SCALE DIFFERENTIATION OF WATERSHED RUNOFF AND SEDIMENT DISCHARGE DUE TO CHANGES OF LANDUSE/VEGETATION COVER IN LOESS PLATEAU
Exploring dynamic characteristics of sediment discharge under different scales is not only the foundation of finding the variablity law of sediment discharge，but also is the front edge of soil erosion research nowadays.In this paper,the changes of runoff and sediment with the dynamic of land use and vegetation cover between the latter and the former period in four watersheds under three different area-scale levels were analyzed.Besides，scale differentiation laws of the effect of land use and vegetation changing on reduction of runoff and sediment were discussed.It was shown that watershed area and runoff modulus/sediment discharge modulus had a reasonable good exponential/linear relationship respectively.Moreover,with increasing of watershed area，runoff modulus and sediment modulus were increasing either.By eliminating the effect of precipitation， runoff modulus and sediment modulus was decreasing 20％-100％and 10％-100％respectively which was caused by increasing of vegetation coverage and optimizing of land use structures.And the reduction ratios of runoff modulus and sediment discharge modulus under different precipitation levels were quite different either.Besides，these four small scale watersheds also showed scale differentiations on reduction of runoff and sediment.In Qiaozidonggou or Qiaozixigou watershed which could be considered as a whole slope surface，the increasing of precipitation could weaken the effect of underlying surface conditions on runoff,especially in wet year with intensive rain events the reduction ration of runoff was only 10％.But in Luoyugou watershed which is much bigger than others，the effect of underlying surface conditions on runoff were more significant and relatively stable without controlled by changing of precipitation.The effect of changing underlying surface conditions on sediment discharge wasn’t equal to that on runoff.Soil erosion was much stronger in wet and dry year comparing with that in normal year. Because vegetation managements actually were very difficult to change the sediment discharge ability of channel in relatively large watersheds and the sources of sediment were plentiful in hill and gully loess area，sloping vegetation managements and water and soil conservation treatments in order to reduce sediment had a certain limitation on a relatively large watershed.Consequently,in order to reduce sediment in relatively large scale watersheds，the key issue is to reduce runoff.The effect of vegetation on reduction runoff and sediment didn’t have an infinite extension，which indicated that some certain effective vegetation coverage existed which was 45％-50％.Under this threshold，the effect on reduction runoff and sediment was dramatically increasing with the increasing of vegetation coverage.Therefore，gully correction project is very necessary for runoff and sediment management in the whole Yellow River watershed.
scale differentiation runoff and sediment discharge Loess Plateau
Zhang Xiaoming Cao Wenhong Yu Xinxiao Wu Sihong Zhang Manliang
China Institute of Water Resources and Hydropower Research，Beijing 100044,China Key Laboratory of Soil & Water Conservation and Desertification Combating,Ministry of Education,Beij Department of Land and Water Resources Engineering,Royal Institute of Technology Stockholm，SE-100 44 Tianshui Soil and Water Conservation Experiment Station，the Yellow River Water Conservancy Committee
国际会议
High-level International Forum on Water Resources and Hydropower(第一届国际水利水电高层论坛)
北京
英文
630-631
2008-10-17（万方平台首次上网日期，不代表论文的发表时间）