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Thurston County Stormwater Utility

Runoff Control from New Development

Drainage Design and Erosion Control Manual

When land is developed, much of the spongy ground that used to soak up rainwater is replaced with impervious surfaces such as roads, roofs and driveways. Thurston county and its cities require developers to manage the rainwater runoff that flows off of these hard surfaces. Those requirements are spelled out in a document called the  Drainage Design and Erosion Control Manual.

drainage manual coverDevelopers use a variety of methods to manage stormwater runoff  -- swales, ditches and stormwater ponds among them. Simply put, the goal is to send rainwater into the ground or nearby streams at the speed and volume that best mimics how the water would have dispersed naturally had the development not been built.

In virtually all cases, the Drainage Design and Erosion Control Manual requires builders to submit a drainage plan when applying for building permits. The drainage plan must clearly show safeguards to prevent erosion, and how the development will direct, store, and dispose of stormwater runoff.

The manual also requires developers to manage the stormwater runoff at the construction site.

An updated version of the Drainage Design and Erosion Control Manual took effect November 16, 2009. The new version complements the state Department of Ecology's Stormwater Management Manual for Western Washington.

Stormwater Site Inspections

Thurston County requires thorough on-site inspections of stormwater facilities before, and after they're built. The requirements are spelled out in the Drainage Design and Erosion Control Manual described above.

Stormwater Pond Maintenance Requirements

Thurston County Ordinance 15.05 requires all property owners to maintain their stormwater facilities according to maintenance plans and schedules filed with the county. These plans are signed by the developer and submitted to Thurston County with the final plat or commercial permit.

In the case of housing developments, developers are held responsible for maintaining stormwater facilities for the first two years. Then, the responsibility is transferred to a homeowner's association.

Assistance for Homeowners

Thurston County and its cities offer free workshops to teach residents how to maintain and inspect neighborhood stormwater ponds and meet reporting requirements. Thurston County also offers free technical assistance for ratepayers who are experiencing drainage problems.

Construction of Stormwater Facilities

Thurston County constructs stormwater facilities to help reduce flooding and erosion in older neighborhoods that were built before development rules were in effect.

Contact Us

 Staff contact: Cathe Linn: (360) 754-4681. E-mail: linnca@co.thurston.wa.us


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