Estimation of environmental flow of the Balikhlochai River and evaluation impact of Yamchi dam operation on hydrological and environmental regime of the river

There are various methods for assessing and regulating flow in order to protect the environment. In total, 207 methods have been identified for determining the environmental flow of rivers in 44 countries around the world, which can be classified into four general methods, including the hydrological method, hydraulic rating, habitat simulation, and holistic methodologies. Among these methods, the hydrological method has been the most used due to its ease of use, access to data and short calculation time. The aim of this study is to determine the environmental flow of Balikhluchay river in Ardabil, using Tennant, Tasman and flow continuity methods. Also, the effects of Yamchi dam construction on environmental and hydrological flow in downstream of the river were investigated and analyzed using IHA software. To achieve the objectives of the present study, some hydrological methods have been used. The input data in these methods is the daily runoff data of the Pole Almas station. The research stages are based on two main steps of calculating the river's environmental flow from 1970 to 2013 without considering the Yamchi dam and applying the Tennant, Tessman and Flow duration curve methods in different months of the year. According to the Tennant criteria, values of 10, 30 and 60% of the mean annual flows, respectively, are allocated as minimum flows, for Short-term survival of fish, maintaining relatively good survival status and maintaining suitable habitat. In Tessman method, if the 40% of mean annual flow was greater than the mean monthly flow, then the average monthly flow would be considered as the minimum monthly flow, otherwise, 40% of mean annual flow would be considered as the minimum monthly flow. The flow duration curves, by presenting the relationship between the amount and frequency of the river flow, show the full range of river discharges, from drought to flood events. The flow duration curves include information on river water planning, drinking use, or construction of diversion dams. In this method, the daily average data is first sorted in descending order. The next step is to investigate and analyze the effects of the Yamchi dam construction (before and after the dam construction in 2004) on environmental and hydrological downstream flows of the river using IHA software. The results showed that the Tennant method calculates the river flow between 1.96 to 3.27 m3/s to keep the river flow regime at the optimum range for all months of the year, while Tessmann method calculates 1.31 m3/s. The results of the FDC indicate that for the protection of the river in suitable and relatively suitable conditions, the flow rate of 2.95 and 2.46 m3/s was required, respectively. The results of the flow duration curve method can be useful to simulate the historical flow regime to maintain good or moderate environmental conditions and to provide a management model for the protection of the Balikhluchay river as well as early planning. The flow duration curve method estimated the environmental flow values more than other methods. The Tenntant method also estimates the environmental flow values less than the other two methods. In all months of the year, the Tenant method estimates the amount of environmental flow less than the Q75. In some months, Tasman method has estimated the amount of environmental flow less than the Q75 and in some months more than the Q75. The results of the periodicity and continuity of the pulsating behavior of the Balikhluchay river in low and high water periods, showed that before and after the construction of Yamchi dam, the duration of low-flow pulse has little hydrological change. However, the hydrological change degree of the wetness period pulse in terms of frequency and continuity is moderate and high, respectively. Changing these parameters can cause the movement of organic and food materials between the river and floodplain, the frequency and severity of soil moisture stress for plants, the frequency and duration of plant oxygen-free activities stress, and the effect on substrate transport, channel sediment texture and duration of disturbance. The intensity of flow decrease and increase in the period after the dam construction has had moderate changes. Generally, it was found that the dam’s operation has influenced downstream hydrological and environmental parameters. The extent of these effects on hydrological parameters such as magnitude of monthly water conditions, magnitude and duration of annual extreme water conditions, timing of annual extreme water conditions, and frequency and duration of high and low pulses status were 61.38% with moderate change degree. Also, despite the dam, 51.6% of the environmental parameters such as monthly low flows, extreme low flows, small floods and large floods have changed.