Comparative assessment of environmental fow using hydrological methods of low fow indexes, Smakhtin, Tennant and fow duration curve

There are diferent methods in hydrological approach for estimating the environmental fow and a comparative assessment is necessary. The low fow indexes (7Q2 and 7Q10), Smakhtin, Tennent and fow duration curve were used to estimate the environmental fow of Zohreh River in the southwest of Iran. The Smakhtin, 7Q2, 7Q10 and Tennant methods resulted in the estimation of constant values of 27.2, 12.7, 5.9 and (8 and 24) cms, so that, on average 52.8, 26.9 and 12.3, 36.7 percent of the monthly fow is allocated to the environmental fow. The monthly environmental fow pattern for these methods does not ft well with the monthly fow pattern, and thus it can be concluded that the Smakhtin, 7Q2, 7Q10 and Tennant methods cannot be used in the initial form. The application of the fow duration curve leads to an environmental fow assessment in the range of 6.8–38 cms in diferent months, whose time pattern completely matched with the monthly fow pattern. In this method, on average, 30.8% (range 18–48%) of the monthly fow allocated to the environmental fow, which is reasonable and acceptable amounts. Investigating the results of this study shows that the time pattern of the results should be analyzed in comparison with the observational fow pattern to estimate the environmental fow with a hydrological approach. The results also suggest that the methods that provide a constant amount of environmental fow in diferent months of the year should be interpreted cautiously along with other methods.