基于SCS-CN与MUSLE模型的三峡库区小流域侵蚀产沙模拟

传统土壤侵蚀模型模拟次降雨产沙时难以确定泥沙输移系数,分布式的侵蚀产沙模型对数据量需求量大。选择三峡库区宋家沟小流域为研究对象,基于2013年的降雨、植被盖度、地形、土壤等数据,利用SCS-CN和MUSLE模型耦合模拟流域的场降雨的产沙量。结果表明:该模型的模拟值的精确度在可接受范围内,整个流域2013年的泥沙流失量是3 923t,全年中5场较大的降雨贡献了泥沙流失量的80%以上;不同土地利用类型的泥沙输出量差异很大,耕地(面积44.63%)贡献了81.54%的泥沙,有林地(面积47.61%)贡献了17.63%的泥沙;坡度在0~8度的区域贡献的产沙量仅为1.75%,大于25度的区域占流域面积的比例是39.21%,产沙量占55.77%;泥沙模拟值相比实测值偏大,其原因可能是流域中分布的池塘改变了径流过程,发挥拦截泥沙功能。

MODELLING SOIL EROSION AND SEDIMENT YIELD IN A SMALL WATERSHED OF THREE GORGES RESERVOIR AREA BASED ON SCS-CN AND MUSLE MODEL

Soil erosion affected by a variety of natural factors and human activities has been a major concern to the public for decades. It is difficult for modelling soil loss using former soil erosion model to determine sediment transport coefficient, while soil erosion distributed models need a large number of input data. Among soil erosion models, the universal soil loss equation (USLE) is the most widely used and misused soil loss estimation equation in the world. The USLE was originally applied to the prediction of soil losses from agriculture in the USA, in order to preserve soil resources, but has been extended for use in numerous countries. USLE is an empirical equation that predicts annual average, long-term soil erosion, but does not simulate dynamic and continuous changes. The MUSLE model estimates sediment yield on a single storm basis and the output is interpreted as sediment yield coming at the outlet of the catchment. This is computed based on a combination of runoff and catchment characteristics. In addition, the integration of GIS has evolved from the advances in geospatial techniques and the increasing availability of spatial databases. The SCS-CN model and the MUSLE model were used to model soil yield for every rainfall. A small watershed, Songjiagou watershed in Three Gorges Area (TGA), was chosen to validate the SCS-CN and the MUSLE model applicability based on rainfall, vegetation coverage, soil, and DEM data. The accuracy of the simulation values of the model is in an acceptable range. Soil loss in the watershed in 2013 was 3 923 t, 80% of which was from the 5 largest rainfall events. Sediment yield from different land uses varies considerably. 81.54% of sediment loss was from cultivated land, which accounted for 44.63%. However, forestland with an area of 47.61% of the whole watershed, only contributed to 17.63% of the sediment loss. Grade differences in slope had a great influence on sediment yield. Only 1.75% of sediment was from area with slope in the 0-8 degrees, while the area with slope more than 25 degrees contributing to 55.77% sediment. The reason of larger sediment simulation value compared with the measured values may be pond interception effect. The role of pond in changing hydrologic effect and migration of sediment need follow-up study.