Investigating Different Methods for Estimating the Need for Environmental Water (Case Study: Alandchay River)

Water resource development plans have several environmental impacts, the most important of which are natural river flow change and downstream surface reduction of flow. Estimation of the environmental flow required for the health of rivers and downstream ecosystems are of particular important. A sustainable strategy is a revision of the allocation of water for various uses and an increase in the share of the environmental flow from the current 10% to (20-40%) annual yields of rivers. The main objective of this study was to evaluate the monthly distribution of the environmental flow of an indicating river with a permanent flow (Alandachay river) using existing hydro-ecological methods.

In this paper, seven hydro-ecological methods were used: (1- Tennant; 2- Tessman; FDC 4- Smakhtin 5- FDC shifting 6-DRM; 7- Water-quality method called Q-relation). The results of environmental estimation of Alandachay River were calculated using different methods.

According to this paper, the environmental law of the Alandachay river in the FDC shifting method and with acceptance of the river conditions at the minimum ecological status acceptable (environmental management class C), at hydrometry station, average annual flow rate was estimated to be 1.56 cubic meters per second, which considering the amount of environmental water, the highest calculated amount of all seven methods and was calculated 0.39 by using Tennant method. The other remaining methods were between these methods.

The results of this paper show the accuracy of the FDC shifting method with the environmental class C at the studied station at 1.56 cubic meters per second as the bio-management class. These results show that quick methods of calculating the environmental flow used in Iran are mainly applied without considering the environmental conditions. This greatly reduces the accuracy of the results and even yields the opposite results.