| Soil erosion is one of the important problems of the ecological environment in the Three Gorges Reservoir area. The soil erosion area is28042.10km2in the Three Gorges Reservoir area, which accounting for48.8percent of the entire area of the Three Gorges Reservoir Area; the moderate and strong soil erosion area occupied64.5percent of the total area, the annual average soil erosion amount up to1.67×109t. There are many studies on the law of soil erosion in Three Gorges Reservoir area, but few that using GIS and RUSLE model. Using the ENVI software to deal with the ETM+remote sensing images in2011of Wanzhou District and make the administrative regionalization map of Wanzhou area as the base to cut out the remote sensing image of the Youfanggou basin. Based on the RUSLE model, according to the national standards of classification of soil erosion and the second soil survey data and terrain data, using the GIS spatial analysis software to obtain various data needed by the model, and obtain the1:10000soil erosion database of spatial and attribute of the Youfanggou basin. Combined with a1:10000land use data of the Youfanggou basin, normalization of the data in ArcGIS (unified standard map parameters, data, etc.), overlay analysis of the data layer to get the whole small basin soil erosion status and the main factors influenced the soil erosion. Undertaking a study on the evolution of the runoff and sediment transport mechanism and characteristics combined with the basin bayonet data. The main conclusions are as follows:(1) According to the rainfall data during2006-2012, the average annual rainfall is1183.3mm, peak value appeared in2009as1303.7mm, valley occurred in2010as1042.4mm and amplitude261.3mm in Youfanggou basin. The distribution of rainfall has two peaks in a whole year, the maximum rainfall mainly concentrated in June and September. The annual maximum rainfall erosivity is2735.04MJ·mm·hm-2·H-1·A-1and the minimum is2002.53MJ-mm-hm-2·H-1·a-1in the Youfanggou basin. The correlation coefficient of the annual rainfall erosivity and annual rainfall is0.602, significantly correlated. The rainfall erosivity law is similar to monthly mean rainfall, as has two peaks. The first peak426.08MJ·mm·m-2·min-1is In June and the second peak480.90MJ·mm·m-2·min-1is in September. On the whole, the rainfall erosivity is uneven distribution in one year, mainly distributed in May to September.(2) There is a marked difference in erodibility K values of different land use in the basin. Pinus massoniana woodland K value is0.025, K value is0.042in cypress forest land. There is no difference in artificial forestland erodibility K value. On the slope land in different planting patterns, soil erodibility K values are sweet (0.037)> vegetable plot (0.034)>corn (0.029)> corn+sweet potato (0.027). The erodibility as follows:artificial land> grassland> slope farmland> Natural forest. The Youfanggou basin soil erodibility K value ranges from0.025to0.042. The vegetation coverage data that from field measurements and that from using the formula in the interpretation of remote sensing used to have a comparative analysis, the correlation coefficient reached0.9681, as the results are reliable.(3) The unobvious soil erosion area is24.28hm2in Youfangggou basin that accounting for14.76percent of total river basin area; soil erosion area is139.69hm2, accounting for85.24percent of total river basin area. In the area of soil erosion, mild erosion area is35.20hm2(25.20percent of the total erosion area); moderate erosion area is85.43hm2(61.16percent of total erosion area); severe soil erosion area is15.35hm2(10.99percent of total erosion area); very strong erosion area is3.71hm2(2.66percent of total erosion area). the average soil erosion modulus is3524.57t/km2·a in the basin, the soil erosion modulus of the Youfangggou watershed in2011is2107.49t/km2·a according to the data reported by the wanzhou district monitoring center, there are some differences between the two results.(4) There is a significant difference between the average soil erosion modulus in different land use types. The six types of average soil erosion modulus size in the order as grassland utilization of land (8955t/km-2·a)> Garden (4483t/km2·a)> slope farmland (4255t/km2·a)> woodland (2332t/km2·a)> residential land (850t/km2·a)> paddy field (358t/km2·a). The slope grade that is bigger than25degrees, the modulus is above8000t/km2·a, so the farmland that slope above25°should return the grain plots to forestry as soon as possible.(5) With the slope degree increasing, the farmland soil erosion modulus also increases. On the slope of0°to10°the average soil erosion modulus is2177t/km2·a, on the slope of10°to15°average soil erosion modulus is3990t/km2·a, on the slope of15°to20°the average soil erosion modulus is4890t/km2·a, on the slope of20°to25°the average soil erosion modulus is7540t/km2·a, on the slope of25°to30°the average soil erosion modulus is9879t/km2·a. The slope of the Garden planting is15°to30°, soil erosion modulus increases with the slope and the correlation coefficient reached0.9898, obvious correlation. By plotting the slope and erosion, the regression analysis to get a two relationship between slope and erosion is:A=-3.571θ2+176.430-758.99(R2 0.9999). The basin soil erosion threshold gradient should be in24.7degrees, the results of this calculation and loess area has a certain gap.(6) The difference between the average monthly runoff in the basin is larger, the maximum value was173100m3, minimum was1300m3. The monthly rainfall and Runoff Curve fitting equation, the coefficient of determination R2=0.7144, normal result. According to the average monthly rainfall and average monthly runoff scatter diagram, fitted and optimized regressive equation and equation is:y=8E-05x2+0.0316x+0.4517(R2=0.9707), better fitting effect, it is better to use the years average data to reflect the true basin production flow. According to the monthly rainfall and monthly sediment yield curve fitting equation, fitted and optimized regressive equation, the coefficient of determination R2=0.8114, normal results. The average monthly rainfall and monthly average sediment fitted and optimized equation, formula is:y=0.0002x2+0.063x+0.7418(R2=0.9743), a good fitting effect.(7) The largest annual runoff is778300m3, the minimum annual runoff is361600m3, the average annual runoff is534000m3in the basin. The annual runoff has the same law with the annual runoff variation coefficient, the maximum value is36.40%, the minimum value is21.15%. The annual runoff and annual rainfall correlation analysis, the correlation coefficient is0.884, obvious correlation. The annual sediment yield reached the maximum is124.98t, minimum is only81.47t. The bedload maximum is44.89t, minimum is19.78t. Variation of load and suspended sediment transport are basically the same, the maximum is80.09t, minimum59.03t. Governing equations are fitted with annual rainfall and annual sediment yield, formula is:y=4E-05x2.0858(R2=0.8356), normal results. |
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