Threshold phenomenon of sediment reduction beneficials from soil-water conservation measures in the Wudinghe river

Based on the period 1956-1969 taking as a baseline period for the Wudinghe river basin,a multiple regression equation is established between the annual sediment yield and some indices of the precipitation characteristics,and used to calculate the sediment yield in the measure period(1970-1993),assuming there are no soil-water conservation measures Then the annual sediment reduction beneficials,defined as the percentage of sediment reduction of the sediment yield without soil-water conservation measures,is calculated,and its temporal variation is plot ed The curve indicates that the soil-water sonservation benef icats is a non-linear variation,which can be divided into three stages:(1)the increasing slowly;(2)increasing rapidly;and(3)remaining unchanged or even decreasing The relationships are plotted between the sediment reduction benef icials and the areas of the soil-water conservation measures such as land terracing,tree-and gras-splanting and the land created through check dams.It also shows the non-linear variations which can be fitted by the two straight lines with different slopes The turning point between the two straight lines can be regarded as a threshold of the area of the soil-water conservation measures,and the two straight lines represent a high-return area and a low-return area of the sediment reduction beneficials,respectively The curve can provide some useful information for the soil-water conservation planning in the studied area.