Progress of Irrigation and Drainage in Korean Paddy Field …9-6)91-120.pdf · · 2006-08-25solely to supply water for irrigation, mostly for paddy field. ... automatic control

is particularly high during transplanting period from late April to late May, when waterresources are least available. The large seasonal variation in water demand has forced thedevelopment 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 mea-surement, short- and long-term storage prediction, water delivery efficiency, real-timemonitoring devices, and equipments for water distribution are also needed. One of theprerequisite for setting up the integrated system is the canal modernization.

In the beginning of irrigation system development, the uppermost priority was put onthe expansion of irrigation facilities such as the construction of reservoirs and canals.These hydraulic structures aged and were damaged with time. Rural water has multi-functions to supply not only irrigation water but also domestic, livestock, industrial, andenvironmental water to the rural area. However, development of new water resources andsupply system are very difficult. Not only is the construction of new dams and canalsvery costly, but land price is also very high and water right complicated. In addition envi-ronmental problems associated with new water resource development may cause seriouscivil disturbances and protests. Therefore, repair and reinforcement of existing irrigationsystems are considered to be the best alternative to meet the increasing water demand.Maximization of water use and supply efficiency through repair and reinforcement ofexisting dams and canals, installation of TM/TC instrumentation systems, networking ofwater resources, and automation of water management have emerged as the major watermanagement policies for large irrigation districts of 300 hectares or more. It is alsobelieved that automated water management systems contribute to the conservation of nat-ural 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 designedsolely to supply water for irrigation, mostly for paddy field. However, the current irriga-tion systems convey water not only for irrigation but also for household, industry, andlivestock breeding as well as environment. Furthermore, these systems also often supplywater to streams to secure a minimum stream flow and water quality. Patterns of irriga-tion have changed from seasonal rice irrigation to year-round irrigation for the agricultur-al productions both in the paddy field and upland. Peak water supply span also haveshortened due to the mechanization of transplanting processes in rice culture. Thesechanges have increased both the peak and normal water demands of the irrigation systemfar higher than the originally assumed values. Therefore, modernization of irrigationstructures, automatic control of water distribution and development of various incomesources are necessary to operate an irrigation system. Rational water distribution basedon real-time flow rate and water level monitoring can be achieved by installing TM/TCand central control system as an integrated central water management system. Successfulinstallation and operation of the central water management system require the improve-ment of canal structures and water delivery efficiency. In addition, prospective incomesources such as generation of hydro-power in agricultural reservoirs and tourist resorts inand around the reservoirs need to be developed to alleviate the operating cost of the cen-tral water management systems.

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Progress of Irrigation and Drainage in Korean Paddy Field Chapter 7

92

Rice Culture in Asia

Modernization of an irrigation system equipped with an integrated central water man-agement system in an irrigation district can increase agricultural production and farmearning by improving the efficiency of water use and timely water distribution. The mod-ernization also helps prevent or reduce disasters such as flood, decreases managementpersonnel, improves local environment, enables multiple use of water, and contributes tothe advancement of water management techniques. An integrated central water manage-ment system must be a real-time system that can monitor, control, and adjust water intakeat a water source, allow delivery through main and branch canals, and provide distribu-tion at gates and regulators by adopting electricity, mechanics, electronics, telecommuni-cation, and computer technologies. In an integrated system, dams, reservoirs, pumpingstations, headworks in streams, irrigation and drainage canals, and other hydraulic struc-tures are integrated into one operation system. In designing and building the system, thefollowing requirements must be considered:

- Minimizing water deficiency - Irrigation water must be supplied to where and whenneeded.

- 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 irri-

gation season must maintain a certain water level.- Maximizing income sources - Development of income sources such as small hydro-

power generation and public resorts must be maximized.

Seongju integrated central water management system completed in 1998 is a typicalexample. Seongju irrigation district covers 3,530 hectares of agricultural fields. Water issupplied from Seongju dam, 60 meters high and 430 meters long, with storage capacity ofabout 40 million m3. Watershed area of the dam is about 14,960 hectares. Irrigationcanals of 240 km was built, repaired or reinforced to improve water delivery efficiencyand are tightly monitored. The dam also supplies domestic water of 8,800 m3 per daythrough irrigation canals, and hydro-power electricity is generated during the irrigationseason. The integrated central water management system was found to contribute to theimprovement of agricultural productivity and saving of a large amount of waterresources. The water saved is used to expand irrigation area and domestic water supply.Estimated profit from the expanded irrigation area and domestic water supply wasassessed to be higher than the construction, maintenance, and operation costs of the inte-grated central water management system. Figures 7.9 and 7.10 show the graphic controlpanel 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 elec-tricity demand in rural areas and adverse impacts of fossil fuel use on the environmenthave driven to generate more hydro-power electricity where possible. Currently, smallhydro-power stations are installed in the Dae-a, Gangneung, Gyeongcheon, and Seongjudams. In Gyeongcheon dam, electricity generation capacity is 800 kW, and the annualamount of electricity generation and sale was 2.33 million kWh and US$ 130,000 in

1996, respectively. The income fromelectricity sale helps to maintain andoperate the Gyeongcheon irrigationsystem. Beside these four dams, 21agricultural dams were evaluated tohave potential for commercial elec-tricity generation. Estimated dis-charge rate and electricity generationcapacities of these 21 dams duringirrigation season ranged from 0.7m3/s to 9.57 m3/s and from 100 kWto 1,640 kW, respectively. Totalamount of electricity generationcapacity of the dams was estimatedto be 11,950 kW. It should be point-ed out that the major role of agricul-tural reservoirs is to supply irriga-tion water mainly during irrigationseason. Furthermore, electricity gen-eration in agricultural reservoirs maynot be possible or be very low dur-ing non-irrigation season. The mini-mum electricity generation capacityto meet economic break-even pointwas estimated to be 1,000 kW undercondition of agricultural reservoirs.Benefit-cost ratio (B/C ratio) ofelectricity generation in agriculturalreservoirs in 1996 was assessed tobe 2.36, an indication that the elec-tricity generation is profitable. It isalso forecasted that if fuel price risesfurther, the marginal profit wouldalso increase. Therefore, it is expect-ed that electricity generation in agri-cultural reservoirs will be increasedand help economically to maintainand operate the irrigation systems.

Raising dam crest An economic and effective way of increasing the reservoir capacitywithout the construction of new dams is to raise the normal water surface level and damcrest. This method has been applied at many dams, though only when the dam or thespillway of the reservoir is structurally and hydrologically safe. For example, dam crestand storage capacity in Wonseon reservoir located in Hampyeong-gun were raised by 2.5meters and 56%, respectively. As a result, the irrigation area was expanded from 45 to 88hectares.

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Figure 7.9 Graphic control panel of the integrated central watermanagement system in Seongju

Figure 7.10 A TM/TC system in an irrigation canal of Seongju

Another method of expanding reservoir capacity is to build a new dam downstream ofthe existing one. Dae-a dam is an example of this method (Figure 7.5). This dam wasoriginally constructed in 1922 as an irrigation dam. The dam thus could not meet theincreasing demand of rural water during the early 1980、s. Therefore, a new dam wasbuilt 300 meters downstream of the existing one. The new dam with a height of 55 metersand a length of 255 meters has a storage and irrigation capacities of 55.3 million m3 and8,125 hectares of farmland. The old dam was partly removed and submerged. The reser-voir supplies domestic, livestock, and industrial water and in-stream flow, in addition toirrigation 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 goodalternative to raise reservoir water level and increase its storage capacity. It can beapplied to reservoirs that have sufficient freeboard on crest and large surface area when itis 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 sed-imentation of reservoirs was surveyed to be about 8% of the total reservoir storage capac-ity. About 160 million m3 of water storage could be increased if the sediments aredredged. However, dredging of sediments is not considered as a viable option because thedredged sediment may cause adverse effects on the environment and secondary pollution.

Fishways Preservation of ecological environments and biodiversity has become animportant issue during the 1990’s. The Fisheries Resources Protection Act, Article 12,Section 2 obligates the provision of fishways in all riverine hydraulic structures, whichhinder the stream flows, and Article 31 of the Act has punitive clauses against the viola-tion. Extensive scientific research on fishways had not been conducted until the act waspassed although tens of fishways have been installed along the streams and rivers nearthe Eastern and Southern coasts. Studies on migrating aquatic animals have revealed thatmore than 23 fish species migrated through fishways. Various fishway models developedabroad were applied, tested, and modified to accommodate the uniqueness in flow mech-anisms, tides, and fish species.

By 2000, 193 fishways were constructed on 121 hydraulic structures in 42 rivers nation-wide. Dominant types of fishways are fish ladder (Figure 7.12; 87 units, 45%) and baffledfishway (66 units, 34%). The average dimension of fishways is 3.2 meters wide, 2.5 metershigh, and 20.2 meters long. As new fishways are installed, the height and length of typicalfishway tend to increase, while the width remains similar. Large lock gate fishways (fishlock) were also established, where sea dike was constructed at the mouth of a river, toreclaim a large tideland for agricultural production and other land uses. It should be pointedout that many old fishways were not constructed friendly to fish migration and have notbeen managed properly because the fishway requirement was under local administrativeregulations and fishways were constructed by unqualified contractors. As a result, manyfishways have been seriously damaged with time and do not function properly. However,with the increase in civil awareness on natural resources and environmental protection, var-ious fishways are expected to be installed in both small hydraulic structures in smallstreams and large dams in major rivers.

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Irrigation canal Irrigation wateris delivered through irrigation canalsto fields. Depending upon the type ofthe canals, water delivery efficiencyand loss show large differences. Therate of water loss in earthen canals isestimated to be about 30~40% whilethat of concrete canals is estimatedbetween 5~10%. Total length of themain irrigation canals is about 24,959km, and concrete main irrigation canalis about 11,148 km. Water loss differ-ence between the earthen and concretecanals may account for about 600 to800 million m3. National projects toconvert earthen canals into concrete orother canals that can minimize waterloss and maintenance cost are beingcarried out.

Earthen canals are widely distrib-uted throughout the country. Thesecanals are generally old and notwell-maintained. Water loss in thecanal is also very high. To minimizewater loss and improve water deliv-ery reliability, earthen canals arecurrently converted into lined chan-nel, concrete canal, or pipelinewhere necessary. There are manyother reasons to convert earthencanal into lined canal. Competitionfor water use and value of waterresources increased as agricultural,industrial, and domestic waterdemands increased. Replacement ofthe earthen canal with concrete orpipeline results in the reduction ofthe 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 irri-gation systems is being modernized by adopting TM/TC techniques. Minimization ofwater loss and maximization of water delivery reliability are prerequisite in setting up theTM/TC system.

Rectangular-shaped cement concrete waterway and earthen canal lined with variousmaterials mostly form the lined open channel structure. Large main canals are usuallylined, but relatively small branch canals are converted into concrete canals. Lining meth-

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Figure 7.11 Gates installed on an existing spillway of Giheungreservoir

Figure 7.12 A ladder-type fishway installed in a Osip-cheon,Yeongdeok (3rd weir from estuary)

ods of a canal are different depend-ing on lining materials. Concrete,concrete block, asphalt and clay lin-ings are typical examples.Liningmethods are selected based on theconditions of site such as topogra-phy, soil texture, groundwater level,safety of canal, economic efficiency,and workability.Rectangular con-crete canal is commonly used formedium to small branch canals(Figure 7.13).

7.2.3 Prospects of rural waterdevelopment

Rice culture in the monsoonregion of Asia has multi-functions,such as reliable food supply to meet

ever-increasing demand, economic development, land and environment conservation, andthe vitalization of rural community. These multi-functions of rice culture will continue tobe effective for the sustainable development of agriculture and rural areas.

The Ministry of Agriculture and Forestry (MAF) is executing the comprehensive ruraldevelopment plan of 1999-2004.

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Figure 7.13 An example of a rectangular-shaped and medium-sizedconcrete irrigation canal.

Figure 7.14 On-going and Mid- & long-term investment plan for comprehensive rural development

Agriculturalland and

water91%

Agriculturalland and

water91%

Mid-&long-term planduring 2005-2024US＄29.1 billion

Rurallivingstandards6% Off-farm

income1%

Rural livingstandards8%

On-going planduring 1999-2004US＄ 10.3 billion

Off-farmincome

3%

→→→ →

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%, thatof 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 agricultureuse, with 1,100,000 hectares for paddy field and 750,000 hectares for upland. A total ofUS$ 10,349 million have been allocated to the on-going plan (Figure 7.14 left).

In the mid- & long-term plan for 2005-2024, the MAF plans to achieve the nationalgoal of attaining self-sufficiency in staple food and establish rural life amenities. A har-monious policy should be also considered in the agricultural sectors for the reunificationof Korea. A total of US$ 29,143 million will be invested for this purpose (Figure 7.14right).

7.2.4 Challenges for rural water development

The purposes of the on-going plan are the achievement of stable food supply and sus-tainable agriculture, the preservation of productive farmland, strengthened collaborationwith North Korea and foreign countries in the agricultural sector, and the improvement ofrural living standards.

During the 21st century, rural areas will undergo urbanization through which urban andrural people will be mixed and space functions as supporting background to large metro-politan areas.

The solutions to complicated problems related to rural water development such as cost,water quality, water pricing, sustainable agriculture, inter-Korea and international co-operations would be major challenges in the future. The strategies for the future mustinvolve the optimization of water usage and mitigation of harmful effects.

Cost Agricultural land and water development projects need significant investments. Theaverage 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 sta-tion, respectively. At these costs, investments in agricultural land and water are difficult tojustify if benefits are projected on the basis of present prices. Improving or rehabilitating anexisting 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 hasdeteriorated the quality of water. Therefore, pollutant sources should be regulated by pro-hibiting the discharge of pollutants into streams, rivers, and lakes. Chemical fertilizer of421 kg per hectare and pesticide of 11 kg per hectare were applied in 1997. By 2004, the

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government plans to reduce the use of chemical fertilizers and other agrochemicals by50% 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 wateruse. All investment, operation, and maintenance costs are subsidized through the govern-ment budget from the year 2000. As a result, farmers and the operating organization havelittle interest in water pricing and saving. Nearly full cost recovery is achieved on domes-tic and industrial water supply, but not on agricultural water supply.

Sustainable agriculture The promotion of sustainable agricultural systems is one ofthe top priorities of the government policies. The sustainable agriculture promotion actwas established in 1997 to develop environment-friendly agriculture, which is classifiedas organic farming, farming without agrochemicals or low input farming. The environ-

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Total

Agricultural land and Water developmentDisaster preventionDrought countermeasureDrainage improvementRepair & ModernizationLand & water developmentRural waterLarge scale projectTidal land reclamationPaddy land consolidationLarge block consolidationUpland consolidationFarm road pavementRegional infrastructureRehabilitationResearch and developmentRural living standardsRural settlement areaAdvanced villageRural sewage treatmentRural domestic waterOff-farm incomeRural industrial complexFarm tourism

22,434 10,349 29,143

18,860 9,468 26,646

2,166 2,814 5,679255 188 215

103 ha 83 871 45 1,147 74 8411,040 1,478 4,623

16,325 6,593 20,522103 ha 881 5,243 27 1,590 41 5,140

Ea 15 2,535 8 1,181 (8) 3,677Ea 179 1,251 14 307 12 2,752

103 ha 690 6,034 42 892 94 2,064“ 73 34 621 111 2,310“ 30 620 36 682 81 1,497

103 km 5.6 510 12 894 17 1,665Ea 5 4 79 (4) 45

103 ha 10 127 36 348 64 1,364369 63 445

2,026 767 1,723492 1,395 305 400 129 270105 378 85 121 578 84068 25 88 32 612 224

Ea 1,864 292 2,850 215 5,286 3891,547 114 774

Ea 292 1,402 6 32 99 734Ea 631 145 225 79 109 38

Source: MAF, 2000. Mid- & long-tern plan for the comprehensive rural developmentMAF, Yearbook of agricultural land and water development.

Table 7.4 Present status and plans for rural development (unit : million US$)

Name of projectfor comprehensive rural development

Present statusin 1998

On-going planduring

1999-2004

Mid- & long-term plan during 2005-2024

No. Fund No. Fund No. Fund

Unit

ment-friendly farming household and area are expected to increase rapidly. Overuse ofagrochemicals has caused deteriorations in human health, ecosystems, and water quality,among others.

Inter-Korea and international co-operations Since North Korea has been sufferingfrom food shortages during the recent years, a harmonious policy should be considered inthe agricultural sectors. The Republic of Korea shares several rivers with North Koreaand proposed a joint-study for the watershed development and farmland restoration.Shortage of cereal food in North Korea reached 28% of total consumption in 1998because floods had seriously deteriorated the cultivated land of 360,000 hectares (19%)in 1995 and 298,000 hectares (16%) in 1996.

Recently, international cooperation in rural development is becoming more importantand active than ever. The government is paying more attention to international coopera-tion.

7.3 Drainage improvement in paddy fields

Sang-Ok Chung

In Korea, irrigation of paddy fields has traditionally received more attention thandrainage. Only after mid 1970’s did modern drainage projects begin in Korea. Surfacedrainage is more important than subsurface drainage for protecting farmland from flood-ing.

Although flooding and sea water intrusion have been national concerns since theancient dynasty, drainage improvement has a very short history in Korea. In Joseondynasty the first river stream bank project was initiated at Susan-je, Milyang-si,Gyeongnam province to protect land areas from flooding (1489). During the Japaneseoccupation, small-scale mole drainage was practiced from 1920’s. Mole drain of 22,000hectares 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 farmlanddrainage improvement project in order to increase double-cropping areas, namely barleyafter rice, to increase crop production. In 1975 the Korean government allocated budgetto the drainage improvement sector for the first time. From 1975 to 1978 three sampledrainage projects of 2,000 to 4,000 hectares including 20 to 50 hectares subsurfacedrainage were executed with the support of UNDP, through which new construction tech-nologies on drainage facilities including subsurface tile drainage were introduced (RDC1999).

The Rural Development Corporation (1999) classified the modern farmland drainage inKorea into three stages:

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(1) 1975 to 1979: Drainage improvement for double cropping, namely barley after rice,to increase crop production. Land consolidation projects completed during 1970’sseparated irrigation and drainage canal systems, which raised problems of poordrainage in lower areas.

(2) 1980 to 1989: Increased demand and expansion of drainage improvement. Drainageprojects mostly dealt with surface drainage such as canals and pumping stations.

(3) 1990 to 1998: Drainage improvement for the prevention of disaster. More farm-lands suffered from flooding due to the urbanization and extreme regional rainfalls.Thus, to prevent frequent flooding of the farmland, surface drainage facilities wereinstalled. During this period, several river rehabilitation projects improved the near-by paddy field drainage condition by reducing water table, which thus decreasedland areas requiring subsurface drainage.

7.3.1 Objectives and effects of paddy field drainage

The main objective of farmland drainage is the removal of excess surface and subsur-face water. For this purpose, surface drainage facilities are installed in paddy fields toprevent the inundation of land during flood seasons, and subsurface drainage facilities areinstalled to improve soil water environment of plants in waterlogged areas.

Direct effects of farmland drainage improvement include prevention of flooding, yieldincrease, rice quality improvement, increased land utilization, multi-purpose land use,and increased labor productivity. Some secondary effects are improved land bearingstress, improved trafficability of farm machineries, dried land, reduced maintenance cost,and improved rural community structure (RDC 1999). In addition, these effects can bringabout economic and social benefits to the farmers.

Based on studies conducted in Korea, some effects of the drainage improvement pro-jects are described below.

Land utilization rate increased from 129.2 to 138.3%, due to the increased double-crop-ping areas achieved through the improved soil water condition.

The drainage improvement projects increased the per hectare yield by reducing landsubmergence. 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 bet-ter water management, which reduced agrochemical application and water contaminationdownstream.

7.3.2 Causes of poor drainage

To improve land drainage, the following causes of poor drainage must be eliminated(RDC 1999):

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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 poorland drainage in Korean paddy fields. The most detrimental causes of poor land drainageare the rise of river flood stage and inundation of low-lying land, followed by insufficientdrainage canal conveyance.

Countermeasures include installation of drainage facilities such as pumping stations,catch drains, canals, and gates, dredging of stream beds, and rearrangement of drainagestreams.

7.3.3 Needs of field drainage in Korea

Yield reduction of rice due to submergence in Korea is shown in Table 7.6. In bootingstage only 0.5 day-long submergence resulted in 27% yield reduction. More than five-daysubmergence should be avoided in order to achieve satisfactory rice yield.

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Chapter 1 Progress of Irrigation and Drainage in Korean Paddy Field Chapter 7

Number Causes Percentage (%)

1 Rise of river flood stage and inundation of low lying land 412 Insufficient drainage canal conveyance 263 Low main drainage stream bed and high flood stage at a

relatively low rainfall intensity 184 High tidal river stage near shore 105 Insufficient drainage canal or pump capacity 36 Insufficient capacity and poor maintenance of lateral canals 2

Total 100

Table 7.5 Main causes of poor land drainage in Korea

(Source: MAF 2000b)

Submergence period(day)

Growth stage0.5 1 2 3 4 5 6 7

Rooting 4 7 13 19 25 31 37 42Tillering 6 11 21 30 39 48 57 65Panicle forming 15 20 29 39 48 58 68 77Booting 27 40 58 73 86 97 - -Heading 28 42 63 80 95 - - -

Table 7.6 Yield reduction of rice due to submergence (%)

(Source: MAF 1983)

Drainage improvement can be achieved as follows: by preventing the intrusion of out-side water into the benefit area, by preventing the stagnation of inside water in the benefitarea, and by controlling groundwater level and soil water contents. Stream banks and seadikes prevent flood and seawater from coming into the benefit area. Catch drains,drainage canals, drainage gates, and pumping stations may prevent submergence of thebenefit area. Subsurface pipe drainage removes excess soil water to keep the soil mois-ture optimum condition for the crop growth.

A survey on the land drainage condition in Korea was performed in 1992 by the RuralDevelopment Administration. Table 7.7 shows the results of the survey. Poor and badconditions represent 62.0 percent of the total paddy field area.

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 ofAgriculture 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 235,000hectares, among which drainage facilities for 84,300 hectares were completed by 1998.Drainage projects for the remaining 150,700 hectares were planned for the period of 1999through 2014. Acreage and investment of drainage improvement projects are shown inTable 7.8. Drainage projects are mostly for surface drainage with only 23% of the totalarea allocated for subsurface drainage. Great emphasis was placed on the water supplysystem development than field drainage because the nation suffers more from droughtsthan from floods. However, whenever the nation suffers from floods, short-term invest-ment to the drainage improvement greatly increases. There has been no sufficient long-term investment for the land drainage.

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Condition Acreage (ha) Percentage (%)

Excellent 4,652 0.4Good 13,954 1.2Fair 423,278 36.4Poor 572,123 49.2Bad 148, 845 12.8Total 1,162,852 100.0

Table 7.7 Drainage condition of paddy fields in Korea

(Source: RDC 1999)

TypeCompleted by 1998

Acreage (%) Investment Investment InvestmentAcreage (%) Acreage (%)

Planned from 1999 Total

Surface 82.7(46) 790.4 97.3(54) 1,857.9 180(100) 2,648.3Subsurface 1.6(3) 13.4 53.4(97) 420.7 55(100) 434.1Total 84.3(36) 803.8 150.7(64) 2,278.6 235(100) 3,082.4

Table 7.8 Acreage and investment of drainage improvement projects in Korea (Unit: thousand ha, million US＄)

(Source: MAF 2000b)

7.3.4 Classification of field drainage methods in paddy fields

Figure 7.15 shows a typical drainage systemlayout in Korea. The drainage area is divided intothree main parts: out-of-boundary mountainousarea, the upper part, and the lower part. A catchdrain is installed to divert incoming water fromhigher area, and the upper part is drained throughgravity and the lower part by pumps.

Field drainage methods can be classified as nor-mal and f lood drainage, gravity and pumpdrainage, and surface and subsurface drainage.

7.3.5 Field drainage facilities in Korea

Field drainage facilities are determined for each specific drainage area based on the topog-raphy, soil, area size, and construction cost, among others.

The paddy field area of 180,000 hectares requiressurface drainage, of which 82,691 hectares werecompleted by 1998 (Tables 7.9 and 7.10).

Drainage canalsTable 7.11 shows number and length of drainage

canals in paddy fields. Total length of drainagecanals is 60,804 km, of which 51,305 km is com-posed of earth and 9,499 km of concrete structure.Earth canals represents 84.4% of the total drainagecanal length.

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Figure 7.15 Schematic of a typical drainage system

↙

Watershedboundarycatch

drain

upperpart

lowerpart

maincanal

← Stream

Remarkpaddy fielduplandforestdrainage gatepump station

No. of sites Benefit area (ha)Drainage stations Canals Catch drain Gate

Facilities

1,139 180,000 840 site 3,458 km 245 km 864 site

Table 7.9 Total surface drainage facilities required in the paddy field

(Source: RDC 1999)

Item Up to 1974 1975-1980 1981-1990 1991-1998 Total

No. of sites 10 89 154 164 417Area (ha) 1,558 15,428 32,654 33,051 82.691Percent (%) 1.9 18.7 39.5 39.9 100

Table 7.10 Surface drainage facilities completed by 1998

(Source: RDC 1999)

Figure 7.16 A main drainage canal with concrete block lining

Recently, the importance of canals withregard to the environment and ecology came tolight. Therefore, transition to the environmentfriendly design and management of the canalswill be the general trend in the future. Designand management of canals will be toward theconservation of the environment and ecology.For this, canals and hydraulic structures shouldbe constructed using natural materials such asearth, rock, and woods rather than concrete.

In particular, small streams acting as maindrainage canals in plains should be conserved nat-urally through bank protection using rocks andwoods. A project of 500 m environment friendlydrainage canal has been recently completed inSongsam area using rocks and grasses (Figure7.17), with a 150 meters long ecological site, a100 meters long natural study area, and a 150meters long rest area with a walk.

Drainage gateThe drain outlets are located at the lowest

point of the project area. Occasionally, drainagegates are needed at the outlet to prevent reverseflow from the downstream into the upstreamdrainage area.

The drainage gate can be operated either man-ually or electrically. Figure 7.18 shows an elec-trically operated drainage gate. The drainage

gates may be installed with a pumping station.

Pumping stationPumping 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, whichinclude horizontal axis, single side suction, and single stage pumps. During 1970’s and

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Main 11,476 6,864 16,226 1,591 27,702 8,475Sub-main 32,886 14,893 57,809 3,579 90,695 18,472Lateral 90,261 29,548 117,688 4,329 207,949 33,877Total 134,623 51,305 191,723 9,499 326,346 60,804

KindEarth

Set Length Set Length Set Length

Structure Total

Table 7.11 Number and length of drainage canals in paddy fields (1999) (unit: km)

(Source: MAF 2000a)

Figure 7.17 An environment friendly main drainagecanal constructed using rocks and grasses

Figure 7.18 An electrically operated drainage gate

1980’s large-size pumps of more than 2,000 mm diameter with vertical axis were intro-duced along with the large scale comprehensive agricultural development projects.

In the case of paddy fields, surface ponding is allowed to some extent. In pumpeddrainage system, normal and flood drainages are processed separately.

The drain flow rate per unit area in pumping stations ranges 0.6 to 1.0 m3/s/km2, whichis much lower than that of the gravity drainage. Drainage pumping stations are normallyrequired to handle large capacities at low lifts. Therefore, centrifugal pumps are generallyused in the drainage pumping stations.

Table 7.12 shows the number of drainage pumping stations in paddy fields as of 1999.The drainage station is used only for drainage, while drainage & irrigation station foreither drainage or irrigation use depending on the need. There are 446 drainage stationsand 122 drainage & irrigation stations, totaling 568 stations. Figure 7.19 shows a pump-ing station with drainage gates.

Pumping stations may require screening systems in order to prevent pumps from beingclogged by solid wastes and debris. Screening can be performed using bar racks only orbar racks with rakes to automatically remove the debris (Figure 7.20).

105


Figure 7.19 A pump house with drainage gate Figure 7.20 A bar screen with an automaticrake.

Drainage only 63 181 106 82 14 446 336,466Drainage & Irrigation

31 42 27 19 3 122 77,946

Total 94 223 133 101 17 568 414,412

TypesTotal

power (hp)

Number of stations

up to100 hp

101~500 hp

501~1,000 hp

1,001~3,000 hp

above3,000 hp

Total

Table 7.12 Drainage pumping stations in paddy fields (1999)

(Source: MAF 2000a)

Subsurface drainageSubsurface drainage is practiced to lower the water table and/or to control soil water con-

tent. 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 veryimportant 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 complet-ed or are under construction. For efficient land utilization, fast desalinization of the

reclaimed tideland is very important.In these areas, dark gray swollenclay with very low hydraulic con-ductivity is dominant.

About 55,000 hectares of the paddyfields require subsurface drainage inKorea (Table 7.14). However, only1,605 hectares or 3% of the total fieldswere equipped with subsurfacedrainage facilities as of 1998 (Table7.15). The most important subsurfacedrainage facility is lateral pipes, fol-lowed by mole drain and collectors.

106


Land use Water table depth 2-3 days Water table depth 7 days after rainfall (cm) after rainfall (cm)

Rice mono culture 30~40 40~50Rice and upland crop rotation 40~50 50~60Perennial crops 50~60 60~100

Table 7.13 Recommended water table depths from the ground surface

(Source: MAF 1988)

1,347 54,560 ha 2,061 km 48,975 ha 5,304 ha 391 km 82,132 ea.

No. of sites Benefit areaCanal Lateral Mole drain Catch drain Collector

Facilities

Table 7.14 Total subsurface drainage facilities required in the paddy field

No. of sites 6 6 6 18Benefit area (ha) 294 571 740 1,605Percentage (%) 18 36 46 100

Item 1976-1980 1981-1990 1991-1998 Total

Table 7.15 Subsurface drainage facilities completed by 1998.

Figure 7.21 A trencher installing drain pipes with a laser control

107

7.4 Land consolidation

Nam-Ho Lee and Ju-Chang Kim

Land consolidation is executed for the elimination of land fragmentation and improve-ment of the prevailing defective land ownership structure which is primarily character-ized by small holding size, intense land fragmentation, mixed land ownership, lack offarm roads, and irregularly shaped plots. All these features constitute major structural andtechnical obstacles to the rational development of agriculture.

Land consolidation provides paddy fieldswith irrigation and drainage canals, andproper farm road network, which changesirregularly shaped plots into large and rec-tangular-shaped plots. All these changeswill lead to increases in the production, incapital and labor productivity, and the num-ber of economically viable holdings, withconsequent rise in the agricultural income.

7.4.1 Role of land consolidation

Increase in land productivityIn general, paddy fields selected for land

consolidation are not properly equippedwith canal systems. Land consolidationthus provides paddy fields with irrigationand drainage canal systems.

Sufficient and stable water supply provides paddies with optimum condition for paddycrop growth. Maximum crop production can be achieved through the supply of irrigationwater at an amount equivalent to the potential crop evapotranspiration.

Water management involves the supply of water to crops at the right time and placeand with right amount, which are guaranteed by properly equipped water supply systems.Proper management of water systems is effective for maximum crop production as wellas water saving. Furthermore, qualified canal systems allow rotational or intermittent irri-gation.

Drainage systems prevent rice paddies from being inundated. In addition, they allowfarmers to perform mid-season drainage exercise in rice paddies needed for crop growthwith proper drainage systems.

Increase in labor productivityAt 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,


Figure 7.22 Land consolidated area (Chogang scheme)

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 throughthe enlargement of paddy plots.

Since the surface of the paddy field is wet, which does not allow the use of heavymachines, immediate and solid drainage work can provide optimum working conditionfor farm machineries during the harvesting period.

7.4.2 Fundamental planning

Planning activities for land consolidation include basic plan, parceling, computation ofland acreage before and after project, land leveling, irrigation and drainage, and farmroad 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 acreagea) efficiency of the mechanized farmingb) topographic conditionsc) operation and maintenance of the irrigation and drainage canalsd) management conditionse) 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


109

- Calculation of canal section

Farm road plan- Decision on typical cross section- Computation of profile on cross section and quantity

7.4.3 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 irri-

gated (i.e. the water level of the canal must be above the maximum water level of thefield).

- Drainage canals must be located along the lowest areas and should be kept as straightas possible.

- Length of the fields should be closely parallel to the contours such that the earthmoving is reduced to a minimum. Thus, the field irrigation canals and drains shouldrun at right angles to the contours to be of minimum length.

Layout of irrigation canals, drainage canals and farm roadsIndividual paddy field must be kept along each irrigation and drainage canal without

making depressions. Positioning of the irrigation canals, drains, and road should be asperpendicular to the contours as possible. Each field must have individual inlet and outletfrom the irrigation canal and to the drain, respectively. It also must have a direct accessto the road for better management, farm mechanization and easy axcess. The farm roadshould be high enough not to be flooded. However, highly elevated roads make it diffi-cult to reach the field by farm machinery.

7.4.4 Parcellation

Size of parcelsSize 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


Recommended standard dimensions are:- Width: 15, 20, 25, 30, 40, 50, and 100 m- Length: 80 and 100 m

Shape of parcelsExisting topographical conditions should be the determining factors for the parcel

shape. In areas flatter than 5% slope, rectangular- or parallelogram-shaped parcels of 40×

100, 50×100 or 100×100 may be planned. For narrow strip paddy areas of slopes steeperthan 10%, shapes requiring minimum cut and fill should be planned. For an effective useof 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

7.4.5 Land consolidation works in Korea

Historically, land consolidation dates back to 1419 A.D., when the irrigation area ofNul-je, about 10,000 hectares, was rearranged in rectangular shape for the purpose ofequitable taxation. During Japanese colonial period, 42,743 hectares was consolidated.However, land consolidation through Government-initiated projects began in 1965, and isbeing 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/yearduring the last 3 decades. Size of plots and farm road width increased gradually and canalsystem was also improved depending on the introduction of farm machinery.

110


Period Before 1945 1965-1970 1971-1980 1981-1990 1991-1999Area consolidated 42,743 101,703 224,248 208,483 214,480(ha)Size of plot (ha) 0.2~0.3 0.2~0.3 Hilly area: Hilly area: Hilly area:

0.2~0.3 0.2~0.3 0.2~0.3Plain area: Plain area: Plain area: 0.3~0.4 0.3~0.5 0.3~0.5

Reclaimed tideland: 0.5~2.0

Canal system Irrigation- Dual or irr. Irrigation Irrigation Irrigationdrainage & drainage & drainage & drainage & drainagedual separated separated separated separatedpurpose and linedcanal canal

Farm road width 2.0~2.5 2.5~3.0 3.0~6.0 4.5~7.0 4.5~7.0(m) pavedFinancing project More than 50:30:20 60~70:20:20~10 80:20:0cost by 50% by(Government:Local farmersgovernment:Farmer)

Table 7.16 Development of land consolidation

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Chapter 1 Progress of Irrigation and Drainage in Korean Paddy Field Chapter 7

(a) Before project

(a) After project

Figure 7.23 Before and after land consolidation of Juam Scheme

Figure 7.23 shows farmlands before and after land consolidation project of Juamscheme in Gyeonggi province of Korea. Road and canal systems are well arranged afterconsolidation.

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7.5 Water management organization

Keun-Hoo Lee

7.5.1 General remarks

The operation and management (O&M) of agricultural water in Korea is classified intotwo categories: management by Korea Agricultural and Rural Infrastructure Corporation(KARICO) and that by non-KARICO. In KARICO area agricultural water is operatedand managed by KARICO, while non-KARICO area by city or county authorities. Someparts of non-KARICO area are operated and maintained by Irrigation Club (IC) throughthe support of city or county authorities. The present system for O & M of agriculturalwater system as of 2001 in Korea is shown in Figure 7.24.

KARICO manages large-size land area exceeding 50 hectares, while ICs and cities orcounties under the authorization of their respective Provinces manage small-size lands of5~50 hectares. KARICO, a government-run corporation, was founded in 2000 throughthe merging of three existing organizations, Rural Development Corporation, FarmlandImprovement Associations and Federation of Farmland Improvement Associations.

The notable features of water management in Korea are the integrated management ofagricultural water system from tertiary to water sources in a package, and the exemptionof irrigation fees in areas operated by KARICO.

7.5.2 Irrigation Club and Cities or Counties

Historical backgroundsBefore 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 asmutually co-operative farmer groupswith long history and backgrounds.They played important roles in over-coming agricultural disasters such asdroughts and floods, and helpingeach other in various agronomicactivities. They also preserved localtraditions and community spirit. ICsare now supported by city or countyauthority.

Roles and functionsIC is a type of water managementclub in rural villages, where it oper-ated and maintained small-scalewater sources such as small ponds,diversion weirs, and wells to supply

Ministry of Agriculture& Forestry

Korea Agricultural & Rural Infrastructure

Corporation

Provincial Office

District Office

Local Office

Integrated city & Province

City & County

Irrigation Club

Figure 7.24 Administrative system for agricultural water management

113

Rice Culture in Asia Chapter 7

water for the scattered small-scale lands. The operation of ICs and collection of operationcosts are subjected to Province regulations legislated through the ministerial ordinance ofthe Ministry of Agriculture.

Land areas and facilities operated and maintainedAmong 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, 169,325hectares 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 main-tained by 404,609 IC members. Reservoirs and pumping stations supplied irrigationwater to 61% of the authorized area, while diversion weirs and others covered the rest.

7.5.3 Farmland Improvement Association (Irrigation Association)

Historical backgroundsFarmland Improvement Association (FIA) played an important role as a typical water

management organization before 2000. The origin of FIA goes back to 1908, with thebirth of the first Irrigation Association (IA) in Jeonbuk Province, at which time the con-struction of reservoirs and large dams were included in the roles and functions of IA inaddition to water management.

In August 1945, the year of independence, the total number of IAs in the southernKorea was 429 benefiting 188,000 hectares of land. Since then, the number of IAs fluctu-ated depending on the social environment. In 1970, IA was renamed as FIA. In 1973 thenumber of FIAs was reduced to 127 for the efficient management. In 1989, democraticoperational system such as election system for staff members and the governing bodywas 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 staffand command areas were transferred to the newly born KARICO.

Roles and functionsThe status of FIA was legalized. As a professional organization, it operated and main-

tained agricultural water systems from the tertiary up to the main level.

The purpose of the FIA established by the authorization of the Minister of theAgriculture and Forestry was to promote the agricultural productivity and to contribute tothe achievement of economical self-sufficiency of association members through effectiveoperation and management of agricultural infrastructure. The highest decision-makingbody of the association was the general assembly, which was composed of representa-tives of the members.

The basic functions of the FIAs were categorized into three parts, organizational, finan-cial, and O & M functions for irrigation and drainage systems. Organizational functionsrefer to the establishment and appointment of the general assembly, the board of repre-sentatives, the board of trustees, the president and staffs, and the management of organi-zation staff members and book-keeping. The financial functions refer to the assessmentand collection of operational budget including special fees, and bond and refund of loans.

The O & M functions refer to the development and management of irrigation anddrainage facilities. Other functions such as water quality conservation were later added tothe 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 1999. 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 anddrainage canals (irrigation canals 62,239 km, drainage canals 32,699 km) were operatedand maintained by an average of 4,042 staff members (administrative staffs 1,397, techni-cians 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 1987. In 1988, thefee was reduced to 10 kg/ha to lighten the financial load of farmers, which was addition-ally reduced to 5 kg/ha in 1989. The deficit of maintenance costs was supported by thecentral government.

Federation of Farmland Improvement AssociationsThis organization was established in 1971 as a center organization representing FIAs

under the name of the Society of Farmland Improvement Association. In 1973, the namewas changed to Federation of Farmland Improvement Association (FFIA).

The functions of FFIA include survey, study, and guidance for the benefit of FIAs, andthe training of FIA staff members, in addition to rearrangement of farmlands, construc-tion supervision for farmland consolidation projects, operation and management of theFIA Self-support Fund including implementation of projects commissioned by the gov-ernment.

All 104 FIAs were members of the FFIA, having one headquarters, 8 provincial offices,and one laboratory.

7.5.4 Korea Agricultural and Rural Infrastructure Corporation (KARICO)

Historical backgroundsThe beginning of KARICO, commissioned to carry out rural development by the gov-

ernment, 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 LandImprovement Association (ULIA) in 1962. In 1970, Agricultural DevelopmentCorporation (ADC) was established through the merging of ULIA and the Corporation ofGroundwater Development, and became a core organization executing the integratedlarge-scale agricultural development projects. In 1990, ADC was expanded, reorganized,and renamed as Rural Development Corporation (RDC) by adding on the functions oftransaction and rental of the farmlands. In 2000, KARICO was born by combining RDC,FIAs and FFIA.

Roles and functionsWhen RDC was newly born as KARICO on January 1, 2000, KARICO took its first

114


step toward the achievement of various goals. It aimed at contributing to the economicaland social development of rural areas based on the increased revenues of farmers andproductivities through rural area development projects. The goals also include compre-hensive management of agricultural infrastructure facilities, construction of environment-friendly production system, and promotion of agricultural scale optimization, among oth-ers. In addition, it formulates agricultural policy for the future unification of the nation.

Furthermore, KARICO intends not only to develop rural areas into agreeable livingareas well harmonized with the natural environment, but also to take the leading role asthe 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 maintainedKARICO 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 andmaintained 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 reservoirsare the major water sources for the paddy fields managed by KARICO.

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1,152,579 ha 878,489 ha 512,426 ha 507,598 ha 4,828 ha 366,063 ha(100%) (58%) (42%)

TotalPaddy fields

Irrigated paddy fields

Land areas covered by KARICO

Total Within jurisdiction Outside jurisdiction

Land areas covered by non-KARICO

Table 7.17 Land area operated and maintained by KARICO

Reservoirs 3,277 27 373,226 73Irrigation pumping stations 2,952 25 91,046 17Irrigation & drainage

pumping stations 98 1 29,956 6

Drainage pumping stations 399 3 552 0Diversion weirs 3,844 32 14,366 3Infiltration galleries 463 4 3,207 1Tube wells 992 8 73 0

Specification

Sum 12,025 100 512,426 100

Number of sites Percentage (%) Benefit area (ha) Percentage (%)

Table 7.18 Irrigation and drainage facilities operated and maintained by KARICO

Details of O&M works executed by KARICOThe 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 func-tions of KARICO.

After the establishment of KARICO, the agricultural water system in KARICO areawas operated and maintained through the financial support from the central government,and no water charges were are collected from the farmers. The farmers forfeited theirpositions as members of the organization as in the case of FIA.

7.6 Tideland reclamation

Sang-Hyun Park

7.6.1 Background

Tideland reclamation was launched after the Mongolian invasion in the year of 1232. Aseadike was constructed in the northeastern coast of Ganghwa island located 50 km westof Seoul aimed at reclaiming paddy fields for food supply of about 10,000 peoplesincluding loyal families and soldiers, who resisted the invasion for more than 30 years.

116


Water quantity management Database set up and planning for water supplyCanal flow gauging and prevention of natural disastersWater saving for drought mitigationPreventive measures for flood protectionAppropriate supply of water at proper timeProper allocation of water to canalsProper drainage of excess waterWeed control and dredging in canals

Water quality management Monitoring agricultural water contaminationTreatment of polluted irrigation waterPlanning for water pollution prevention

District/user management Enrollment and exclusion of benefit areaBookkeeping of user list

Record management Transfer and take over of facilitiesRegistration and abolition of facilities

Inspection and maintenance Planning of O & M for irrigation system Inspection of facilitiesMaintenance and rehabilitation of facilitiesPlanning for emergency measuresConstruction of safety facilities, disaster prevention measures, and

communication systemsDecision on utilization of facilities for purposes other than normalDiagnostic inspection of facilities

Specification

Table 7.19 Functions of KARICO

117


Tideland reclamation projects have been carried out for several centuries in the westerncoast of Korean Peninsula. The tidal range of western coast is between 6 to 9 meter dur-ing the spring tide and wave height is 3 to 4 meters during the winter season. The bottomslope of the tideland area is mild, and new tideland is created at the shoreline after theconstruction 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. Manyprojects were carried out from 1917 to 1938 during the Japanese colonial period when40,000 hectares of paddy fields were developed. Paddy fields of 75,000 hectares havesince then been reclaimed and 60,000 hectares are under development, bring 30% of totalpaddy fields as reclaimed tideland in the south and western coasts as shown in Figure7.25. During the recent decades, more than 20,000 hectares of farmland has been convert-ed yearly into industrial estate or other purposes. Therefore, as a compensation, tidelandreclamation projects have been continued.

7.6.2 Recent tideland development

Since 1945, 75,738 hectares of tideland have beenreclaimed in 185 project areas by the Korean governmen-tand private companies for the development of paddy fieldsas shown in Table 7.20.

However, new tideland reclamation projects arescheduled only for 21,074 hectares due to the increas-ing environ-mental issues of recent years. Korean gov-ernment adjusted the long-term plan of tideland recla-mation 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 that59,854 hectares of tidal area are under constructionthrough 16 projects including Saemangeum projectthat will provide 28,300 hectares of paddy fields.Figure 7.25 shows tidal land reclaimed area from 1945to 2000.

During 1960’s and 1970’s, many medium sized tide-land reclamation projects were completed to increasefood production through the expansion of farmland,irrigation water supply, and flood protection in the

Constructed 75,738 35,549 40,189Under construction 59,854 59,854Scheduled 21,074 21,074Total 156,666 116,477 40,189

Total By Government By Non-Government

Table 7.20 Tideland development in Korea (unit: ha)

Figure 7. 25 Tideland development projects in Korea

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 pad-dy fields. During this period, Gimpo project (1,649 hectares) and Seosan project (11,114hectares) were completed by two private companies.

Figure 7.26 shows the development areas and the changes in development area per pro-ject, i.e., 15 hectares per project during 1960’s increased to 1,100 hectares during 1990’s.

This increase resulted from the improvement ofconstruction technology and efforts to increase theeconomic efficiency of the project. With thedevelopment of larger area, bigger and longersized seadike was needed.

Table 7.21 shows the representative large-andmedium-scale tideland reclamation projects. Afterthe completion of the projects, 300,000 tons ofrice are expected to be produced from the area.

In tideland reclamation project, final gap clo-sure of the dike is the most difficult work.Generally, big stones and gabions are dumped atthe gap to resist high velocity current and formdike body. In Seosan project implemented byHyundai Construction Company, a special gapclosure method, using an old big ship, wasapplied (Figure 7.27).

118


Figure 7.26 Tideland development

Total area (km2)Unit area (ha)

Total (16 projects) 113,98 59,854 295,288Yeongsangang (Ⅲ-1) 1985-2002 13,160 7,960 38,486Yeongsangang (Ⅲ-2) 1989-2004 7,840 4,540 21,542Saemangeum 1991-2004 40,100 28,300 86,429Hongbo 1991-2003 8,100 420 20,034Siwha 1987-2008 24,430 3,636 30,122Hwa-ong 1991-2008 5,802 4,482 29,703Other 10 projects 1985-2005 14,552 10,516 68,972

Table 7.21 Tideland reclamation project under construction

ProjectsConstruction

period Project

area (ha)Reclaimed for

paddy field (ha)Rice products (t)

Figure 7.27 Final gap closure by ship at Seosan tide-land reclamation project

1,200

1,000

800

600

400

200

0 50’s 60’s 70’s 80’s 90’s

Rec

laim

ed a

rea

(ha)

Decades

7.6.3 Multi-functions of tideland reclamation

Tideland reclamation has contributed to the self-sufficiency of rice in Korea for severalcenturies. In addition, it produces several advantageous functions such as waterresources, flood protection, resort area, and new traffic roads, among others. The impor-tance of this multi-function of tideland reclamation has been increasing with the risingprominence of the environmental amenity. Table 7.22 shows the multi-functions of tide-land reclamation projects constructed recently in the western coast of Korea, with waterresoures development of 1,395 million m3 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 com-pletion of the 5 tideland reclamation projects. According to the survey carried out in1998, annually 35 million cars will use annually 5 seadike roads of the projects at a bene-fit of US$ 165 million. Furthermore, 4 million people are expected to visit the resortareas near seadikes, spending US$ 154 million annually (Table 7.22).

7.6.4 Environmental issues in tideland reclamation area.

After the final closure of Sihwa tideland development project located near AnsanIndustrial Estate in the western coast, newly constructed Sihwa estuary reservoir receiv-ing effluent from the nearby industrial area was severely contaminated.

119


New land area (ha) 2,682 989 - 5,500 7,960 17,131Developed area (ha) 18,419 24,574 43,000 20,700 13,160 119.853Rice product (t/yr) 54,983 38,489 74,908 55,600 38,486 262.466Water resources

(Mill.㎥/yr) 364 156 365 324 186 1.395

Effective storage (Mill. ㎥) 101 63 122 181 153 620

Flood control(Mill. ㎥) 86 45 96 161 89 477

- In lake 78 42 96 145 65 426- In paddy field 8 3 - 16 24 51

Employment in const.(Mill. man-day) 19 21 2 16 10 68

Traffics 28 29 56 33 19 165improvement

Resort & tours 50 47 43 10 4 154Land expansion 36 13 - 74 90 213Flood control 17 9 19 32 18 95Total 131 98 118 149 131 627

Multi-functionsAsan,

NamyangSapgyo-cheon

Geumestuary

Yeongsan-gang (Ⅱ)

Yeongsan-gang (Ⅲ-1)

Total

Table 7.22 Multi - function of tideland reclamation project

* Based on exchange rate of US$=1,000 won.

Benefit(Mill.

$/yr)*

Figure 7.28 shows the distribution of totalphosphorus in the upstream of the lake (RE) tothe downstream in the sluice (SB). When thewater quality of the lake dropped severely in1994, government decided to open the sluice gateto fill the lake with seawater in 1995, whichpromptly improved the water quality as shown inFigure 7.28. Tidal difference in the project area is9 m, and the current velocity at the gate is 12 m/sduring the spring tide. However the lake has

turned into a (brackish) salt-water lake, and the irrigation water for 3,636 hectares of the pro-ject area thus must be supplied from the adjacent Hwaong Lake in the future. The water quali-ty problem of Sihwa Lake became a serious issue for the tideland reclamation projects in thewestern coast.

The seadike of Saemangeum project, which is under construction, is 33 km long withthe final closure of seadike scheduled at 2004. However this schedule will inevitably beextended for several years, because the project was suspended for two years due to envi-ronmental concerns. The major issues involved the water quality of new estuary lake andthe tidal flat conservation. Various mitigation schemes will thus be introduced to the pro-ject.

7.6.5 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 tidelandreclamation projects. In Geum estuary dam, a fish ladder was installed for the passage of eels and oth-

er migrating fishes into the reservoirs asshown in Figure 7.29.

The fish ladder is 9m wide 78m longwith a bottom slope of 1:20. For thegathering of fishes in the inlet of lad-der, 0.2 m3/s of attraction flows arereleased from the reservoir during lowtide. However, because the sill eleva-tion of the inlet gate is below the meansea level, the gate should be closedduring high tide.

A navigation lock in Yeongsan-gang3rd stage project was a little modi-fied with provision of attractionflow. Thus, the lock has the functionof a fish lock for the migratory fishespassing into the fresh water lake.

120


Figure 7.28 Total phosphorus changes in the Sihwa Lake

Figure 7.29 Fish ladder in Geum Estuary dam

94 TP

95 TP

RE RD RC RB RA SA SB

1.5

1

0.5

0

Station

TP (

mg/

1)

Documents

Progress of Irrigation and Drainage in Korean Paddy Field …9-6)91-120.pdf · · 2006-08-25solely to supply water for irrigation, mostly for paddy field. ... automatic control