Using the WEAP model to evaluate the consumption management of Ayushan dam for different uses

Introduction
One of the most important challenges of exploiting water resource management systems and specifically surface reservoirs in facing hydrological changes is to consider the occurrence of drought in the way of exploiting water resources. In addition to the changes in discharge compared to the average, another important factor is the continuation of the drought phenomenon. One of the ways to deal with drought is the proper use of water resources in drought conditions. Various models such as WEAP have been developed to exploit water resources. But such a model does not have the ability to model the exploitation of reservoirs in drought conditions. Therefore, developing such a possibility in the WEAP model is very important for water resources engineers. Considering the development of the WEAP model as a tool for flexible, comprehensive, and transparent planning in evaluating the various long-term conditions of the basin, this model has been used to simulate the water resources and develop different scenarios for the exploitation of water resources.
 
Materials and Methods
The studied area is located in the southwestern part of Iran, in Lorestan province, and in the range of Zagros slopes, which is called the catchment area of the Chaghlund reservoir dam. The area of this watershed is about 1187.8 square kilometers, which is surrounded by the Chaglundi watershed. Working with the WEAP model is done in several steps including problem definition, time frame, spatial boundaries and system components, and problem settings. The scenarios are made in the existing conditions and by using them, the effect of different assumptions or policies on the availability and consumption of water in the future can be checked. Finally, the scenarios are evaluated according to the amount of water, costs, and benefits, compatibility with environmental goals, and sensitivity to uncertainty in key variables. In the WEAP model, system components (including nodes of water resources and uses, how they are related to each other, and allocation priorities) and the introduction of time characteristics (base year, time period, time steps of calculations, etc.) are defined. In the base year, water needs, capacity, and characteristics of resources, pollution loads, system costs in the current state are entered. By initially running the model in the base year and comparing the results with the available information, this step can be considered a calibration step. To prepare the main framework of the model in the WEAP software, first, the basic maps that include the borders of the studied basin, the routes of the rivers in the basin, the location of dams and diversion dams for water intake and hydrometric stations, all the points of need and available water resources and in general all the tolls which are needed to determine the main framework of the model was prepared in the GIS environment. After this work, the prepared maps were called in the WEAP software environment.
 
Results and Discussion
To calibrate the model, the monthly discharge data of the Ayushan dam before the intersection of the Herod river and the observation storage volume of the simulated reservoir were considered as observation values from the Ayushan hydrometric station at the site of the Ayushan dam. In order to ensure the performance of the simulation model, the observed and simulated values of the Mokhren storage volume in Herod River were drawn. A correlation of 0.57 was obtained between the observed and calculated values ​of the model, and the maximum values simulated by the model are close to the observed values. Also, at this stage, the storage volume of the Ayushan dam reservoir was simulated in the existing conditions, and it was observed that the correlation between the storage volume of the reservoir dam and the computational storage volume of the model was 0.49, and contrary to the low The degree of simulation correlation is simulated in maximum values ​with a small time difference and in some places the values ​are lower than the observed values. Based on the existing conditions, the monthly amounts of agricultural needs were simulated for each network. Based on this diagram and the reliability percentage diagram, it can be seen that the needs are 100 % provided except for the Dolisan range, every month. Reliability or reliability, in fact, means the probability that the system will perform the assigned tasks without failure, this value has been obtained. For this scenario, it can be seen that the amount of water withdrawal for drinking and industry and the irrigation networks downstream of the Ayushan dam is 100%, and the irrigation networks of the two aquifers of Chaglundi and Yesian are 100%, and for Dolisan agriculture is less than 80% was achieved by first providing surface water sources (Herod River) and then underground water. From the results of the first scenario for the environmental needs of the region, it can be seen that in the months of April and May, during the simulation period, for the months of spring, which should be around 60%, around 10% less than the allowed limit is provided, and this is undesirable. In a study conducted in the Lifan Basin in South Africa using the WEAP model to simulate and analyze its allocation scenarios, it was observed that 85% of the water demand was provided under the existing conditions.
 
Conclusion
The results showed that the simulation of water resources exploitation of the study basin using the WEAP model was done with appropriate accuracy and the performance had a good. The results of the evaluation of the scenarios showed that in the scenario of the existing conditions, due to the limitation created by the relevant bodies in allocating water to a limited area of the covered plain, the reliability coefficient for drinking and irrigation and drainage networks is 100% and the environmental needs of the region under these conditions in the months of April and May during the simulation period were provided about 10% less than the allowed limit and this is undesirable for the spring months which should be around 60%. In the reference scenario, despite the population increase in the coming years, due to setting the first priority in the allocation to drinking consumption in the simulation model, the need for drinking and industry will be fully provided. The agricultural needs in the irrigation networks downstream of the studied dam are 100% provided in all months, but the agricultural needs supplied from the Dolisan Plain aquifer in all months were less than 60% of the water needs. The minimum environmental requirement of the lower reaches of Herod River, which is considered for the survival of the region's ecosystem, is less than 50% in the spring months and is significant.