关键词: DEM, 数字河网提取, 河源密度, 集水面积阈值, 幂函数

Abstract:

The relationship between the threshold of catchment area for extraction of river network from digital elevation model (DEM) and the density of river source was analyzed by nonlinear fitting method, using 3030 river basins chosen as study areas. The results showed that the relationship between threshold of catchment area and density of river source was a power function relationship, and the power exponent was approximately -1, which could be regarded as an inverse function. The constant coefficient k in fitting formula indicates the development degree. The larger the k value, the more the river sources per unit, the denser the river network, and the better the development of the watershed. Across China from north to south, and from east to west, the value of the coefficient k was gradually increased. The coefficient k has the maximum value in the area where the climate is humid, the slope is large, and the landform is broken. On the contrary, a minimum value was observed in the dry, wetted, flat area. According to the statistics, the mode of k appeared in the mountainous areas of the south Yangtze River. Two threshold demarcation points were discovered by analyzing the variation of the river source density with the increase of the catchment area. The two threshold demarcation points could be considered as the critical points of watershed area for watershed delineation from DEM, which can be used to distinguish the slope, the channel, and the channel and the river, respectively. According to the distribution interval of k, Gongqu river basin, Chenqing River basin and Tengtiao River basin were selected as the sample catchments. Based on the Digital Orthophoto Map (DOM), graphical information and hydrological information of the river network of the valley, the main river networks were extracted in the sample catchments. The physical meaning of the threshold demarcation points was tested by using the relative error rate of the river network density which was obtained from the analytical data. The results showed that the error of the boundary points was less than 10%. According to the dividing point of the relation curve between the catchment area threshold and the river source density, the confluence calculation method zonation of different river basin for geomorphologic unit hydrograph derivation could be ascertained.

Key words: DEM, Digital river network exaction, river source density, catchment area threshold, power function