Vol.:(0123456789) Acta Geophysica https://doi.org/10.1007/s11600-023-01264-5 RESEARCH ARTICLE - HYDROLOGY AND HYDRAULICS Modifed ideal point method for estimating minimum environmental fow of rivers Mohammad Sedghi‑Asl 1  · Seyed‑Jamal Poursalehan 2 Received: 26 April 2023 / Accepted: 3 December 2023 © The Author(s) under exclusive licence to Institute of Geophysics, Polish Academy of Sciences & Polish Academy of Sciences 2024 Abstract This research aims to compare the results of diferent hydraulic methods and choose the appropriate discharge for the envi- ronmental fow of the Beshar River. At some periods between 2013 and 2018, the Beshar River practically turned into a dry river in the areas near Yasouj city during the summer time, and only a small subsurface stream trickled down from it. For the preparation of hydraulic sections and calculations of hydraulic methods of the wetted perimeter, 15 cross sections between Dehno and Pataveh stations were selected and their cross sections were mapped and digitized. The present study showed that an accurate wetted perimeter method, including both slope method (SM) and ideal point method (IPM), will produce acceptable results. The fnal result indicates that the newly presented method called Modifed Ideal Point Method (MIPM) is an accurate and conservative hydraulic method for calculating environmental fow. Keywords Beshar river · Environmental fow · Wetted perimeter method · Modifed ideal point method List of symbols MIPM Modifed ideal point method IPM Ideal point method IPM1 Ideal point method with scaling factor equal to 1 IPM2 Ideal point method with scaling factor equal to 2 SM Slope Method CM Curvature method P Wetted perimeter (L) Q Discharge fow (L 3 /T) Q max Average annual fow (L 3 /T) P max Wetted perimeter due to average annual fow (L) p P/P Max (−) q Q/Q Max (−) a Constant coefcient in p–q relation b Constant coefcient in p–q relation C Constant coefcient in p–q relation k Curvature w Non-negative weighting coefcient d Distance from the reference point in IPM r A scaling coefcient equal to or greater than 1 D Distance from the reference point in MIPM MAF Mean annual fow (L 3 /T) MMF Mean monthly fow (L 3 /T) Introduction Water ecosystems signifcance is one of the foremost goals of comprehensive water resources management. Determin- ing and allocating the environmental fow of rivers is the most efective approach to prevent the negative efects of regulating surface fows on them, which makes it possible to achieve this goal. The key problem that we have faced in Iranduring the past years is the lack of a clear environmental policy about determining the minimum environmental fow for rivers. To date, the focus has been the use of hydrological methods; however, little action has been taken to adopt more accurate methods, such as the hydraulic method, in this feld. Cal- culation errors and the lack of familiarity with the method mean that the research is limited, and the results cannot be deemed reliable. Numerous methods have been identifed worldwide to determine the environmental water requirements of rivers Edited by Dr. Hossein Hamidifar (ASSOCIATE EDITOR) / Prof. Jochen Aberle (CO-EDITOR-IN-CHIEF). * Mohammad Sedghi-Asl msedghi@yu.ac.ir 1 Department of Soil Science, College of Agriculture, Yasouj University, Yasouj, Iran 2 Khuzestan Province Construction Engineering Organization, Behbahan, Iran