黄土丘陵沟壑区坡沟系统侵蚀产沙过程与机理研究

Slope-gully systems are the major sediment source of the hilly-gully loess region. Few studies have investigated the processes and mechanisms of soil erosion on natural slope-gully systems. This inevitably limits the understanding on the spatiotemporal pattern of soil erosion on the slope-gully system and effects of up-slope runoff on gully-slope soil erosion processes, and constrains the development of soil erosion models for the slope-gully system. The project will study soil erosion processes of the natural slope-gully system in the hilly-gully loess region and their underlying mechanisms based on field observations, runoff scouring experiments, 3d laser scanner, numerical modelling, and available historical observation records. We will investigate the dynamic changes of soil erosion occurring on different geomorphic units of the slope-gully system, and analyze the spatiotemporal pattern of soil erosion on the slope-gully system and their quantitative relationships with the main influencing factors such as precipitation, runoff flow and slope gradients. We will study the increase in soil erosion rates and changes in hydrodynamic parameters of gully slopes driven by the up-slope runoff, and their quantitative relationships with the major influencing factors including up-slope runoff flow, sediment concentration of up-slope runoff, and morphological parameters of gully-slope soil erosion. Based on the results of our field experiments and available historical observation records, we will develop a soil erosion model for the slope-gully system of the hilly-gully loess region, through modifying an internationally well-known soil erosion model, Pan-European Soil Erosion Risk Assessment (PESERA). We will modify the soil erosion module of the PESERA model and enable the model to separately simulate soil erosion processes on gentle slopes and gully slopes (i.e. steep slopes), and to take account of the impact of up-slope runoff on soil erosion processes of gully slopes.

坡沟系统是黄土丘陵沟壑区的主要产沙源地，已有工作较少研究野外真实坡沟系统的侵蚀产沙过程与机理，对坡沟系统侵蚀产沙特征和上方来水来沙影响机制的认识不足，限制了坡沟系统土壤侵蚀模型的研发。本项目以黄土丘陵沟壑区野外自然坡沟系统土壤侵蚀为研究对象，采用定位观测、放水冲刷试验，三维激光扫描及数值模拟等方法，结合已有资料，研究坡沟系统侵蚀产沙的动态演化过程，分析坡沟系统侵蚀产沙的时空变化特征及其与降水、汇水流量、坡度等的定量关系，阐明坡沟系统侵蚀产沙过程的发生发展规律；研究梁峁坡来水来沙导致沟谷坡的产沙增量和水动力学参数变化及它们与来水量、来水含沙量、沟谷坡侵蚀发育形态参数等的定量关系，揭示梁峁坡来水来沙对沟谷坡侵蚀产沙过程的影响及其动力学机制；改进国际知名土壤侵蚀过程模型PESERA，构建考虑“梁峁坡-沟谷坡”分异及来水来沙影响的侵蚀模块，实现对黄土丘陵沟壑区坡沟系统侵蚀产沙过程和机理的模型表达。

黄土丘陵沟壑区是全世界土壤侵蚀最严重的区域之一，而坡沟系统是黄土丘陵沟壑区的主要产沙源地。受限于监测手段，已有工作较少开展野外真实坡沟系统的侵蚀产沙时空变化研究，限制了对坡沟系统土壤侵蚀过程和机理的理解，制约了土壤侵蚀模型的研发。鉴于此，本项目以黄土丘陵沟壑区自然坡沟系统为研究对象，采用放水冲刷试验、三维激光扫描和数值模拟等方法，结合野外定位观测历史资料，开展了基于三维激光扫描的土壤侵蚀监测精度评估和算法研发、坡沟系统侵蚀产沙过程和机理研究及侵蚀产沙过程模型模拟与PESERA模型改进等工作。在土壤侵蚀监测研究方面，评价了地基三维激光扫描在粱峁坡和沟谷坡侵蚀产沙监测中的精度；开发了基于地形点云的沟道侵蚀体积三维计算方法，克服了传统二维算法应用于极端复杂地形中存在的误差；对比了无人机激光雷达点云滤波和插值算法，为后续使用无人机激光雷达监测大范围土壤侵蚀提供了参考。在侵蚀产沙过程与机理研究方面，基于野外试验和三维激光扫描等手段，探讨了粱峁坡侵蚀发育过程与细沟发育对粱峁坡侵蚀产沙过程的影响；研究了沟道侵蚀水平和垂直发展过程及重力侵蚀对沟道侵蚀产沙的贡献；基于Darcy-Weisbach阻力系数、径流剪切力等，分析了坡沟系统沟谷坡侵蚀产沙的水动力学机制。在模型模拟方面，验证了修订的通用土壤流失模型RUSLE在黄土高原土壤侵蚀模拟的精度，并利用其构建了20世纪以来黄土高原历史侵蚀速率；对比了RUSLE和PESERA在黄土丘陵沟壑区的适用性，明确了PESERA模型改进策略；基于过程和机理研究结果及历史观测资料，修改了PESERA模型的侵蚀产沙模块，提升了其模拟黄土丘陵沟壑区土壤侵蚀过程的能力和精度。研究结果可为黄土高原土壤侵蚀监测、过程机理研究和模型模拟提供参考。