Evaluation of the Effect of Flow Release Based on River Environmental Guidelines on the Water Balance of Anzali Wetland

Rising demand for water consumption has exacerbated complex conflicts between the agricultural, drinking, and industrial sectors. The main purpose of this study is to investigate the effect of reducing the discharge of rivers entering the wetland based on environmental guidelines on the water balance of the wetland. Due to the location of Anzali Wetland in the downstream of a catchment, it is necessary to determine the minimum flow of incoming rivers in such a way as to ensure the survival and dynamism of the downstream ecosystem.

In this study, the regulatory flow of the river is estimated based on environmental scenarios in Tenant, Texas, and transfer continuity curves, then the effect of discharge allocation in each scenario on the water balance of the wetland, and finally, the volume of the wetland is investigated. To calculate the water balance of the Anzali wetland, changes in the volume of the wetland per month are identified. To calculate the changes in the volume of the wetland in each month, it is necessary to calculate the volume of the wetland in two consecutive months. According to the discharge of environmental flow, the level of the Caspian Sea, and net evaporation in March and based on the balanced equation, the volume of the wetland in March is calculated as the initial conditions. Then, for the environmental flow on a monthly scale, the difference in elevation between the water level of the wetland and the sea is obtained. In the next step, according to the sea level values, the wetland water level is also calculated. Afterward, based on the surface-volume-height relationships of the wetland reservoir, the volume of the wetland is additionally obtained.

The results showed that the highest discharge of environmental flow and consequently the highest volume of the wetland is obtained by applying the flow continuity curve transfer method and the lowest is obtained by applying the conservative scenario of the tenant method. Evaluation of wetland volume in flow allocation scenarios based on environmental guidelines defined for rivers demonstrates that the release of flow in the range of environmental discharges is not able to provide suitable ecological conditions as well as appropriate status for tourism. Therefore, deciding on any water withdrawal from the upstream requires a comprehensive analysis of the swamp water balance. By applying the correct management of input and output components in the water balance equation of the wetland, it is possible to increase the volume of water in the Anzali wetland to the extent that the maximum economic benefit of the functions and services in the wetland can be done by considering all stakeholders.

The present study gives the important conclusion that it is not possible to exploit any of the rivers entering Anzali Wetland, even if environmental considerations are observed, and before deciding on any operation and construction of dams such as Shafarood Dam, it is essential to analyze the response of the swamp, accurately. To make the results of this study practical, it should be acknowledged that recognizing the balance components and observing the ecological water content of the rivers entering the Anzali Wetland are doubly important, especially in cases where the wetland is subject to special regulations and competition of multiple users.