The Effect of Dam Construction on flood and low flow Indices in South of Lake Urmia

Rivers are the naturally dynamic features of the landscape that exhibit different characteristics at specific times and in different places as the response of different environmental factors. Dams are among the most important man-made structures along the river that can make major changes in the river regime and ultimately in the entire drainage basin. Therefore, the purpose of this study was to investigate the change of hydrological flow indexes under the dam effect (pre and post-dam periods) using an Independent T-test in southern rivers of Lake Urmia. Toward this attempt, at first, nineteen hydrological indicators of the flow discharge were calculated in four main groups including Peak flows, Flow variability, Low flows, and Flow duration. Then, the effect of dam construction on pre-and post-dam periods before and after the construction of the dam on the hydrological parameters of the flow was analyzed using an independent T-test. According to the results, the values of 1-day minimum discharge, average daily flow in the period after the construction of the dam were significantly different in the period after the construction of the dams. Also, the amount of flow at 10, 50, 75, and 95% exceedance levels were different based on Flow Duration Curves constructed for pre and post dam periods. Meanwhile, the number of days zero flow, skewness, average annual coefficient of variation, Falling rate, Falling days, Flashinnes index, had a significant difference compared to the period before the construction of the dam. Also, the effect of dam construction on the five studied stations, the lowest effects of dam construction was related to Alasagle-Rast hydrometric station and the Sariqamish hydrometric station had the most effective under the dam construction. The construction of the dam has the effect of changing the hydrological parameters of the river, which can harm plant and animal species. Therefore, the effects of human activities (such as dam construction) provide the possibility of making logical management decisions that can play an important role in optimizing the exploitation of rivers.