GK:1.2.3 Rivers and Plains of the Korean Peninsula
Geography of Korea: I. Natural Environment > 2. Topography > 3) Rivers and Plains of the Korean Peninsula
3) Rivers and Plains of the Korean Peninsula
(1) Rivers
In their volume, the rivers of the Korean peninsula exhibit extreme seasonal variations, making them difficult to rely upon as resources. The fundamental cause of this instability in water flow is that heavy rainfall in Korea is limited to the summer monsoon season. When these monsoon rains do arrive, rainfalls of several hundred millimeters are not unheard of, yet in the long dry season that precedes the monsoon rains the rivers and reservoirs can dry up, threatening drinking water supplies to say nothing of crop irrigation. Another factor contributing to the unstable water levels of the peninsula’s rivers has to do with the narrowness of the river basins. During times of heavy rainfall water levels in the rivers can rise precipitously with flooding along the major rivers lasting for days.
Today, multipurpose dams along Korea’s major rivers are able to regulate the seasonal water flow. The government of South Korea has been constructing these multipurpose dams since the 1960s, important ones being the Han River’s Soyang River Dam (1973), Chungju Dam (1985), and Hwangseong Dam (2000); the Nakdong River’s Andong Dam (1976), Hapcheon Dam (1989), Imha Dam (1992), Namgang Dam (2001), and Miryang Dam (2001); the Geum River’s Daecheong Dam (1980) and Yongdam Dam (2001); and the Seomjin River’s Seomjin River Dam (1965) and Juam Dam (2001). The construction of these multipurpose dams has gone far in mitigating the seasonal instability of the water flow and preventing flooding. However, they have also revealed the limits of our ability to prevent flooding caused by massive rainfall.
The mid and upper reaches of the Yalu (Amnok), Tumen (Duman), Han, Nakdong, and Geum Rivers are replete with incised meanders (Figure 1-4). These incised meanders are closely related to the asymmetric Yogok Disturbance that took place peninsula-wide from the mid-Cenozoic period. Up to the mid-Cenozoic the Korean Peninsula was almost a uniform and flat peneplain across which it is thought rivers roamed freely. However, from the mid-Cenozoic the peninsula experienced great upheavals, causing the rivers, though maintaining their same course, to increase their downward erosion, thus creating the incised meanders.
On the other hand, the peninsula also has many straight valleys that reflect the influence of the geological structural lines called tectolineaments. Representative examples of these valleys include the Chugaryeong tectonic valley, traversed by the Gyeongwon Line Railroad that historically ran from Seoul in the west to Wonsan on the east coast of Korea, and the valley traversed by National Highways 45 and 46 connecting Cheongpyeong and Yangsuri. These valleys were formed through the gradual erosion of high altitude plateaus, a process of differential erosion that followed the lines of tectolineaments.
Because the Korean Peninsula’s primary watersheds are located on its eastern side, those rivers with effluences in the East Sea are relatively short and with steep descents. One exception to this is the Tumen River, which runs for about 520 kilometers and is exceptionally tortuous. Besides the Tumen, the other major rivers flowing into the East Sea are (from the north), the Suseongcheon, Eorangcheon, Dancheon Namdaecheon, Bukdaecheon, Bukcheong Namdaecheon, Seongcheong, Yongheung, Anbyeon Namdaecheon, and Hyeongsan Rivers.
The rivers emptying into the Yellow or Southern Seas are relatively lengthy and with gentle descents. Because these rivers are very much effected by tidal variations, their water levels exhibit regular variations twice per day. During high tide, the seaward river flow is reversed and water levels rise; during low tide the river flow reverses again towards the sea and water levels drop. The Yalu (Amnok) River, which empties into the Yellow Sea, is the Korean Peninsula’s largest river, but because it flows between mountain ranges it exhibits extreme incised meanders and development of its riparian plains is minimal. Besides the Yalu, the major rivers of the peninsula flowing into the Yellow and Southern Seas are, from north to south, the Cheongcheon, Daedong (Taedong), Yeseong, Imjin, Han, Geum, Yeongsan, Seomjin, and Nakdong Rivers (Table 1-2). Of note among these are the Daedong, Han, and Nakdong, which flow respectively through the North Korean capital of Pyongyang, the South Korean capital of Seoul, and Busan, the largest city in South Korea’s Yeongnam region.
| River | Total basin area(km2) | Total length(km) | Source | Effluence |
|---|---|---|---|---|
| Yalu(Amnok) | 62,639 | 790 | Bohye township, Gapsan county, Hamgyeong-namdo province | empties into Yellow Sea (West Sea) |
| Tumen(Duman) | 42,243 | 521 | Samjang township, Musan county, Hamgyeong-bukdo province | empties into East Sea |
| Han | 26,018 | 482 | Hajang township, Samcheok city, Gangwon province | empties into Yellow Sea (West Sea) |
| Nakdong | 23,817 | 522 | Taebaek city, Gangwon province | empties into Southern Sea |
| Daedong(Taedong) | 16,465 | 431 | Somaek township, Yeongwon county, South Pyeongan-namdo province | empties into Yellow Sea (West Sea) |
| Geum | 9,810 | 396 | Changsu township, Changsu county, Jeolla-bukdo province | empties into Yellow Sea (West Sea) |
| Imjin | 8,118 | 254 | Pungsang township, Muncheon county, Hamgyeong-namdo province | empties into Yellow Sea (West Sea) |
| Cheongcheon | 6,144 | 213 | Sinpung township, Hoecheon county, Pyeongan-bukdo province | empties into Yellow Sea (West Sea) |
| Seomjin | 4,897 | 212 | Baekun township, Jinan county, Jeolla-bukdo province | empties into Southern Sea |
| Yeseong | 4,049 | 174 | Seochon township, Suan county, Hwanghae province | empties into Yellow Sea (West Sea) |
| Jaeryeong | 3,671 | 129 | Nadeok township, Haeju city, Hwanghae province | empties into Yellow Sea (West Sea) |
| Daeryeong | 3,635 | 150 | Namseo township, Sakju county, Pyeongan-bukdo province | empties into Yellow Sea (West Sea) |
| Yeongsan | 3,371 | 136 | Yong township, Damyang county, Jeolla-namdo province | empties into Yellow Sea (West Sea) |
| Dancheon Namdaecheon | 2,405 | 161 | Jindong township, Gapsan county, Hamgyeong-namdo province | empties into East Sea |
| Seongcheon | 2,338 | 99 | Hawoncheon township, Sinheung county, Hamgyeong-namdo province | empties into East Sea |
| Bukcheong Namdaecheon | 2,056 | 67 | Goki township, Bukcheong county, Hamgyeong-namdo province | empties into East Sea |
(2) Plains
The Korean Peninsula boasts no great plains where the sky stretches to the horizon in all directions. The most significant agriculturally developed plains are concentrated along the lower reaches of the major rivers flowing into the Yellow and Southern Seas. These plains can be categorized into formation types: alluvial plains formed by the sedimentary deposits of meandering rivers; so-called chimsik jeoji, erosional lowlands formed through long erosion; and finally reclaimed land, that is, flatlands reclaimed from the sea.
But the heart of the peninsula’s agricultural flatlands are its alluvial plains formed through the accumulation of river sediments. These alluvial plains are comprised of alluvial fans on the upper stretches of the rivers, flood plains along the middle reaches, and fan deltas on the lower portions. However, alluvial fans and fan deltas are only weakly developed on the Korean Peninsula. The reason for the lack of development of alluvial fans has to do with the fact that Korea’s old landforms are relatively free of transition points from massive sloping, points that typically form the source of an alluvial fan formation. As to the lack of fan deltas, this can be traced to the fact that the tidal range of the Yellow Sea, into which most of Korea’s major rivers empty, is very large and as a result most sedimentary deposits reach the estuary to be deposited on the seabed.
On the other hand, Korea’s major rivers have relatively wide flood plains along their lower reaches. Floodplains may be divided into natural levees and backswamps. The natural levees found along the banks of rivers have high loamy soil embankments composed of roughly equal proportions of fine sand, clay, and silt, such that from a very early period they were areas of settlement and agricultural activity. The backswamps, situated beyond these natural levees and composed primarily of clay soils, sit at a lower altitude making them prone to frequent flooding. In the past, these backswamp areas were simply marshes along the natural levees, but today artificial embankments have been built around the backswamps and pumping stations installed so that the majority of these areas have been transformed into paddy fields.
The topography of the flood plains along the lower reaches of the peninsula’s major rivers reveals the contours of the final stage of the sea-level rise of the post-glacial age. These flood plains were created by the accumulation of river sediment based on the current sea level along the deep ravines carved during the glacial period. Therefore, these flood plains do not exceed ten meters in height.
The erosional lowlands are situated along the periphery of the alluvial plains or in relatively low-lying watersheds between them. Though they sit a little higher in elevation from the alluvial plains, and are somewhat more undulating, they are nevertheless visibly more level and plain-like relative to mountainous areas. The weathered laterite soil of the bedrock is in narrow layers and tinged with red, making it readily distinguishable from alluvial soil. And whereas the alluvial plains have generally been used as paddy fields, the erosional lowlands find use as dry fields, orchards, pasturage, and woodlands. The erosional lowlands are primarily distributed in the peninsula’s western and southern portions, but can also be found in the erosion basins along the mid and upper stretches of major rivers.
Reclaimed lands have also been created through the construction of tidal embankments off the coasts of the plains distributed in the Yellow (West) and Southern Sea coastal areas. Such reclamation efforts date back as far as the Goryeo period (918–1392), when it was practiced on a small scale. However, large-scale reclamation projects did not commence until the early twentieth century and continue to the present, with the result that Korea’s tidal flats are in decline.
The peninsula’s major plains include the Yongcheon plains along the Yalu River, Anju and Bakcheon plains along the Cheongcheon River, Pyongyang plains along the Taedong River, Jaeryeong plains along the Jaeryeong River, Yeonbaek plains in coastal southeastern Hwanghae-do province, Gimpo plains along the Han River, Pyeongtaek (or Anseong) plains of the Anseongcheon River valley, Yedang plains of the Sapgyo River valley, Nonsan plains along the Geum River, Kimje and Mangyeong plains (Honam plains) in the Dongjin River and Mangyeong River valley, Naju plains along the middle reaches of the Yeongsan River, and Gimhae plains along the Nakdong River. Korea’s eastern coast also has plains though on a more modest scale. The major plains of the eastern coast include the Suseong plains along the Suseong River, Hamheung plains along the Seongcheon River, Yeongheung plains along the Yongheung River, and Pohang plains along the Hyeongsan River.
