基于SWAT模型的延河流域径流侵蚀能量空间分布

Spatial distribution of runoff erosion power based on SWAT Model in Yanhe River Basin

降雨侵蚀力是通用土壤流失方程(universal soil loss equation,USLE)等流域土壤侵蚀模型中应用最广泛的侵蚀动力因子,但仍具有一定的局限性,相比之下,径流侵蚀功率可以更充分地反映地表水力侵蚀动力的综合作用。分析径流侵蚀功率的空间分布,以期从能量的角度阐明流域侵蚀的分布情况,研究流域空间侵蚀的特征。该研究运用SWAT模型在延河流域的模拟结果,将次暴雨径流侵蚀功率推广到年尺度,提出年径流侵蚀功率的概念,并研究年径流侵蚀功率的空间分布规律及尺度效应。研究结果表明:在延河流域年径流侵蚀功率的空间分布具有"支流大、干流小;上游大、下游小"的特点;将子流域出口断面控制面积作为空间尺度因子,与径流侵蚀功率拟合,呈幂函数关系,空间尺度效应阈值在155 km2;将子流域出口断面以上河长作为空间尺度因子,与径流侵蚀功率拟合,呈指数函数关系,且干、支流的空间尺度效应不同。研究结果从能量角度阐明了延河流域水力侵蚀动力的空间分布,为在延河流域不同地区进行针对性的水土资源管理、水土保持工程建设提供理论支持。

The Loess Plateau is the region with the most concentrated and largest loess area in the world. It is also one of the regions suffering the most severe water and soil erosion and with the most fragile eco-environment. Loess Plateau features complex and diverse landform with ravines and gullies criss-cross. It is a key region for implementing water and soil conservation and ecological restoration in China. With this regard, researches on spatial distribution of soil erosion are quite necessary. In the common basin soil erosion models used at home and abroad, the most widely applied erosion factor is the rainfall erosivity, which reflects the comprehensive effect of raindrop splash on soil erosion, but does not reflect the effects of runoff erosion and sediment transport during water erosion process, while runoff erosion power may better reflect the comprehensive effect of water erosion force from the perspective of the energy. This research introduces the concept of runoff erosion power of storm. It extends the runoff erosion power of a single storm to a year scale based on the simulation results with SWAT （soil and water assessment tool） model in Yanhe River Basin, and obtains the annual runoff erosion power of each sub-stream. Then, researches on spatial distribution and spatial scale are performed, so as to reveal the impact of different spatial distributions and spatial scales on the water erosion process. The results show that in the SWAT model, Yanhe Basin is divided into 81 sub-streams, and the simulation effects are good, which proves that the SWAT model is feasible in this region, and can reflect the actual water regime of this basin. Runoff erosion power of Yanhe Basin has regular spatial distribution, i.e. ＂large in tributary, small in main stream; large at upstream, small at downstream; large in the south and small in the north＂. Besides, runoff erosion power of possesses present obvious spatial scale effect. The runoff erosion power is in power function relation with the control area of sub-stream outlet section, and the threshold of spatial scale effect is at about 155 km2, and is in exponential relation with the river length above the sub-stream outlet section. The spatial scale effect thresholds of runoff erosion power of the Xingzi River, the Xichuan River and the Yanhe River are 53, 90 and 17 km, respectively. The spatial scale effect is different due to the different spatial position. In addition, the spatial scale factor, river network density and other factors will also affect the runoff erosion power. The spatial scale has a significant effect on most areas of the Yanhe River, and the main stream is mainly affected. The density of the river network has a great influence on the runoff erosion power in the tributary distribution area, but has no effect on the mainstream area. This research has clarified spatial distribution and scale effect of the water erosion power in Yanhe Basin, which provides the theoretical support for implementation of specific land and water resources management, water and soil conservation projects and ecological restoration measures in the regions along Yanhe Basin.