Environmentally Critical Area Overlay for Zoned Development Capacity Model Current

Environmentally critical area layer used as an overlay for the City of Seattle Zone Development Capacity Model.  Areas represent the ECAs that would reduce the amount of development on a development site.  This layer is for analytical purposes only and does not represent actual regulatory areas or development regulation, rather an approximation of the potential impact on a development site.

• Remove all steep slope polygons less than 1,000 square feet in size 

• Treat areas within steep slope ECAs as if only 30% is developable. For example, on a 10,000 square foot site where half is in a steep slope ECA, we would treat it like at 6,500 square foot site (5,000100% + 5,00030%)

Riparian Corridors

• Ignore riparian corridors where the creek is in a culvert

For other riparian corridors:

• Assume there will be no development in that riparian corridor and a buffer of 50 feet for streams without salmon and 75 feet for streams with salmon
• Assume 30% of regular development potential in remainder of a 100 feet buffer from the riparian corridor (i.e. the next 50 feet for streams without salmon and the next 25 feet for streams with salmon).

Wetlands

• Remove all wetlands polygons less than 1,000 square feet in size

For all other wetland polygons:

• For all wetland polygons greater than or equal to an acre, put a 200 foot buffer around them and assume no development will occur in the wetland or the buffer
• For all wetlands less than an acre, put an 80 foot buffer around them and assume no development in wetland or buffer.  Wetlands other than category I have a variety of buffers, but in general we see about half have 50 foot buffers and the other half have 110 foot buffers (with an average of 80 feet)