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Republic of Korea
Most of the rivers flow west and south through the plains. There are five main drainage systems, which altogether cover two-thirds of the territory:
- Han river basin in the northwest: average runoff 19.4 km3/year, drainage area 26 018 km2;
- Kum river basin in the west: average runoff 6.2 km3/year, drainage area 9 810 km2;
- Nakdong river basin in the south: average runoff 13.9 km3/year, drainage area 23 817 km2;
- Seomjin river basin in the south: average runoff 3.8 km3/year, drainage area 4 897 km2; and the
- Yeongsan river basin in the south: average runoff 2.6 km3/year, drainage area 3 371 km2.
The total annual volume of surface runoff produced internally is about 62.25 km3, while internal groundwater resources are approximately 13.3 km3. Since about 10.7 km3 of groundwater resources comprise the base flow of the rivers, the total internal renewable water resources are an estimated 62.25+13.3-10.7 = 64.85 km3/year. Some transboundary rivers cross the border with the Democratic People’s Republic of Korea. Compared with the annual discharge of the Han river in the Democratic People’s Republic of Korea (19.4 km3/year with a catchment basin four times that of the basin flow into the Republic of Korea), the inflow to the Republic of Korea from the Democratic People’s Republic of Korea is an estimated 4.85 km3/year. The total average surface water discharge in the Republic of Korea is, therefore, an estimated 67.1 km³/year, bringing the total renewable water resources to 69.7 km3/year (Table 2). Owing to the intensive nature of the rainfall and the steeper natural channel slopes, about 37 percent of the annual water resources are flood runoffs, concentrated in summer.
During the last 60 years, a considerable effort has been made to regulate the course of rivers. Multipurpose river basin schemes have been developed for flood control, irrigation, community water supply and hydropower production. In 1997, there were 765 dams that were over 15 m high. There are more than 18 000 small irrigation reservoirs. Artificial lakes account for 93 percent of all lakes in the Republic of Korea. In 1994, the water storage for dams and reservoirs totals 16.2 km3.
In 1997, total hydropower electricity generation amounted to 5 404 GWh, representing 2.4 percent of the country’s total electricity generation.
In 1996, total produced wastewater was an estimated 7 947 million m3. Only 4 180 million m3 were treated.