River Environmental Flow Assessment Using Tennant, Tessman, FDC Shifting and DRM Hydrological Methods

Different approaches have been presented for estimating river environmental flow which hydrological approach has a lot addressed because of its need to access to limited data and moderately rapid assessment. This approach incorporates various methods therefore comparison between results of different methods is essential. The objective of this study is to investigate and compare the consequences of Tennant, flow duration curve shifting (FDC shifting), desktop reserve model and Tessman methods for environmental flow assessment of Zohreh river (Dehmolla hydrometry station) located in southwestern Iran. According to the long-term flow data the annual mean flow is 80.18 cms and August-October and February-April with 22.5 and 156.2 cms are low and high flow periods of the year. Investigation of consequences of different methods demonstrate FDC shifting is most admissible method for environmental flow assessment in this study because of its reasonable exhibited environmental flows in different months in comparison with monthly and annual mean flow, good compatibility of within-year patterns of monthly environmental and river flow, and lack of allocation of all river flow to environmental flow in all months of the year. Considering the results of the FDC shifting method the monthly environmental flow are estimated between 6.8 to 53.2 cms and its mean annual is 27.79 cms. The mean environmental flow for low and high flow periods are 7.7 and 49.3 cms respectively too.