, commissioned to carry out rural development by the government, goes back to the Joseon Union of Irrigation Associations established in 1940, which was renamed as Union of Korea Irrigation Association in 1949 and Union of Land Improvement Association (ULIA) in In 1970, Agricultural Development Corporation (ADC) was established through the merging of ULIA and the Corporation of Groundwater Development, and became a core organization executing the integrated large-scale agricultural development projects. In 1990, ADC was expanded, reorganized, and renamed as Rural Development Corporation (RDC) by adding on the functions of transaction and rental of the farmlands. In 2000, KARICO was born by combining RDC, FIAs and FFIA. Roles and functions When RDC was newly born as KARICO on January 1, 2000, KARICO took its first 114

25 Progress of Irrigation and Drainage in Korean Paddy Field Chapter 7 step toward the achievement of various goals. It aimed at contributing to the economical and social development of rural areas based on the increased revenues of farmers and productivities through rural area development projects. The goals also include comprehensive management of agricultural infrastructure facilities, construction of environmentfriendly production system, and promotion of agricultural scale optimization, among others. In addition, it formulates agricultural policy for the future unification of the nation. Furthermore, KARICO intends not only to develop rural areas into agreeable living areas well harmonized with the natural environment, but also to take the leading role as the key agency in charge of executing such agricultural policy aims as rice production, efficient management of national resources, and disaster prevention. Organization structure KARICO is composed of 1 headquarters with 6 executive directors and 1 research institute, 9 provincial offices, 87 district offices, and 4 comprehensive project offices. Land areas and facilities to be operated and maintained KARICO manages 58% of the total irrigated areas in Korea (Table 7.17). In addition, 12,025 water source facilities covering 512,426 hectares of paddy fields are operated and maintained by KARICO (Table 7.18). The number of reservoirs out of total water sources facilities in KARICO area is 3,277, covering only 27%. However, their benefit area is 73%. These indicate that the reservoirs are the major water sources for the paddy fields managed by KARICO. Table 7.17 Land area operated and maintained by KARICO Total Paddy fields Irrigated paddy fields Land areas covered by KARICO Total Within jurisdiction Outside jurisdiction Land areas covered by non-karico 1,152,579 ha 878,489 ha 512,426 ha 507,598 ha 4,828 ha 366,063 ha (100%) (58%) (42%) Table 7.18 Specification Irrigation and drainage facilities operated and maintained by KARICO Number of sites Percentage (%) Benefit area (ha) Percentage (%) Sum 12, , Reservoirs 3, , Irrigation pumping stations 2, , Irrigation & drainage pumping stations ,956 6 Drainage pumping stations Diversion weirs 3, ,366 3 Infiltration galleries ,207 1 Tube wells

26 Rice Culture in Asia Details of O&M works executed by KARICO The O&M for irrigation and drainage systems by KARICO are categorized into two parts; water management and facility maintenance. Table 7.19 shows the detailed functions of KARICO. After the establishment of KARICO, the agricultural water system in KARICO area was operated and maintained through the financial support from the central government, and no water charges were are collected from the farmers. The farmers forfeited their positions as members of the organization as in the case of FIA. Table 7.19 Functions of KARICO Specification Water quantity management Water quality management District/user management Record management Inspection and maintenance Database set up and planning for water supply Canal flow gauging and prevention of natural disasters Water saving for drought mitigation Preventive measures for flood protection Appropriate supply of water at proper time Proper allocation of water to canals Proper drainage of excess water Weed control and dredging in canals Monitoring agricultural water contamination Treatment of polluted irrigation water Planning for water pollution prevention Enrollment and exclusion of benefit area Bookkeeping of user list Transfer and take over of facilities Registration and abolition of facilities Planning of O & M for irrigation system Inspection of facilities Maintenance and rehabilitation of facilities Planning for emergency measures Construction of safety facilities, disaster prevention measures, and communication systems Decision on utilization of facilities for purposes other than normal Diagnostic inspection of facilities 7.6 Tideland reclamation Sang-Hyun Park Background Tideland reclamation was launched after the Mongolian invasion in the year of A seadike was constructed in the northeastern coast of Ganghwa island located 50 km west of Seoul aimed at reclaiming paddy fields for food supply of about 10,000 peoples including loyal families and soldiers, who resisted the invasion for more than 30 years. 116

27 Progress of Irrigation and Drainage in Korean Paddy Field Chapter 7 Tideland reclamation projects have been carried out for several centuries in the western coast of Korean Peninsula. The tidal range of western coast is between 6 to 9 meter during the spring tide and wave height is 3 to 4 meters during the winter season. The bottom slope of the tideland area is mild, and new tideland is created at the shoreline after the construction of a seadike. In 18th century, Sir Cheong Yak-Yong, a famous engineer, applied crane machine to move dumping stones during the construction of seadike. Many projects were carried out from 1917 to 1938 during the Japanese colonial period when 40,000 hectares of paddy fields were developed. Paddy fields of 75,000 hectares have since then been reclaimed and 60,000 hectares are under development, bring 30% of total paddy fields as reclaimed tideland in the south and western coasts as shown in Figure During the recent decades, more than 20,000 hectares of farmland has been converted yearly into industrial estate or other purposes. Therefore, as a compensation, tideland reclamation projects have been continued Recent tideland development Since 1945, 75,738 hectares of tideland have been reclaimed in 185 project areas by the Korean governmentand private companies for the development of paddy fields as shown in Table However, new tideland reclamation projects are scheduled only for 21,074 hectares due to the increasing environ-mental issues of recent years. Korean government adjusted the long-term plan of tideland reclamation area from 402,000 to 208,000 hectares in 1995, which was readjusted to 157,000 hectares in 1998, excluding large-scale projects. Table 7.20 shows that 59,854 hectares of tidal area are under construction through 16 projects including Saemangeum project that will provide 28,300 hectares of paddy fields. Figure 7.25 shows tidal land reclaimed area from 1945 to During 1960 s and 1970 s, many medium sized tideland reclamation projects were completed to increase food production through the expansion of farmland, irrigation water supply, and flood protection in the Figure Tideland development projects in Korea Table 7.20 Tideland development in Korea (unit: ha) Total By Government By Non-Government Constructed 75,738 35,549 40,189 Under construction 59,854 59,854 Scheduled 21,074 21,074 Total 156, ,477 40,

28 Rice Culture in Asia coastal area. Several large projects had been undertaken during 1980s. From 1990 to 1997, 15 tideland development projects were completed, supplying 22,000 hectares of new paddy fields. During this period, Gimpo project (1,649 hectares) and Seosan project (11,114 hectares) were completed by two private companies. Reclaimed area (ha) 1,200 1, Figure 7.26 Figure 7.26 shows the development areas and the changes in development area per project, i.e., 15 hectares per project during 1960 s increased to 1,100 hectares during 1990 s. This increase resulted from the improvement of Total area (km 2 ) Unit area (ha) 50 s 60 s 70 s 80 s 90 s Decades Tideland development construction technology and efforts to increase the economic efficiency of the project. With the development of larger area, bigger and longer sized seadike was needed. Table 7.21 shows the representative large-and medium-scale tideland reclamation projects. After the completion of the projects, 300,000 tons of rice are expected to be produced from the area. Table 7.21 Projects Tideland reclamation project under construction Construction period Project area (ha) Reclaimed for paddy field (ha) Rice products (t) Total (16 projects) 113,98 59, ,288 Yeongsangang (Ⅲ-1) ,160 7,960 38,486 Yeongsangang (Ⅲ-2) ,840 4,540 21,542 Saemangeum ,100 28,300 86,429 Hongbo , ,034 Siwha ,430 3,636 30,122 Hwa-ong ,802 4,482 29,703 Other 10 projects ,552 10,516 68,972 In tideland reclamation project, final gap closure of the dike is the most difficult work. Generally, big stones and gabions are dumped at the gap to resist high velocity current and form dike body. In Seosan project implemented by Hyundai Construction Company, a special gap closure method, using an old big ship, was applied (Figure 7.27). Figure 7.27 Final gap closure by ship at Seosan tideland reclamation project 118

29 Progress of Irrigation and Drainage in Korean Paddy Field Chapter Multi-functions of tideland reclamation Tideland reclamation has contributed to the self-sufficiency of rice in Korea for several centuries. In addition, it produces several advantageous functions such as water resources, flood protection, resort area, and new traffic roads, among others. The importance of this multi-function of tideland reclamation has been increasing with the rising prominence of the environmental amenity. Table 7.22 shows the multi-functions of tideland reclamation projects constructed recently in the western coast of Korea, with water resoures development of 1,395 million m 3 from 5 projects. In addition, the annual contribution to the improvement of traffics, tours and resorts, and provision of land and flood protection is estimated at US$ 627 million after the completion of the 5 tideland reclamation projects. According to the survey carried out in 1998, annually 35 million cars will use annually 5 seadike roads of the projects at a benefit of US$ 165 million. Furthermore, 4 million people are expected to visit the resort areas near seadikes, spending US$ 154 million annually (Table 7.22). Table 7.22 Multi - function of tideland reclamation project Multi-functions Asan, Namyang Geum estuary Sapgyocheon Yeongsangang (Ⅱ) Yeongsangang (Ⅲ-1) Total New land area (ha) 2, ,500 7,960 17,131 Developed area (ha) 18,419 24,574 43,000 20,700 13, Rice product (t/yr) 54,983 38,489 74,908 55,600 38, Water resources (Mill. m3 /yr) Effective storage (Mill. m3 ) Flood control (Mill. m3 ) In lake In paddy field Employment in const. (Mill. man-day) Benefit (Mill. $/yr)* Traffics improvement Resort & tours Land expansion Flood control Total * Based on exchange rate of US$=1,000 won Environmental issues in tideland reclamation area. After the final closure of Sihwa tideland development project located near Ansan Industrial Estate in the western coast, newly constructed Sihwa estuary reservoir receiving effluent from the nearby industrial area was severely contaminated. 119

30 Rice Culture in Asia TP Figure 7.28 shows the distribution of total 1 95 TP phosphorus in the upstream of the lake (RE) to 0.5 the downstream in the sluice (SB). When the water quality of the lake dropped severely in 0 RE RD RC RB RA SA SB 1994, government decided to open the sluice gate to fill the lake with seawater in 1995, which Station promptly improved the water quality as shown in Figure 7.28 Total phosphorus changes in the Sihwa Lake Figure Tidal difference in the project area is 9 m, and the current velocity at the gate is 12 m/s during the spring tide. However the lake has turned into a (brackish) salt-water lake, and the irrigation water for 3,636 hectares of the project area thus must be supplied from the adjacent Hwaong Lake in the future. The water quality problem of Sihwa Lake became a serious issue for the tideland reclamation projects in the western coast. TP ( mg/1) The seadike of Saemangeum project, which is under construction, is 33 km long with the final closure of seadike scheduled at However this schedule will inevitably be extended for several years, because the project was suspended for two years due to environmental concerns. The major issues involved the water quality of new estuary lake and the tidal flat conservation. Various mitigation schemes will thus be introduced to the project Mitigation schemes of environmental impacts in tideland reclamation Fish way Coastal ecological system will be changed into the fresh water environment, closing fish passages by the seadikes. For the migration of fishes, fish ways have been installed in the seadikes of tideland reclamation projects. In Geum estuary dam, a fish ladder was installed for the passage of eels and other migrating fishes into the reservoirs as shown in Figure The fish ladder is 9m wide 78m long with a bottom slope of 1:20. For the gathering of fishes in the inlet of ladder, 0.2 m 3 /s of attraction flows are released from the reservoir during low tide. However, because the sill elevation of the inlet gate is below the mean sea level, the gate should be closed during high tide. Figure 7.29 Fish ladder in Geum Estuary dam A navigation lock in Yeongsan-gang 3rd stage project was a little modified with provision of attraction flow. Thus, the lock has the function of a fish lock for the migratory fishes passing into the fresh water lake. 120