Influence of Channel Networks on the Sediment Yield Under Variant Temporal and Spatial Scales:A Case Study of Chabagou Watershed
LIAO Yishan1,2,3, CAI Qiangguo3, ZHUO Muning1, ZHENG Mingguo3, LUO Xuan2 (1. Guangdong Institute of Eco-environment and Soil Science, Guangzhou 510650, China; 2. College of Resources and Environment, Huazhong Agricultural University. Wuhan 430070, China; 3. Key Laboratory of Water Cycle and Related Land Surface Processes, Institute of Geographic Sciences and Natural Resources Research, CAS, Beijing 100101, China)
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 wa- tersheds 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 decreas- ing 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 e- qual 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 rain- fall 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; further- more, the mass movements of those places were inefficiency to the sediment yield of the water- shed. 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.