Estimation of subsurface flow in Marghab and Abgelal Watersheds using Salas Model in Khuzestan Province

Due to the water resources limitation in the country, subsurface flow of the seasonal rivers has an important role. These water resources can be used when collected by underground dams in locations with appropriate properties. In order to use the subsurface flow, it is necessary to estimate water resources potential accurately. Therefore, the aim of this study is to estimate the volume of subsurface flow using Salas model based on hydrologic balance. For this reason, the meteorologic and hydrometric information and data of 15 stations were by gathered and two hydrometric stations of Abgelal and Marghab were chosen as suitable ones by assessing and field survey. At these stations, the balance of subsurface flow was estimated using the above mentioned model. The results showed that in Abgelal watershed, 73 and 11 percent of the total rainfall were lost due to evapotranspiration and infiltration respectively, and just 16 percent was outflowed from watershed in the form of surface runoff. Also, most of the rainfall was outflowed through surface runoff in Marghab watershed and the coefficient of runoff was 58.7 percent. In this watershed, 41.2 percent of the total rainfall was infiltrated and 29.9 percent was lost due to evapotranspiration and 27.4 percent was infiltrated. Considering the area of Abgelal watershed of 151.6 km2, about 8.4 million m3 is drained annually as subsurface flows. According to the area of Marghab watershed of 664.3 km2, annually about 250 and 43 million m3 are drained as surface and subsurface flows, respectively. Also, evaluation of the model in both stations using relative root mean square error, Nash-Sutcliffe efficiency and mean absolute error, showed the amounts of 2.53, 0.53 and 10.08 in Marghab and 0.97, 0.32 and 8.9 in Abgelal station.