A. Applicability.
1. This chapter applies to all geologically hazardous areas classified pursuant to subsection B of this section except as specified in subsection B.2 of this section.
B. Classification.
1. Geologically hazardous areas include erosion hazard areas, landslide hazard areas, and seismic hazard areas (including fault and liquefaction hazard areas). Zone of influence areas are not considered geologically hazardous areas.
2. Geologically hazardous areas shall be classified based upon landslide history and the presence of unstable soils, steepness of slopes, erosion potential, and seismic hazards. Areas in this category are a potential threat to public health, safety, and welfare when construction is allowed. While some potential risk due to construction can be reduced through engineering design, construction in these areas should be avoided when the potential risk cannot be reduced to a level comparable to the risk if the site were initially stable prior to construction. Classification and rating shall be based upon the risk to the environment and to development in geologically hazardous areas.
C. Permit and Review Procedures.
1. Any development, use or activity proposed on a site containing any geologically hazardous area or a landslide hazard area setback shall require a critical area permit unless it qualifies as an exempt activity, as provided in BIMC 16.20.040 or is allowed without review pursuant to BIMC 16.20.090.
2. Critical area permits shall be reviewed pursuant to the criteria in BIMC 16.20.070.
3. Applications for critical area permits for geologically hazardous areas shall include:
a. City of Bainbridge Island master land use application (http://www.bainbridgewa.gov/161/Documents-Forms-Applications);
b. Indemnification. An indemnification or hold harmless agreement shall be required for all projects in geologically hazardous areas, except erosion hazard areas and landslide hazard area setbacks. The form of the agreement shall be approved by the city and executed prior to the commencement of construction or any land disturbing activity;
c. Notice. A notice of intent to construct on a landslide hazard area or reduce the standard setback in a landslide hazard area shall be given pursuant to BIMC 2.16.020.M. The notice of intent shall be issued within 14 days of a complete application pursuant to BIMC 2.16.020.J.2. The notice shall include a 21-day comment period and no permits or approval of reduced setbacks shall be issued before the end of the comment period; and
d. Geological Hazards Assessment. A geological hazards assessment is required for all projects in geologically hazardous areas and landslide hazard area setbacks in accordance with BIMC 16.20.180, Critical area reports. To protect public health, safety and welfare, the director may require third party review of any geological hazards assessment or geotechnical report in cases where there may be potential for substantial damage to life, property or the environment should the proposed engineering solution fail. When a third party review is required, costs incurred for a qualified third party geologist or geotechnical engineer to perform the review shall be borne by the applicant.
D. Development Standards – General. The following development standards apply to all activities within any geologically hazardous area or associated landslide hazard area setback:
1. The proposed activity shall not create a net increase in geological instability, either on or off site, which is defined as follows:
a. The subject parcel shall not be less stable after the planned development than before; and
b. The adjacent parcels shall not have greater risk or be less stable after the planned development than before.
2. The proposed activity shall not increase the risk of life safety due to geological hazards above professionally acceptable levels.
3. The proposed activity shall not increase the risk due to geological hazards above professionally acceptable levels for:
a. Property loss of any habitable structures or their necessary supporting infrastructure on site; or
b. Risk to any off-site structures or property of any kind.
4. Proposed buildings shall be constructed using appropriate engineering methods that respond to the geologic characteristics specific to the site in order to achieve a high standard of safety and meet professional practice standards and codes.
5. The proposed activity shall not further degrade the values and functions of the associated critical areas.
6. Unless allowed pursuant to BIMC 16.20.090 or as part of an approved building permit, removal of vegetation from an erosion or landslide hazard area or setback is prohibited.
E. Development Standards – Landslide Hazard Areas. The following requirements shall apply to any land disturbing activity or construction within a landslide hazard area or its setback as described herein:
1. Prohibited Activities. Development of habitable structures and critical facilities is prohibited in landslide hazard areas and landslide hazard area setbacks.
2. Allowed Activities. The following minor development may be allowed in landslide hazard areas on slopes 40 percent or greater and landslide hazard area setbacks if the development standards of this section are met:
a. Surface water management, including outfalls;
b. Septic facilities, including drainfields;
c. Trails and stairs;
d. Cable lifts and trams;
e. Public or private utilities or streets;
f. Seismic or other safety upgrades to protect existing habitable structures; and
g. Other nonhabitable structures.
3. Any land disturbing activity or construction within a landslide hazard area or its setback shall meet the following requirements:
a. All development proposals shall be designed to avoid impacts to geologically hazardous areas. The development shall be designed to minimize the footprint of building in other disturbed areas, minimize removal of vegetation, minimize topographic change, and retain open space to the maximum extent practicable;
b. Development design shall utilize clustering, understructure parking, multilevel construction, and tiered foundations to the extent feasible to minimize impervious lot coverage, slope disturbance, and changes to the natural topography;
c. Access shall be in the least sensitive part of the site, and common access drives and utility corridors are required to the extent feasible;
d. Roads, walkways and parking areas shall be designed to parallel the natural contours to the extent feasible;
e. Cut and fill slopes shall be prepared and maintained to control against erosion and instability; and
f. Drainage and stormwater designs in zones of influence shall incorporate elements of low impact design, add examples to the extent feasible, and shall be designed in such a manner that stormwater outlet discharges do not create additional impacts.
4. Factors of Safety. Factors of safety in accordance with Table 2 of this section are required. Analysis of dynamic conditions shall be based on the minimum horizontal acceleration for the probabilistic maximum considered earthquake as established by the currently adopted version of the International Building Code.
|
Structure, use or activity |
Static factor of safety |
Dynamic (seismic) factor of safety |
Standard setback |
|---|---|---|---|
|
Habitable structure |
1.5 |
1.0 |
Top of slope: Height of slope up to maximum of 75 feet Bottom of slope: Height of slope |
|
High-risk nonhabitable structure |
1.3 |
As determined by geological hazards assessment. |
Top of slope: Height of slope up to maximum of 75 feet Bottom of slope: Height of slope |
|
Lower-risk nonhabitable structures |
As determined by geological hazards assessment. |
As determined by geological hazards assessment. |
Height of slope up to 75 feet. |
|
Other structure or use |
As determined by geological hazards assessment. |
As determined by geological hazards assessment. |
Height of slope up to 75 feet. |
|
Tree and vegetation activities in accordance with BIMC 16.20.090 |
n/a |
n/a |
25 feet only from top of slope. |
5. Setback Requirement. Setbacks from landslide hazard areas are required. A setback shall be established from all edges of a landslide hazard area as follows:
a. A standard setback in accordance with Table 2 of this section;
b. A setback established by the findings of a geological hazards assessment prepared by a licensed geologist or geotechnical engineer that protects and minimizes the risk of property damage, death or injury resulting from a potential landslide impact. The geological hazards assessment shall require a third-party independent review by a qualified geologist or geotechnical engineer at the cost to the applicant;
c. A setback less than 20 feet is prohibited for habitable structures;
d. The setback for tree and vegetation activities in accordance with BIMC 16.20.090 is 25 feet only from the top of slope;
e. No setback is required for slopes 40 percent or greater with a vertical elevation change of up to 20 feet, if compliance with development standards in subsections D and E of this section is documented by a geotechnical engineer licensed in the state of Washington; or
f. The setback may be increased beyond that specified in subsection E.5.a of this section if the director determines a larger setback is necessary to prevent risk of damage to proposed adjacent development and the associated critical areas.
6. For the purposes of establishing the factors of safety and setback using Table 2 of this section, the following categories shall apply:
a. Habitable structure: residences, accessory dwelling units, garages;
b. High-risk nonhabitable structure: decks, patios, pools/hot tubs, driveways, trams, cable lifts, carports;
c. Lower-risk nonhabitable structure: storage shed, boathouse, stairs, pathways, structures intended for short-term use;
d. Other structures or uses: septic facilities including drainfields, drainage outfalls, bulkheads, landscape walls, other utilities; and
e. If a proposed structure, use or activity is not included in subsections E.6.a through d of this section, the category shall be determined by the city engineer.
7. Zone of Influence. A zone of influence shall be established 300 feet upslope from slopes greater than 40 percent and 200 feet upslope from slopes greater than 15 percent but less than 40 percent that are determined to be geologically hazardous areas to assess changes in land use and hydrology that may affect the stability of the geologically hazardous area.
a. The applicant shall have the stormwater pollution prevention plan (erosion control plan) for the project reviewed by a geotechnical engineer to determine if there are any potentially adverse impacts to the landslide hazardous area. The report shall contain recommendations to avoid adverse impacts to the geologically hazardous area. Concentrated discharge of stormwater shall only be allowed where specifically recommended in the report and authorized by the city engineer.
b. If the geotechnical engineer or the city engineer determines that there are potential adverse impacts, the applicant shall provide a geotechnical analysis containing information specified by the city engineer which analyzes the potential impacts to the geological hazard from the proposed development in the zone of influence and meets the standards of this section.
8. Field Marking Requirements. Proposed clearing and work limit lines and landslide hazard setbacks shall be marked in the field for inspection and approval by the city prior to start of any land disturbing activity. Field marking shall remain in place until construction is completed and final inspection is completed by the city. (Ord. 2018-01 § 2 (Exh. A), 2018)