Water balance investigation of selected watersheds led to west-south frontiers and Persian Gulf (Case Study: Khuzestan Province)

Due to water scarcity in arid and Semiarid, using a combination of different approaches is inevitable that in this regard, the underground dams are important. One of the basic parameters for design of underground dams is amount of subsurface flow. The potential of subsurface flow depends on upland rainfall, amount of evaporation, surface flow discharge, watershed area, and morphology of river bed. Up to now, the discharge and volume of subsurface water have generally been calculated by using equilibrium and water balance equation. However, the goal of this project is calculating the volume of subsurface flow through hydrologic budget at suitable hydrometric stations. In this project, by assessing the gathered meteorological and hydrometrical information and data of 15 stations and after visiting them by considering the parameters such as the mountain area, slope restrictions, river discharge, electrical conductivity, geological formations, watershed area and land use, consequently two hydrometric stations were defined as suitable in Marghab and Abgelal watersheds. The results showed in Abgelal watershed, of the total rainfall, 73 and 11 percent is evaporated and infiltrated respectively, and about 15.9 percent of precipitation flows as runoff. Also in Marghab watershed, most of the rainfall is flowed through surface runoff, as the results of the model, in this basin the coefficient of runoff is equivalent to 58.76 percent. In this watershed, of the total rainfall, 41.24 percent is infiltrated. Of this infiltrated water, about 72.59 percent is evaporated and return to the atmosphere and 27.41 percent of it flows as groundwater. Consequently, 11.3 percent of this infiltrated water is percolated on ground water. Considering the area of Abgelal watershed (151.62 km2), annually about 8.4 million cubic meters are drained as subsurface flows. According to the area of Marghab watershed (664.33 km2), annually about 250, and 43 million cubic meters are drained as surface flows and subsurface flows respectively. Therefore, in a summary, it can be said that the amount of subsurface flow depending on the watershed characteristics will be different from one watershed to another watershed. Therefore, with proper planning and finding the proper location for Construction the underground dams can be used optimal utilization of subsurface flow. In this study, evaluation of Salas model was investigated for both Marghab and Baghmalek station using relative root mean square error, Nash Sutcliffe efficiency, mean biased error, and mean absolute error .The results showed that the runoff estimation model, Salas model, is more effective in Marghab than in Baghmalek. Also in Baghmalek station, according to Nash Sutcliffe efficiency (0.32), relative root mean squared error (0.97), and mean biased error (7.8 percent) showed that the Salas model is effective approximately.