Distributed Parameter Watershed Model
The Distributed Parameter Watershed Model (DPWM) is a water balance model developed by DBS&A scientists that quantifies groundwater recharge and produces highly defensible results that stand up in court and with regulatory agencies.
|In Nevada, the sustainable quantity of groundwater water rights in a basin is typically equated to the quantity of recharge. DBS&A applied DPWM to estimate the mean annual recharge to a basin in the southeastern part of the State. The model was supported by field measurements of precipitation, recharge, and runoff.|
DPWM enables users to assess the variability of groundwater recharge on a broad geographic scale and time period, offering significant improvement over traditional techniques commonly used in groundwater/surface water balance studies.
Based on the unique combination of climate, soil, vegetation, impervious surface coverage, and bedrock properties at a grid cell location within a watershed, DPWM estimates daily water balance components, including:
- Surface water runoff
- Evapotranspiration (ET)
- Snow melt
- Change in soil-water storage
Once recharge quantities are estimated, scientists can quantify the amount of water available within a groundwater basin to determine fair and correct allocation of water rights.
DPWM produces an output that can map the location and quantity of recharge within a watershed, as well as estimates of how recharge rates vary over time in water rights and environmental projects using highly defensible methods. DPWM yields results that are:
- Site-specific. Detailed site-specific data on climate, soils, and vegetation that are electronically published by government agencies are incorporated into groundwater basin studies.
- Flexible. Code may be efficiently modified or extended to meet unique project needs.
- Efficient and cost-effective. DPWM streamlines processes to include data acquisition from several regional and national databases and maximizes execution speed of large watershed files, resulting in more detailed analyses.
“DPWM is the most technical of the methods employed.”
~Nevada State Engineer
Based on the internationally recognized United Nations FAO 56 method, DBS&A has used DPWM in more than a dozen watersheds in the southwestern U.S. Specific applications include:
- Water Rights Adjudication
- DBS&A used DPWM to assess the quantity of groundwater recharge originating in the San Gabriel and Tehachapi Mountains to estimate the quantity of water rights available to the ranchers in the Antelope Valley Groundwater Adjudication.
- Estimating Evapotranspiration
- In support of water rights applications for a private water company in southeastern Nevada, DBS&A applied the DPWM to a riparian area to estimate the annual quantity of evapotranspiration. DPWM was supported by satellite measurements of evapotranspiration from select days during the growing season.
- Groundwater Modeling
- DPWM was an integral tool in developing a groundwater model of the Ojai Basin in Ventura County, California. DBS&A coupled DPWM with a groundwater model (MODFLOW-SURFACT) to evaluate the basin safe yield and response to several possible future alternative scenarios and climactic conditions, and to evaluate a proposed aquifer storage and recovery project.
- Environmental Assessment
- In DBS&A’s estimation of the spatial and temporal distribution of recharge at the Little Rock Mine in southeastern New Mexico, DPWM improved model calibration and was a cost-effective approach to address the limited hydrogeologic data available.
- DBS&A developed a water balance of the Newport Bay Watershed in Orange County, California, to address a U.S. EPA Total Maximum Daily Load regulation for selenium and nitrogen. Results were used to identify drivers of observed shallow groundwater and selenium flux to surface water channels.
- Water Planning for Development, Irrigation, or Conservation
- In consideration of future real estate development for the County of Inyo, California, DBS&A used DPWM to assess the impact of proposed groundwater pumping on groundwater discharge to springs and wetlands that supply a shallow lake nearby.
- DBS&A assisted the New Mexico Interstate Stream Commission to conduct a water resources investigation in the Salt Basin in southern New Mexico and western Texas, to develop a pre-development estimate of naturally occurring recharge rates for the entire basin.