Harnessing the Power of Geophysical Imaging to Recharge California’s Groundwater: Fastpath Web Application
The Place
Groundwater basins across California
The Problem
In 2014, in the midst of a record-breaking drought, the California Legislature passed the Sustainable Groundwater Management Act (SGMA), heralding a new approach to the management of groundwater in the state. The implementation of SGMA depends on local agencies, referred to as groundwater sustainability agencies (GSAs), that are vested with the responsibility for achieving sustainability. In order to address a systemic imbalance in the water budget - the water taken out of the groundwater system is much greater than the water going back in – many of the GSAs have plans to achieve sustainability that include a commitment to increase the “water going back in” – the recharge of the groundwater system. Recharge occurs naturally through the distributed infiltration of rainfall and snowmelt, and the more localized infiltration of water from rivers and lakes. Plans developed by the GSAs propose to supplement the natural recharge by selecting and allocating land for surface-spreading managed aquifer recharge which involves the spreading of water on the ground surface, and the movement of that water from the surface to the water table, tens of meters below the surface. Land that can be used for managed aquifer recharge includes dedicated recharge basins, agricultural land, and restored floodplains. The challenge is finding land where the composition of the subsurface materials is appropriate for recharge, that is, there are “fast-paths” of coarse-grained sand and gravel through impermeable clay-rich material, that can efficiently move the water from the ground surface to the target zones within the groundwater system.
Our Approach
Using two methods for geophysical imaging, one a helicopter-deployed airborne electromagnetic (AEM) system to acquire data at a regional-scale and one a towed system (tTEM) to acquire data at a local (site-specific) scale, we have acquired geophysical data, refined processing workflows, and developed new algorithms for assessment of sites for recharge. In Figure 1a we show the remarkable image of sediment type, to a depth of 400 m, recovered from data obtained over a 12-mile by 4-mile area in two hours with an AEM system, allowing us to identify fast-paths for recharge through the connected sand and gravel. In Figure 1b we show the scaled-down, higher-resolution image, identifying fast-paths for recharge beneath an almond grove, recovered from tTEM data acquired by driving the towed system for four hours between the rows of almond trees.
Our objective: to make all we have done readily available so that water managers, consultants, and technical staff in state and local agencies and in non-profit organizations can download the geophysical data sets and select the most favorable sites for recharge.
Results
We created a web-based software, making available the workflows developed over years of research, with the help of engineers at Curvenote. This applications allows anyone to access a database of the publicly available EM data and well data, and run through our workflows using cloud computing, to produce downloadable decision-support products. We collaborated with many partners throughout the state, representing local water management agencies, nonprofits, consultants, and state agencies, with the goal of understanding the diverse needs of the potential end-users of the software, and catering the development of the software to meet these needs.
Project Leads / Contacts
Sponsor: The Sustainability Accelerator through the Stanford Doerr School of Sustainability