Evaluating and Modifying the Texas Method as a Hydrologic Method for Prescribing Ecological Regime in Perennial Rivers

This study aims at evaluating and modifying the Texas method for allocating environmental flow. This hydrologic method, while using the minimum amount of data, is a rival for the Tenant method and has the capability of introducing an amount of discharge to maintain the ecological regime of rivers. In this paper, after distinguishing the worthiness of the Texas method and observing some differences between the results of the method and the historical regime in the case study, the method was modified in such a way that while preserving the basic principal of the original method, could propose a flow regime which was laid between the observed long-term minimum and mean monthly discharges. The new method is called the Modified Texas method. For evaluating the Texas and Modified Texas methods concerning the allocated annual volume, the equivalent scenario from the Tennant method was employed. The allocated volumes by the Modified Texas, Texas, and Tenant methods were 50%, 47%, and 40-60%, respectively. This paper, concerning the achieved results for the case study, shows that employing the Texas and Modified Texas methods instead of the Tenant method and enhancing the method to the level of a native method provides reasonable results comparable with those of the habitat simulation or holistic methods.