40.430.010    Introduction

A.    Purpose.

    The purpose of this chapter 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.

(Amended: Ord. 2005-04-15; Ord. 2012-02-03; Ord. 2018-01-09)

B.    Applicability and Exemptions.

1.    Applicability. This chapter applies to all construction, development, earth movement, clearing, or other site disturbance which requires a permit, approval or authorization from the county in or within one hundred (100) feet of a geologic hazard area except for exempt activities listed in Section 40.430.010(B)(3). Regulated geologic hazards include steep slope hazard areas, landslide hazard areas, seismic hazard areas, and volcanic hazard areas.

2.    Shoreline Master Program. Within shoreline jurisdiction, development may be allowed for those uses in the Shoreline Master Program (Chapter 40.460) either through a statement of exemption or through an application with a geohazard review as part of the shoreline permit process.

3.    Exempt Activities and Uses. The following activities and uses are exempt from the provisions of this chapter:

a.    Emergency activities which require immediate action to prevent an imminent threat to health, safety or property. As soon as practical, the responsible party shall provide written notification to the responsible official and obtain all applicable permits;

b.    Residential remodels that do not alter the footprint or increase the gross floor area of the structure;

c.    Any replacement, operation, repair, modification, installation or construction by a state or locally franchised utility company in an improved right-of-way or utility corridor;

d.    Normal and routine maintenance and repair of existing utility facilities, equipment and appurtenances;

e.    Any development activity on or within one hundred (100) feet of steep slopes that have been created through previous, legal grading activities is exempt from steep slope hazard regulations; and

f.    Applications for short plats in the rural area that are certified by a registered geologist or professional engineer licensed in the state of Washington to be exempt from the requirements of this chapter even though a mapped geohazard exists on the plat or within one hundred (100) feet of the boundaries of the plat. Certification shall be provided with the preliminary plat application by means of one of the following:

(1)    A development envelope is designated on the plat which is certified to be over one hundred (100) feet from any regulated geologic hazard area. A stamped letter which documents how the designated envelope is exempt from the requirements of this chapter shall accompany the development envelope diagram; or

(2)    A stamped letter which documents there are no areas within the boundaries of the plat that are within one hundred (100) feet of any regulated geologic hazard area.

g.    All forest practices other than Class IV G (conversions).

4.    This chapter applies to Class IV G forest practices (conversions).

(Amended: Ord. 2005-04-15; Ord. 2012-02-03; Ord. 2012-07-16; Ord. 2018-01-09)

C.    Definitions.

    For purposes of this chapter, the following definitions shall apply:

1.    “Steep slope hazard area” means an area where there is not a mapped or designated landslide hazard, but where there are steep slopes equal to or greater than forty percent (40%) slope. Steep slopes which are less than ten (10) feet in vertical height and not part of a larger steep slope system, and steep slopes created through previous legal grading activity are not regulated steep slope hazard areas. The presence of steep slope suggests that slope stability problems are possible.

2.    “Landslide hazard area” means an area that, due to a combination of slope inclination, soil type and presence of water is susceptible to landsliding 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 (3) of the following characteristics:

(1)    Slopes steeper than fifteen percent (15%),

(2)    Hillsides intersecting geologic contacts with permeable sediment overlying a low permeability sediment or bedrock, and

(3)    Any springs or groundwater seepage;

c.    Slopes that are parallel or sub-parallel to planes of weakness, such as bedding planes, joint systems and fault planes in subsurface materials;

d.    Areas mapped by:

(1)    Washington Department of Natural Resources Open File Report: Slope Stability of Clark County, 1975, as having potential instability, historical or active landslides, or as older landslide debris, and

(2)    The Washington Department of Natural Resources Open File Report Geologic Map of the Vancouver Quadrangle, Washington and Oregon, 1987, as landslides;

e.    Slopes greater than eighty percent (80%), 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;

h.    Areas within one hundred (100) feet of an open-pit mine sites subject to steep slope hazard or landslide hazard.

3.    “Seismic hazard area” means an area subject to severe risk of damage as a result of earthquake-induced soil liquefaction, ground shaking amplification, slope failure, settlement, or surface faulting. Relative seismic hazard is mapped on the NEHRP Site Class Map of Clark County, published by the Washington Department of Natural Resources.

4.    “Volcanic hazard area” means an area subject to possible low and high density pyroclastic flows as shown on the Volcanic Hazard Map of Clark County.

(Amended: Ord. 2005-04-15)

D.    Maps.

1.    Adopted Maps. The following geologic hazard maps signed by Council are adopted by reference and are on file with the County Auditor:

a.    Clark County, Washington Severe Erosion Hazard Areas;

b.    Clark County, Washington NEHRP Site Classes;

c.    Clark County, Washington Steep Slopes and Landslide Hazards;

d.    Clark County, Washington Liquefaction Susceptibility; and

e.    Clark County, Washington Volcanic Hazard.

2.    Identification. Geologic hazards are usually localized individual occurrences that may affect only small, separate areas. In addition, activities such as grading and clearing can create or increase slope instability where none was previously identified. Because of this, geologic hazard areas have not been identified on a site-specific basis. Where the geologic hazard area maps and definitions conflict, the definitions shall prevail.

3.    Source Data. The approximate location and extent of geologic hazard areas are shown on the geologic hazard area maps adopted herein. The maps are intended to meet the designation criteria listed in WAC 365-190-080 and are based on the best available information, including:

a.    Slope Areas Mapping for Clark County, Clark County Department of Assessment and GIS;

b.    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;

c.    Construction of Liquefaction Susceptibility and NEHRP Soil-type Maps for Clark County, Washington, Washington Department of Natural Resources, 2004;

d.    Volcanic hazard zonation for Mount St. Helens, Washington, U.S. Geological Survey, 1995; and

e.    Natural Resources Conservation Service, Soil Survey Geographic Database (SSURGO), 2004.

4.    Map Updates. Results of binding pre-determinations and other site investigations required under this chapter and the building code will be compiled by the department and incorporated into future geologic hazard area map revisions. The county will adopt updated maps as more detailed information becomes available. The review of such new information shall include local geologists and engineers familiar with the requirements of this chapter and how it is applied to new development.

(Amended: Ord. 2005-04-15; Ord. 2019-05-07)

E.    Relationship to Chapter 40.570 Environmental Impacts.

    Geologic hazard area protective measures required by this section shall constitute adequate mitigation of significant adverse environmental impacts related to geologic hazards for purposes of Chapter 40.570.

(Amended: Ord. 2005-04-15)

F.    Reasonable Use Assurance.

    Nothing in this section shall preclude the issuance of a single-family building permit on a lawfully created lot.

(Amended: Ord. 2005-04-15)

G.    Density Transfer.

    Land divisions regulated by this section may be eligible for density transfers under Section 40.220.010(C)(5).

(Amended: Ord. 2005-04-15)

H.    Open Space Tax Incentives.

    Tax incentives may be available for owners of land set aside in landslide protection hazard areas through the open space taxation program.

(Amended: Ord. 2005-04-15)