Part 20.25H Art. IV Streams | Bellevue Land Use Code

IV. STREAMS

20.25H.075 Designation of critical area and buffers.

A. Definition of Stream. An aquatic area where surface water produces a channel, not including a wholly artificial channel, unless the artificial channel is:

1. Used by salmonids; or

2. Used to convey a stream that occurred naturally before construction of the artificial channel.

B. Designation of Streams. The following streams are hereby designated as critical areas subject to the regulations of this part:

1. “Type S water” means all waters, within their bankfull width, as inventoried as “shorelines of the state” under Chapter 90.58 RCW and the rules promulgated pursuant to Chapter 90.58 RCW including periodically inundated areas of their associated wetlands. As of May 21, 2018, the only known Type S waters are Lower Kelsey Creek and Mercer Slough.

2. “Type F water” means all segments of waters that are not type S waters, and that contain fish or fish habitat, including waters diverted for use by a federal, state, or tribal fish hatchery from the point of diversion for 1,500 feet or the entire tributary if the tributary is highly significant for protection of downstream water quality.

3. “Type N water” means all segments of waters that are not type S or type F waters and that are physically connected to a type S or F waters by an above ground channel system, stream or wetland.

4. “Type O water” means all segments of waters that are not type S, F or N waters and that are not physically connected to type S, F or N waters by an above ground channel system, stream, or wetland.

C. Designation of Stream Critical Area Buffers. The following critical areas buffers are established:

1. Stream Critical Area Buffers:

a. General – Open Streams (Except West Tributary in the Kelsey Basin).

i. Undeveloped Site. An undeveloped site is a site that contains no primary structure. Open streams on undeveloped sites shall have the following critical area buffers, measured from the top-of-bank:

Type S	100 feet
Type F	100 feet
Type N	50 feet
Type O	25 feet

ii. Developed Site. A developed site is a site that contains a primary structure or any site where the stream and stream buffer have been included within an approved and recorded NGPE or NGPA prior to August 1, 2006. Lots created through subdivision, short subdivision, or the Planned Unit Development process from a developed site shall be considered undeveloped and subject to the requirements of subsection C.1.a.i of this section, except that the lot containing the existing primary structure shall be considered developed. Open streams on developed sites shall have the following critical area buffers, measured from the top-of-bank:

Type S	50 feet or the buffer established with the existing NGPE/NGPA, whichever is greater
Type F	50 feet or the buffer established with the existing NGPE/NGPA, whichever is greater
Type N	25 feet or the buffer established with the existing NGPE/NGPA, whichever is greater
Type O	25 feet or the buffer established with the existing NGPE/NGPA, whichever is greater

b. General – Closed Stream Segments. Regardless of type, closed stream segments shall have no critical area buffer and shall have the structure setback established in subsection D.2.b of this section.

c. West Tributary, Kelsey Basin – Open Streams. Regardless of type, open stream segments of the West Tributary on developed and undeveloped sites shall have a stream critical area buffer of 50 feet, measured from the top-of-bank.

d. Buffer and Setback on Sites with Existing Primary Structure(s). Where a primary structure legally established on a site prior to August 1, 2006, encroaches into the critical area buffer or structure setback established in this section, the critical area buffer and/or structure setback shall be modified to exclude the footprint of the existing primary structure. Expansion of any existing structure into the critical area buffer or critical area structure setback shall be allowed only pursuant to the provisions of LUC 20.25H.055 (single-family primary structures) or LUC 20.25H.230 (all other primary structures).

e. Measurement of Buffer on Eroding Stream Bank. A stream critical area buffer and any applicable structure setback may be measured from a fixed location representing the historic location of the top-of-bank where an applicant demonstrates that:

i. The location of the top-of-bank has changed over time as a result of natural stream processes; and

ii. The applicant provides a delineation of the top-of-bank conducted within the past five years.

f. Buffers Modified Under Prior LUC 20.25H.070.A.2.d. Where the critical area buffer on a site was modified through an approved reach study and restoration plan pursuant to the City’s previous critical areas regulations (prior LUC 20.25H.070.A.2.d), the critical area buffer for that site shall be as determined in that adopted reach study and restoration plan.

2. Buffer Modification. Modifications to the stream critical area buffer may be approved pursuant to this section. Modifications to the stream critical area buffer that do not meet the criteria of this subsection may be considered through a critical areas report, LUC 20.25H.230:

a. Buffer Averaging. Buffer averaging may be allowed if all the following criteria are satisfied. Proposals to average the stream critical area buffer under this subsection shall require a Critical Areas Land Use Permit; provided, that a mitigation or restoration plan is not required for buffer averaging.

i. Buffer averaging may be approved only if the applicant demonstrates that a modification to non-critical area setbacks pursuant to LUC 20.25H.040 would not accommodate the proposed development in a manner consistent with its intended use and function.

ii. Through buffer averaging, the ecological structure and function of the resulting buffer is equivalent to or greater than the structure and function before averaging;

iii. The total buffer area is not reduced;

iv. The buffer area is contiguous;

v. Averaging does not result in any impact to slope stability and does not increase the likelihood of erosion or landslide hazard;

vi. Averaging does not result in a significant adverse impact to habitat associated with species of local importance; and

vii. At no point is the critical area buffer width less than 75 percent of the required buffer dimension.

b. Transportation or Utility Infrastructure. Where a legally established right-of-way, railroad right-of-way or other similar infrastructure of a linear nature crosses a stream critical area buffer, the edge of the improved right-of-way shall be the extent of the buffer, if the part of the critical area buffer on the other side of the right-of-way provides insignificant biological or hydrological function in relation to the portion of the buffer adjacent to the stream.

1. General. The requirements of this section apply along with any other dimensional requirements of the Land Use Code (see LUC 20.20.010, 20.20.130, 20.20.190 and Parts 20.25A – 20.25G LUC). The most restrictive dimension controls. Structure setbacks are required in order to:

a. Minimize long-term impacts of development adjacent to critical areas and critical area buffers; and

b. Protect critical areas and critical area buffers from adverse impacts during construction.

a. General – Open Streams (Except West Tributary in Kelsey Basin).

i. Undeveloped Site. An undeveloped site is a site that contains no primary structure. The following structure setbacks apply on undeveloped sites, measured from the edge of the critical area buffer:

Type S	20 feet
Type F	20 feet
Type N	15 feet
Type O	10 feet

ii. Developed Site. A developed site is a site that contains a primary structure or any site where the stream and stream buffer have been included within an approved and recorded NGPE or NGPA prior to August 1, 2006. Lots created through subdivision, short subdivision, or the Planned Unit Development process from a developed site shall be considered undeveloped and subject to the requirements of subsection D.2.a.i of this section, except that the lot containing the existing primary structure shall be considered developed. The following structure setbacks apply on developed sites, measured from the edge of the critical area buffer or the boundary of the existing NGPE/NGPA, as applicable:

Type S	50 feet
Type F	50 feet
Type N	25 feet
Type O	None

b. General – Closed Stream Segments. Closed stream segments, regardless of type, shall have a structure setback of 10 feet; provided, that closed stream segments in the Kelsey Creek drainage basin shall have a structure setback of 50 feet or a structure setback representing the combined dimension of the critical area buffer and structure setback required for its stream type, whichever is less.

c. West Tributary – Open Stream Segments. Regardless of type, open stream segments of the West Tributary on developed and undeveloped sites shall have a structure setback of 20 feet, measured from the edge of the critical area buffer.

3. Structure Setback Modification – Open Streams on Undeveloped Sites. The Director may waive or modify the structure setback on an undeveloped site as part of the permit or approval for the underlying proposal if the applicant demonstrates that:

a. Water quality, or slope stability as documented in a geotechnical report, will not be adversely affected;

b. Encroachment into the structure setback will not disturb habitat of a species of local importance within a critical area or critical area buffer;

c. Vegetation in the critical area and critical area buffer will not be disturbed by construction, development or maintenance activities and will be maintained in a healthy condition for the anticipated life of the development; and

d. Enhancement planting on the boundary between the structure setback and the critical area buffer will reduce impacts of development within the structure setback.

4. Structure Setback Modification – Open Streams on Developed Sites. Structure setbacks on developed sites may be modified only through an approved critical areas report.

5. Structure Setback Modification – Closed Stream Segments. Structure setbacks associated with closed streams may be modified only through an approved critical areas report. (Ord. 6417, 5-21-18, §§ 30, 31; Ord. 5680, 6-26-06, § 3)