Hydraulics of Flow over the Weir of Subsurface Dams

One of the most substantial water resources in water engineering is the groundwater, stored in
aquifers. In arid and tropical regions having monsoon climate, the groundwater accumulated under the
ground and used later during 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 the excess water from the aquifer. Without an appropriate weir to
withdraw the excess water, groundwater level will reach the ground surface and in addition to
disrupting the lands application, will cause 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 an increase of the flow discharge. By increasing the weir height, 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 were prepared and the effect of each influential parameter
on the groundwater discharge through the weir was 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.