Impacts Of Soil Type And Slope Gradient On Sloping Sheet Eroison And Rill Erosion In Loess Region

Effects of soil type and slope gradient on sloping sheet erosion and rill erosion can provide theoretical support for controlling soil erosion to local conditions and establishing erosion model. Based on simulated rainfall experiments and the three-dimensional laser scanning technology, effects of soil type and slope gradient on sloping sheet erosion and rill erosion were studied in loess region and rill erosion mechanism was also analyzed. The main results were as follows:(1) Effects of soil type on sloping sheet erosion were investigated. Under the same soil bulk density and precipitation, the runoff from Heilu soil treatment was 1-1.2 and 1.2-1.6 times that from Lou soil and loessial soil treatments at 90 mm/h and was 1-1.3 and 1.3-1.5 times that from Lou soil and loessial soil treatment at 120 mm/h, respectively. The sheet erosion rate from the Heilu soil was 2.1-2.2 and 4.6-5.5 times that from the Lou soil and loessial soil treatments at 90 mm/h and was 1.2-1.8 and 3.8-4.5 times that from the Lou soil and loessial soil treatments at 120 mm/h, respectively. At the the same soil bulk density and rainfall duration, the runoff from the Heilu soil treatment was 1-1.2 and 1.3-1.4 times that from the Lou soil and loessial soil treatments at 90 mm/h, respectively. The sheet erosion rate from the Heilu soil treatment was 2.1-2.2 and 5.1-6.7 times that from the Lou soil and loessial soil treatments at 90 mm/h, respectively.(2) Effects of slope gradient on sloping sheet erosion were investigated under different soil types. At the same soil bulk density and precipitation, the sheet erosion rate increased 1.8%-129.2% whenslope gradient increased from 10° to 25°; the increment of sheet erosion rate followed the order as: Heilu soil >Lou soil > loessial soil at 90 mm/h, and loessial soil > Heilu soil >Lou soil at 120 mm/h. At the the same soil bulk density and rainfall duration, the sheet erosion rate increased 1.0%-129.2% with increase of slope gradient from from 10° to 25°; the increments of sheet erosion rate followed the order as: Lou soil > Heilu soil > loessial soil at 90 mm/h, and loessial soil > Heilu soil > Lou soil at 120 mm/h.(3) Effects of soil type and slope gradient on stable-stage sheet erosion rate were discussed. At the same soil bulk density, when slope gradient increased from 10° to 25°, the stable-stage sheet erosion rate of Lou soil, Heilu soil and loessial soil increased 12.0%-102.4%, 10.2%-76.6% and 30.6%-117.7% at 90 mm/h, respectively, and increased 12.5%-113.5%, 60.2%-135.2% and 11.3%-30.7% at 120 mm/h, respectively. The relative contribution of rainfall intensity on stable-stage sheet erosion rate was above 60%, which was much higher than that of slope gradient. The relative contribution of slope gradient on stable-stage sheet erosion rate increased with the increase of slope gradient. The equation of stable-stage sheet erosion rate with soil type, slope gradient and rainfall intensity was established and the coefficient of determination and Nash-Sutcliffe simulation efficiency of the equation were 0.96 and 0.92, respectively.(4) Effects of soil type and slope gradient on sloping interrill and rill erosion were investigated. Waterfall occurrence time of Heilu soil was later 1.5-17.7 min than that of sandy loess and runoff of Heilu soil was 1.5-3.5 times that of sandy loess. However, the total soil loss of sandy loess soil was 1.3-1.7 times that of Heilu soil. The total soil loss firstly increased, and then decreased with increase of slope gradient. The critical slope gradient of Heilu soil and sandy loess soil were 23° and 21°, respectively. The rill erosion contribution rate increased with the increase of slope gradient. The rill erosion contribution rate of Heilu soil increased 48.84%-73.78% when slope gradient increased from 15° to 25°; the rill erosion contribution rate of sandy loess soil increased 7.71%-76.78% as slope gradient increased from 10° to 25°. The rill erosion contribution rate of sandy loess soil was higher than that of Heilu soil.(5) The mechanism of sloping erosion was analyzed. Unit stream power was the best hydrodynamic parameter closely to correlate with the average sediment delivery and relationships beween them were liner function. The grey relativities of the average sediment delivery of Heilu soil and sandy loess soil with average unit stream power were 0.7969 and 0.5823, respectively.