Using RVA Model for Defining River's Ecological Regime for Determining Environmental Flow

In many countries, especially developing countries, because of data shortage and costly environmental studies, simple hydrologic methods such as the Tenant and Q95 methods, are main methods for determining environmental flow requirements. In this study, the compatibility of these methods with ecological conditions of rivers was investigated. For illustrating difficulties in providing required data for running physical habitat simulation models the River2D as a 2D hydraulic model was used. The ecological regime of the studied river derived by the River2D was compared with the outcomes of the two aforementioned hydrologic methods. The RVA method, based on the assumption that this method is as simple as the other hydrologic methods while it is capable of giving results as precise as habitat simulation models, was investigated. In the case study, the situation of the river based on the suggested EF by the Tenant and Q95 methods was shown and it was illustrated that the monthly ecological flow determined via River2D was captured by the upper and lower limits of the RVA method. Moreover, It was concluded that using monthly median flow instead of mean monthly flow s is preferable in the presence of skewness. Finally, it was determined that the discharges prescribed by River2D could not be supplied in all months, while RVA yielded minimum monthly environmental flows that could satisfy all the necessary conditions for conserving biotic and abiotic habitat in the study river.