Scale Effect of Runoff and Sediment Reduction Effects of Soil and Water Conservation Measures in Chabagou, Dalihe and Wudinghe Basins
岔巴沟、大理河与无定河水土保持减水减沙作用的尺度效应

The study of runoff and sediment reduction benefits of soil and water conservation measures has been improved at different scales separately; however, there are relatively few studies on the scale effect of runoff and sediment reduction benefits of soil and water conservation measures in basins of different scales. In this study for Chabagou, Dalihe and Wudinghe basins, runoff and sediment reduction benefits of soil and water conservation measures in the 1970s are calculated by three methods: rainfall-runoff and rainfall-sediment statistical model (R-RSM), double accumulative curve method (DACM) and time series contrasting method (TSCM) accordingly. As a result, average runoff reduction benefits are 14.47%, 20.22% and 20.78% respectively and average sediment reduction benefits are 64.97%, 43.62% and 47.26% respectively. The results show that there is no scale effect in the results from the three methods when they are applied separately to calculate runoff and sediment reduction benefits in basins of three scales. Runoff reduction efficiency (RRE) and sediment reduction efficiency (SRE) indicating the“efficiency”of the runoff and sediment reduction benefits are introduced, and after analyzing the relationship between runoff reduction efficiency and sediment reduction efficiency of basins of three scales, several conclusions are obtained. (1) Sediment reduction efficiency is always greater than runoff reduction efficiency in basins of three scales, however, the ratio of sediment reduction efficiency to runoff reduction efficiency of small scale basin is greater than that of middle and large scale basins and there is no scale effect of the ratio between middle and large scale basins. (2) Sediment reduction efficiency of small scale basin is lower than that of middle and large scale basins, while runoff reduction efficiency of small scale basin is greater, and runoff reduction efficiency and sediment reduction efficiency of middle and large scale basins are so close that there is no scale effect.