CONSTRAINING PUMPING TESTS WITH GRAVITY MEASUREMENTS

Abstract

Geophysical methods offer potential benefits for hydrologic investigations because they incorporate non-invasive, non-destructive measurements that are hydrologically relevant. This study compares the utility of gravity measurements to the utility of water-level measurements for constraining aquifer parameters in a model of transient ground-water flow in an unconfined aquifer. Gravity and/or water-level data with appropriate measurement uncertainty added are used to constrain aquifer transmissivity or hydraulic conductivity (K) and specific yield (Sy) estimates using the computer program UCO DE. The results demonstrate that the high correlation of the K and Sy parameters using only gravity measurement sets makes estimating unique Kand Sy parameters difficult and influences the quality of the estimated parameters. Parameter correlation is higher for the gravimeter response than for the well response because of the complex dependence of the gravity response on the shape and density change of the drawdown cone and because of spatial averaging by the gravimeter.