Standards are specific to each of the three watershed overlay zones and vary by watershed. In general the regulations are low impact development standards that are intended to protect a valuable resource, whether it be drinking water or aquatic habitat. For full list of requirements and standards related to watersheds please see Whatcom County code Title 20.
Stormwater Special Districts
As described by WCC 20.80.635, the three stormwater special districts are the Lake Whatcom, Lake Samish, Lake Padden, Birch Bay, and Drayton Harbor watersheds.
On-Site Stormwater Facilities. On lots less than five acres, single family
homes and duplexes are required to install permanent on-site
stormwater quantity and quality facilities for:
• New construction or remodels that increase impervious surfaces by
more than 500 square feet; or
• Renovation projects where the estimated cost of the work exceeds
50% of the assessed value of the existing structure.
Protected Native Growth Areas. On lots larger than two acres, but less than five acres, 65% of a site must be set aside and dedicated as a Protected
Native Growth Area (PNGA). A PNGA shall preserve existing forested areas, vegetation, and critical areas.
Water Resource Special Management Areas
As described by WCC 20.80.735, these areas include the Lake Whatcom, Lake Samish, Lake Padden, Birch Bay, and Drayton Harbor watersheds. In these areas, the following actions are required:
Temporary Erosion and Sediment Control measures (e.g., silt fences, check
dams, mulching) must be installed and inspected prior to any regulated clearing
Phased Clearing may be required to limit the amount of exposed soils that
occur on a site at any one time if the technical administrator determines that
it is appropriate based on specific site characteristics or constraints, such as
slopes or critical areas.
Soil Stabilization. All disturbed areas must be stabilized with approved erosion and sediment control measures within two days of disturbance.
Tree Retention. On lots within the Lake Whatcom, Lake Padden, and Lake Samish watersheds only, 65% of the existing tree canopy area is to be retained. Up to 5,000 square feet or 35% of the existing tree canopy area, whichever is greater, may be cleared for a building site, driveway, parking and landscaping.
Seasonal Clearing Limitations. On lots within the Lake Whatcom, Lake Padden, and Lake Samish watersheds, clearing activities (during the wet season Oct. 1st – May 31st), will not be permitted unless the Technical Administrator determines that erosion control measures will control erosion and prevent silt-laden runoff from leaving the site. Clearing activities exceeding the thresholds during the wet season may be required to wait until the dry season. During the wet season the review threshold for clearing is reduced to 500 square feet of exposed soils.
Water Resource Protection Overlay District
The following provisions of WCC 20.71 apply only within the Lake Whatcom, Lake Padden, and Lake Samish Watersheds:
Impervious surface limits are based on the zoning designation and the lot size. The allowable impervious surface area ranges between 10% and 20% of the total lot area, or 2,500 square feet of impervious surface, whichever is greater.
Cluster subdivisions are required for all land divisions resulting in lots smaller than five acres. Cluster subdivision is a compact form of development that concentrates density on one portion of a site in exchange for larger buffers and open space between sensitive areas of the site and development.