Stormwater Code and Manual

2026 Clark County Stormwater Manual

The 2026 Clark County Stormwater Manual (CCSM) was adopted by Clark County Council on June 16, 2026, and is effective starting July 1, 2026. The Washington State Department of Ecology found the 2026 Clark County Stormwater Manual equivalent to the 2024 Ecology Stormwater Management Manual for Western Washington, making it suitable for use by any western Washington municipality to meet state stormwater management requirements for development projects.

The purpose of the County’s Stormwater Manual is to minimize the impact of the built environment on our local waterways and to protect groundwater, which is the main drinking water source in Clark County. 

The County’s Stormwater Manual is implemented by Community Development through development engineering review and permitting. If you have questions about the 2026 Stormwater Code and Manual and how it relates to your development or redevelopment project, contact Community Development.  

The Clark County Stormwater Code and Manual includes an Introduction, and four technical Books with different requirements.

Final 2026 Clark County Stormwater Manual: Effective July, 1 2026

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Since 1999, Clark County has had a National Pollutant Discharge Elimination System (NPDES) Phase I Municipal Stormwater Permit. The County’s current Permit is effective August 1, 2024, through July 31, 2029. The Washington State Department of Ecology issues NPDES Stormwater Permits as part of its responsibility to enforce the federal Clean Water Act in Washington State. 

This Stormwater Permit requires the county to implement regulations for managing the quantity and quality of stormwater discharged from the county’s stormwater system to our local streams, rivers, lakes and groundwater.

To achieve this, the Clean Water division maintains the Clark County Stormwater Manual and related codes. The Manual guides new development and redevelopment practices, stipulates pollution prevention best management practices (BMPs), and defines operations and maintenance standards for stormwater treatment facilities.

Clean Water coordinates with Clark County Community Development and the Development Engineering Advisory Board (DEAB) to review and update the Manual every five years, as required by the Washington State Department of Ecology’s Phase I Municipal Stormwater Permit. 

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Note: The ordinance adopted by County Council on June 16, 2026 has not be updated on the code pages linked below. Please refer to this ordinance, which is effective July 1, 2026 for Clark County Code Chapter 13.26A Water Quality, Chapter 40.100 Unified Development Code - General Provisions, Chapter 40.386 Unified Development Code - Stormwater and Erosion Control, and Chapter 40.500 Unified Development Code - Overview of Procedures.  

The County’s Stormwater Manual is adopted through local code, which set regulations for local land use and development, along with best management practices to minimize pollution and harmful effects of stormwater on water quality. Specific codes for regulating stormwater include:

  • 13.26A Water Quality - sets regulations for how to protect water quality during activities at existing development. 

  • Title 40 – sets regulations for development practices, including the use of low impact development and requirements for landscaping, parking and building to minimize impacts to stormwater. 

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2021 Clark County Stormwater Manual

Clark County created the Clark County Stormwater Manual in 2015. The subsequent Clark County Stormwater Manual 2021 was effective July 1, 2021, through June, 2026 and applies to most projects that submitted an application to Community Development prior to July 1, 2026. The Department of Ecology's Phase I Municipal Stormwater Permit requires stormwater approvals under older versions of the Manual to expire at a certain point. If you have questions about which Stormwater Manual applies to your project, reference Clark County Code Chapter 40.500.010.B.4. or contact Community Development.

The Washington Department of Ecology found the 2021 Clark County Stormwater Manual equivalent to the 2019 Ecology Stormwater Management Manual for Western Washington, making it suitable for use by any western Washington municipality to meet state stormwater management requirements for development projects that are vested under the timelines established in the 2019 Phase I Permit and 2021 CCSM.

Resources

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Conditionally Approved BMPs 

  • Proprietary BMPs – the following BMPs are accepted conditionally approved for use in ROW and residential development:

    • StormFilter® using ZPG Media is accepted for Basic Treatment.
    • Filterra® System and Filterra® Bioscape™ are accepted for Oil Treatment, Basic Treatment, Enhanced Treatment, and Phosphorous Treatment. 
    • Perk Filter® is accepted for Basic Treatment and Phosphorous Treatment. 
    • Stormfilter® using Phosphosorb for basic treatment and phosphorus treatment.

          Consult a BMP’s GULD and manufacturer for design, specifications, and installation criteria.