Riverside Basin Groundwater Modeling

The Riverside Groundwater Basin is a large alluvial fill basin that is bounded by major faults and topographic barriers. Recharge to the basin occurs by the underflow from basins to the north, contributions from the Santa Ana River, and from percolation of surface water runoff from the surrounding uplands, in particular the Box Spring Mountains to the east.

At the time of this project, City of Riverside produced about 18,000 acre-feet per year (ac-ft/yr) of water from the southern portion of the Riverside Basin and is planning to increase production up to a total of 45,000 ac-ft/yr in the future. To address the issues associated with increasing groundwater production in the southern portion of the Riverside Basin, SAWPA assisted the City of Riverside in developing a groundwater flow modeling study.

Phase 2 of the Riverside Groundwater Basin Study was specifically designed to address the following:

  • Identifying sources of artificial recharge and assessing the impacts of production and climate on groundwater levels in the Riverside area. This also entails estimating artificial recharge volumes and identifying optimal locations where artificial recharge could be developed to improve the reliability of groundwater production.
  • Increase Riverside Pumping to determine if the Riverside area can sustain a production level of 45,000 ac-ft/yr and assess the impacts of this production level on groundwater levels at the City’s wells. If a production level of 45,000 ac-ft/yr cannot be sustained, then determine the maximum sustainable production level for the basin.
  • Evaluate the impacts of groundwater production south of Highway 60 on other wells, specifically those in the North Orange area.

Tasks that were completed for this study include:

  • Define Planning Environment (Data Assembly) – assemble all pertinent information for development of the conceptual model (including recharge sources and volumes) and construction of the numerical models.
  • Evaluate Hydrogeology of Study Area (Develop Conceptual Model) – review and evaluate data assembled to refine our conceptual hydrogeologic model of the Riverside Basin. The task shall be assisted by interpretations of the USGS provided in public reports and recent studies and modeling conducted by the City of Riverside and SAWPA.
  • Prepare Hydrogeologic Planning Tool (Numerical Flow Model Development) – design a model of the Riverside Basin to represent all aspects of the conceptual model.
  • Conduct Basin Production Assessment – use the calibrated groundwater flow model to conduct a series of predictive simulations designed to specifically address the basin issues.
  • Prepare Study Report (Model Run Results and Model Documentation) – generate a comprehensive report that summarizes development of the groundwater flow and transport model. The report shall include a description of the Riverside Basin hydrogeology and conceptual model development.