Analysis of Changes in Hydrological Indices of Karun River Flow before and after periods Gotvand Dam Using Range of Variability Approach

Hydrological regimes play a major role in restructuring and operating ecological processes, wetlands and river ecosystems. Hydrological regimes of rivers flowing due to the construction of significant changes in the dam cause spatial and temporal heterogeneity of river systems and degradation of natural ecosystem services and threat to biodiversity. In this regard, effective management of the river ecosystem needs to describe the parameters of the hydrological regime of the natural flow and determine the degree of changes in the two statistical periods before dam construction and altered flow regime (after dam construction). In this study using IHA software, 33 hydrological parameters as indicators of hydrological change, in five statistical groups at Molasani and Ahvaz Hydrometric stations, to evaluate changes in Karun River downstream of Gotvand Dam from 1983 to 2018 in two periods Statistical normal flow regime and modified flow regime were used. According to the results, the hydrological indices at the Molasani and Ahvaz hydrometry stations changed significantly during the changed flow regime, so that the mean discharge values significant decrease in most months. Also, the percentage of hydrological change of 23 parameters in Molasani Hydrometry Station high, and 11 other parameters were low, and in Ahwaz Hydrometry Station, 24 parameter medium to high, and 12 other their changes were low. This indicates the high degree of hydrological changes in the Karun River Basin. The results of maximum daily, weekly, monthly and quarterly flows show that the construction of the dam has a negative effect on the Karun River discharge. The results of the study on the variability of the river variability approach also showed that the appropriate range of monthly discharge values at Molasani Hydrometric Station for the first six months of the water year, provided river life goals proportional to 2231.4 to 532.3 m3/s and for the second six months of the year this range was between 345.5 to 1235.4 m3/s, while at Ahvaz Hydrometric Station, for the first six months of the year, the appropriate range of monthly discharge ranges between 272.7 to 562.8 m3/s and for the second six months of the year this range was between 314.2 to 1255.6 m3/s. Finally, up to the annual values of each hydrological index of the river after the dam construction as far as possible in equilibrium with the flow domain reported inof the range of variability approach, in order to maintain optimal ecological conditions and integrity of the Karun River ecosystem water resources management (Regulatory role of Gotvand dam on flow regime).