Modeling the response of groundwater levels in wells to changes in barometric pressure

Abstract

For many practical situations, the effect of barometric pressure variations on the water level in a well has been ignored. However, in many cases, water levels in wells are observed to fluctuate significantly in response to changes in barometric pressure. In this study, a physically based conceptual model for the influence of barometric pressure on groundwater wells was developed and tested. It is proposed that water level fluctuations in response to barometric pressure are due, in large part, to the different manner in which the pressure is propagated through the water column in the well and the porous media outside the well. Changes in pressure transmit through the water column in the well to the screened region with essentially negligible loss in pressure. On the contrary, pressure changes transferred through the porous media to the screened elevation outside the well undergo an irreversible transformation of fluid potential (head loss). Consequently, the loss in pressure head through the porous medium causes a lateral hydraulic head gradient to be developed around the well-screen region, as well as a vertical one through the porous medium. In response to the head gradient developed due to changes in barometric pressure, groundwater flows are induced through the well screen, with subsequent changes in well-casing storage. In the proposed model the well itself is an essential element. The well-water flux across the screen and the consequent change in wellcasing storage were appropriately linked with groundwater flow in the surroimding porous medium and estimated through an iteration technique. This approach incorporates the traditional governing theories on groundwater flow: conservation of mass and Darcy's law. Groundwater flow was modeled as two-dimensional (radial and vertical) unsteady flow, and