ABSTRA C T Recently, one of the most substantial water resources in water resources management is the groundwater, stored in aquifers. In arid and tropical regions having monsoon climate, the groundwater should be accumulated under the ground to be used in dry seasons. The use of subsurface dams in aquifers to store water behind the dam is one of the common techniques in recent years. But a weir should be constructed in subsurface dam body to convey out the excess water from the aquifer. Without an appropriate weir to withdrawal the extra water, groundwater level would reach to the ground surface and in addition to disrupting the lands application, will enter inevitable damages to the environment. In this study, the effects of characteristics of weir together with the aquifer hydrodynamic properties on groundwater flow discharge are studied. The effects of different hydraulic parameters on the flow rate through the weir of the dam are also investigated. An experimental model of the aquifer, including underground reservoir, dam and weir is built and the effects of different parameters such as hydraulic conductivity of the aquifer, head above the weir, height of the weir and weir crest length on the discharge through the weir in steady state condition are tested. The results show that increasing the hydraulic conductivity of the aquifer, yields to increase the flow discharge. By increasing the weir height or the head above the weir or the weir crest length, the discharge increases. In order to evaluate all the influential parameters and analyze their effects on flow discharge through the subsurface weir, the Seep3D software is used. The results of numerical models are verified using the measured data. Then different models of underground dams and weirs prepared and the effect of each influential parameter on the groundwater discharge through the weir has been studied. Results of numerical models showed that the hydraulic conductivity of aquifer, head above the weir and the effective width of the aquifer are the most significant parameters to establish a certain groundwater discharge through the weir. Keywords: Aquifer, Subsurface Dam, Flow Hydraulics, Weir, Hydraulic Conductivity
