SOIL EROSION AND SEDIMENT DISTRIBUTION IN SMALL WATERSHED SCALE ON LOESS PLATEAU OF SOUTHWEST SHANXI PROVINCE IN NORTH CHINA

摘要

This paper studies on soil erosion and sediment distribution in small watershed scale in the gullied-hilly loess region in southwest Shanxi Province hi north China. The research aim is to analyze the relationship between erosion environment and soil loss, and distinguish the amount of soil loss from hillslopes and gullies, channels, in order to rationally arrange the measures of soil and water conservation in the watershed scale. The research sites include 2 small watersheds in Caijiachuan watershed and 4 small watersheds hi Qingshuihe watershed, which are the tributary of the middle reach of the Huanghe River (Yellow River).Based on on-site measures data on the rainfall event, sediment yields are analyzed in the small watershed. Erosion amount of the area of gully, channel and niter gullies and channels by runoff plots on hillslope and weir in the exit of the watersheds was caculated sediment source in the different land use, using the datum of on - site observation on hillslopes for 11 years was analysed. The result shows that the source of sediment at the small watershed comes mainly from the gullies. The sediment yield of gullies and channels (including gully head, gully floor and gully sidewall) is larger than that of area of niter gullies and channels (hillslopes, including hillslope and mound of loess). Sediment yield from gullies and channels occupies above 60% of the total watershed. In the 4 rainfall events, erosion rate in the area of gullies and channels are 7.49 t · km~(-2) - 22.38 t · km~(-2), but in the area inter gullies and channels is 3.61 t · km~(-2) -18.42 t · km~(-2) respectively, in the Beipo and Nanbeiyao small watershed which are the branch of the Caijiachuan watershed. Erosion rates of the area of gullies and channels are the 1.26-2.94 times as that of the area inter gullies and channels in small watershed scale. From the data of rainfall events on-site oberservation in 1998-1999, the sediment yields of erosion gully with good vegetation coverage in the gully floor and sidewall are 2,941 t · km~(-2) and 3,357 t · km~(-2). The sediment yield amount of gully occupy its 93.7%-99% of the total sediment yield of the catchments. On the contrary, compared with controlled gully, the sediment yield is only 0.361 t · km~(-2). Analyzing sediment source from the type of land, the slope cropland and bare land are main sources of sediment erosion. If there are no control measures, the steep slope cultivate farmland is apt to produce sediment.