When Does the Loading Efficiency Effect the Groundwater Response to Stage Variations in Shallow Streams?

Abstract:

The tidal efficiency is commonly included when analyzing the aquifer response to tidal variations in shallow streams that only partially penetrate the aquifer. Strangely enough, the tidal efficiency (more properly called the loading efficiency) is not commonly included in analyzing the aquifer response to arbitrary stage variations. The loading efficiency is the ratio between the instantaneous head response below a stream and the change in the stream stage. In soft soils, such as sand and clay, the instantaneous head response below a stream is equal to the stage change, which means that the loading efficiency is near one. For stiffer porous media, such as sand stones and other porous rocks, the loading efficiency is significantly smaller than one. New solutions are derived for the aquifer response to arbitrary stream stage variations in both single layer and multiple layer models while taking the loading efficiency into account. The effect of the loading efficiency on the aquifer response is analyzed for shallow streams that partially penetrate the aquifer. Guidelines are developed for when to include the loading efficiency for unconfined, semi-confined, and confined flow.