Optimal Management of Water Resources Using Application of Various Scenarios of Water Allocation (case study: Dez basin))

Introduction
Water allocation in arid and semi-arid regions is considered a human challenge all around the world. The need for optimum utilization of water resources, especially in agricultural use, is very important. Agriculture, which uses the greatest percentage of most water resources, has also penetrated in human life and culture.  The aim of this study is to provide an approach to allocate and optimize water use in Dez basin using WEAP model.
 
Methodology
The date regarding the users of water resources in Dez basin including the agricultural, domestic and industrial water demands, the precipitation, and the flow of rivers were collected from 2009 to 2014. All data were averaged monthly. The conceptual model was defined in WEAP. In term of model calibration, 60 percent of runoff data were used. The other 30 percent of remaining data were employed for the validation part. The optimum utilization policy of water resources in various scenarios were defined in WEAP. The scenarios were tested based on cropping pattern changes, reducing agricultural area, and the changes in irrigated and rain-fed ratio. All scenarios were compared by the reference scenario. In this scenario, the lowest percentage of need was related to the Western Dose. In this scenario, the course was 100 percent selected for drinking and industrial purposes in cities (Dezful, Andimeshk, Shoosh, Safi Abad, Dezab, Mardrood, Hor, Hamza and Saleh Shahr) and the entire villages of the region and some small industries due to the priority of providing higher, water use efficiency. On the other hand, due to the water withdrawal, regardless of the needs of the downstream and the transition to Karkheh, the percentage of providing low consumption needs as well as the percentage of the environmental need was not satisfactory. In order to improve the status of the reference scenario and the basin, two scenarios were defined. Considering that the agricultural sector is the largest water consumer in the region, it would be possible to significantly balance the supply-demand balance between water supply and demand by reducing the consumption in this sector. The scenarios were designed to reduce water consumption in agriculture and increase its economic efficiency in the basin. In all scenarios, the objective function was to optimize the benefit by cost ratio. In the scenarios implemented, the confidence level of other water uses, including the needs of the plain, downstream, environmental requirements, and energy requirements, was calculated to be 100%. In the second scenario, the water consumption of each product was studied in each plain. Regarding the diversity of products, in each plain, the products with high crop yields were considered and given the amount of water consumed by each plant. Moreover, the performance and the guaranteed price of purchasing those high-value products were identified and replaced with low-cost products. Finally, in the third scenario, by varying the percentage of irrigated and rain-fed products, the study of the amount of water saved versus the decline in the production of products was studied. Then, by evaluating the price of water versus crop products, the efficiency of this scenario was examined. Also, for each plain, the optimal percentage of irrigated and rain-fed area was determined. The optimal water and dry crop percentage was estimated based on the performance of these products and the amount of water consumed.