Chapter 18.300
GEOLOGICALLY HAZARDOUS AREAS
Sections:
18.300.020 Applicability and exemptions.
18.300.030 Designation and mapping.
18.300.040 Report requirements—Geologic hazards.
18.300.050 Permanent protection for geologic hazard areas and buffers.
18.300.060 Geologic hazard area approval criteria.
18.300.070 Steep slope hazard areas.
18.300.080 Landslide hazard areas.
18.300.090 Seismic hazard areas.
18.300.010 Purpose.
The purpose of this section is to safeguard public health, safety and welfare by placing limitations on development in geologically hazardous areas consistent with the requirements of the Growth Management Act and WAC 365-190-080. (Ord. 04-025 § 7 (part), 2004)
18.300.020 Applicability and exemptions.
A. This section applies to all development activities in or within one hundred feet of geologic hazard areas except those activities exempted in subsection B of this section. Geologic hazard areas include steep slope hazard areas, landslide hazard areas and seismic hazard areas.
B. In addition to the general exceptions contained in Chapter 18.260 BGMC, the expansion, remodel, reconstruction or replacement of any structures which will be set back from the geologic hazard area a distance which is greater than or equal to the setback of the original structure and which will not increase the building footprint by more than one thousand square feet inside a steep slope hazard area, landslide hazard area or their buffers is exempt. (Ord. 04-025 § 7 (part), 2004)
18.300.030 Designation and mapping.
A. Geologic hazards are usually localized individual occurrences that may affect only small, separate areas. Because geologic hazards such as areas susceptible to landslides may be small and localized, no complete mapping exists identifying the presence or absence of each geologic hazard at any particular site. Also, activities such as grading and clearing can create or increase slope instability where none was previously identified.
B. Battle Ground shall adopt updated mapping as more detailed information becomes available. Until updated information becomes available, Battle Ground shall refer to the following Clark County hazard maps:
1. Slope Areas Mapping for Clark County, Clark County department of assessment and GIS;
2. Slope Stability of Clark County, Washington Department of Natural Resources, 1975 and landslides mapped in Geologic Map of the Vancouver Quadrangle, Washington and Oregon, Washington Department of Natural Resources, 1987; and
3. Relative Earthquake Hazard Map for the Vancouver, Washington Urban Region, Washington Department of Natural Resources, 1994.
C. Where the geologic hazard area maps and designation criteria conflict, the following designation criteria shall prevail.
1. Steep slope hazard areas include all lands that exceed a forty percent slope;
2. Landslide hazard areas include areas that, due to a combination of slope inclination, soil type and presence of water, are susceptible to landslides in accordance with the following criteria:
a. Areas of previous slope failures including areas of unstable old or recent landslides;
b. Areas with all three of the following characteristics:
i. Slopes steeper than fifteen percent,
ii. Hillsides intersecting geologic contacts with permeable sediment overlying a low permeability sediment or bedrock, and
iii. Any springs or groundwater seepage;
c. Slopes that are parallel or subparallel to planes of weakness, such as bedding planes, joint systems and fault planes in subsurface materials;
d. Areas mapped by:
i. Washington Department of Natural Resources Open File Report: Slope Stability of Clark County, as having potential instability, historical or active landslides, or as older landslide debris, and
ii. The Washington Department of Natural Resources Open File Report Geologic Map of the Vancouver Quadrangle, Washington and Oregon, as landslides;
e. Slopes greater than eighty percent, subject to rock fall during earthquake shaking;
f. Areas potentially unstable as a result of rapid stream incision, stream bank erosion, and stream undercutting the toe of a slope;
g. Areas located in a canyon or on an active alluvial fan, presently or potentially subject to inundation by debris flows, debris torrents or catastrophic flooding; and
h. Areas adjacent to open-pit mine sites subject to steep slope hazard or landslide hazard. (Ord. 04-025 § 7 (part), 2004)
18.300.040 Report requirements—Geologic hazards.
A. For development activity regulated by this section, submittal requirements will vary depending on the type of project and the type of hazard mitigations that are proposed. Pursuant to Chapter 18.260 BGMC, a review of a geologic hazard area will be conducted in conjunction with the primary development application. Projects are required to submit a basic site description sufficient to verify that the location of proposed building and access road improvements comply with buffers, setbacks, and vegetation preservation required by BGMC 18.300.070 and 18.300.080. If a nonexempt activity is proposed within a geologic hazard area, additional information in the form of a geologic hazard area study must be provided to assure the project is feasible and will not cause an increased geologic hazard. The information required for a site description is included in subsection C of this section. The requirements for a geologic hazard area study for projects wishing to build in a geologic hazard area are included in subsection D of this section. To avoid duplication, the director shall coordinate the information required by this section with the assessments and requirements for other critical areas.
B. The director shall waive parts of the submittal requirements if the department determines that they are not applicable to the proposed activity.
C. Site Description. As part of the development permit application, the following information describing the subject property and areas within twenty-five feet of the property lines or smaller area of concern as deemed appropriate by the department, drawn to an engineering scale no larger than one inch equals twenty feet and no smaller than one inch equals one hundred feet as deemed appropriate by the director:
1. The site boundary lines;
2. The topography at contour interval of no greater than two feet;
3. The location of all drainage-flow characteristics, streams, groundwater seeps, springs, and evidence of seasonal surface water runoff or groundwater;
4. The location and extent of all existing and proposed grading activities and existing natural or artificial drainage control facilities and systems;
5. The location and description of all geologic hazards located on the site and observed on adjacent properties within one hundred feet of site boundaries;
6. The general location of all vegetation and the general location, number and description of all trees over six-inch diameter measured three feet above the ground; and
7. The location of all proposed buffers and setbacks.
D. Geologic Hazard Area Study. A geologic hazard area study is required if the proposed development does not comply with requirements of BGMC 18.300.070, Steep slope hazard areas, or BGMC 18.300.080, Landslide hazard areas. Geologic investigation may also be required in some cases to meet Uniform Building Code requirements for foundations and for seismic design. Geologic hazard area studies shall be prepared, stamped and signed by a geotechnical engineer or geologist licensed in the state of Washington with expertise in the field. Based on the site characteristics and the information submitted by the applicant, the director may require all or part of the following information to be included in a geotechnical report:
1. The requirements for the site description listed above in subsection C of this section;
2. Site Geology Information.
a. Topographic contours at two-foot intervals or as specified by the director;
b. Subsurface data that includes the exploration method, location of soil borings, borings, logs, soil and rock stratigraphy and groundwater levels including seasonal changes;
c. The location of landslides, or downslope soil movement, faults, and geologic contacts on the subject property and adjacent properties;
d. A site history that describes any prior grading, soil instability or slope failure; and
e. A description of the site vulnerability to seismic events;
3. Geotechnical Information and Plan Requirements.
a. A slope stability study and opinion of slope stability on the subject property and adjacent properties;
b. Grading plan;
c. Structural foundation requirements and estimated foundation settlements;
d. Soil compaction criteria;
e. Allowable soil-bearing pressure for foundations, minimum footing widths, piling recommendations for foundations, and design pressure for retaining walls;
f. Laboratory data and soil index properties for soil samples;
g. Suitability for fill;
h. Lateral earth pressures;
i. Description of erosion vulnerability and an erosion control plan including:
i. A description of the extent and type of vegetative cover;
ii. An estimate of load capacity including surface and groundwater conditions, public and private sewage disposal systems, fills and excavations and all structural development;
iii. An estimate of slope stability and the effect construction and placement of structures will have on the slope over the estimated life of the structure;
iv. An estimate of the bluff retreat rate that recognizes and reflects potential catastrophic events such as seismic activity or a one-hundred-year storm event;
v. Consideration of the run-out hazard of landslide debris and/or the impacts of landslide run-out on down-slope properties;
vi. A study of slope stability including an analysis of proposed angles of cut and fill and site grading;
vii. Recommendations for building limitations, structural foundations, and an estimate of foundation settlement; and
viii. An analysis of proposed surface and subsurface drainage, and the vulnerability of the site to erosion;
j. An evaluation of proposed surface and subsurface drainage in a stormwater control plan including information regarding the collection, transport, treatment, discharge and/or recycle of surface water prepared in accordance with Chapter 18.250 BGMC. The evaluation should consider on-site septic system disposal volumes where the additional volume will affect the erosion or landslide hazard area;
k. Building limitations; and
l. A vegetation management and restoration plan or other means for maintaining long-term stability of slopes;
4. A site evaluation that describes the suitability of the site to accommodate the proposed activity; and
5. Such additional information describing existing physical features for the site and surrounding area as required by the director to complete review of the project under standards of the International Building Code. (Ord. 04-025 § 7 (part), 2004)
18.300.050 Permanent protection for geologic hazard areas and buffers.
A. Steep slope hazard areas and landslide hazard areas and buffers for which permanent protection is required pursuant to BGMC 18.300.070 and 18.300.080 shall be designated landslide protection areas.
B. Landslide protection area requirements apply only to site plans and land divisions. For all development activities subject to this section, landslide protection areas shall be delineated on all land divisions and plots.
C. A conservation covenant applicable to the landslide protection areas shall be recorded in a form approved by the city attorney as adequate to incorporate the restrictions of this section.
D. Prior to any site development activity, the applicant shall mark with temporary markers in the field the boundary of all landslide protection areas required by this section, or the limits of the proposed site disturbance outside of the landslide protection areas, using methods and materials acceptable to the city.
E. Landslide protection area boundaries shall be permanently marked on the site prior to final inspection by the city using methods and materials acceptable to the city.
F. Clearing or vegetation removal in landslide protection areas, steep slope hazard areas or landslide hazard areas or their buffers is prohibited except for:
1. Activities included in an approved geologic hazard area study as defined in BGMC 18.300.040;
2. Limited vegetation removal for surveying and testing necessary for development approvals;
3. Emergency or fire hazard removal authorized by the fire marshal;
4. Removal of nuisance vegetation utilizing methods that minimize disruption of soil and nonnuisance vegetation provided it is replaced with appropriate native vegetation;
5. Clearing necessary for placement or maintenance of fencing;
6. Clearing necessary for hillside vegetation restoration;
7. Clearing necessary for vegetation or resource conservation projects authorized by a public agency; and
8. Clearing for three-foot-wide or narrower footpaths surfaced with wood, soil or gravel. (Ord. 04-025 § 7 (part), 2004)
18.300.060 Geologic hazard area approval criteria.
If an applicant wishes to perform development activities not allowed by BGMC 18.300.070 and 18.300.080, a geologic hazard area study meeting the requirements of BGMC 18.300.040 must be completed. The development proposal may be approved, approved with conditions, or denied based on the director’s evaluation of the suitability of the mitigation measures proposed by the geologic hazard area study to protect life, safety, and slope stability on contiguous properties. (Ord. 04-025 § 7 (part), 2004)
18.300.070 Steep slope hazard areas.
A. Nonexempt development activity on or adjacent to slopes steeper than forty percent that do not have a mapped or designated landslide hazard shall comply with the requirements of this section.
B. Buffer and Setback Distances.
1. Activities at the base of ascending slopes (building at the bottom of a steep slope):
a. For slopes greater than or equal to forty percent and less than one hundred percent, buffers shall extend a distance away from the toe of the slope that is equal to the vertical height of the slope divided by two, but not to exceed fifteen feet. For slopes less than one hundred percent, the toe of the slope is defined as a distinct break in slope at the base of a steep slope.
b. For slopes greater than one hundred percent, the buffer shall extend a distance back from the toe of the slope equal to the height of the slope divided by two, not to exceed fifteen feet. The buffer shall be measured horizontally from a plane, drawn tangent to the top of the slope at an angle of forty-five degrees to the proposed structure.
c. The setback shall be eight feet beyond the buffer.
2. Activities at the tops of descending slopes (building at the top of a steep slope):
a. For slopes greater than or equal to forty percent and less than one hundred percent, buffers shall extend a distance back from the top of the slope equal to the vertical height of the slope divided by three, but not to exceed forty feet. The top of the slope is defined as a distinct break in slope at the top of a steep slope.
b. For slopes greater than one hundred percent, the buffer shall extend a distance back from the top of the slope equal to the height of the slope divided by three, but not to exceed forty feet. The buffer shall be measured horizontally from a plain drawn at forty-five degrees (one hundred percent slope) from the toe of the slope to the proposed structure.
c. The setback shall be eight feet beyond the buffer.
3. For projects not required to have a landslide protection area under BGMC 18.300.050, the setback from the steep slope shall be equal to the buffer distance set in this subsection.
4. The director may approve buffers and setbacks which differ from those required by subsection (B)(1) of this section if the applicant submits a geologic hazard area study described in BGMC 18.300.040, which technically demonstrates and illustrates that the alternative buffer provides protection which is greater than or equal to that provided by the buffer required in subsection (B)(2) of this section.
5. The department may increase buffers or setbacks where necessary to meet requirements of the International Building Code.
6. Other than for exemptions specifically listed, vegetation removal is not allowed on slopes over forty percent without an approved geologic hazard area study described in BGMC 18.300.040.
7. Buffers, landslide protection areas and setbacks for steep slopes on projects having approved grading shall be based on regulated steep slopes that remain after that grading. (Ord. 04-025 § 7 (part), 2004)
18.300.080 Landslide hazard areas.
A. A development proposal on a site containing a landslide hazard area shall meet the following requirements:
1. A minimum buffer of fifty feet shall be established from all edges of the landslide hazard area. The buffer shall be extended as required to mitigate a steep slope or erosion hazard or as otherwise necessary to protect the public health, safety and welfare; and
2. All portions of landslide hazard areas and buffers shall be designated as landslide protection areas.
B. Other than exempt activities, clearing or alteration of a landslide hazard area is allowed only if the following are met:
1. A development proposal does not decrease slope stability on contiguous properties; and
2. Mitigation is based on best available engineering and geological practice and is described in an approved geologic hazard area study as specified in BGMC 18.300.040.
C. Neither buffers or a landslide protection area will be required if the activity meets the requirements of subsection (B)(2) of this section. (Ord. 04-025 § 7 (part), 2004)
18.300.090 Seismic hazard areas.
Development activity in a seismic hazard area shall meet all applicable provisions of the Uniform Building Code, as adopted by Battle Ground. The building department shall use the site-specific seismic hazard investigation requirements based on relative earthquake hazard mapping described in Using Relative Earthquake Hazard Mapping for Land Use Planning and Building Permit Administration published by Metro, Portland, Oregon, May 1996, attached as Table 18.300.090.
|
Land Use Group |
Land Uses |
Relative Earthquake Hazard Zone |
|||
|---|---|---|---|---|---|
|
A |
B |
C |
D |
||
|
Earthquake Performance Objective is Fully Functional (Acceptable risk is near zero) |
|||||
|
Potential Catastrophe if Damaged |
Large dams |
4 |
4 |
4 |
4 |
|
Nuclear plants |
4 |
4 |
4 |
4 |
|
|
Facilities using/storing large quantities of hazardous materials |
4 |
3 |
3 |
3 |
|
|
Earthquake Performance Objective is Immediate Occupancy (Acceptable risk is very low) |
|||||
|
High-Occupancy with Involuntary or Dependent Occupants |
Day care centers <250 kids |
3 |
3 |
2 |
1 |
|
Day care centers >250 kids |
3 |
3 |
2 |
1 |
|
|
Schools K—12 <300 students |
3 |
3 |
2 |
1 |
|
|
Schools K—12 >300 students |
3 |
3 |
2 |
1 |
|
|
Convalescent homes <50 persons |
3 |
3 |
2 |
1 |
|
|
Convalescent homes >50 persons |
3 |
3 |
2 |
1 |
|
|
Jails and detention facilities |
3 |
3 |
2 |
1 |
|
|
Essential for Emergency Response |
Fire and police stations |
3 |
3 |
3 |
2 |
|
Garages for emergency vehicles |
3 |
3 |
3 |
2 |
|
|
Water tanks |
3 |
3 |
3 |
2 |
|
|
Structures housing fire suppressants |
3 |
3 |
3 |
2 |
|
|
Government communications centers |
3 |
3 |
3 |
2 |
|
|
Emergency response centers |
3 |
3 |
3 |
2 |
|
|
Hospitals |
3 |
3 |
3 |
2 |
|
|
Medical building with surgical services |
3 |
3 |
3 |
2 |
|
|
Critical to the Functioning of Battle Ground |
Large power plants |
3 |
3 |
3 |
2 |
|
Power interties |
3 |
3 |
3 |
2 |
|
|
Sewage treatment plants |
3 |
3 |
3 |
2 |
|
|
Water plants |
3 |
3 |
3 |
2 |
|
|
Regional highways and bridges and tunnels |
3 |
3 |
3 |
2 |
|
|
Regional rail lines |
3 |
3 |
3 |
2 |
|
|
Airports |
3 |
3 |
3 |
2 |
|
|
Port facilities |
3 |
3 |
3 |
2 |
|
|
Major communications facilities |
3 |
3 |
3 |
2 |
|
|
Telephone exchanges |
3 |
3 |
3 |
2 |
|
|
Radio and TV stations |
3 |
3 |
3 |
2 |
|
|
Earthquake Performance Objective is Damage Control (Acceptable risk is very low) |
|||||
|
High Occupancy |
Buildings >10 stories |
3 |
3 |
2 |
1 |
|
Public and private colleges <500 occupants |
3 |
3 |
2 |
1 |
|
|
Public and private colleges >500 occupants |
3 |
3 |
2 |
1 |
|
|
Public assembly places with >300 capacity |
3 |
3 |
2 |
1 |
|
|
Hotels/motels >50 rooms >60,000' >10 stories |
3 |
3 |
2 |
1 |
|
|
Major industries and employers |
3 |
3 |
2 |
1 |
|
|
Apartments >25 units |
3 |
3 |
2 |
1 |
|
|
Buildings with >150 employees |
3 |
3 |
2 |
1 |
|
|
Important Local Impacts if Damaged |
Facilities using/storing small quantities of hazardous materials |
3 |
3 |
2 |
1 |
|
Small dams that could cause flooding |
3 |
3 |
2 |
1 |
|
|
Gas stations |
2 |
2 |
2 |
1 |
|
|
Highways, streets, bridges |
2 |
2 |
2 |
1 |
|
|
Utility lines, substations, and gas mains |
3 |
3 |
2 |
1 |
|
|
Water and sewer mains |
3 |
3 |
2 |
1 |
|
|
Industries/business important to economy |
2 |
2 |
2 |
1 |
|
|
Health care clinics |
2 |
2 |
2 |
1 |
|
|
Co-generation power plants |
3 |
3 |
2 |
1 |
|
|
Earthquake Performance Objective is Substantial Life Safety (Acceptable risk is moderate) |
|||||
|
Moderate Occupancy |
Buildings with 4 to 10 stories |
3 |
3 |
2 |
1 |
|
Apartments 9 to 25 units (b) |
3 |
3 |
2 |
1 |
|
|
Buildings with 50 to 150 employees |
3 |
3 |
2 |
1 |
|
|
Buildings with 50 to 150 employees >60,000' >10 stories |
3 |
3 |
2 |
1 |
|
|
Public assembly places: 50 to 300 capacity |
3 |
3 |
2 |
1 |
|
|
Hotels/motels <50 rooms <60,000' <10 stories |
3 |
3 |
2 |
1 |
|
|
Low Occupancy |
Apartment buildings with 2 to 8 units (a) |
2 |
2 |
1 |
1 |
|
Buildings with <50 employees (a) |
2 |
2 |
1 |
1 |
|
|
Buildings with 1 to 3 stories (a) |
2 |
2 |
1 |
1 |
|
|
Public assembly places with <50 capacity (a) |
2 |
2 |
1 |
1 |
|
|
Single-family houses (b) |
2 |
2 |
1 |
1 |
|
|
Manufactured dwelling (b) |
2 |
2 |
1 |
1 |
|
4 = Site investigation with panel peer review required.
3 = Site investigation required unless data suggest otherwise.
2 = Site investigation not required unless data suggest otherwise.
1 = Site investigation not required.
(a) Discretion should be applied so that unnecessary site investigations are not required for smaller buildings within these categories. Guidelines to determine when investigations are needed should be established.
(b) Site investigation required if stipulated in a subdivision approval or other development approval of the planning agency.
(Ord. 04-025 § 7 (part), 2004)