An instream ecological flow method for data-scarce regulated rivers

► This study deals with an instream ecological flow determination method for regulated rivers called the Adapted Ecological Hydraulic Radius Approach (AEHRA). ► It considers information of both instream ecosystem and river course, while it does not require any flow regime. Beside monthly IEF, it outputs monthly Instream Ecological Water-level (IEW) as well. The latter can greatly facilitate dam operation. ► AEHRA is especially predictive for rivers with limited ecological and hydrological data. ► It can reflect the seasonal variation of IEF and IEW. Reliability of traditional methodologies is often challenged in determination of instream ecological flow (IEF) for a regulated river due to its non-natural condition. This paper deals with an IEF determination method for regulated rivers called the Adapted Ecological Hydraulic Radius Approach (AEHRA). It considers information of both instream ecosystem and river course, while it does not require any flow regime. Beside monthly IEF, it outputs monthly Instream Ecological Water-level (IEW) as well. The latter can greatly facilitate dam operation. Application of this method to the Huai River which is completely regulated by dams suggest: (1) AEHRA is especially predictive for rivers with limited ecological and hydrological data; (2) it can reflect the seasonal variation of IEF and IEW; (3) errors of AEHRA introduced by using a geometric shape generalized cross-section in an un-gauged site are generally acceptable; (4) comparison of the IEF values estimated by AEHRA with those by Tennant approach, Wetted Perimeter method and R2CROSS method showed fairly good agreement in terms of practical capability of the AEHRA. This method will be of great help for regionally sustainable water management in data-scarce regulated rivers