UC groundwater research: A survey

California Agriculture (UCANR) | March 13th, 2018

As California implements the Sustainable Groundwater Management Act (SGMA), UC research is building knowledge and supporting innovation in groundwater recharge, groundwat

As California implements the Sustainable Groundwater Management Act (SGMA), UC research is building knowledge and supporting innovation in groundwater recharge, groundwater accounting, groundwater quality, groundwater governance and more. Here's a sample of work from across the UC system: whole watershed accounting; water availability for recharge; precision data on snowmelt; spatial data on well vulnerability; large scale groundwater recharge and agricultural systems; groundwater-surface water interactions; groundwater quality and salinity; water supply, land use and rural communities; data on water use and water rights; managed aquifer recharge on farmland; soil suitability for recharge; distributed stormwater collection; net metering for groundwater; geophysical imaging; groundwater governance; lessons on groundwater permitting from around the West; supporting Groundwater Sustainability Plan development; the economics of sustainable groundwater management; and considerations for groundwater markets.

Use of a Three-Dimensional Model for the Analysis of the Ground-Water Flow System in Parker Valley, Arizona and California

U.S. Geological Survey (USGS) | December 1st, 1982

User Manual for the California Central Valley Groundwater-Surface Water Simulation Model

California Department of Water Resources (DWR) | June 13th, 2013

This report describes the input and output files for the California Central Valley Groundwater-Surface Water Simulation Model (C2VSim). C2VSim is an integrated numeri

This report describes the input and output files for the California Central Valley Groundwater-Surface Water Simulation Model (C2VSim). C2VSim is an integrated numerical model simulating land surface processes and groundwater and surface water flows in the main alluvial aquifer system of California’s Central Valley (figure 1). C2VSim was developed using the Integrated Water Flow Model (IWFM) application, which couples a three-dimensional finite element groundwater simulation process with one-dimensional land surface, stream flow, lake, unsaturated zone and smallstream watershed simulation processes. The C2VSim version described in this report runs under IWFM version 3.02 and utilizes a coarse grid, and is thus referred to as version 3.02-CG. In addition, the input files for the C2VSim model are regularly updated to correct errors, incorporate improved input data or extend the simulation time period. These updates are referred to as revisions; this report describes the data in revision R374, released in June 2013. The C2VSim model inputs include monthly historical precipitation, stream inflows, surface water diversions, land use and crop acreages for the simulation period, October 1921 through September 2009. C2VSim dynamically calculates crop water demands, allocates contributions from precipitation, soil moisture and surface water diversions, and calculates the groundwater pumpage required to meet the remaining demand. The coarse grid version of the C2VSim model incorporates a finite element grid with 1392 elements, grouped into 21 water budget subregions (figure 1), which are further grouped by drainage basin into five hydrologic regions. The model subregions are based on Depletion Study Areas (DSAs), originally created by the DWR Division of Planning for estimating regional water supplies and demands. Hydrologic parameters (including hydraulic conductivities, storage parameters and recession coefficients) were calibrated to match observed values including groundwater heads, groundwater head differences between well pairs, surface water flows, and stream-groundwater flows for the period between September 1975 and October 2003. The model simulates the historical response of the Central Valley’s groundwater flow system to historical stresses, and can also be used to simulate the response to projected future stresses. Agricultural groundwater pumping is not monitored in the Central Valley, and the C2VSim model provides pumpage estimates that are considered robust because they are constrained spatially and temporally by the estimated demand and surface water supplies. The calibrated model is also being used as the basis for the groundwater flow component of CalSim 3, a water resources planning model for simulating operation of the California State Water Project (SWP) and Federal Central Valley Project (CVP).

Widespread potential loss of streamflow into underlying aquifers across the USA

Nature Portfolio (Springer Nature) | March 17th, 2021

Most rivers exchange water with surrounding aquifers. Where groundwater levels lie below nearby streams, streamwater can infiltrate through the streambed, reducing stream

Most rivers exchange water with surrounding aquifers. Where groundwater levels lie below nearby streams, streamwater can infiltrate through the streambed, reducing streamflow and recharging the aquifer. These ‘losing’ streams have important implications for water availability, riparian ecosystems and environmental flows, but the prevalence of losing streams remains poorly constrained by continent-wide in situ observations. Here we analyse water levels in 4.2 million wells across the contiguous USA and show that nearly two-thirds (64 per cent) of them lie below nearby stream surfaces, implying that these streamwaters will seep into the subsurface if it is sufficiently permeable. A lack of adequate permeability data prevents us from quantifying the magnitudes of these subsurface flows, but our analysis nonetheless demonstrates widespread potential for streamwater losses into underlying aquifers. These potentially losing rivers are more common in drier climates, flatter landscapes and regions with extensive groundwater pumping. Our results thus imply that climatic factors, geological conditions and historic groundwater pumping jointly contribute to the widespread risk of streams losing flow into surrounding aquifers instead of gaining flow from them. Recent modelling studies have suggested that losing streams could become common in future decades, but our direct observations show that many rivers across the USA are already potentially losing flow, highlighting the importance of coordinating groundwater and surface water policy.