Watershed Characteristics Extraction and Subsequent Terrain Analysis Based on Digital Elevation Model in Flat Region

Abstract

Extraction of watershed characteristics (stream position, stream length, watershed area, slope, and others) using a digital elevation model (DEM) is an important prerequisite of hydrologic analysis. Detecting these surface hydrologic features in flat regions using a DEM is a known problem. Using a known stream network to improve DEM performance has been done in a variety of methods; many methods can improve calculation of watershed area, stream position, and length, but there are strong impacts (e.g., slope) on subsequent terrain analysis from altering the DEM. To solve this problem, a new method, water depth gradient burning (WDGB), is proposed in this paper to extract watershed characteristics and subsequent terrain analysis in a flat region. In WDGB, the stream network map is used as an input dataset; a burning value at headwater, stream connection, and outlet nodes of the stream is defined, which is consistent with three parts: water depth correction, peak depth correction, and additional depth for gradient, ensuring that an upstream node elevation is higher than a downstream one. Other stream elevations are calculated by linear interpolation using the aforementioned node elevations. Because the adjusted DEM (the stream) has a positive gradient with no pits or inverse slope along the flow direction, it can be used to extract watershed characteristics and obtain the hydrologically correct result. At the same time, the elevation of the stream is not altered too much in WDGB. The effect of the adjusted DEM on subsequent terrain analysis is addressed with regard to the D8 algorithm, AGREE, and WDGB methods. The result indicates that WDGB can not only achieve watershed characteristics correctly in a flat region but also have the least influence on the original DEM and the subsequent terrain analysis.