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FAQ - Drainage and Erosion Control Plans

Who should I contact about questions about drainage and erosion control plans?

Call the Development Review Division of the Public Works Department at (360) 867-2050.

What is a drainage and erosion control plan?

When land is developed in Thurston County, the developer must meet certain requirements for managing runoff or erosion that might result from the project. The requirements are set forth in a document called the “2016 Drainage Design and Erosion Control Manual for Thurston County.” In virtually all cases, the manual requires builders to submit a drainage plan along with their building applications. The drainage plan must either be an “abbreviated” plan an “engineered abbreviated” plan, or a full "drainage and erosion control plan" depending on the size of the project and its impact on drainage.

What’s the difference between abbreviated plans and engineered abbreviated plans?

Abbreviated plans and engineered abbreviated plans share a common goal: to protect Thurston County’s water resources from pollution, erosion, and damage to wildlife habitat. Abbreviated plans, however, do not require the seal of a licensed engineer.

How do I know whether my project is eligible for an abbreviated plan or an engineered abbreviated plan?

Generally, abbreviated plans are allowed for building houses on a single lot if the project creates less than 2,000 square feet of new impervious surfaces and clears less than 7,000 square feet of land or creates less than 5,000 square feet of new impervious surface and clears less than 3/4 acre of land and the soils are predominantly outwash type soils (Type A/B).  Or, if the lot is part of a subdivision that has a functioning stormwater facility.

Engineered abbreviated plans are typically required for projects that have critical areas within 200 feet of the project area or where soils are predominantly Type C/D (till).

What kind of information is required on the plans?

Click here to see information about the drainage design and erosion control manual, including plan requirements.

What is a scoping report and when is it required?

Please click here to learn about scoping reports.

Are there any exemptions to the drainage and erosion control plan requirements?

Virtually all developments require some sort of drainage plan. The 2016 Drainage Design and Erosion Control Manual offers a few limited exemptions. Examples include: public works, emergency projects, and certain projects on right-of-ways.

When do I submit my plan?

A drainage plan is part of the permit-application process. Applications, including those for residential building permits, are considered incomplete until a drainage plan is supplied.

What should I do if drainage is to be directed to or through a critical area or buffer?

You may face additional requirements under the Critical Areas Ordinance or the Shoreline Master Program.  Please contact the Building Development Center for more information.

Contact Us

For drainage plan information: (360) 754-3355 ext. 7287 or e-mail: E-mail: permit@co.thurston.wa.us. For scoping report information: Pat Allen, PE, (360) 867-2078 or e-mail pat.allen@co.thurston.wa.us.

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