基于水文气象条件的河道临界集水面积确定的方法研究

Minimum support area of riverhead based on regional hydro-climate factors

河流源头是最小河流的起点位置,源头位置的确定具有较大的困难,一般采用该点以上集水面积的大小来判定。河道集水面积临界阈值是数字化河网的一个核心问题,直接影响着河网密度与流域划分结果。以往人们主要是利用常数面积法或经验值确定区域的河道集水面积的临界阈值,对于利用水文气象条件确定河流集水面积临界阈值研究甚少。本文分析了现有确定集水区阈值面积的方法,并基于河流源头主要特性,提出了以河道枯季临界流量（0.005~0.01m3/s）作为河源起点的判定标准,并提出利用水文数据（年降雨量、年蒸发量以及最枯月流量）来推算流域内临界集水面积阈值的新方法。选择西藏尼洋河的白水曲流域DEM数据提取河网来对该方法进行了检验,得到当临界流量0.0085 m3/s时,从DEM自动提取的河网与实际河网最相匹配。该方法能够考虑区域的水文气象条件对河流特征的影响,所得的结果比较合理,对于复杂水文条件下的地区进行数字化河网提取具有重要意义。

Riverhead is a source area forming a tributary but it is difficult to determine accurately, so it is often judged by a threshold size of the catchment area above the river starting location （minimum support area）. How to define this threshold is a key issue in digitization of river network, directly affecting drainage density and watershed division. Traditionally, a given constant threshold value or some empirical thresholds are used, and methods based on meteorological and hydrological conditions for determination of the catchment area threshold are lacking. This paper analyses the existing methods for determination of the threshold and the main characteristics of riverheads, and presents a new criterion that the river starting location is a cross section with mean flow rate of 0.005-0.010 m^3/s in dry season. And by this criterion, we suggest a new method for threshold calculation using three hydro-climate factors： annual rainfall, annual evaporation, and minimum stream flow in arid season. Then, a series of thresholds were calculated by using the digital elevation map （DEM） of the Beishuiqu sub-basin of the Niyang River and extracting the river networks with ArcSWAT, and verified via comparison with a reference river network that had been extracted from a larger-scale digitized map. The results show that for this sub-basin, if a minimum flow Qc=0.0085 m^3/s is taken as the. critical support flow, a good agreement with the real river networks can be achieved and the corresponding threshold riverhead area is 4.91 km^2. The suggested method considers meteorological and hydrological conditions and gives reasonable results, networks in complex hydro-climate conditions.