Stream aquifer interaction in a multi-layered system – A research report by National Institute of Hydrology

In the present report a mathematical model has been developed for the study of stream aquifer interaction in multilayered system viz. a three-aquifer system, in which aquifers are separated by aquitards, considering varying stream-stage and vertical flow through aquitards. The model enables the computation of rates of recharge to the upper aquifer and exchanges of flow among aquifers along with the spatial and temporal distributions of piezometric heads in the aquifers.

A system of extensive aquifers sandwiched between silty or clayey beds are common in alluvial basins. Such a system is known as multi-aquifer or multi-layered system. Often a river penetrates the upper aquifer in such a multi-layered system fully or partially. When the river stage rises during the passage of flood, the upper aquifer is recharged through the bed and banks of the river. The lower aquifers are recharged through the intervening aquitards.

The methodology presented by Mishra (1978b) for a two-aquifer system, has been shown to be the special case of present formulation. The model has been validated against the numerical simulation using MODFLOW for different cases. MODFLOW source code was modified to get the exchange of flow from each strip and its spatial & temporal summation. Close reproduction of results using MODFLOW show that the methodology based on discrete kernel approach, is valid for the analysis of the interaction of stream and multi-aquifer system.

The following conclusions can be drawn from the study:

• A methodology based on discrete kernel approach has been evolved for solving stream-aquifer interaction in multi-layered aquifer system in which three aquifers are separated by two intervening aquitards. In this, time varying stream-stage and vertical transfer of flow between aquifers through aquitards, can be accounted. Using the present approach, recharge from stream and exchange of flow between aquifers along with the rise in piezometric surface in each aquifer, can be obtained. The methodology can easily be extended to more than three aquifers.
• Three dimensional groundwater flow model (MODFLOW) has been used to reproduce the results of stream-aquifer interaction in two-aquifer system using discrete kernel approach for four different cases.

Download the report here: