BDU partition for extracting distributed soil erosion slope length in large-and medium-scale watersheds
CAO Xiayu, YANG Qinke, LAN Min, WANG Chunmei
1. College of Urban and Environment, Northwest University, 710069, Xi'an, China;
2. Institute of Soil and Water Conservation, Chinese Academy of Sciences and Ministry of Water Resources, 712100, Yangling, Shaanxi, China;
3. China Coal Xi'an Design Engineering Co., Ltd., 710054, Xi'an, China
Abstract：[Background] The strategy for partitioning DEMs into basic data units (BDU) is a key issue in the efficient extraction of watershed slope length in large-area regions.[Methods] This paper took the mild undulating hills of the Northeast China and the loessial hilly areas of the Loess Plateau as study regions, in each case single DEM mosaics were formed from nine standard 1:250 000 scale map sheets. The slope lengths were then extracted by BDU which were taken to be mid-sized watersheds in the standard map sheets provided with effective buffer zones to fill a rectangular map. The maps were then compared and analyzed using information from the extracted units such as statistical characteristics, efficiency and other aspects.[Results] 1) Based on the implications and extraction algorithms of slope length for distributed watershed soil erosion, the basic data units (BDU) for watershed slope length extraction (The minimum effective watershed, WME) were the smallest basins which were distinguishable and also had clear hydro-geomorphic significance. If the workspace was much larger than the area of a WME, the connecting line of the peripheral watershed boundary of the WME(BNDWME) was included in the rectangle. 2) Rectangular data areas (For example, standard map sheets) after reasonable extension avoided the detrimental influences that occurred from incomplete slope length zones and was used as suitable map sheets for the BDU to extract the complete set of watershed slope lengths. 3) Comparing cases in the Northeast China (Mild terrain) and the Loess Plateau (Steep hilly terrain), common extents of surrounding areas of incomplete slope length (The data buffer width) were different at 3 km and 5 km respectively.[Conclusions] In the extraction of slope length in large area, after suitably extending data by the buffer widths, we can then use the extended rectangular data as inputs to extract slope length directly. This work allows efficient methods that take standard map sheets or rectangular blocks as data units to be applied for general watershed slope length extraction in large-area regions.
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2018, Vol. 16 
