Groundwater Model Update and Basin Study

The Paso Robles Groundwater Basin (Basin) encompasses a 790‐square mile area in the upper Salinas River watershed in Central California. During the last 15 years, the area has experienced both a growth in population as well as an increase in water use from a burgeoning wine industry. In 2012, the San Luis Obispo County Flood Control and Water Conservation District (District), along with other Basin stakeholders, recognized the need to begin a comprehensive groundwater basin study to better understand the basin’s hydrogeology, and to implement long range water resource planning tools to prevent critical overdraft.

The District and stakeholders recognized the need to update the Basin’s existing groundwater model. GEOSCIENCE served as part of a team to develop an up‐to‐date numerical groundwater flow model, which the District and stakeholders could use as a precursor for evaluating potential projects and programs for future basin management.

Making effective use of available data, along with GIS and other data collected, GEOSCIENCE developed a model that could support the District’s future model updates, as well as any related groundwater management efforts. GEOSCIENCE also conducted a new water balance analysis, evaluating rainfall recharge, subsurface inflow, stream‐groundwater interactions, agricultural irrigation rates, rural water use and groundwater storage change. GEOSCIENCE also calibrated the Basin Watershed Model, extending the analysis from the Basin to the surrounding watershed, by cost‐effective use of recent data and geographical and modeling software, therefore providing the District with a more comprehensive planning tool.

GEOSCIENCE’s approach included the:

  • Review and analysis of available and acquisition of current data to update the groundwater basin model to water year 2011
  • Development and calibration of the Basin Watershed Model
  • Update of groundwater basin water balance and safe yield
  • Development and performance of basin management scenarios, including supplemental water supply option