| The major soil types in Chongqing are yellow soil and purplish soil, most for crop. The area of yellow soil is1994000hm2, which occurs in the hill and gully area. This soil has a loose crumb structure with easy soil and water loss. It is of significance to study laws of sediment yield of yellow soil in Chongqing, for decreasing soil and water loss and maintaining sustainable development of ecology, economy and agriculture. This paper studied the laws of sediment yield of yellow soil on different rainfall condition, based on simulated rainfall examination. The conclusions are as followings:(1) In simulated rainfall examination, the characteristic parameters of rainfall were similar to nature. Rainfall homogeneity greater than0.8, could meet the requirement of simulated rainfall. This experiment was closed to nature rainfall. According to analysis and study of simulated rainfall information, raindrop size distribution is also content with the Best raindrop function, type in a=1.92I0.34, n=5.95I-3.33.(2) Splash amount were correlated to rainfall intensity and raindrop size, and rain fall intensity changed to raindrop size. The amount of splash erosion, changes in rainfall intensity and raindrop. Rainfall intensity and raindrop diameter, strong impact on soil, easily dispersed the soil, destroy soil aggregates structure. Diameter was significantly correlated with the raindrop diameter, for a very significant positive correlation between the analysis of splash erosion can be expressed as a linear function of the raindrop diameter, coefficient is8.65.(3) Rainfall characteristic factors, including rainfall, rainfall intensity, runoff. Have a significant impact on erosion and sediment yield of any one factor caused by change in sediment yield response. Through correlation analysis were positively correlated to soil loss amount significantly through correlation analysis. The relationship of rainfall and erosion sediment yield was significant (P<0.05), the correlation coefficient is0.461, so is that of rainfall intensity and erosion sediment yield. Runoff was correlated to erosion sediment yield very significantly (P<0.01),the correlation coefficient is0.592.(4) According to path analysis of erosion sediment yield to rainfall, rainfall intensity and runoff, we discovered that runoff, rainfall intensity, rainfall had positive linear effect to erosion sediment yield, which were the decision variables. However, there is a big interaction between the three (one of the three factors had indirect effects to erosion sediment yield from two other factors). The largest direct effect of the erosion sediment yield was runoff, with direct path coefficient0.547and decision coefficient0.540. The following was rainfall intensity with decision coefficient0.437, and rainfall mainly indirect effected to erosion sediment yield, with indirect path coefficient0.543and decision coefficient0.255. And we had developed the formulation for estimating the erosion sediment yield.(5) Initial soil moisture contention effected to erosion sediment yield of yellow soil. Initial soil moisture contention firstly affected runoff. The more content of initial soil moisture, the more quickly runoff appeared, the shorter time to reach runoff stably. If the total amount of runoff was large, and the speed of runoffwas high, the scour against soil was strong. In addition, initial soil water content affects the soil physical and chemical properties, different level different soil aggregate stability, soil shear resistance, the sediment yield with the water content increases.(6) Slope and slope length were the major factors of soil erosion. In the range of10°～15°of slope, erosion sediment yield increased by slope with high growth rate. While in the range of15°～20°of slope, erosion sediment yield increased by slope with low growth rate, and in the range of20°～25°,erosion sediment yield maintained the same level or decreased. There was a critical erosion slope to erosion sediment yield. When the slope was gentler than the critical erosion slope, erosion sediment yield had an exponential function with slope, otherwise erosion sediment yield decreased. When rainfall intensity was0.9mm/min, the critical erosion slope was19.89°, while the rainfall intensity was1.8mm/min, it became25.52°.Erosion sediment yield increased with slope length. Erosion sediment yield produced in the slope of4m was significant more than that in the slope of2m. And if rainfall intensity was stronger, erosion sediment yield was influenced more significantly by slope length. |
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