沟床植被对冲沟沟头活跃程度的影响机理

Dry-hot Valley of Jinsha River is an ecologically fragile zone in southwest of China, and gully erosion is one of the most important environmental problems in this region. But comparing with slope erosion, gully erosion was lack of systematic studies. Vegetation sigificantly influences soil erosion process, and previous studies often focused on control effects of vegetation to slope erosion, however, little research were focused on the influences of vegetation to gully erosion, especially lack of quantitative research on gully bed vegetition which could impact gully development process by trapping sediment yield and changing microtopography of gully..This study will aim at gully head which is the main erosion part of the gully. The in-situ runoff scouring experiment will be carried out at gully head with different vegetation pattern at gully bed, which will be used to study the vegetation effects on runoff and sediment transport process, and then analyze the vegetation impaction to gully bed microtopography changing process. Finally, the influences of vegetation to gully development process will be studied. The results of the study will make a further understanding of the development process and the stabilization mechanism of gully, which could provide the theoretical basis for the gully management and ecological restoration of Dry-hot Valley.

干热河谷是我国西南地区特殊的脆弱生态类型区，冲沟侵蚀是其突出的生态环境问题之一，但迄今为止，相对于坡面侵蚀，国内外对于冲沟侵蚀的研究仍不够系统深入。植被对土壤侵蚀有着重要影响，以往的研究主要针对坡面侵蚀中植被对侵蚀的控制作用，而植被对冲沟发育的影响机理研究鲜有报道，尤其对于沟床植被导致泥沙淤积改变冲沟微地形后，对冲沟后续发育的影响机理缺乏量化研究。.本研究拟针对沟头这一冲沟侵蚀的活跃部位，通过人为配置沟床植被的野外放水冲刷试验，查明不同植被配置对沟床径流的消能拦沙效用，探明植被对沟床微地形的影响，进而揭示沟床微地形改变对沟头活跃程度的影响机理。研究结果将有助于进一步认识冲沟的发育过程和稳定机制，为冲沟治理与区域生态恢复提理论依据。

沟床植被通过影响集中流对沟床土体的冲刷侵蚀，进而显著影响沟头溯源侵蚀的过程。本研究的目标是通过查明沟床不同植被带长度影响下，集中流的水力学特性和侵蚀产沙过程，以及后续的沟头溯源侵蚀过程的影响。通过构建5个初始地形、土壤条件相似的原位沟头小区，在沟床按相同的植被密度布设5个不同的植被带长度梯度。每个小区开展11次放水冲刷试验（7组流量为5m3/h，4组流量为10m3/h）。水动力参数主要选择平均流速（V），雷诺数（Re)，弗罗德数（Fr），径流剪切力（τ），而径流阻力参数选择Darcy-Weisbach 阻力系数（f）和曼宁糙率系数（n）。研究发现，在沟床植被区域，其径流水动力参数仅为裸地区域的53%到77%，而阻力参数分则为裸地区域的1.1-1.2倍。总侵蚀量随着植被带长度的增加而呈指数递减关系（R2=0.94，P=0.006）。而平均径流泥沙含量与沟床植被带长度也存在相似关系（R2=0.90，P=0.015）。在裸地区域，所有选择的水力学参数与侵蚀总量均显著相关（0.43<R2<0.71, P<0.01），而在植被区域则没有显著相关。本实验中植被地上部分的分流作用及根系固土效应是最主要的作用方式。沟头侵蚀量与邻近沟头的沟床侵蚀量显著相关（R2=0.80，P<0.01)，侵蚀的差异与主要受沟床土体性质影响。