Simulating impacts of EFR consideration on reservoir operation policy and irrigation management in the Hari Rod River Basin, Afghanistan

Abstract

The concept of the river environmental flow requirement (EFR) is emerged from the necessity of establishing a certain water level in the river to which the flow regime of the river can be altered from natural condition while preserving sustainability of the riverine ecosystem (Song et al., 2007; Tharme, 2003). There exists an unbalanced ecological environment in the Hari Rod River basin in Afghanistan, where the natural flora and fauna have been affected due to the years of civil war, severe drought, and growing pressure on the available water resources by different sectors. Sustainable utilization and effective allocation of the water resource while preserving integrity in the riverine ecosystem require understanding of the river flow systems in all river basins of Afghanistan. Thus, the present study attempts to quantify EFR required for healthy ecosystem, and potential impacts on the reservoir (proposed Salma dam reservoir) operation policy as well as irrigation management due to EFR allocation in the Hari Rod River basin of Afghanistan. The methodology followed in this study is largely based on observed data and information in the field. Recent (2001-2008) and past (1961-1980) records of available daily discharge and river bathymetry surveyed data are collected from Tagab Gaza monitoring station in the Hari Rod River. The secondary hydrological data is collected from irrigation department and FAO-EIRP office in Herat city of Afghanistan, and primary data is taken directly from field. The Tagab Gaza station is located immediately downstream of the reservoir and thus, EFR is estimated in this station to be applied in reservoir simulation model. Mean monthly precipitation, temperature, evaporation and soil data for the whole basin are also collected to calculate irrigation water requirement (IWR) for reservoir simulation. The methodological framework is divided into two parts: estimation of EFR and potential impacts of allocating EFR on reservoir operation policy and irrigation management by applying simulation technique. Well-known hydrological methods: (e.g. Tessman, Flow Duration Curve, 7Q10, Indicators of Hydrologic Alteration) and hydraulic method (e.g. Wetted Perimeter) were applied to quantify EFR. Details of all these approaches can be found in (Smakhtin and Anputhas, 2006). Two public domain models, HEC-ResSim and CROPWAT were used as tools to simulate reservoir system and to calculate IWR respectively. The result shows that hydrological based approaches are appropriate to estimate EFR in the Hari Rod River basin of Afghanistan. Generally, there is an indirect effect of allocating EFR on other existing demands from different sectors. Based on this assumption, reservoir model is simulated to operate the proposed reservoir (Salma dam) in the Hari Rod River basin of Afghanistan. Different alternative scenarios based on with or without EFR following existing or proposed guide curve, were generated to evaluate the possible impacts of EFR consideration on reservoir operation policy as well as on other (i.e. irrigation and hydropower) demands. Different mitigation options were also developed to minimize the impacts. Using simulation technique, a new conservation rule curve is developed to decrease the water shortages for irrigation caused by the additional demand due to EFR allocation. The present study conclusively proves that only 5% improvement in irrigation efficiency (IE) can mitigate entire water shortage impact in the Hari Rod River basin of Afghanistan.