Improved Imaging of the Large-Scale Structure of a Groundwater System
with Airborne Electromagnetic Data
Abstract
Working with airborne electromagnetic (AEM) data acquired in the Kaweah
Subbasin in the Central Valley of California, U.S.A., we developed a new
approach for imaging the top of the bedrock and the confining Corcoran
Clay layer. Our approach included multiple L2-norm and Lp-norm
inversions as well as an interpolation process. The major improvement in
imaging the two targets was made in the Lp-norm inversion step by
incorporating prior knowledge. For the Corcoran Clay, pairs of
resistivity and driller’s logs at two wells guided the selection of the
best resistivity model and were used to increase the accuracy of the
estimated Clay thickness. The bedrock surface was poorly constrained by
well data in the existing groundwater model, appearing as a flat
surface. We had good AEM data coverage in the area so had higher
confidence in the obtained map of the bedrock surface at depths ranging
from 15 m to 160 m. There was relatively good agreement between the
location of the Corcoran Clay in the AEM data (depth ranging from 50 to
130 m and thickness ranging from 3 to 25 m) and the existing groundwater
model, with both depth and thickness showing ~15%
relative difference. The AEM data provided information about the
continuity of the Corcoran Clay that is challenging to capture in the
well data. The locations of the bedrock and Corcoran Clay were used in a
structurally-constrained inversion to improve the imaging of the
smaller-scale resistivity structure.