Stormwater System Plan (SWSP)

City Council approved the Stormwater System Plan on February 11, 2025.

Stormwater System Plan - October, 2024 (PDF)     

Stormwater System Plan Development:

In 2022 through 2024, the City embarked on a comprehensive Stormwater Planning effort to meet Council priorities for an Island-wide Stormwater System Plan. The plan supports Comprehensive Plan Policy U13.1, to maintain a comprehensive storm drainage plan that identifies problems, proposes solutions, provides a strategy for implementation and funding; and to meet requirements included in the Western Washington Phase II Municipal Stormwater National Pollutant Discharge Elimination System (NPDES) Permit webpage.

The methodology for the Stormwater System Plan (SWSP) was to conduct a full appraisal of current and needed City programs, projects and staffing levels weighed against present and projected future service demands and regulatory requirements surrounding operations, maintenance, planning, development/re-development and internal and external compliance. The subsequent analysis resulted in over 150 unique, specific recommendations that present opportunities for COBI to continue to meet state and federal regulations while simultaneously attaining larger City goals in becoming a recognized leader in water resource management. The SWSP is intended to serve as both a starting place and a roadmap towards executing an adaptive, long term comprehensive storm drainage plan.

Stormwater System Plan Primary Objectives:

• Offer a single comprehensive resource guide for stakeholders, staff, and decision makers for sustainable and adaptive stormwater and surface water management on Bainbridge Island.
• Support full compliance of the Western Washington Phase II Municipal Stormwater NPDES permit and Industrial Stormwater General Permit; and provide a Stormwater Management Action Plan to follow.
• Inform strategy and transparency with identifying and prioritizing stormwater infrastructure asset improvement projects. Including enhancements to address deficiencies in asset inventory data, tracking, and reporting.
• Appraisal of current and needed relevant City programs, projects, and staff levels to meet present and future service demands and regulatory requirements for surface water and stormwater management, operations and maintenance, planning, development, and re-development.
• Evaluation of funding sources and fund utilization for surface water and stormwater management, including but not limited to grants and Storm and Surface Water Utility (SSWM) fee rates and revenue.
• Assess real and potential impacts of climate change on surface water and stormwater on Bainbridge Island and measures and activities to apply to minimize impacts.
• Propose improvements to internal and external enforcement mechanisms and procedures to implement to successfully achieve the objectives therein.

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Stormwater Management Action Planning (SMAP) efforts embedded into the Stormwater System Plan:

First SMAP Step:

• COBI Watershed Assessment for SMAP
• COBI Watershed Assessment for SMAP - Appendix A

Second SMAP Step: 

• COBI Watershed Prioritization for SMAP

Final SMAP Step:

• COBI SMAP for Manzanita Watershed-East Catchment (included in the Stormwater System Plan and pending Council approval to implement)

Local studies used to inform SMAP:

• Watershed Assessment of Manzanita
• Springbrook Creek Watershed Study