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Republic of Korea
Irrigation and drainage
Evolution of irrigation development
Irrigation development in Korea has a long history. Weirs (headworks) were built in the first century, and the first reservoirs were constructed at the end of the fourth century. Historical records show that in 1910 there were about 26 000 diversion weirs, ponds and dykes for irrigation water supply.
Irrigation development in the Republic of Korea can be divided into three stages:
- Stage I, before 1945, when numerous small-scale systems were constructed by mobilizing local technology;
- Stage II, 1946-1961, when existing systems damaged by the war were repaired;
- Stage III, since 1961, when large-scale comprehensive agricultural development projects have been implemented. During this stage, the Government invested large amounts from international loans for the development and rehabilitation of irrigation systems and for the improvement of technical, institutional and social aspects of irrigation.
In 1982, the estimation of water requirements for irrigation was adjusted to cover the ten-year drought frequency, and an inventory of existing irrigation systems throughout the country was prepared to identify rehabilitation requirements. As a result, many systems with insufficient capacities were categorized for rehabilitation.
In 2007, the irrigation potential area was taken as being the same as the total cultivated area, or 1 782 000 ha, since it is considered that all cultivable land is currently under cultivation. In 2002, total irrigated area was around 880 400 ha, a reduction compared to 1996, since some land has been diverted to other purposes such as construction of public facilities, houses and factories (Table 4).
Irrigation systems cover approximately half of the cultivated area. However, most of the cultivated areas are irrigated by virtually any means during the critical crop periods when threatened by drought. Typically, in high valleys where irrigation systems are not economically viable, farmers irrigate by pumping water from rivers, streams and reservoirs using small portable pumps or power tillers.
As fertile paddy fields can be more easily and economically developed on flat plains than hilly areas, more farmland and, consequently, the accompanying irrigation systems have been developed by reclaiming river plains and tidelands. This partly explains why surface drainage predominates. It is difficult to find a large and shallow river-swamp left idle. Irrigation development along the west coast is often implemented as part of tideland reclamation.
In 1996, out of a total irrigated area of 888 800 ha the area served by surface water was an estimated 843 500 ha (95 percent) of which 65 percent was fed by 18 000 reservoirs, 21 percent by 6 000 pumping stations, and 14 percent by 18 000 headworks. The area served by groundwater accounted for 45 300 ha (5 percent) (Figure 2).
In 1996, small schemes (< 50 ha) covered 41 percent of the total equipped area for irrigation, medium-size schemes (50–3 000 ha) 41 percent and large schemes (>3 000 ha) 18 percent (Figure 3). Using local government budgets, small systems are constructed by the cities or counties, and handed over to farmers’ organizations for operation and maintenance (O&M). Medium-size systems are funded from the central government’s budget, constructed by the provinces, and handed over for O&M to Farmland Improvement Associations (FLIAs). Large systems are financed by the central government, executed by the Rural Development Corporation (RDC), and then handed over to FLIAs for O&M. In any case, the full cost of construction is paid for by the Government. There are some privately developed and owned irrigation systems, but no data are available on their area.
Role of irrigation in agricultural production, the economy and society
Total harvested irrigated cropped area in 2006 was around 1 038 000 ha. The major irrigated crops are paddy rice accounting for 73 percent of the total harvested area, followed by vegetables, which represent 13 percent, soybeans 5 percent and perennial crops 5 percent of which citrus accounts for 17 percent (Table 4 and Figure 4). Winter barley is mostly sown on paddy fields after the rice harvest in autumn, and grown without irrigation during the winter with residual soil moisture until spring. Wheat and maize are seldom cultivated on irrigated paddy for economic reasons. The average yield of irrigated rice was 6.8 tonnes/ha for single cultivation in 1996. In that year, approximately 76 percent of all paddy was under irrigation.