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Research Project: Rethinking California’s Managed Aquifer Recharge Beyond Flat Terrains: A Multi-Method Assessment of Hillslope Processes

Location: Sustainable Agricultural Water Systems Research

Project Number: 2032-13220-002-018-S
Project Type: Non-Assistance Cooperative Agreement

Start Date: Jun 1, 2023
End Date: Jun 1, 2025

The main objectives of this research are 1) to investigate the mechanisms and processes controlling groundwater recharge on hillslopes and head watersheds, 2) to quantify the contribution of diffuse upland recharge contribution to California’s Central Valley aquifer using numerical modeling, and 3) to identify areas that are suitable for upland recharge and design methods to enhance groundwater recharge, thereby improving groundwater quantity in the Central Valley.

Hillslope processes in areas with complex topography and high lineament density is an important component of groundwater recharge that is presently poorly quantified. Existing hillslope models with various complexities will be utilized to understand and quantify the hydrologic fluxes with particular focus on diffuse and focused recharge as well as enhanced recharge scenarios. The partitioning of rainfall into runoff versus infiltration, and infiltration connectivity to aquifers, is also expected to depend on the precipitation received at the higher elevations, hillslope geology (i.e., bedrock type, the presence of unconsolidated material and fold/fault systems and their density), geomorphic properties (slopes, aspects, shape, slope length, etc.), land cover type and vegetation characteristics. The scope of this research is limited to the piedmont zone in the Turlock and Merced area to complement the integrated hydrological modeling studies underway aiming at investigating the impacts of climate change and management scenarios. The model will explore enhanced recharge scenarios on the foothills of the Turlock and Merced groundwater sub-basins. The hillslope simulations will be implemented using a surface runoff model (KINEROS2-K2), coupled KINEROS/Hydrus-1D model, and an integrated hydrologic model MIKE SHE, using model parameters determined from the available literature and existing modeling efforts. Scenario analysis will explore the efficacy of various management practices, including structural and biological slope modification techniques, and the impacts of lineaments in various managed aquifer recharge scenarios. In addition to the hillslope recharge scenario analysis, the project will explore the potential runoff outputs received in roadside channel structures to supplement groundwater replenishment efforts. Such outputs are currently diverted to nearby waterways and rivers, constituting considerable potential losses, whose extent remains poorly quantified. The project workflow will involve (1) the development of a database of road systems and necessary hydrologic, geomorphic, and climate variables, (2) the computation of hillslope runoff outputs received in the roadside channel structures, and (3) designing plans to repurpose the drainage systems on hillslope road systems which requires a close collaboration with hydrologists and design engineers in the California Transportation Department. The proposed work finds ways to expand the existing Managed Aquifer Recharge (MAR) techniques that are specific to flat terrain. This involves employing numerical techniques to assess the viability of management interventions aimed at augmenting groundwater in the piedmont zone surrounding the Central Valley, as well as designing efficient interventions.