Abstract
A recent assessment that quantified potential impacts of solar energy development on water resources in the southwestern United States necessitated the development of a methodology to identify locations of mountain front recharge (MFR) in order to guide land development decisions. A spatially explicit, slope-based algorithm was created to delineate MFR zones in 17 arid, mountainous watersheds using elevation and land cover data. Slopes were calculated from elevation data and grouped into 100 classes using iterative self-organizing classification. Candidate MFR zones were identified based on slope classes that were consistent with MFR. Land cover types that were inconsistent with groundwater recharge were excluded from the candidate areas to determine the final MFR zones. No MFR reference maps exist for comparison with the study’s results, so the reliability of the resulting MFR zone maps was evaluated qualitatively using slope, surficial geology, soil, and land cover datasets. MFR zones ranged from 74 km2 to 1547 km2 and accounted for 40% of the total watershed area studied. Slopes and surficial geologic materials that were present in the MFR zones were consistent with conditions at the mountain front, while soils and land cover that were present would generally promote groundwater recharge. Visual inspection of the MFR zone maps also confirmed the presence of well-recognized alluvial fan features in several study watersheds. While qualitative evaluation suggested that the algorithm reliably delineated MFR zones in most watersheds overall, the algorithm was better suited for application in watersheds that had characteristic Basin and Range topography and relatively flat basin floors than areas without these characteristics. Because the algorithm performed well to reliably delineate the spatial distribution of MFR, it would allow researchers to quantify aspects of the hydrologic processes associated with MFR and help local land resource managers to consider protection of critical groundwater recharge regions in their development decisions.
Highlights
Groundwater in the southwestern United States is limited by arid and semiarid climates, rising regional water demand, and potentially increasing climate variability
Delineating the spatial distribution of mountain front recharge (MFR) is valuable for allowing researchers to quantify aspects of the hydrologic processes associated with these areas and for helping local managers to consider protection of critical groundwater recharge regions when making land development decisions
The algorithm developed in this study is a novel approach for delineating MFR locations that integrates a terrain analysis approach with land cover that accounts for groundwater recharge rates
Summary
Groundwater in the southwestern United States is limited by arid and semiarid climates, rising regional water demand, and potentially increasing climate variability. This resource is replenished through groundwater recharge, a process that is affected by the expansion of land development. The US Department of Energy (DOE), Energy Efficiency and Renewable Energy Program, and the US Department of the Interior, Bureau of Land Management (BLM), released the Solar Programmatic Environmental Impact Statement (Solar PEIS) in 2012 [5], which evaluated a range of potential development options for production of utility-scale solar energy on federal lands in the southwestern United States. One of the options examined in the PEIS was to focus development of solar facilities in selected areas called solar energy zones (SEZs) that are located in large arid and semiarid basins in order to limit environmental impacts. This assessment necessitated the development of a methodology to identify locations of mountain front recharge (MFR) in order to facilitate land development decisions that would minimize impacts on ground water recharge occurring at the mountain front
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