基于湿周法的西南山区河流生态需水量计算与验证

Calculation and Verification of Ecological Water Demand in Southwestern Mountains River Based on the Wetted Perimeter Method

研究湿周法的适用条件及转折点的确定方法,为计算河流最小生态需水提供参考。收集了我国西南山区岷江和大渡河流域河流上、中和下游共计8个水文站的实测大断面数据,通过建立各断面湿周与流量关系及其拟合曲线,分别采用斜率法、曲率法和经验法分析确定了各断面最小生态需水,并参考相关参数标准对计算结果进行了合理性检验。研究表明,湿周法适用于河床稳定且形态近似抛物线形或矩形的断面,以斜率为1的点（斜率法）确定断面湿周与流量关系曲线的转折点及断面最小生态需水更有利于保护河流生境;对于形态近似为抛物线形或矩形的断面,其计算结果约占多年平均流量的8.9%~13.2%,各断面最小生态需水所对应平均水深、湿周率和平均流速均能满足检验标准。湿周法适用于近似抛物线形或矩形的断面,不建议用于近似三角形或梯形的断面。

Ecological water demand（EWD）,also referred to as the environmental flow,is the minimum water flow required to sustain an aquatic ecosystem and the human livelihoods that depend on the ecosystem.Scientifically determining the EWD is a basic requirement for river conservation and rational configuration of water resources.The wetted perimeter method is widely used for estimating EWD and is the recommended method when the data are not sufficient for a more precise determination.In this paper,we discuss the application conditions for the wetted perimeter and turning point determination methods,in order to provide a reference for calculating the EWD of mountain rivers.The discussion was based on data collected at eight monitoring stations located in different sections of a river system in the mountains of southwestern China.Data on wetted perimeter as a function of flow for each section was curve-fitted and three methods（slope,curvature and empirical）were used to define the minimum EWD for each section.The results were then subjected to a reasonableness test using standard reference parameters.This case study indicates that the wetted perimeter method is suitable for approximately parabolic or rectangular cross sections of stable riverbeds.Using the point at which slope is 1（slope method）to determine the turning point of curves between wetted perimeter and flow and the minimum water flow required in section more conducive for protecting river habitats.For approximately parabolic or rectangular cross sections,the calculated result gives a minimum EWD flow 8.9%-13.2% of the average flow rate over many years and results in average a water depth,wetted frequency and average flow velocity that meets the inspection standards.