Classification and identification of changes in river flow regime using the Indicators of Hydrologic Alteration (IHA)Case study: (The Khormarud River- Tilabad Watershed- Golestan Province)

In this research, using the Indicators of Hydrologic Alteration (IHA), the hydrologic regime alteration in two periods "natural flow regime" and "altered flow regime" at the hydrometric station of Nodeh Khandus, located at the outlet of the Tilabad Watershed in Golestan Province was investigated. On the basis of IHA method, a total of 67 statistical parameters are calculated using IHA7 software. These parameters are subdivided into 2 main groups, the IHA parameters and the Environmental Flow Component (EFC) parameters. A significance count used to determine the significant difference between the median values of the pre- and post- alterating periods. To classify flow regime, the classification method developed by Oueslati et al. was used. The results of this research indicate that the annual flow regime during the period of 1968 to 2016 from "Perennial Runoff" to "Perennial Flashy" has altered. Human activities in the Tilabad Watershed can be responsible for the magnitude of low flows, the minimum and mean monthly discharge, frequency and duration of high pulses, duration of small and large floods, indicators of annual minimum, 1, 7 and 90-day means, as well as indicators of annual maximum 7 and 90-day means. On the contrary, the agents are responsible for an increase the magnitude and frequency of small and large floods peak flow, number of zero-flow days, frequency of extreme low flows during each water year, annual maximum, 1-day mean, as well as changein timing of annual extreme water conditions, frequency and duration of high and low pulses.