不同时空尺度下沟壑对流域侵蚀产沙的影响--以黄土丘陵沟壑区岔巴沟流域为例

Influence of Channel Networks on the Sediment Yield Under Variant Temporal and Spatial Scales:A Case Study of Chabagou Watershed

基于DEM,分别以不同的沟壑发育所需的汇水面积为阈值,提取岔巴沟流域等6个不同空间尺度流域的沟壑,并求出不同级别沟壑的差值。结合黄河子洲观测站多年的水沙观测资料,分析不同级别的沟壑及沟壑的不同部位在不同时间尺度下对流域侵蚀产沙的影响。分析结果表明:沟壑密度并不是简单地随着流域面积的增大而减小,沟壑密度的空间尺度效应与所提取沟壑的级别有关;黄土丘陵沟壑区梁峁坡、沟坡的次暴雨产沙量占流域产沙总量的比重与降雨特性有关;重力侵蚀多发生在毛沟的中、上部及沟头处,而支沟、干沟主干道的沟坡比较稳定,且其发生的重力侵蚀对流域产沙的影响多为"无效"部分;沟壑发育汇水面积的阈值为1500、1800、2000个栅格提取的沟壑对流域侵蚀产沙的作用较大,同时沟壑对流域侵蚀产沙的影响与时间尺度有关,在多年平均尺度下,高级别沟壑只起到泥沙输送通道的作用。

Different threshold areas of catchments, expressed in 100, 250, 500, 1000, 1500, 1800, 2000, 4000 and 40000 pixels, were selected based on the DEM. The channel networks of six watersheds lying in Chabagou gully with different spatial scales and the deviation between them were extracted. Employing the long-term field observation data of Zizhou hydrological station within the Yellow River, the influence of different spatial scales channel networks and variant places of channel on sediment yield of watershed were analyzed. The results showed that no simple decreasing relationship existed between gully density and area of watershed and the spatial scale effects of gully density associated with the level of extraction. When the threshold areas of catchments equal to 4000 pixels, the gully density decreased gradually with the increase of areas of watersheds. The characteristics of rainfall event have impacts on the ratio of sediment yield during single rainfall events of the channel slopes to the total sediment yield of the watershed. The sediment yield of channel slopes composed the main source of the total sediment yield when the rainfall intensity was relatively low. But, the upslope makes a main contribution to the total sediment yield when the rainfall intensity was comparatively great. Mass movement developed frequently at the upriver and head of the gully, but the slopes of branch ditch and main ditch were fairly stable; furthermore, the mass movements of those places were inefficiency to the sediment yield of the watershed. The channel network extracted under threshold areas of 1500, 1800 and 2000 had the most significant contribution to the total sediment yield; meanwhile, the influence of channel network on the sediment yield of watershed associate with the time scales. The high-level channel was merely a transport passage of sediment under long-term time scale.