Contra Costa Hydromodification Management Plan

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The Contra Costa Clean Water Program (CWP) is responsible for interacting with regulatory and elected officials to ensure compliance with the Municipal Stormwater National Pollutant Discharge Elimination System (NPDES) Permit. The CWP provides guidance to19 incorporated cities and towns in Contra Costa County, the County Flood Control District, and the Water Conservation District.

ESA led a team to develop a Hydrograph Modification or "Hydromodification" Management Plan (HMP) for the CWP in response to the County's NPDES permit requirements. The HMP establishes flow control requirements for new development projects to minimize increased stormwater runoff and help protect receiving stream channels from accelerated erosion. Our team created a series of simple to use implementation tools and protocols that have been incorporated into the CWP's "C.3 Guidebook." The Guidebook provides step-by-step HMP compliance guidelines for project proponents and municipal reviewers, emphasizing Low Impact Development methods for treating and controlling stormwater runoff. ESA produced design details for the Guidebook's best management practices to support Low Impact Development approaches to stormwater management. The designs complement site planning guidance and sizing protocols to assist project proponents with HMP compliance and facilitate staff review. We used extensive continuous simulation rainfall-runoff modeling to evaluate facility performance and identify the appropriate sizing factor for the different facility types and hydrologic settings within the County.

ESA led a team in developing a Hydromodification Plan (HMP) in compliance with NPDES permit requirements for the Contra Costa County Clean Water Program.

Specialized Services

  • Hydrologic and hydraulic modeling
  • Low impact development
  • Stormwater management