基于岩性分异和水土过程特点的喀斯特流域土壤侵蚀产沙模型研究

The carbonate and non-carbonate rocks distribute crossly in karst area of southwest China. The hydrogeological structure has two levels in carbonate area. The runoff and erosion processes are complex and significantly different with other types. But the application of soil erosion models lacks considering lithology differentiation and corresponding correction analysis. This project may study on RUSLE and RMMF model for a karst basin in northwest Guangxi. Based on the statistical analysis of the relationship between the terrain characteristics and soil erosion rates in karst runoff plots, the equation of RUSLE topographic factor for karst hillslopes will be established. By using the runoff equation for karst slopes replace the original one, we construct the karst RMMF runoff module. According to the 137Cs information record, the simulation accuracy of the two models and the corresponding karst correction modules are verified respectively on non-karst and karst small watersheds. Then the RUSLE, RMMF model, karst correction modules and sediment transport ratio distribution model will be integrated to simulate the soil erosion and sediment yield in the whole basin. By combining the monitoring of sediment transport at Hydrologic station, the simulation performance and the advantages and disadvantages of the two modified models in karst basin will be analyzed. On the basis of the above research, the change of soil conservation function in the basin for nearly 20 years will be evaluated. The study will improve the accuracy of soil erosion simulation and provide scientific support for the evaluation for the performance of rocky desertification treatments in karst area.

西南喀斯特地区碳酸盐岩与非碳酸盐岩交错分布，碳酸盐岩区域二元水文地质结构发育，水土过程复杂且与其他类型区差异显著，但现有侵蚀模型应用缺乏考虑岩性分异和相应修正。本项目拟以桂西北喀斯特流域为研究对象，基于RUSLE和RMMF模型，通过统计分析喀斯特坡面径流小区地形特征与产沙模数，建立喀斯特RUSLE地形因子方程；选取喀斯特地表产流公式替代RMMF原有方程，结合汇流方法选择，构建喀斯特RMMF径流模块；分别在喀斯特和非喀斯特小流域应用修正后或原模型，利用137Cs信息校验中分辨率数据下两模型精度；基于岩性分异，集成RUSLE和RMMF、喀斯特修正模块及泥沙输移比分布模型，模拟全流域的土壤侵蚀产沙特征；结合流域水文站输沙监测，验证并综合评价修正后两模型在喀斯特流域的模拟性能；在此基础上评估流域近20年土壤保持功能变化。研究结果可提高喀斯特流域侵蚀产沙模拟的精度，为石漠化治理效应评估提供科学支撑。

喀斯特坡面近地面溶蚀空间形态的发育导致坡面地表径流不能沿坡连续汇流，坡面地表径流系数和土壤侵蚀模数较小。RUSLE模型原坡长因子公式建立在坡面任意坡长范围内平均地表径流强度恒定，径流和侵蚀沿坡连续累积的假设条件下，直接应用与喀斯特地区会导致严重高估。本研究依据较分散的多流向汇流（MD），并结合地表径流输移比例（Tr，由面岩溶率决定）的算法进行汇流，建立了喀斯特坡面地表径流强度与坡长的关系式，据此改进了RUSLE喀斯特坡面坡长因子公式。改进后的坡长因子公式能有效反映喀斯特坡面地表间断汇流而平均地表径流系数微小的特征，且不受地形数据分辨率限制。RMMF模型地表径流模块，通过添加对应栅格大小导致的坡长效应带来的经验调整比例进行修正，修正后模拟径流结果显示，地形数据分辨率增加会导致计算的区域平均有效径流量降低。RUSLE修正模型可成功地在径流小区、峰丛洼地小流域及龙江流域等各空间尺度应用。龙江流域2005和2015年RUSLE修正模型土壤侵蚀速率模拟结果显示，流域内土壤侵蚀速率喀斯特区域平均值为3.2和6.3 t km-2 y-1，非喀斯特区域平均为389.5和698.2 t km-2 y-1。本研究为喀斯特和非喀斯特混合区域RUSLE土壤侵蚀模拟提供了成功地修正方法和应用参考。