Study On The Slope Erosion Characteristics Of Runoff And Sediment Of The Black Soil Under The Different Slope Indoors

The black soil is a kind of luvisols, with good character and high fertility, which is very suitable for the growth of plant. But serious erosion of black soil which is mainly dominated by water and wind erosion, due to natural factors and irrational production activities in the last decades, which caused declining fertility. However the black soil is one of the major commodity grain production bases in china, which soil fertility decline can cause serious impact on the soil productivity, food production and social and economic development of the region. To study the principle of the runoff and sediment of the black soil on slope, the paper adjusts the slope to compare characteristics of runoff and sediment on slopes of 1°, 3°, 5°, 7°and 9°under the condition of rainfall intensity for the 60mm/h.The tested soil recovered in sloped farmland of the black soil in Northeast China and the manual simulation rainfall experiment was carried out by manual simulation rain-dropping machine indoors. The characteristics of runoff contains the flow time, flow velocity,the infiltration rate, flow rate and cumulative runoff,and the characteristics of sediment contains the sediment amount, cumulative sediments and the rate of sediment in runoff. The results are as follows:(1)It showed that the trend of flow time is different under the different rainfall condition by keeping the rainfall intensity unchanged. It shorted the flow time when the slope gradient increasing under the under the dry rainfall condition, the change trend of the flow time were not pronounced under the wet rainfall condition.(2) The infiltration rate gradually decreased with the slope gradient increasing under the dry and wet rainfall condition, and it shorted with the increased of the duration of rainfall, and there is little change in the in average infiltration rate under the same slope under the entire dry and wet rainfall.(3)The flow velocity speeded up with the slope gradient increasing under the dry and wet rainfall condition, while the flow velocity also speeded up with the increased of the duration of rainfall by keeping the same slope, but the flow velocity in the dry rainfall condition increased faster than which in the wet rainfall condition. The relationship between the flow velocity and duration of rainfall can be expressed by the power function available on the slope of 3°,5°and 7°under the dry condition rainfall, while the relationship was linear when the slope is 9°; The flow velocity has exponent relation to duration of rainfall on the slope of 1°,7°,9°under the wet condition rainfall, and there is a typical power function relation between the flow velocity and duration of rainfall when the slope is 3°,5°.(4)The cumulative runoff increased with the slope gradient increasing by keeping the same duration of rainfall, and it also increased with e increased of the duration of rainfall under the same slope. The relationship between cumulative runoff and the duration of rainfall was linear under the dry condition rainfall, and it can be expressed by the power function available under the wet condition rainfall.(5)The sediment amount increased with the slope gradient increasing under the dry and wet rainfall condition. When the rainfall condition is dry, the sediment amount increased with the increased of the duration of rainfall on the slope of 3°and5°,it increased first and then remained constant almost when reach a certain value; When the rainfall condition is wet,it increased first and then remained constant almost when reach a certain value on the slope of 1°,3°,5°and7°,while it increased continuously on the slope is 9.(6) The cumulative sediments all increased with the slope gradient increasing under the dry and wet rainfall condition. It also increased with the increased of the duration of rainfall under the both dry and wet rainfall condition of the slope unchanged.(7) The rate of sediment in runoff gradually increased with the slope gradient increasing under the dry and wet rainfall condition, and the relationship between the rate of sediment in runoff and duration of rainfall is a quadratic function.(8) The sediment which is carried by the runoff of the slope of the black soil mainly is clay and silt which size is small. And characterizes of sediments has significant relationship to the mechanical components of sediment, but larger-grained sands has the most striking relationship to the erosion sediment. The quantities of gravel which size larger than two millimeters in sediment yields has the varying degrees of positive correlation to the sediment amount and the cumulative sediments and the rate of sediment in runoff; The quantities of silts which size between 0.05 millimeters and 0.002 millimeters degreed with the increased of the sediment amount and the cumulative sediments and the rate of sediment in runoff, and the quantities of clay which size smaller than 0.002 millimeters also decrease.(9)The relationship of the characteristics of slope runoff and sediment of the black soil is significant under the condition of manual simulated rainfall, especially flow velocity and accumulated sediment. Which has significant positive correlation on the slope of 1°, 3°, 5°, 7°and 9°, accumulated sediment is increased gradually with the increase of accumulated sediment.