Chapter 18.10F
CRITICAL AREAS CODE – GEOLOGICALLY HAZARDOUS AREAS
Sections:
18.10F.010 Permitted uses and activities.
18.10F.040 Application requirements.
18.10F.060 Specific standards.
18.10F.010 Permitted uses and activities.
Uses and activities allowed within designated geologically hazardous areas are those uses permitted by the zoning district, subject to the provisions of this chapter. (Ord. 1020 § 1, 2002).
18.10F.020 Classification.
A. Geologically hazardous areas in the city consist of erosion hazard areas (wind and water) and steep slopes. Classification and rating of geologically hazardous areas will be based upon the risk to development. The categories of risk shall be (1) known or suspected risk; (2) no risk; and (3) risk unknown, meaning data is not available to determine the presence or absence of a geological hazard. The classification system for geologically hazardous areas shall be as described below.
1. Level 1 Critical hazard areas shall be those areas with a known or suspected risk.
2. Level 2 Awareness hazard areas shall be those areas that have an unknown risk.
B. The determination of the level of risk will be established through an approved geotechnical report submitted by the applicant for any development permit. The city may use on-site inspections and the information sources identified within this title as guidance in identifying the presence of potential geologically hazardous areas.
C. Any land containing soils, geology or slopes that meet any of the following criteria shall be classified as having a known or suspected risk of being geologically hazardous areas:
1. Soils classified in the soil survey of Chelan County Area as having a moderate or high hazard for wind and/or water erosion;
2. Soil complexes containing at least one soil type classified as a moderate to severe erosion hazard when occurring on slopes of 15 percent or greater;
3. Any areas with slopes 30 percent and greater;
4. Areas of historic failures or potentially unstable slopes designated on the Natural Resource Conservation Service slide hazard area studies, and those areas mapped as slumps, earthflows, mudflows, lahars or landslides on maps published by the United States Geological Survey or Department of Natural Resources Division of Geology and Earth Resources;
5. Any area with a combination of:
a. Slopes 15 percent or steeper, and
b. Impermeable soils (typically silt and clay) frequently interbedded with granular soils (predominantly sand and gravel), and
c. Springs or ground water seepage;
6. Any area which has shown geologically significant movement during the past 10,000 years or which is underlain by mass wastage debris from that period of time;
7. Any area potentially unstable as a result of rapid stream incision or stream bank erosion;
8. Areas located in a canyon or ravine, or on a bluff;
9. Any area located on an alluvial fan, presently or potentially subject to inundation by debris flows or deposition of stream-transported sediments. (Ord. 1020 § 1, 2002).
18.10F.030 Designation.
All existing areas of the city classified according to the provisions contained in this chapter, as determined by the city, are designated as geologically hazardous areas. (Ord. 1020 § 1, 2002).
18.10F.040 Application requirements.
Development permit applications shall provide appropriate information on forms provided by the city, including without limitation the information described below. Additional reports or information to identify potential impacts and mitigation measures to geologically hazardous areas may be required if deemed necessary. Generally, within Level 1 Critical hazard areas, detailed studies and reports will be required to determine whether or not development will be allowed, and if so, what mitigation measures will be required. Within Level 2 Awareness hazard areas, detailed studies and reports may be necessary to determine the existence of a geologically hazardous area, and if so, whether or not development will be allowed and what mitigation measures might be necessary where development may occur.
A. A site plan which discloses the following:
1. The location and boundaries of the geologically hazardous area;
2. The location and dimensions of all existing and proposed buildings, roads and other improvements, and their physical relationship to the geologically hazardous area;
3. The location and type of any proposed buffers, including the identification of any other protective measures; and
4. Locations and results of any test holes, excavations, etc., used in evaluating the existence and extent of the geologic hazard;
B. A geotechnical report prepared as described within this title; and
C. A certification from the geotechnical engineer and/or geologist preparing the study and report stating all of the following:
1. The risk of damage from the project, both on- and off-site, is minimal;
2. The project will not materially increase the risk of occurrence of the hazard; and
3. The specific measures incorporated into the design and operational plan of the project to eliminate or reduce the risk of damage due to the hazard. (Ord. 1020 § 1, 2002).
18.10F.050 General standards.
The following minimum standards shall apply to all development activities occurring within designated geologically hazardous areas and their buffers.
A. All projects shall be evaluated to determine whether the project is proposed to be located in a geologically hazardous area, the project’s potential impact on the geologically hazardous area, and the potential impact of the geologic hazard on the proposed project.
B. Appropriate buffer areas shall be maintained between all permitted uses and activities and designated geologically hazardous areas.
1. A minimum buffer of 50 feet shall be established from the top, toe and all edges of geologically hazardous areas.
2. Existing native vegetation within the buffer area shall be maintained.
3. The buffer may be reduced to a minimum of 30 feet when an applicant demonstrates, to the satisfaction of the city, that the reduction will adequately protect the proposed development and the designated geologically hazardous area.
4. Normal nondestructive pruning and trimming of vegetation for maintenance purposes, or thinning of limbs of individual trees to provide for a view corridor, is allowed within the buffer area.
C. Appropriate drainage and erosion control measures, as determined by the city, shall be implemented in designated geologically hazardous areas.
1. All development shall submit for review and approval a drainage and erosion control plan pursuant to the provisions of this title, unless waived by the city.
2. All disturbed areas shall be revegetated in accordance with an approved plan, and completed within six months.
3. Surface drainage shall not be directed across the face of a bluff or into a ravine. If drainage must be discharged from the bluff into adjacent waters, it shall be collected above the face of the bluff and directed to the water by a sealed drain line, and provided with an energy dissipating device.
D. Appropriate grading and excavation measures, as determined by the city, shall be implemented in designated geologically hazardous areas.
1. All development shall submit for review and approval a grading and excavation plan as specified in Chapter 18.10A CMC, unless waived by the city. There shall be minimum disturbance of trees and vegetation on steep slopes and in ravines to minimize erosion and instability.
2. Excavation, grading and earthwork construction in designated geologically hazardous areas shall only be allowed from April 1st to October 15th, except for the following circumstances:
a. Up to 5,000 square feet may be cleared on any lot, subject to approval of a drainage and erosion control and grading plan as required above; and
b. Timber harvest pursuant to DNR-approved forest practices or a clearing and grading permit may be allowed.
3. All disturbed areas shall be revegetated in accordance with an approved plan, and completed within six months.
4. All clearing shall be marked in the field for inspection and approval prior to alteration of the site.
5. The face of any cuts and/or fills on slopes will be prepared, maintained and revegetated to control against erosion.
E. Construction methods should be utilized which minimize risks to structures and which do not increase the risk to the site, or to adjacent properties and their structures, from the geologic hazard.
F. Site planning shall minimize disruption of existing topography and natural vegetation, and shall incorporate opportunities for phased clearing.
G. Impervious surface coverage shall be minimized.
H. Any limitations to site disturbance, such as clearing restrictions, imposed as a condition of development approval shall be marked in the field and approved by the city prior to undertaking the project.
I. A monitoring program shall be prepared for construction activities occurring in critical geologic hazard areas.
J. Development shall not increase instability or create a hazard to the site or adjacent properties, or result in a significant increase in sedimentation or erosion. (Ord. 1020 § 1, 2002).
18.10F.060 Specific standards.
The following standards shall apply to the activity identified below, in addition to the general standards outlined in CMC 18.10F.050.
A. Road Repair and Construction. Construction of any new public or private road is prohibited in a designated geologically hazardous area. Any existing private or public road repair or maintenance may be authorized, subject to the following minimum standards:
1. The repair and maintenance shall not create additional significant adverse impacts to the geologically hazardous area; and
2. Road repair and maintenance is the minimum necessary to provide safe traveling surfaces.
B. Major Developments. All major developments processed by the city according to the provisions governing full administrative review or quasi-judicial review authorized within a designated geologically hazardous area shall comply with the following minimum standards:
1. All plats shall disclose the presence on each residential lot of one building site, including sufficient building area, sewage system, setbacks, and access, that is suitable for development and which is not within the designated geologically hazardous area or its associated buffer;
2. All geologically hazardous areas and their buffers shall be clearly identified on all plats, maps, documents, etc.;
3. Designated geologically hazardous areas and their associated buffers shall be designated and disclosed on the final plats, maps, documents, etc., as open space tracts, nonbuildable lot and buffer areas, or as common areas, with ownership and control transferred to a homeowner’s association. Associated geologically hazardous area buffers may alternatively be designated and disclosed on the final plats, maps, documents, etc., as an easement or covenant encumbering the property; and
4. Areas which pose an immediate, significant threat to public safety shall be appropriately fenced and identified, as determined by the city.
C. Surface Water Management. Stormwater retention and detention systems, including percolation systems utilizing buried pipe or french drain, are prohibited within designated geologically hazardous areas and their buffers, unless a geotechnical report indicates such a system shall not affect slope stability and the systems are designed by an engineer. The engineer shall also certify that the systems were installed as designed.
D. Trails and Trail-Related Facilities. Construction of public and private trails and trail-related facilities, such as picnic tables, benches, interpretive centers and signs, viewing platforms and campsites may be authorized within a designated geologically hazardous area, subject to the following minimum standards:
1. Trail facilities shall, to the extent feasible, be placed on existing road grades, utility corridors, or any other previously disturbed areas;
2. Trail facilities shall minimize the removal of trees, shrubs, snags and other important features;
3. Viewing platforms, interpretive centers, campsites, picnic areas, benches and their associated access shall be designed and located to minimize disturbance of the geologically hazardous area; and
4. All structures shall be constructed with materials complementary to the surrounding environment.
E. Utilities. When no other practical alternative exists, construction of utilities within a designated geologically hazardous area may be authorized, subject to the following minimum standards:
1. Utility corridor shall be jointly used;
2. Corridors shall be revegetated to pre-construction densities with appropriate native vegetation immediately upon completion of construction, or as soon thereafter as possible given seasonal growing constraints. The utility purveyor shall provide an assurance device or surety in accordance with CMC which ensures that such vegetation survives;
3. Any additional corridor access for maintenance shall be provided as much as possible at specific points rather than by parallel roads. If parallel roads are necessary they shall be no greater than 15 feet in width, and shall be contiguous to the location of the utility corridor on the side opposite the designated geologically hazardous area;
4. Construction of sewer lines within a designated geologically hazardous area which are necessary to meet state and/or local health code requirements may be authorized, provided the severity of the designated geologically hazardous area is not increased;
5. Septic system drain fields shall be located outside of the geologically hazardous area and the associated buffers, unless otherwise justified and certified by a qualified geotechnical engineer. (Ord. 1020 § 1, 2002).