喀斯特分布区小比例尺地表水系提取及阈值分析——以黔中水利枢纽工程区为例

Extraction of small-scale surface water system in karst distribution area and analysis on its threshold——A case of area of Qianzhong Water Control Project

针对喀斯特峰丛洼地集中连片分布区小比例尺水系提取及该尺度下阈值的合理确定,以精准、快速和经济提取大范围区域主干河网水系为目标,选取黔中水利枢纽工程区为研究对象,基于改进的30 m ASTER-GDEM数字高程数据,利用ArcGIS10. 2的Hydrology水文地理分析技术,探讨了无大比例尺水系图参照条件下喀斯特分布区地表水系提取及其合理汇流阈值的确定。结果表明:汇流累积量阈值的大小是决定河网密度的关键因子,阈值由小到大变化过程中河网密度的变化呈现出先快速降低后渐缓变化的趋势,即河流的数量随汇流累积量阈值门槛的升高而减少。通过分析汇流累积量与河网密度、河流总条数、河道总长之间的关系及其斜率变化,发现汇流累积阈值10 000是一个变点,阈值10 000以下河网密度、河流总条数、河道总长变化剧烈,10 000以上则变化趋缓。取汇流阈值10 000提取的水系叠加在Google Earth高分辨率遥感影像上与研究区互相独立的横江流域进行验证,结果发现该阈值下的水系基本与现状河流吻合。

Aiming at the extraction of the small-scale water system from the concentrated contiguously distributed area within the karst peak-cluster depression region and the reasonable determination of its threshold under this kind of scale as well as taking an accurate,quick and economic extraction of the water system of the river network as the target,the area of Qianzhong Water Control Project is selected as the study object,and then the extraction of the surface water system within the karst distribution region and the determination of its reasonable determination of the confluence threshold under the condition without any references from large-scale map of water system are discussed herein with the hydro-geographic analysis technique from the Hydrology of ArcGIS10.2 on the basis of ASTER-GDEM digital elevation data of 30 m.The result shows that the size of the accumulated confluence threshold is the key factor to determine the density of river network,for which the change of the density of river network exhibits a trend of quickly lowering and then gradually being moderated during the changing process of the threshold from the small to the large,that is to say,the number of rivers is decreased along with the increase of the accumulated confluence threshold.Through the analysis made on the relationship in-between the confluence accumulation,the density of river network,the total number of rivers and the total length of rivers as well as the change of the slope,it is found out that the value of 10 000 for the accumulated confluence threshold is a changing-point,in other words,the density of river network,the total number of rivers and the total length of rivers are drastically changed under the threshold of 10 000 and tend to be moderated above this value.Verifying the water system extracted with the confluence threshold of 10 000 and superimposed on the high-resolution remote sensing image of Google Earth with that of the mutually independent Hengjiang River Watershed within the study area,the result shows that the water system under the value of the threshold is basically coincided with the status of the river therein at present.