Hydraulics of Flow over the Weir of Subsurface Dams

One of the most substantial water resources in water engineering is the groundwater, stored inaquifers. In arid and tropical regions having monsoon climate, the groundwater accumulated under theground and used later during dry seasons. The use of subsurface dams in aquifers to store water behindthe dam is one of the common techniques in recent years. But a weir should be constructed insubsurface dam body to convey the excess water from the aquifer. Without an appropriate weir towithdraw the excess water, groundwater level will reach the ground surface and in addition todisrupting the lands application, will cause inevitable damages to the environment. In this study, theeffects of characteristics of weir together with the aquifer hydrodynamic properties on groundwaterflow discharge are studied. The effects of different hydraulic parameters on the flow rate through theweir of the dam are also investigated. An experimental model of the aquifer, including undergroundreservoir, dam and weir is built and the effects of different parameters such as hydraulic conductivityof the aquifer, head above the weir, height of the weir and weir crest length on the discharge throughthe weir in steady state condition are tested. The results show that increasing the hydraulicconductivity of the aquifer, yields an increase of the flow discharge. By increasing the weir height, thehead above the weir or the weir crest length, the discharge increases. In order to evaluate all theinfluential parameters and analyze their effects on flow discharge through the subsurface weir, theSeep3D software is used. The results of numerical models are verified using the measured data. Thendifferent models of underground dams and were prepared and the effect of each influential parameteron the groundwater discharge through the weir was studied. Results of numerical models showed thatthe hydraulic conductivity of aquifer, head above the weir and the effective width of the aquifer are themost significant parameters to establish a certain groundwater discharge through the weir.