Hydrological Based Environmental Flow Assessment Methods (Case Study- Gharasou River, Ardabil)

Abstract

Water flow management is one of the most important parts of river engineering. Non-uniformity distribution of rainfall and various flow demand with unreasonable flow management will be caused destroyed of river ecosystem. Then, it is very serious to determine ecosystem flow requirement. In this paper, four hydrological based environmental flow assessment methods have been used to calculate environmental flow in Gharasou River, Ardabil, Iran as following- Flow duration curve indices method, Range of variability approach, Tessman method, and Global environmental flow calculator. In the first method, Q90 and Q95 for different return periods were calculated. Their magnitude were determined as 1-day, 3-day, 7-day and 30 day. According the second method, hydraulic alteration indices often had low and medium range. In order to maintain river at an acceptable ecological condition, July based flow was selected as environmental flow, i. e. 15 m3s-1. Using Tessman method, minimum and maximum values of monthly environmental flow was estimated 1. 8 and 13. 72 m3s-1, respectively. Based on the last method, seven scenarios were studied. Of all scenarios, scenario C indicates moderate situation of ecological habitat of river. according to calculations, the amount of the C scenario was determined as 6 m3s-1