A. Modification of Standard Buffer.
1. The City may approve a modification of the minimum required buffer in cases where an improved right-of-way, associated with a legally established roadway, transects the stream or lake buffer. The buffer may be reduced to match the edge of the right-of-way closest to the stream or lake if the portion of the buffer on the other side of the roadway meets the following criteria:
a. Does not provide additional protection to the proposed development from flooding or other hazard, or to the lake or stream; and
b. Provides insignificant biological, geological or hydrological buffer functions relating to the other portion of the buffer adjacent to the lake or stream.
Improved rights-of-way are those that are maintained out of necessity as a cleared, graded, paved, mowed or otherwise altered surface to allow for access, maintenance, or safety.
2. The City may approve a modification of the minimum required buffer width where the proposed development or use is isolated from the critical area and its contiguous buffer by an existing legally established building, detached garage, accessory dwelling unit, commercial parking area, retaining wall over six feet in height, or similar structure. The modification may not be requested for such improvements as fences, sheds, patios, decks, driveways, or other similar structures and impervious surfaces. For the buffer modification to be approved, the applicant must demonstrate conclusively in a critical area report that all of the following criteria are met:
a. The existing legal improvement between the proposed development or use and the stream or lake creates a substantial barrier to buffer function;
b. The isolated section of buffer does not provide additional protection of the critical area from the proposed development; and
c. The isolated section of buffer does not provide significant hydrological, water quality, and wildlife buffer functions relating to the portion of the buffer adjacent to the critical area.
B. Buffer Reduction with Enhancement. Standard
buffer widths for degraded
buffers of Type F, Ns, or Np waters may be reduced a maximum of 25 percent of the standard width through a combination of
buffer enhancement and
low impact development strategies. The
applicant shall demonstrate that through enhancing the
buffer and use of
low impact development strategies the reduced
buffer will function at a higher level than the standard
buffer. Type S
buffers and
setbacks may only be reduced as outlined in KMC §
16.60.030 or under the shoreline variance requirements of KMC §
16.75.030.
The following table describes the maximum buffer reduction and minimum buffer width when a degraded buffer is enhanced:
Stream Type | Maximum Buffer Reduction | Minimum Buffer Width (Feet) |
|---|
Type S – Swamp Creek, Lake Washington and Sammamish River | |
Type F – Little Swamp Creek | 25 percent | 112.5 feet |
Type F (other water bodies used by or containing habitat suitable for salmonid fish) | 25 percent | 75 feet |
Type F (water bodies used by or containing habitat suitable for fish other than salmonids) | 25 percent | 37.5 feet |
Type Np or Ns | 25 percent | 18.75 feet |
Any type stream restored from a pipe | 25 percent | 18.75 feet |
1. Prior to approval of a reduced buffer, a critical areas application shall meet all of the decisional criteria listed below. A reduced buffer will be approved in a degraded stream or lake buffer only if:
a. It will provide an overall improvement in water quality;
b. It will provide an overall enhancement to fish, wildlife, or their habitat;
c. It will provide a net improvement in drainage and/or stormwater detention capabilities;
d. It will not lead to unstable earth conditions or create an erosion hazard;
e. It will not be materially detrimental to any other property or the City as a whole; and
f. All exposed areas are stabilized with native vegetation, as appropriate;
g. The use of stream buffer averaging does not expand the buffer further onto any adjoining property not a part of the subject land development application.
2. As part of the buffer reduction request, the applicant shall submit a buffer enhancement plan prepared by a qualified professional and fund a review of the plan by the City’s critical areas consultant. The plan shall assess the habitat, water quality, stormwater detention, groundwater recharge, shoreline protection, and erosion protection functions of the buffer; assess the effects of the proposed modification on those functions; and address the seven criteria listed in subsection (B)(1) of this section.
C. Stream Crossings. Stream crossings may be allowed and may encroach on the otherwise required stream buffer if:
1. All crossings are designed using the most recent version of Washington Department of Fish and Wildlife’s Water Crossing Design Guidelines (Barnard and others, 2013, or as revised), prioritizing bridges or other construction techniques which do not disturb the stream bed or bank, except that bottomless culverts or other appropriate methods demonstrated to provide fisheries protection may be used for Type F streams if the applicant demonstrates that such methods and their implementation will pose no harm to the stream or inhibit migration of fish;
2. All crossings are constructed during the summer low flow and are timed to avoid stream disturbance during periods when use is critical to salmonids;
3. Crossings do not occur over salmonid spawning areas unless the City determines that no other possible crossing site exists;
4. Bridge piers or abutments are not placed within the Federal Emergency Management Agency (FEMA) floodway or below the ordinary high water mark;
5. Crossings do not diminish the flood-carrying capacity of the stream;
6. Underground utility crossings are laterally drilled and located at a depth of four feet below the maximum depth of scour for the base flood predicted by a civil engineer licensed by the State of Washington. Temporary bore pits to perform such crossings may be permitted within the stream buffer established in this chapter; and
7. Crossings are minimized and serve multiple purposes and properties whenever possible.
D. Stream Relocations.
1. Stream relocations may be allowed only for:
a. Types F, Np, and Ns streams as part of a public project for which a public agency and utility exception is granted pursuant to this chapter; or
b. Type F streams with fish use other than salmonids, Np or Ns streams for the purpose of enhancing resources in the stream;
c. The location occurs on site except that relocation off site may be allowed if the applicant demonstrates that any on-site relocation is impracticable, the applicant provides all necessary easements and waivers from affected property owners and the off-site location is in the same drainage subbasin as the original stream.
2. For any relocation allowed by this section, the applicant shall base the design on the most recent version of the multiagency Stream Habitat Restoration Guidelines (Cramer, 2012, or as revised), and demonstrate, based on information provided by a civil engineer and a qualified biologist, that:
a. The equivalent base flood storage volume and function will be maintained;
b. There will be no adverse impact to local groundwater;
c. There will be no increase in velocity;
d. There will be no interbasin transfer of water;
e. There will be no increase in the sediment load;
f. There is an overall increase in habitat function and value for salmonids and other fish;
g. Requirements set out in the mitigation plan are met;
h. The relocation conforms to other applicable laws; and
i. All work will be carried out under the direct supervision of a qualified biologist.
E. Stream or Lake Enhancement/Restoration. Stream or lake enhancement and restoration not associated with any other development proposal may be allowed if:
1. Accomplished according to a plan consistent with the most recent version of the multiagency Stream Habitat Restoration Guidelines (Cramer, 2012, or as revised) for its design, implementation, maintenance and monitoring prepared by a civil engineer and a qualified biologist and carried out under the direction of a qualified biologist;
2. The project results in a net increase in stream or lake functions and values;
3. The enhancement or restoration is not associated with mitigation of a specific development proposal; and
4. The enhancement or restoration is limited to removal of nonnative vegetation and enhancement of riparian vegetation, placement of rock weirs, log controls, spawning gravel and other specific habitat improvements.
(Ord. 11-0329 § 3 (Exh. 1); Ord. 19-0488 § 2 (Exh. 1); Ord. 24-0624 § 5 (Exh. C))