基于DEM的水系提取及集水阈值确定方法研究

目的]确定适宜的集水阈值,使自动提取的水系河网与实际河道相符。方法]以DEM数据为基础,利用ArcGIS水文分析模块对研究区流域河网水系进行自动提取,基于河网密度与集水阈值的相关性,在已提出的拟合函数一阶导数求转折点、二阶导数求拐点法确定集水阈值的基础上,以龙川江流域为例,提出求解河网密度变化率等于集水阈值变化率的数值方法,得到适宜的集水阈值。结果]通过设置不同集水阈值生成河网,发现不同集水阈值对主河道长度及地理空间位置影响较小,但对提取的河网特征影响较大,最终确定龙川江流域集水阈值设置为0.12km2为宜。结论]集水阈值的确定影响着河网提取的精度,通过变化率确定集水阈值的方法主观因素较少,避免了人为干扰,相对客观,可对区域水土流失监测提供一定依据。

Information Extraction of River Networks and Determination of Drainage Area Threshold Using DEM Data

Objective] Method of determining appropriate drain area threshold was demonstrated to reflect the actual river drainage network.Methods] Based on the DEM data of Longchuan River basin, the automatic extraction module of watershed drainage network in ArcGIS software was used to extract relevant drainage information. After that, a function between river network density and catchment threshold was fitted, which was used to determine the appropriate drainage threshold by finding the turning point of its first derivative function and/or the inflection point of the second order derivative. This was simultaneously exemplified by the Longchuan River basin. In this case, the threshold was determined by finding where the ratio change of river network density equal to the change rate of the water drainage threshold.Results] The river networks under different catchment drainage threshold were compared and found that no obvious differences existed with regard to the catchment threshold length of the main channel and the geographic location, but other features of river network were apparently different. In the case of the Longchuan River basin, its appropriate threshold was thought to be 0.12 km².Conclusion] The river network extraction precision varied with the drain area threshold. The proposed method in the determination of the catchment threshold is less subjective, and is more objective, which can be used to provide some bases for the monitoring of regional soil erosion.