基于DEM数字河网提取时集水面积阈值与河源密度关系的研究

以研究区3030个流域水文数据为基础,利用数字高程模型（DEM）并运用非线性拟合法分析中小流域集水面积阈值与河源密度的相关关系,分析集水面积阈值与河源密度的幂函数关系可得,幂指数a近似为-1,拟合公式常系数k具有区域分布特征,反映了不同地区的河网发育程度,k值越大,河源密度越大,河网越密集,河网发育程度越高。对河源密度随集水面积阈值的变化趋势进行分析,发现2个具有统计意义的阈值临界点,分别为河源从坡面到沟道及从沟道到河道的集水面积分界点,在研究区内选择不同k值区间的贡曲流域、辰清河流域和藤条江流域作为样本流域,利用样本流域数字正射影像（DOM）手工提取其沟谷河网及主河道河网的图形信息和水文信息,并与分界点处阈值提取的河网作对比,将分析得出的河网密度相对误差率作为检验标准,对临界点的物理意义进行检验。

The Relationship Between the Threshold of Catchment Area for Extraction of Digital River Network from DEM and the River Source Density

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.