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Improving Groundwater Models by Combining Airborne EM and InSAR data

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Kaweah Subbasin Map
Figure 1: Map of the Kaweah subbasin, outline of the groundwater model, and location of AEM datasets collected in the basin.

The Place

The Kaweah subbasin, located in California’s San Joaquin Valley, in a critically overdrafted groundwater basin. Within the basin, chronic groundwater overdraft has resulted in a number of issues, including declining head levels and land subsidence. Like many other basins within the state, Groundwater managers have been tasked with developing plans for sustainable groundwater management under the SGMA legislation. Their groundwater model is one of the tools being used as they develop and implement their management plans.

The Problem

A groundwater model is one of the key tools used for decision-making in the management of groundwater resources. Most existing models however, utilize limited geologic data at depths relevant to these management decisions. To improve the prediction accuracy of all the available models there is a critical need for data to inform the models. But the currently employed, traditional methods of acquiring data, through the drilling of wells with testing and logging, are slow, expensive and insufficient in terms of data coverage.

Our Approach

The goal of this work is to improve the spatial resolution and prediction accuracy of groundwater models by incorporating information derived from interferometric synthetic aperture radar (InSAR) data and airborne electromagnetic (AEM) data. We will develop a methodology that will update the groundwater model in the Kaweah subbasin to obtain a model with the required spatial resolution and hydrologic/geomechanical properties so as to provide improved accuracy in prediction of groundwater flow and in prediction of pumping-induced aquifer system compaction and resulting subsidence. Figure 1 shows a map of our study area, along with the boundaries of the groundwater model and the locations where AEM has been acquired over the basin.

Results to Date

The Kaweah groundwater model has been updated to include a subsidence package, and to incorporate information derived from AEM data collected across the basin. Specifically, the AEM data had been used to map the large scale hydrogeologic structure, defining the model layers, and had been used to determine the spatially varying clay content within the aquifer layers of the model. As part of this project, a new method was developed for the inversion of the AEM data, to best inform this model. Figure 2 shows the resistivity models derived from this new inversion approach, and highlights the key structure identified within these models.  Calibration of the groundwater model, using both head and land subsidence data (derived from InSAR) is ongoing. One of the InSAR datasets used for this calibration is shown in Figure 3.

Kaweah resistivity models
Figure 2: Resistivity models derived from the inversion of AEM data within the Kaweah subbasin, using the new inversion approach developed by Kang et al. (2022).
Kaweah InSAR deformation
Figure 3: Map showing the deformation derived from InSAR from 2015-2019 in the study area. The groundwater model boundary is noted in red. The InSAR deformation shows good agreement with the two continuously monitoring GPS stations within the basins.

Project Sponsors

NASA Applied Sciences Water Resources Program

The Gordon and Betty Moore Foundation

Project Publications and Presentations

Kang, S., Knight, R., & Goebel, M. (2022). Improved Imaging of the Large-Scale Structure of a Groundwater System With Airborne Electromagnetic Data. Water Resources Research, 58(4), e2021WR031439. https://doi.org/https://doi.org/10.1029/2021WR031439

Project Leads / Contacts

Meredith Goebel

Rosemary Knight

Seogi Kang