| Soil erosion has become a kind of geological disaster is the most common human face. All the countries in the world have different degrees of soil erosion. With the increasingly serious harm, both developed and developing countries will be regarded as ecological environment problems of soil and water loss and soil erosion is also important, the United Nations included in the three major global environmental problems. China is the largest developing country in the world, is also one of the most serious countries around the world in soil erosion, soil erosion has become one of the most important environmental problems in china. In the hilly area of purple soil due to the fragile ecological environment, the reclamation rate is high, many characteristics of slope land, soil erosion is more serious. On purple soil erosion of rainfall and erosion characteristics of the research is the foundation to understand and grasp the law of soil erosion, but also for the comprehensive control of soil erosion in purple soil area and provide a theoretical basis and technical support. This paper is based on the observation data of runoff plots in Wanzhou District Liu Jia Gou watershed in Chongqing City, using the method of statistical analysis, studies the types of rainfall and soil runoff and sediment production of different land use in Chongqing hilly area of purple soil,. The results show that:(1) the distribution characteristics of2004-2012years of rainfall runoff plots in small watershed in Chongqing city Wanzhou District Liujiagou:annual average rainfall years distribution showed a single peak curve, the peak in June, January for the minimum value. Average annual rainfall days in Shuangfeng monthly distribution curve, May and peaked in October, August for the valley. The average annual rainfall days for120.33d, and in May-10month average rainfall days for67.33d; the maximum monthly average daily rainfall distribution curve in Shuangfeng. In each of the rainfall intensity, moderate rainfall of276.35mm, heavy rainfall is245.08mm; two in total, total rainfall throughout the year accounted for49%; heavy rain, heavy rainfall were172.34mm and64.76, mm, two were accounted for22%of total rainfall. Frequency of precipitation rain for91.56times, accounting for the total annual rainfall of76%rainfall times; rain for17.89times, accounting for the total annual rainfall times15%.(2) Chongqing city Wanzhou District Liujiagou slope runoff of small watershed2004-2012years of rainfall interannual distribution:the maximum annual rainfall of20121238.2mm, the minimum annual rainfall of2007768.4mm. The flood season rainfall to a maximum of997.4mm in2011, the minimum annual rainfall was594.8mm in2007. Variation of annual rainfall and flood season rainfall are respectively469.8mm,402.6mm. Annual rainfall and flood season rainfall was significantly correlated, the correlation coefficient was0.9870. Change trend of annual rainfall and flood season rainfall is consistent. Flood season rainfall accounted for annual rainfall days45.38%-69.71%, in addition to the rest of the year2006, the proportion of more than50%. Interannual distribution showing three peaks of curves of the maximum daily rainfall. The maximum annual rainfall distribution, the maximum value is142mm; the minimum value is49.5mm; the maximum rainfall maximum value and the minimum value difference is92.5mm, is1.87times the minimum value. An average annual rainfall of maximum rainfall intensity distribution have great volatility.(3) the CREAMS model of rainfall erosivity values were calculated,5-10monthly rainfall erosivity Rm were324.18,383.57,395.90,438.50,452.41,105.46MJ·mmVhm2· mmVhm2;2111.14MJ average annual rainfall erosivity2004-2012years; in the flood season of monthly rainfall erosion force of Rm value was unimodal curve, reached the maximum in September,452.41MJ mmVhm2;6,7,8,9and four months of rainfall erosion force accounted for the flood season of81.25%.2004-2012annual rainfall erosivity Ry value is consistent with the distribution of rainfall. The maximum value appeared in2011, the minimum value occurred in2007, the maximum is1067.70MJ·mmVhm.2and the minimum value. Erosive rainfall basically occurred in flood season, mainly occurred in6,7,8,9and four months,73%of the total number of accounts for the flood season. Rainfall erosivity2004-2012years of frequency has no rule changes, which occur most frequently in2011,27;2007times at least, for the14time. Monthly rainfall erosivity Rm and monthly rainfall Pm annual rainfall erosivity Ry and annual rainfall of Py regression analysis, the best algorithm of monthly rainfall erosivity values for Rm regression equation power function relation, the optimal algorithm of rainfall erosivity values for Ry regression equation with negative exponential relation.(4) through the DPS2.0software on the rainfall and runoff analysis with negative exponential function between monthly rainfall and runoff in flood season, with negative exponential function between total rainfall and runoff in flood season. Statistics according to the2006-2012years10°,15°,20°three different slope runoff plots observation data, three small total annual runoff distribution curve is basically the same. The district average monthly runoff mainly occurred in5-9months, including10°area accounted for85.93%of the year;15°area accounted for85.50%of the year;20°area accounted for86.16%of the year. The areas of vegetation coverage conditions are basically the same, the amount of soil erosion of the slope area has the same peak, appeared in2009. The amount of soil erosion in the monthly rainfall generated can be expressed with negative exponential relation, amount of soil erosion can be represented by a negative exponential relationship between total rainfall of flood season, the relationship between monthly rainfall erosivity Rm value and the amount of soil erosion can be used with hyperbolic equation, annual rainfall erosivity Ry value and the relationship between the amount of soil erosion the available negative exponential regression equation. The area of soil erosion mainly occurred mainly in5-10months, that occurred during the. The maximum value of each district appeared in September,10°smallest area, its value is317.02tVkm2·a,20°area maximum,470.34tVkm2, a,5-10month total soil erosion accounted for the proportion of:10°area accounted for94.04%,15°area accounted for93.86%, accounting for20°area93.61%of the year. Rain, rain, rain had significant correlation with soil erosion, and the relation between rain and soil erosion is not obvious, at the same time, all the slope runoff plots of soil erosion volume and correlation between moderate rain, heavy rain, heavy rain was first increased and then decreased, and the correlation coefficient was10°area were0.6028,0.8399,0.7337; the correlation coefficient of15°area were0.6054,0.8561,0.7204;-the correlation coefficient of20°area were0.6151,0.8696,0.7452. Slope gradient and soil erosion in the flood season (5-10months) and the relationship between more clearly than other months, through the correlation analysis, the correlation coefficient of flood season5-10month achieves above0.90, among them,5,6,7,8and four months of correlation coefficient reached more than0.95. |
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