Investigating Hydrological Changes of Tejan River Estuary (Southern Caspian Sea-Mazandaran Province)

Although estuaries are considered as one of the most fertile ecosystems in the world, today they are under the influence of various threats and one of them is hydrological changes. In this study, by using the IHA hydrological change indicators, the changes in the hydrological regime in two statistical periods "natural flow regime" and "altered flow regime" were investigated in Soleiman Tange and Kordkheil hydrometric stations in Tejan watershed (Mazandaran province). Based on the IHA method, a total of 67 statistical parameters have been estimated by "IHA7 software"; these parameters are divided into two groups of indicators of (IHA) hydrological changes in the target range of (RVA) and the environmental flow component of EFC. According to the results, the minimum days of flow in the period before the construction of the dam is 227.5 days, while in the period after the construction of the dam, it is 48.5 days, and the number of days when the minimum flow occurs before the construction of the dam is 351 days. It has decreased to 286 days after the construction of the dam, so the annual limit flows in the Tejan River have experienced disturbances and moderate changes. Considering that the change in the hydrological indicators of the flow is mainly influenced by the construction of the dam, therefore the hydrological management of the dam will have a great effect on the ecological condition of the Tejan river estuary.