红壤丘陵区小流域路网的水沙效应作用机理与模拟

Road networks have been reported can alter hydrological process and enhance soil loss risk. Meanwhile, unpaved road also should be treated as a sediment source in a watershed. Thus, several questions are raised: How many manners of roads in affecting the watershed hydrology? What factors would determine the runoff and sediment process in road influenced areas? How about the contribution of sediment from road and adjacent lands to the total watershed sediment yields? This study is aimed at the effect of road networks on small watershed hydrology and sediment generation in hilly red soil region of China. Firstly, the spatial interaction between road networks and hydro-geomorphic factors would be studied based on the RS and GIS methods. In turn road network in a typical small watershed would be divided into different hydrological units, which can reflect the unique characteristics of road related hydrology. After that, field GPS survey, runoff and sediment monitoring and field hydraulic experiments would be conducted within the typical road related units. Therefore the runoff and sediment generation processes on different part of road can be quantified, and the influence of road in both upstream and downstream hydrological process can be clarified. According to the above results and using the GIS hydrological analysis method, a road erosion model would be developed to simulate the effect of road network on watershed hydrology. By using the paired catchments method, the erosion model would be validated and the contribution of road related soil loss in watershed sediment generation can be estimated. This study can enhance the accuracy of watershed erosion evaluation and provide assistance to local soil and water conservation in red soil region of South China.

道路网系影响自然地表的汇水过程，从而加剧水土流失风险，同时土质道路本身也是一种侵蚀泥沙策源地。那么，在一个流域内，路网对自然水文过程有哪些影响方式？道路影响范围内的水沙过程受哪些因素控制？发生在道路及其相邻地块上的水土流失对流域产沙贡献有多大？针对以上问题，本研究以我国南方红壤丘陵区小流域路网的水沙效应为研究对象，首先通过遥感和GIS方法厘清路网在空间上与流域水文地貌要素之间的关系，划分能体现道路不同影响方式的路域水文单元。然后在典型路域单元内开展实地调查、径流泥沙监测和水动力学模拟试验，探明道路不同部位的产流产沙机理以及道路对上下游水文泥沙过程的影响机制，在此基础上构建道路侵蚀估算模型。对比典型路域水文单元内和无道路分布的对照集水区径流泥沙过程，验证模型结果并评价路网对流域的侵蚀泥沙贡献。以上研究可以提高南方红壤区小流域水土流失估算精度，从而为区域水土保持工作提供依据。

道路网络是流域内广泛分布的线状地物要素，路网改变自然地表水流路径和泥沙搬运过程，同时土质道路也是不可忽视的泥沙策源地，在流域尺度上阐明道路的水文影响及泥沙贡献可提高小流域水土流失估算精度。由于目前国内学者对土质道路侵蚀机理研究不够充分，再加上路网水文影响评价模型仍不完善，制约了人们对小流域流域道路水沙效应的认识。针对上述问题，本项目以南方红壤丘陵区小流域路网为研究对象，通过遥感解译、GIS空间分析、水动力学模拟试验、野外调查和测量、模型模拟等方法，在流域尺度上揭示道路的水沙效应作用机理，评估道路对流域侵蚀产沙的贡献。得到如下主要结果：（1）研究区路网与水系之间存在密切的空间交互关系，典型小流域内土质道路路面平均侵蚀模数达到极强烈标准，侵蚀量与路段长度、坡度以及上方汇水面积密切相关，当路段坡度超过10%时侵蚀量将剧增。（2）3D激光扫描道路剖面形态可知，路段沿程侵蚀峰值大多位于下部接近2/3坡长处的凸形坡向凹形坡过渡部位，从道路延伸方向上来看长直路段下方或急转弯处存在较高侵蚀风险。自动提取的道路坡度随DEM栅格尺寸增大而增大，体现了道路线状地形指标的特殊性。（3）模拟冲刷试验结果表明水流剪切力是估算道路土壤分离能力的最佳指标，由此计算了道路细沟侵蚀临界剪切力和细沟可蚀性等因子，进而采用坡面版WEPP在33个路段上得到可靠的侵蚀估算结果。（4）GIS水文分析结果显示了道路拦截效应导致自然水流路径的增减变化，整体上使典型小流域不同级别水系密度增加12.09%~20.45%，流域尺度的WEPP模拟表明道路使沟道侵蚀量增加86.68%，是加剧流域侵蚀风险的主要形式。通过以上研究揭示了红壤土质道路的侵蚀产沙机理，明确了道路对小流域水系和水沙过程的影响方式和程度，研究结果可以为红壤丘陵区小流域水土流失评价以及相关治理措施的优化布设提供依据。