M&A provided technical support since the start of SGMA implementation. We successfully submitted an application for a basin boundary modification, assisted with preparing a GSP, and continue to serve as technical consultant.

Santa Cruz Mid-County Groundwater Agency

Location: Santa Cruz County, California
M&A was integral in developing all the technical aspects of the Santa Cruz Mid-County Basin GSP including an integrated surface water-groundwater model.


M&A (as HydroMetrics WRI) provided technical assistance for Groundwater Sustainability Agency (GSA) formation and a basin boundary modification that combined parts of four basins into a single basin and excluded fringe areas of the basin that do not impact groundwater management. M&A helped the MGA develop its GSP for the critically overdrafted basin, focusing on the GSP advisory committee of stakeholders’ common understanding of the hydrogeology of the basin and its historical and current conditions.

M&A also developed a basin-wide GSFLOW (groundwater and surface-water flow) model to quantify water budgets, support development of sustainable management criteria, and assess the benefits of various groundwater management projects and actions. The GSFLOW model combines the Precipitation-Runoff Modeling System model for surface watersheds with a MODFLOW-based groundwater model. New regulations for GSPs set surface water-groundwater models as a technical standard, and the California Department of Water Resources staff has provided positive feedback on the choice to use GSFLOW.


Groundwater Management

  • Integrate with the executive team of the MGA’s member agencies, a facilitation firm, and agency staff members to develop the sustainable management criteria and other required technical elements of the GSP
  • Present technical content to the GSP advisory committee
  • Develop subsequent iterations of the sustainable management criteria based on input received from the GSP advisory committee
  • Provide technical justification and apply to modify groundwater basin boundaries
  • Apply for grant funding
  • Prepare GSP annual reports

Groundwater Modeling

  • Refine the hydrogeological conceptual model
  • Develop a groundwater and surface-water FLOW (GSFLOW) model of the Basin that integrates groundwater flow with surface watershed processes
  • Develop estimates of non-metered pumping and return flow
  • Calibrate model to measured stream flows and groundwater levels
  • Lead Technical Review Committee meetings and present results to the MGA Board on model development progress
  • Provide groundwater modeling to assess the impacts of various groundwater management projects or actions

The groundwater model is used to evaluate potential projects in the Basin in an effort to achieve sustainability and will be updated annually to meet annual reporting requirements.

M&A’s integrated groundwater and surface water model is used to evaluate supplemental supply projects for the Basin including Pure Water Soquel, replenishment of the Basin with highly purified water, and City of Santa Cruz Aquifer Storage and Recovery, in-lieu or direct recharge of excess river water supplies to the Basin for the City’s drought supply.