水保措施群对黄土高原沟壑区水文过程影响的强化观测、三维可视化模拟及机理分析

The measures of water conservation, such as returning farmland to forest and grassland, plastic mulching, check dam, pond, slope-to-terrace, cistern and gully head protection is affecting the hydrological processes of the Loess Plateau gully region. A correct understanding of the overall effect of all kinds of measures group of water conservation on hydrological processes in the watershed scale is very important for calculating the runoff, base flow, storage capacity of soil reservoir and sediment. This project is based on the Nanxiaohegou experiment basin which belongs to the Yellow River Conservancy Commission, the following research will be carried out: 1 ) increasing the intensive observation of hydrological processes which affected by all kinds of the measures group of water conservation in the Nanxiaohegou river basin, analyzing the mechanism and accessing to relevant physical parameters; 2 ) building 3D visual simulation model to simulate the effect of the measures group of water conservation on the Nanxiaohegou watershed hydrologic process; 3 ) studying the hydrologic process mechanism of three kinds of vegetation coverage ( tableland: economic forest, crops, slope: ecological forest ), two kinds of the measures of water conservation ( plastic mulching, slope-to-terrace ); 4 ) studying the temporal and spatial heterogeneous of soil reservoir, soil loss and supply water characteristics, the relationship between soil reservoir storage and runoff, evaporation; spatial variation of soil dry layer.

水保措施，如退耕还林还草、地膜覆盖、淤地坝、涝池、坡改梯、水窖和沟头防护等正在影响着黄土高原沟壑区水文过程。应正确认识流域内水保措施群对流域水文过程的整体影响，其对准确计算流域径流、基流、土壤水库蓄量、产沙等有重要的意义。本项目以黄委会南小河沟实验流域为基础，从流域系统角度出发，主要进行以下几个方面的研究：1)增加南小河沟流域水文过程的强化观测项目，进行水保措施群影响下水文过程机理分析，获取相关的物理参数；2)构建南小河沟流域水保措施群影响下水文过程的3D可视化模拟模型；3)研究三种植被覆盖(塬面经济林、农作物、坡面生态林)，两种措施(地膜覆盖、坡改梯)下水文过程机理；4)研究水保措施群影响下土壤水库蓄量空间、时间的差异性，补水失水特征；土壤水库蓄量与产流、蒸发的关系；土壤干层的发育机理及空间变化。

为了解决黄土高原地区的水土流失等生态环境问题，当地实施了如退耕还林等一系列的水土保持措施，使得土地利用发生了深刻的变化，进而影响水文过程。.以位于黄土高原沟壑区的南小河沟流域作为研究对象，基于实测资料，分析研究区近50年的土地利用变化趋势，通过相似流域的产流对比，分析不同类型土地利用产流的差异性；选择流域内以及邻近流域内的标准径流小区，基于实测资料，分析植被变化对径流小区产流产沙的影响，坡度变化对产流产沙的影响，以及土壤含水率的影响因素；构建适用于研究区的DHSVM模型；基于基准年2009年的土地利用模式构建8种土地利用情景，运用DHSVM模型模拟这8种土地利用情景下的产流过程。.1. 南小河沟的土地利用类型发生了很大的变化，草地及耕地产流较少，公路及庭院等产流较多，坡面产流<沟谷产流<塬面产流。.2. 同场降雨，随着植被被覆度的增大，径流系数明显减少，侧柏地<油松地<荒地<草地，小区产沙量，草地<荒地<侧柏地<油松地。.3. 径流系数随坡度的增大而减小，而且随着坡度的增大，减小的幅度越大；冲刷量随坡度的增大而减小，而且随着坡度的增大，减小的幅度越大；在15°左右的坡面产流及产沙过程可能存在特殊状况。.4. 不同种类的植被对于土壤含水率的空间分布有着重要的影响，垂线平均含水率的变化与降雨量整体上呈正比关系。.5. 林地的保水效益最高，其次是耕地，草地的保水效益最差。汛期不同土地利用类型对于径流的影响比枯季明显。汛期各种情景下产流较基准年的变化幅度增大，而枯季则变化幅度减小。