Geophysical Input to Improve the Conceptual Model of the Hydrogeological Framework of a Coastal Karstic Aquifer: Uley South Basin, South Australia

Abstract

A lack of closely spaced datasets on layer elevations, aquifer parameters, identification of areas with high recharge potential, dominant conduit porosity zones, and well defined boundary conditions hampers the ability of groundwater models to produce a reliable water balance. Typically, geological structure, aquifer properties, and groundwater heads are obtained from point measurements which are sparse. The drillhole information in aquifers is usually available at locations far apart, distances ranging from hundreds to thousands of meters. Furthermore, pump tests are usually conducted at limited locations and generalized to the aquifer. This limited knowledge leads to errors in the conceptual understanding of the aquifer. In this study, Airborne Electromagnetic Survey (AEM) was used to define base elevations of the aquifers where drillhole information was lacking. Surface Nuclear Magnetic Resonance (sNMR), borehole NMR, Transient Electromagnetic (TEM), and downhole geophysical surveys have given new insight to the conceptualization of hydrogeological framework. These methods are relatively low in cost compared to traditional well drilling and provide information on layer elevations, aquifer parameters, point and diffuse recharge zones, and conduit porosity zones in the profile, which improves our definition of the boundary conditions. From a practical point of view, combining drillhole information with a variety of geophysical techniques provides sound datasets to develop a comprehensive conceptual model. This in turn can be used to build a robust groundwater model.

Combining geophysical and geological datasets to improve a conceptual aquifer model of the Oak Openings Region in northwest Ohio, USA

“…Areas with relatively lower resistivity within the bedrock could be associated with potential fractures or dissolution cavities within the dolomite. Such fractures and or dissolution cavities within carbonate aquifers result in higher secondary porosity and permeability, allow a higher amount of groundwater ow, and are associated with lower electrical resistivity (Redhaounia et al, 2016;Somaratne et al, 2018). While the electrical resistivity identi es contrast between all four lithostratigraphic units, the method is limited in delineating the exact lithological boundaries.…”

“…However, a common problem with 3-D geological models is obtaining hydrostratigraphic data that meets the required quality, quantity, and spatial distribution, especially in regional studies where high costs of acquiring detailed, high-density subsurface data generally result in dependence on less reliable data that still needs to be standardized and validated (Ross et al, 2005;Ventris, 2007). The shortage of input data to the models is often compensated by combining geological data with meteorological (Karlović et al, 2021), hydrogeochemical (Kpegli et al, 2018), and geophysical data (Francés et al, 2015;Somaratne et al, 2018).…”