Applied Geophysics for Managed Aquifer Recharge

Abstract

Increasing water stress and decreasing supplies caused by growth and climate variability have expanded demand for managed aquifer recharge (MAR) projects to provide water supply resilience. Some of the most important factors in determining the performance of a MAR project include site selection, subsurface hydrogeologic characteristics and associated properties of the storage zone. Costs for invasive subsurface investigations to address these factors have slowly increased over the past two decades, with drilling costs increasing dramatically by as much as 30% or more since COVID‐19 hit, a result of supply chain issues, steel prices, and manpower challenges. This paper provides a high‐level review of major geophysical methods that have become more mainstream over the past decade or two to supplement invasive subsurface investigations and are very cost effective when compared to drilling boreholes and installing wells, which provide only point data. The more commonly used surface geophysical methods include ground‐based and airborne time‐domain electromagnetic methods (TEM), electrical resistivity, and seismic reflection. Airborne TEM methods (AEM) collect data very quickly, avoiding ground‐based access constraints, and land‐based methods are especially efficient using towed arrays. Electrical resistivity measurements provide resolution comparable to TEM but require more time than towed methods. Seismic reflection surveys are more expensive than other methods but typically have a much greater depth of penetration and can provide high resolution information on aquifer geometry, geology, and faults. Borehole geophysics is one of the more common methods used in MAR, providing near hole formation data and ground truths surface geophysics.

Controls on flood managed aquifer recharge through a heterogeneous vadose zone: hydrologic modeling at a site characterized with surface geophysics

“…Given the importance of quantifying geologic heterogeneity at recharge sites, near-surface geophysical methods have become a popular tool for MAR site evaluation, as they can provide cost-effective, high-resolution imaging of the subsurface. Common techniques include electrical resistivity tomography, transient electromagnetic, frequency domain electromagnetic, seismic reflection and nuclear magnetic res-onance methods (Haines et al, 2009;Maliva et al, 2009;Gottschalk et al, 2017;Goebel and Knight, 2021;Sendrós et al, 2020a;Walsh et al, 2014;Parker et al, 2022). The use and availability of near-surface geophysical data are expected to continue growing in the future.…”

Controls on managed aquifer recharge through a heterogeneous vadose zone: hydrologic modeling at a site characterized with surface geophysics

“…Given the importance of quantifying geologic heterogeneity at recharge sites, near-surface geophysical methods have become a popular tool for MAR site evaluation, as they can provide cost effective, high resolution imaging of the subsurface. Common techniques include electrical resistivity tomography, transient electromagnetic, frequency domain electromagnetic, seismic reflection and nuclear magnetic resonance methods (Haines et al, 2009;Maliva et al, 2009;Gottschalk et al, 2017;Goebel and Knight, 2021;Sendrós et al, 2020a;Walsh et al, 2014;Parker et al, 2022). The use and availability of near-surface geophysical data is expected to continue growing in the future.…”