The Role of Stormwater in Alleviating a Coastal Water Supply Shortage: The Monterey Peninsula Story
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As populations grow, the climate changes, and water resources are allocated to critical ecological needs, and the water available for municipal uses is diminished.

Water supply concerns have been building in the Monterey Peninsula region in recent years due to regulatory limits on the two main sources of municipal water – the Carmel River and the Seaside Groundwater Basin. The State Water Resources Control Board issued a Cease and Desist Order for diversions from the Carmel River in 2009 and the Seaside Groundwater Basin was adjudicated by the Superior Court in 2006. The region is currently developing a recycled water facility but has additional supply needs.

Within this setting, the Monterey Regional Stormwater Management Program (MRSWMP) completed their collaborative regional Stormwater Resource Plan (SWRP) for the Monterey Peninsula, Carmel Bay, and South Monterey Bay planning region. The region includes the political boundaries of six coastal cities and several unincorporated portions of Monterey County and ranges from sea level to 5,000 feet in elevation. The region also includes two groundwater basins, three areas of special biological significance (ASBS), and is adjacent to the Monterey Bay National Marine Sanctuary; as such, maintenance or improvement of water quality and environmental resources is crucial.

As part of the SWRP planning process, MRSWMP explored whether water supply could be supplemented via stormwater capture projects through the locally funded Monterey Peninsula Water Recovery Study (WRS). The WRS evaluated the feasibility of establishing a Peninsula-wide water recovery and reclamation system by identifying and evaluating potential projects to capture sources of wet and dry weather runoff for recovery and use. The study also considered how to store, treat, and transport potential sources of runoff.

A GIS-based approach was used to synthesize public hydrologic, geotechnical, and geophysical data, identifying hundreds of potential water recovery projects, along with thousands of potential stormwater capture (i.e., green infrastructure) projects. Additionally, dozens of already-planned projects from local municipalities and agencies were compiled from responses to a stakeholder project request. Water recovery projects identified as part of the SWRP included lake/reservoir storage, diversions to sanitary sewer to supplement recycled water, direct on-site capture and use, and infiltration to aquifer type projects.

Identified potential water recovery study projects were evaluated for feasibility by examining the estimated annual volume that could be recovered for water supply; the planning level estimate of unit cost; and the ease of implementation (i.e., project financing, permitting, environmental, water rights, and other considerations). Additionally, all projects were prioritized in the region using a quantitative multiple-benefit scoring approach and input received from a Stakeholder Outreach effort and from the project Technical Advisory Committee (TAC). Concept designs (10% designs) were developed for the top seven projects identified, and a 30% design and CEQA Checklist was developed for the highest priority project, the Hartnell Gulch Restoration and Runoff Diversion Project. Project prioritization methods included considerations of hydrology and existing stormwater and water resources infrastructure. The existing natural and infrastructure-based drainage systems require additional connection and integration to provide water supply through stormwater capture projects.

The presentation will focus on how potential water supply augmentation projects were identified and evaluated as part of the Water Recovery Study, and how these stormwater capture projects fit into the broader multi-benefit goals of the region's SWRP. The presentation will engage the audience with specific questions related to identification of alternative water supply sources and multi-benefit stormwater capture projects.

Publication Summary

  • Geosyntec Authors: Kelly Havens
  • All Authors: Kelly Havens, Geosyntec Consultants; Jeff Condit, MRSMP
  • Title: 2019 CASQA Annual Conference
  • Event or Publication: Event
  • Practice Areas: Urban Stormwater Management Planning and Design
  • Citation: Geosyntec will make substantial technical contributions at the California Stormwater Quality Association (CASQA) Annual Conference at the Monterey Conference Center in Monterey, California on October 7-9, 2019.
  • Date: October 7-9, 2019
  • Location: Monterey, California
  • Publication Type: Platform Presentation