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Island County > Planning > residential

Island County Best Management Practices

Erosion & Sedimentation Control Requirements for Residential Construction

All applicants for new residential construction are required to:

  1. Minimize erosion and movement of sediment on and from the site.
  2. Protect properties and water courses downstream from erosion and sediment originating on the site.
  3. Minimize the transport of sediment onto paved surfaces, and clean any sediment from roads at the end of each day.
  4. Stabilize denuded areas and soil stockpiles.
  5. Maintain temporary erosion and sedimentation control measures until final site stabilization, such as paving, lawn, or landscaping.
  6. Route storm water runoff to remove sediment via an approved sediment retention facility.

(ICC 11.03.230, Erosion and Sedimentation Control Requirements.)

Why? Each year Island County issues hundreds of residential building permits. The cumulative acreage of exposed soil associated with residential development far exceeds the acreage associated with large and highly-visible commercial projects.

The impact of erosion and sediment originating from residential construction is more widespread and is therefore much greater than that resulting from commercial development. This causes large amounts of sediment to be transported to our lakes, streams and Puget Sound. Surface runoff from construction sites carries suspended solids that pollute water and damage fish and wildlife habitat. Silt and sediment originating from construction sites can clog ditches and outfalls, create flooding problems thus requiring increased efforts to maintain and repair roads, ditches, and other drainage facilities; and ultimately deteriorate quality of life on the Islands. This costs us all more money. Be smart in the beginning and we all benefit.

How? Use Best Management Practices (BMPs) to achieve the best way to contain surface runoff.

Minimize erosion and movement of sediment.

Prevention of erosion and generation of sediment is much cheaper and easier than controlling it once it occurs. The single most effective way to reduce erosion and sediment is to preserve vegetation and limit clearing to the minimum necessary. Each square foot that is cleared unnecessarily increases your costs of erosion and sediment control.

Prior to development of the lot, mark the clearing limits with a continuous strand of surveyor's tape or other highly visible method. Establish buffer zones. Ensure the equipment operator is aware of the clearing limits.

Protect properties and water courses downstream.

Once erosion has occurred, you are required to take steps to remove as much sediment as is practical from water leaving the site. This is commonly accomplished using silt fences. Silt fences work only in specific situations, and only if properly installed. Other commonly used measures include straw bales and check dams.

Minimize transport of sediment onto paved surfaces.

To help accomplish this, establish a stabilized construction entrance. Use only one site access, and maintain it by adding crushed rock or quarry spalls. Minimize traffic on unstabilized soils.

Stabilize denuded areas.

Cover exposed soils and stockpiles, such as backfill or topsoil, with mulch or matting. Remember, the less soil that is exposed, the less costs and efforts will be required for mulch and matting.

Maintain temporary erosion and sedimentation control measures.

Clean out sediment that has built up behind check dams, straw bales, and silt fences, and put it at an appropriate location where it will not re-erode. Re-mulch as it blows away or is worked into the soil.

Route storm water runoff to remove sediment.

Dispersing runoff through a thickly vegetated strip of at least 25' in width at the point of discharge will accomplish this requirement. Sparse vegetation will require a wider strip. Various types of sediment traps can also be used, but usually cost more, require effort and time to install, and require maintenance to ensure their continued effectiveness. A sediment trap which has failed due to inadequate maintenance ma​y cause more problems than no trap at all.

The above are provided as examples only, and represent the most commonly used BMPs. The BMPs that will be most effective depend on site-specific characteristics of soils, slopes, design, access, season, existing vegetation, etc.

Contact us for more information or any questions. Staff is here to help you. Specify that you have questions on Best Management Practices.

NOTE: Failure to meet these requirements may result in unnecessary delays and costs. For development with 5000 square feet or greater of impervious surface, and/or near steep slopes, bluffs, wetlands, streams, and other protected features, additional requirements may apply.