Last Updated 07/21/2026
Stormwater Management Manual for Western Washington
Executive Summary
The Stormwater Management Manual for Western Washington (SWMMWW) provides guidance on the measures necessary to control the quantity and quality of stormwater runoff. Local jurisdictions use this manual to set stormwater requirements for new development and redevelopment projects. Land developers and designers use this manual to design permanent stormwater control plans, develop construction stormwater pollution prevention plans, and determine stormwater infrastructure for their project. Businesses use this manual to help design their stormwater pollution prevention plans.
The greatest use of the SWMMWW has been through National Pollutant Discharge Elimination System (NPDES) stormwater permits. The Municipal Stormwater General Permits for western Washington incorporate and reference the SWMMWW. The Industrial Stormwater General Permit, Construction Stormwater General Permit, Boatyard General Permit, and the Sand and Gravel General Permit reference the SWMMWW. Since 2005, Ecology has reissued or issued for the first time all of these NPDES stormwater permits. The 2024 revisions to the SWMMWW will continue to help permittees comply with these permits.
Objective of the Manual
The objective of this manual is to provide guidance on the measures necessary to control the quantity and quality of stormwater produced by new development and redevelopment. The goal of the measures is to comply with water quality standards and contribute to the protection of beneficial uses of the receiving waters. Application of appropriate Minimum Requirements (MRs) and Best Management Practices (BMPs) identified in this manual are necessary but sometimes insufficient measures to achieve these objectives. See I-1.3 Effects of Urbanization on Stormwater for further information about the impacts of development on water quality.
Water quality standards include:
- Chapter 173-200 of the Washington Administrative Code (WAC), Water Quality Standards for Groundwaters of the State of Washington
- Chapter 173-201A WAC, Water Quality Standards for Surface Waters of the State of Washington
- Chapter 173-204 WAC, Sediment Management Standards
More Stringent Requirements
Federal, state, and local permitting authorities with jurisdiction can require more stringent measures that are deemed necessary to meet locally established goals, state water quality standards, or other established natural resource or drainage objectives. Water cleanup plans or Total Maximum Daily Loads (TMDLs) may also identify more stringent measures needed to restore water quality in an impaired water body
7.3.5 Maintenance of Best Management Practices
All best management practices that are implemented to achieve nitrogen or phosphorus reduction and flow attenuation will require complete legal documentation and a maintenance plan and must comply with all requirements of Section 4.4.6(G), Engineered Stormwater Control Structures.
Applicability
This manual applies to all of western Washington. This includes the area bounded on the south by the Columbia River, on the west by the Pacific Ocean, on the north by the Canadian border, and on the east by the Cascade Mountains crest. This manual also applies to those areas of Skamania and Cowlitz counties that lie east of the Cascade crest.
The following counties are included in the area described above:
- Clallum
- Clark
- Cowlitz
- Grays Harbor
- Island
- Jefferson
- King
- Kitsap
- Lewis
- Mason
- Pacific
- Pierce
- San Juan
- Skagit
- Skamania
- Snohomish
- Thurston
- Wahkiakum
- Whatcom
7.3.8 Variance
To the extent any state or federal law or regulations requires the Town to establish a variance procedure for any requirement of this section 7.3, excluding section 7.3.6, the variance procedure established in Section 4.4.6(I) of the LDO shall be utilized. The provisions of section 7.3.6 shall not be subject to this requirement.
11.3.5 Activities Inconsistent with Conditions of Plan Approval or Permit
It shall be a violation of this Ordinance to engage in any development, use of land, construction, remodeling, or other activity contrary to the terms and conditions of any plan approval, permit, or other form of authorization required to engage in such an activity.
11.6.1 Notice of Violation Procedure
Except as otherwise provided, the following notice procedure shall be used to enforce the provisions of this Ordinance. The notice of violation and assessment procedure for violations of the soil erosion and sedimentation control provisions in Section 7.4 of this Ordinance are set forth in Section 11.4.4.
- Notice Required Before Penalty
No penalty shall be assessed pursuant to this chapter unless and until the person alleged to be in violation has been notified of the violation in accordance with this section, with the exception of a violation of a stop work order, illegal placement of a temporary sign or violation of the soil erosion and sedimentation control provisions in Section 7.4. In the case of stop work orders, violations shall subject the violator to immediate imposition of a penalty. In the case of an illegal temporary sign, the Director shall be authorized to remove such sign immediately without notice. - Notice of Violation and Opportunity to Cure
Whenever the Director has reasonable cause to believe that a person is violating any of the provisions of this Ordinance or any plan, order, or condition which has been approved, issued, or imposed pursuant to this Ordinance, the Director shall notify that person of the violation. - Written Notice
Such notice of violation shall be in writing and shall be served by personal delivery or by certified or registered mail, return receipt requested. A copy of the notice may also be sent by regular mail. Service shall be deemed sufficient if the registered or certified mail is unclaimed or refused, and the regular mail is not returned by the post office within ten (10) days after the mailing. - Content of Written Notice
The notice of violation shall describe the violation, shall identify the provision or provisions of this Ordinance that are being violated, shall specify what actions must be taken to correct the violation (including an order to stop any and all work which violates this Ordinance), shall direct the person to correct the violation within a specified reasonable time period (beginning on the date such notice is received), and shall warn that more severe measures (such as a civil penalty or criminal prosecution) may be assessed or brought against the person if he or she fails to take appropriate action to cure or correct the violation. If the violator cannot be ascertained, then the notice of violation shall be sent to the record owner of the land on which the violation occurs. - Extension of Time to Cure
Upon receipt of a written request from the alleged violator or the property owner for an extension of time to cure or correct the violation, the Director may grant a single extension of time, not to exceed a period of thirty (30) days, in which the alleged violator may cure or correct the violation before the Director issues a citation pursuant to Section 11.6.2. Such extension of time shall not be granted unless the alleged violator or the property owner can demonstrate to the Director that the violation cannot be cured or corrected within the time period specified in the notice of violation because the labor or materials needed to take appropriate action are unavailable due to circumstances beyond the control of the alleged violator or the property owner. - Corrective Action Taken
If the violation is cured or corrected within the time period specified in the notice of violation, or extension of time granted in Section 11.6.1(E), then the Town shall take no further action against the person.
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The information on this page is provided for general informational purposes only and is not legal advice. Regulations change frequently — AQUALIS makes no warranty as to the accuracy or completeness of this content, and any reliance on it is at your own risk. Consult a qualified professional or your local regulatory authority to confirm requirements applicable to your specific property.
