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 Padden, and Lake Shamish 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) if dispersion stormwater facilities are used (please see Section 221 of Whatcom County Development Standards). 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 Padden and Lake Shamish 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 prior to any clearing activity.
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 Padden and Lake Shamish watersheds, 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 parcels within the Lake Padden and Lake Shamish watersheds, clearing activities which expose more than 500 sq. ft. of soil are not permitted from October 1st through May 31st per WCC 20.80.735(2)(e).
- Development permits may be submitted at any time during the year. However, permits for work that exceeds 500 sq.ft. of exposed soil cannot be issued prior to June 1.
- Development permits which propose to exceed more than 500 sq. ft. of exposed soil will not be issued during the two weeks prior to October 1 to allow for earthwork to be done and stabilized prior to October 1.
Water Resource Protection Overlay District
The following provisions of WCC 20.71 apply only within the Lake Padden, and Lake Shamish 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.