干热河谷土地整理台地-边坡系统的沟蚀发育动力过程及形态演变机制研究

Dry-hot Valley Region of Jinsha River is now recognized as one of the most severe sediment production regions in the Upper Reach of Yangtze River, which is due to the fact that gullies are well developed in this region. In recent years, a series of land consolidation projects were conducted to control gully erosion, as a consequence, a large amount of terrace-slope systems come into being in Jinsha Dry-hot Valley Region. However, gullies can developed again very well in the terrace-slope systems in only 2~3 rainy seasons, whose soil erosion modulus can up to 8000 t/(km2 a), that is to say, the costly land consolidation projects are failed to restrain the gully erosion in this studied area. The most important underlying cause of this is lack of clear recognition to the dynamic process and morphological evolution mechanism of gully erosion in terrace-slope systems. Therefore, this study will seek to explore the major influencing factors and the dominant dynamic conditions of gully erosion, as well as the change process of gully morphology characteristics in order to reveal the dynamic process and morphological evolution mechanism of gully erosion in terrace-slope systems by means of field investigation, in-situ control trials (artificial rain and runoff scouring experiments), laboratory tests, and comprehensive analysis. The results of the study will be helpful to provide the theoretical basis for revealing the laws of gully initiation and development in terrace-slope systems.

干热河谷是长江上游水土流失最为强烈的地区之一，沟道侵蚀是其中一个主要原因。近年来，为有效控制沟道侵蚀，该区通过土地整理工程形成了一系列“台地-边坡系统”，但台地-边坡系统在2~3个雨季之内就再次发育沟道侵蚀，且其土壤侵蚀模数可达8000t/(km2a)以上，导致该区的沟道侵蚀问题未能从根本上得到遏制，究其原因是对台地-边坡系统沟蚀发育的动力过程和演变机制认识不清。因此，本项目拟以金沙江干热河谷为重点研究区，以台地-边坡系统沟蚀发育动力过程及其形态演变机制为研究主线，采用野外调查、原位控制试验、室内试验等综合研究手段，系统地研究台地-边坡系统沟蚀发育的关键影响因素及其主导动力条件，探索其侵蚀形态演变过程，揭示台地-边坡系统的沟蚀发育动力过程及形态演变机制。研究结果为进一步揭示土地整理台地-边坡系统沟道侵蚀的发生发展规律奠定基础。

干热河谷是我国西南典型的生态环境脆弱区，因土地整理而导致的沟道侵蚀已成为该区流域产沙的重要来源，本研究以干热河谷典型土地整理台地-边坡系统为研究对象，重点分析了土地整理台地-边坡系统沟蚀发育的关键影响因素，揭示了土地整理台地-边坡系统沟蚀发育的动力过程及产输沙机制，并阐明了其沟蚀发育形态演变机制。本研究的主要结论如下：（1）台地边坡系统沟蚀发育强度受边坡成因、土壤类型、植被状况、汇水状况及土壤理化性质共同影响，但随沟蚀发育强度的变化，影响其形态特征的主要因素及方式存在一定差异。（2）土壤类型、植被状况和边坡成因是影响台地边坡系统水动力过程特征及产输沙特征的重要因素，但上述因素的影响方式和影响程度因相关参数的变化有较大差异。边坡成因是影响径流水动力过程特征和产输沙特征的首要因素，土壤类型和植被状况的影响程度的对比关系与水动力特征参数和产输沙特征参数有关。（3）边坡成因是决定台地边坡系统侵蚀方式及其演变过程的关键因素。自然边坡不发生沟蚀，而土地整理台地边坡系统不同程度的发育细沟侵蚀或切沟侵蚀。土壤类型影响台地边坡系统侵蚀方式演变过程、侵蚀阶段的持续时间及各侵蚀阶段内的主要扩展方式，决定台地边坡系统沟蚀发育过程的快慢及其最终发育阶段。植被残茬可延长台地边坡系统在低侵蚀强度阶段的持续时间，但并不能从根本上改变台地边坡系统的沟蚀发育过程。（4）台地边坡系统发生细沟侵蚀的临界动力条件为径流剪切力、径流功率分别介于2.669~4.701 Pa、0.444~0.823 N/(ms)之间，发生切沟侵蚀的临界动力条件为二者分别介于4.701~6.252 Pa、0.823~0.907 N/(ms)之间。以上研究成果确定了台地边坡系统沟蚀发育的关键影响因素、揭示了其沟蚀发育的动力过程及形态演变机制，为进一步明晰山区水土耦合作用机制，有的放矢地采取相应措施防治土地整理台地边坡系统发生沟蚀提供了有价值的指导。