基于形态指数的山丘区中小河流滩地分类方法及演变分析

Morphological indexes-based quantitative classification of floodplains in hilly areas

滩地是河道生态系统的重要组成部分,具有保护生物多样性、维持生态系统的动态平衡、提高河流的自我修复能力等作用,对河道水土保持与河流健康具有重要意义。为探究中小河流滩地的分类方法,笔者选取浙江省龙游县灵山港滩地为研究对象,利用Image J获取河道滩地几何特征参数,在计算圆形率、紧凑度、延伸率、形状率和平均曲率等基本形态指数的基础上,应用主成分分析法,获得描述滩地形态的2个主成分,以其构建平面直角坐标系,根据形态指数数对所在象限,对滩地的几何形态进行定量分析。结果表明:山丘区中小河流滩地可划分为短宽规则型、窄长规则型、窄长不规则型与短宽不规则型等4种类型;分别在2003、2010及2013年,对龙游灵山港各类型滩地的面积与数量进行统计,发现灵山港滩地面积减少约17.82%;其中,短宽不规则型滩地面积减少幅度最大,约达60.76%,且滩地几何形态明显呈窄长化与不规则化趋势。本文提出的滩地形态分类方法,能够反映滩地的纵横比例和边缘规则程度,并用于分析不同类型滩地的增长与衰退趋势。

[Background] The floodplain which is an important part of the river ecosystem,can protect the biodiversity,decrease the over-exploitation of sources,keep the homeostasis of the ecological system,and improve the abilities of the self-adjustment and self-healing of the system for the improvement of the human living environment,then has an important significance for the river water and soil conservation and the river health protection. In order to prove the classification method of medium or small river floodplains in hilly areas,this paper takes the geometric feature parameters of the Lingshan River floodplains in Longyou County of Zhejiang Province as research objects. [Methods] The geometric feature parameters of the Lingshan River floodplains were obtained through Image J software. And based on the basic morphology indexes, including circularity ratio, compact ration, elongation, form ratio, and meancurvature,the principal component analysis was used to get two principal components,P1 and P2,the two principal components can represent the information of all the basic morphology indexes. Using the two principal components as the plane coordinate axes and according to their values,the quantitative analysis of floodplain geometrical morphology was carried out. [Results] The research result indicated that the floodplains were classified into four types： the short wide regular floodplains,the narrow long regular floodplains,the narrow long irregular floodplains,and the short wide irregular floodplains. Analyzing the area and amount of floodplains in 2003,2010 and 2013,it could be concluded that the area of floodplains decreased by about 17. 82% in Lingshan River from 2003 to 2013,and the area of short wide irregular floodplains declined fastest by about 60. 76%. The geometrical morphology of floodplain obviously presented the narrow long and irregular trend. Then,taking the Muchen village floodplain and Mei village floodplain as examples,the Muchen village floodplain was short wide and regular in 2003.However,in 2010 and 2013,it became a short wide irregular floodplain. This is mainly because that the Muchen village floodplain is located in the lower reaches of Muchen reservoir. The dam enhanced the turbulent fluctuation of the stream of the floodplain fringe and the irregularity of the floodplain fringe. The whole Mei village floodplain in 2003 was separated from some unrelatedly small floodplains in 2010 and2013,and the whole area reduced by about 60%. Since 2003,due to the effects of human activities and excessive utilization,the Mei village floodplain fringe has been becoming more and more irregular.[Conclusions] Therefore,the classification method proposed in this paper can reflect the length and width rate and the degree of edge rules of the floodplains. In addition,it can be applied to analyze the morphology change tendency of floodplains in medium or small rivers.