TR-23 : Determination of aquifer recharge for varying river stages

Abstract

In a sedimentary groundwater basin occurrence of multiple aquifer separated by confining layers of low and negligible permeability is quite common. A stream in such basin may penetrate either partially or fully the top aquifer. During the passage of a flood the river stage changes rapidly. The rise in river stages above the aquifer water level in the vicinity of the river leads to recharge of groundwater. Consequent to rise in river stage, the upper aquifer is recharged directly through the bed and banks of the river and the lower aquifers are recharged from the top aquifer through the intervening aquitard. In the present report, the interaction of two aquifers and a river has been studied analytically. The recharge from the river to the upper aquifer and exchange of flow between the two aquifers through the aquitard have been quantified for a known fluctuation pattern in river stage. Each aquifer has been assumed to be homogeneous isotropic and of large areal extent. The time parameter has been discretised and interaction problem has been solved assuming each of the aquifers to be a linear system. The analytical solution is tractable for numerical computation. The storage coefficient of the lower aquifer controls the quantity of recharge from the upper aquifer.