Abstract

The study taking the controlled Qiaozidong watershed and uncontrolled Qiaozixi watershed in third sub-region of Loess Plateau as example, has analyzed the effects of land use/cover change on sediment discharge. The results showed that the impact of land use/land cover on annual sediment discharge is significant. The sediment discharge rate of controlled watershed has reduced by 44%, 75%, 86% respectively in wet, normal and dry year over the uncontrolled watershed. Comparing the amount of sediment discharge in the land use period of 1995-2004 to 1986-1994 in controlled Qiaozidong, it is in period of 1995-2004 that sediment discharge reduced more. In addition, the impacts of land use/cover on sediment discharge demonstrated seasonal fluctuation characteristic. The effects of reducing sediment discharge in controlled watershed displayed more significant than that in uncontrolled Qiaozixi in May and September. To controlled Qiaozidong, the effect of reducing sediment discharge consisted with rainfall distribution. For example, in a month with 45 mm precipitation, the mean monthly sediment discharge concentration in the latter period was reduced by 12% than that in the former period, while in a month with 80mm precipitation, the reduction was 25%. Finally, the flood-sediment discharge had closely correlation with the rainfall, rainfall intensity in 60 min and the flood volume, and had greater impacts on flood sediment discharge in uncontrolled watershed than that in controlled watershed. Rainstorm-runoff process and the rainstorm-sediment discharge process demonstrated that large vegetation coverage had stronger function in regulating and controlling flood process and sediment discharge process in rainstorm. At the same time, precipitation and flood peak discharge frequencies had indicated that it is any recurrence period that mean sediment discharge concentration in land-use period of the latter was fewer than that of the former when with the same precipitation frequency distribution.

Keywords: Land use/cover change (LUCC), sediment discharge, frequency distribution, the loess hilly-gully region