Significance of a seepage face on flows to wells in unconfined aquifers

Abstract

When pumping occurs from a well in an unconfined aquifer, a seepage face develops between the elevation where water table intercepts the well face and the water level in the well. The existence of a seepage face often leads to well yields which are less than values determined by conventional analysis. Using numerical models to represent the two-dimensional flow through an aquifer to a well bore, the distribution of inflows at the well face are determined; flows per unit depth (incremental flows) from the seepage face are normally less than those into the water column. Two case studies are examined; numerical model simulations show that as the pumping rate is increased and the water level in the well falls, incremental flows from the seepage face into the well bore are unchanged although incremental flows into the water column do increase. When pumping ceases from a well with a significant seepage face, rapid recovery of the well water level occurs, this allows estimates to be made of water table elevations at a pumping station; the methodology is illustrated by a field example.