FAQ - Drainage and Erosion Control Plans
Call the Development Review Division of the Public Works Department at (360) 867-2050.
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 “2009 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.
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.
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).
Click here to see information about the drainage design and erosion control manual, including plan requirements.
Please click here to learn about scoping reports.
Virtually all developments require some sort of drainage plan. The 2009 Drainage Design and Erosion Control Manual offers a few limited exemptions. Examples include: public works, emergency projects, and certain projects on right-of-ways.
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.
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