Author(s): Hyoseop Woo; Moon Hyeong Park; Sang Joon Jeong; Han Tae Kim
Linked Author(s): Hyoseop Woo
Keywords: White River; Green River; Riparian Vegetation Succession; Hydrogeo-morphic Process; Gravel/sand Bars
Abstract: In Korea, rapid development of water and river resources and continuous channelization since 1960s have caused the flow and sediment regimes of the river artificially changed, which in turn caused to the accelerated hydrogeomorphic processes in the rivers. These resulted in a drastic change in the colour of the rivers from “white” to “green”, in which “white” means sand and gravel bars and “green” means vegetation. Before the river developments began in full-scale in late 1960s, all of the rivers in the Korean Peninsula were virtually “white river” due to the high seasonal variation of flow regime, which is typical in the monsoon-affected regions. Now, many of the river reach in Korea, especially downstream of dams, are covered with herbaceous plants such as reeds and shrubs and trees such as willows. “Green rivers” may cause a serious engineering problem of increase in flood hazard through increase in flow resistance and fixation and heightening of riparian lands. On the other hands, “green rivers” can support more diverse species as compared with “white rivers” in some cases. This study generally classifies the patterns and causes of “white” bars succession to “green” vegetations in the rivers, Korea. For this analysis, comparisons of timespanned aerial photos of several river reaches were made and rates of vegetation expansions were calculated. Through this comparative analysis and several fieldtrip, three patterns of the riparian vegetation establishment can be identified in Korea, which are basically similar to those found in literature with some exception. Pattern 1is the flow and sediment regime changes due mostly to damming, which is highlighted as decreases in the bed shear stress and fresh sediment supply. Pattern 2 is the artificial disturbance of the river such as channelization, dredging, gravel mining, and weir (barrage) construction, which can be further categorized into three subpatterns; 2-1) digging and dredging of the river channel to concentrate the flow with the other part of the channel being dried, 2-2) construction of weir to have one or few new narrow channels downstream to cause the same phenomenon as Pattern 2-1; and2-3) inclusion of riparian cultivated land into the river by the construction of levees. Pattern 3 is the increase in nutrients in the river flow water due mainly to the increase in non-point pollution influx, which has not been proved in the field yet. Some typical cases of each pattern are introduced with relevant aerial and field photos.
Year: 2010