Ecological hydraulics radius model for estimating instream ecological water requirement: Theory

based on summarizing the methods for calculating in-stream ecological water requirement, the conceptions of ecological flow velocity and ecological hydraulic radius are bring forward and decided, the ecological hydraulic radius model (EHRM) for estimating in-stream ecological water requirement is built up by taking account of the information of river course (e. g. hydraulic radius, roughness coefficient, hydraulic gradient slope) and ecological flow velocity for satisfying stream ecosystem to keep its some ecological function. The key parameter of EHRM is the channel cross-section area of ecological hydraulic radius corresponding, the paper discusses the calculating method about the relationship between differ regulation stream cross section, inartificial stream cross section and hydraulic radius, meanwhile, the application of EHRM for estimating in-stream ecological water requirement is discussed and explained, and the instream ecological water requirement by EHRM can adapt better the demand of fish for flow velocity.