Document Type : Original Manuscript
Authors
1 1. Department of Geology, Faculty of Marine Natural Resources, Khorramshahr University of Marine Science and Technology, Khorramshahr, Iran.
2 Watershed Management Engineering Department, Sari Agricultural Sciences and Natural Resources University, Sari, Iran.
Abstract
In this study, to investigate the hydrological regime and determine the environmental flow requirement of Beshar River at the Pataveh hydrometric station, hydrological methods (Tennant, Tessman, flow duration curve shifting) and hydraulic methods (wetted area) were used. For this purpose, the river flow data were used in the statistical period of 1998-2020. First, the homogeneity and normality of the data were checked with the Run and Klomogrov-Smirnov tests. Then the hydrological characteristics of the stream were calculated in the IHA software. Finally, the environmental flow (EF) for the desired station was obtained with the above-mentioned methods. The results of this research showed that the flow rate has decreased for at least one to 90 days and the continuous period for the minimum annual flow has increased, which can be a threat to the life of plants and animals of the Beshar river ecosystem if the increasing trend continues. The environmental flow for semi-saturated and dehydrated periods by using Tennant's method were determined at 3.99 and 11.97 m3/s, respectively. Also, the environmental flow by the Tessman method indicated that the environmental demand is particularly important in the low water season and the first half of the full water period, and this amount of flow should be maintained to prevent the destruction of the river ecosystem. In the FDC-Shifting method, the environmental flow requirement (EFR) in Class A (normal), 69.60%, in class B (slightly changed) 50.10%, in class C (relatively changed) 37.80%, in Class D (largely changed) was 29.70%, in class E (severely changed) 24.20% and in class F (critically changed) 20.10%. Based on this, the FDC-Shifting class C method with an EF of about 72.54 cubic meters per second was selected as an environmental component. The environmental flow series in class C showed a decrease in flow rate over time. Based on the hydraulic method of the wet environment, the amount of environmental flow required was found to be about 20.6% of MAR.
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