A. Designation and Typing. Watercourses shall be classified by the following types:
1. Type S (there are no known Type S watercourses on Mercer Island);
2. Type F;
3. Type Np;
4. Type Ns; and
B. General Review Requirements.
a. The proposed activity is specifically exempt pursuant to MICC 19.07.120;
C. Development Standards – Buffers.
3. Any watercourse adjoined by a riparian wetland or other contiguous critical area shall have the buffer required for the stream type involved or the buffer that applies to the wetland or other critical area, whichever is greater.
4. Buffer Averaging. Buffer width averaging shall be allowed provided the following requirements are met:
b. The applicant has demonstrated how all proposed impacts have been mitigated consistent with subsection E of this section, Mitigation Requirements, and will not result in a loss of ecological function;
d. The total area of the buffer is equal to the area required without averaging.
5. Buffer Reduction. Buffer width reduction shall be allowed provided the following requirements are met:
6. Piped Watercourse Setbacks.
a. The intent of applying setbacks to piped watercourses is to preserve the opportunity to daylight watercourses that were previously piped, to provide incentives to property owners to daylight and enhance previously piped watercourses, and to allow flexibility for development where daylighting piped watercourses is demonstrated to be infeasible.
c. Piped watercourses setback widths shall be reduced to a 15-foot buffer when the portion of the piped watercourse on the applicant’s property is daylighted and where the watercourse has been restored to an open channel, provided a restoration plan demonstrates:
i. The watercourse channel will be stable and is not expected to cause safety risks or environmental damage; and
d. Piped watercourse setback widths shall be reduced to: (i) 10 feet on lots with a lot width of 50 feet or more, and (ii) five feet on lots with a width of less than 50 feet, when daylighting is determined by qualified professional(s) to result in one or more of the following outcomes:
i. Increased risk of landslide or other potential hazard that cannot be mitigated;
ii. Increased risk of environmental damage (e.g., erosion, diminished water quality) that cannot be mitigated;
iii. The inability of a legally established existing lot to meet the vehicular access requirements of this title; or
a. The watercourse is Type Ns;
b. The buffer does not contain habitat for WDFW priority species;
d. Survey markers are installed along the perimeter of the buffer to establish its field location.
b. Uncovered decks less than 30 inches above existing or finished grade, whichever is lower;
e. Split-rail fences;
f. Trails, consistent with the requirements of this chapter; and
D. Development Standards – Additional Criteria for Specific Activities.
a. Trail surfaces shall be constructed of pervious materials and may not be wider than five feet;
b. Trails shall be located to minimize the need for tree removal; and
c. Trails shall be located only in the outer 25 percent of the buffer area.
3. The trail width shall be added to the buffer width applied to the watercourse (e.g., if a trail is three feet wide, the watercourse buffer for the portion of the watercourse where the trail is located shall be expanded by three feet); except that the trail width shall not be added to the buffer width when trails are being created for public access and contained within a public access easement or right-of-way.
1. Habitat complexity, connectivity, and other biological functions;
2. Seasonal hydrological dynamics, water storage capacity and water quality; and
3. Geomorphic and habitat processes and functions. (Ord. 19C-05 § 1 (Exh. A), 2019.)