7-20-50 Geologic Hazards

This section identifies development standards applicable to specific geologic hazard areas. Major geologic hazards are identified on the Geologic Hazards Map maintained in the Community Development Department.

(a) Avalanche Areas

Restrictions on activities or development in avalanche areas are set forth in subsections (1) and (2) below. In the event that an application is denied because there is no hazard-free area on a site, or because the proposed activity or development does not comply with the restrictions in this section, and an appeal is later granted pursuant to Sec. 2-20-180 or relief is granted pursuant to Sec. 2-40-90 or Sec. 2-40-130, the proposed activity or development shall incorporate hazard mitigation according to the standards in subsection (3) below.
1. High Hazard Avalanche Zone
  - Development is prohibited within High Hazard Avalanche Zones.
2. Moderate Hazard Avalanche Zone
  - Development within a Moderate Hazard Avalanche Zone may only be permitted under the following circumstances:
    - (a) If an entire property is affected by the Moderate Hazard Avalanche Zone, development may be permitted if the hazard can be adequately mitigated to ensure public safety pursuant to the standards in subsection (3) below.
    - (b) In the event that development outside of the Moderate Hazard Avalanche Zone will result in significant incursions into or impacts on Constrained Areas, the County may, in its discretion, approve such development with adequate mitigation measures to assure the safety of the occupants of the property.
    - (c) If the County finds that other hazards present on a property outweigh the risks associated with development in the Moderate Hazard Avalanche Zone, the County may, in its discretion, grant approval to such project subject to compliance with the mitigation measures specified in subsection (3) below.
3. Mitigation Standards
  - (a) Development shall be restricted to the least hazardous area of a project site.
  - (b) If structural avalanche defenses are required to protect people or structures, they shall be designed by a certified professional engineer licensed in the State of Colorado to withstand avalanche impact forces.
  - (c) Clear-cutting or other large scale removal of vegetation, particularly within avalanche path starting zones, shall be prohibited.
  - (d) Extractive operations are prohibited within avalanche hazard zones during the winter unless there is an approved program of avalanche control and defense measures.
  - (e) Utility lines or pipes crossing avalanche hazard zones shall be buried. Surface pipes, poles or towers for suspended transmission lines in avalanche hazard zones shall be protected by utilizing avalanche diversion methods or protection structures.
  - (f) Roads intended for winter use shall avoid avalanche hazard areas. If the County finds that it is not possible to construct a road that avoids high or moderate avalanche hazard areas, then the County may approve a road subject to site specific mitigation methods. Roads that must cross hazardous areas shall be designed to limit exposure and utilize avalanche control practices to reduce the danger along exposed road segments. Where the main access road to a proposed development is crossed by an avalanche path, a secondary access may be required.
  - (g) Warning signs shall be placed along commonly traveled winter roads and trails that cross avalanche hazard zones.
  - (h) Property owners who develop in avalanche areas or obtain driveway access through avalanche areas shall bear the costs of any avalanche control measures that may be required to mitigate the hazard.

(b) Landslide Areas

Development is prohibited within landslide areas. In the event that an application is denied because there is no landslide hazard-free area on a site, and an appeal is later granted pursuant to Sec. 2-20-180 or relief is granted pursuant to Sec. 2-40-90 or Sec. 2-40-130, the proposed activity or development shall be reviewed according to the following standards:
1. Ensure strict adherence to recommended design, construction and maintenance procedures approved by qualified professional geologists or engineers licensed in the State of Colorado;
2. Avoid adding water to the site that would cause decreased stability;
3. Avoid removing the toe of the slide without adequate mechanical support;
4. Avoid increasing the weight load on the top of the slide;
5. Avoid removing vegetation from the site; and
6. Avoid steepening the existing slope of the slide area.

(c) Rockfall Areas

Development is prohibited within Rockfall Areas. In the event that an application is denied because there is no hazard-free area on a site, and an appeal is later granted pursuant to Sec. 2-20-180 or relief is granted pursuant to Sec 2-40-90 or Sec. 2-40-130, the proposed activity or development shall be reviewed according to the following standards:
1. Activities and development shall only be permitted if design and construction stabilization and maintenance measures approved by a qualified professional geologist or engineer licensed in the State of Colorado and the County are utilized. Construction stabilization measures may include but are not limited to:
  - (a) Stabilization of rocks by bolting, gunite application (cementing), removal of unstable rocks (scaling), cribbing or installation of retaining walls;
  - (b) Slowing or diverting the moving rocks by rock fences, screening, channeling and dams, or by concrete barriers or covered galleries;
  - (c) Physical barriers around vulnerable structures; and
  - (d) Periodic maintenance of mitigation measures.
2. Activities and development shall not:
  - (a) Increase water supply to cliffs or overhangs.
  - (b) Remove protective vegetation.
  - (c) Add weight or otherwise disturb overhanging strata.
  - (d) Make any excavations that remove underlying support.
  - (e) Increase erosion that removes underlying support.

(d) Alluvial Fans (Areas of Shallow Flooding)

Alluvial Fans or Areas of Shallow Flooding (AO/AH Zones) have special flood hazards associated with base flood depths of 1 to 3 feet where a clearly defined channel does not exist and where the path of flooding is unpredictable and where velocity flow may be evident. Such flooding is characterized by ponding or sheet flow. In the event there is not an adequate hazard-free area on a site, activities or development may proceed within an alluvial fan if the use: however, the following shall apply:
1. All new construction and substantial improvements of residential structures have the lowest floor (including basement) elevated above the highest adjacent grade at least one foot above the depth number specified in feet on the community’s FIRM and at least three feet if no depth number is specified.
2. All new construction and substantial improvements of non-residential structures; have the lowest floor (including basements) elevated above the highest adjacent grade at least one foot above the depth number specified in feet on the community’s FIRM (at least three feet if no depth number is specified), or;
3. Together with attendant, utility and sanitary facilities be designed so that below one foot above the base flood level the structure is watertight with walls substantially impermeable to the passage of water and with structural components having the capability of resisting hydrostatic and hydrodynamic loads effects of buoyancy.
4. A registered professional engineer, geologist or architect licensed in the State of Colorado shall submit a certification to the Floodplain Administrator that the standards of this Section are satisfied.
5. Require within Zones AH or AO adequate drainage paths around structures on slopes, to guide flood waters around and away from proposed structures.
6. The development may be required to be protected by channelizing, damming or diverting potential flows utilizing engineering structures by a professional engineer or geologist licensed in the State of Colorado; and
7. Avoids disturbance in the drainage basin above the fan unless an evaluation of the effect on runoff and stability of the fan shows that disturbance is acceptable.

(e) Talus Slope

In the event there is not an adequate hazard-free area on a site, activities and development associated with residential, commercial, industrial and high impact recreational activity may be permitted on talus slopes only if design and construction stabilization and maintenance measures approved by a qualified professional geologist or engineer (licensed in the State of Colorado) and the County are utilized and:
1. Developments are designed to withstand downslope movement;
2. Foundations and utilities in talus slope areas are buried below the active surface;
3. Site disturbance in talus slope areas is minimized to avoid inducing slope instability; and
4. The toe of a talus slope is not removed without providing adequate mechanical support.

(f) Mancos Shale

Activities and development within a mancos shale area may be permitted if they:
1. Include design and construction stabilization and maintenance measures approved by a qualified professional geologist or engineer (licensed in the State of Colorado) and the County are utilized;
2. Are based on an evaluation of the development's effect on slope stability and shrink-swell properties;
3. Are designed to provide adequate surface drainage; and
4. Avoid concentrated runoff from impervious surfaces into natural drainages unless it is demonstrated that there will be no adverse effects.

(g) Faults

Known faults are identified on the Geological Hazards Maps. In the event there is not a hazard-free area on the site, land uses shall incorporate adequate mitigation measures determined by a qualified professional engineer or geologist (licensed in the State of Colorado) and approved by the County.

(h) Expansive Soil and Rock

Development may be permitted in an identified area of expansive soil and rock upon County approval of engineered foundations and floor systems designs.

(i) Ground Subsidence

In the event a development site is comprised exclusively of moderate and extremely hazardous areas, development may be permitted if design and construction stabilization and maintenance measures approved by a qualified professional geologist or engineer (licensed in the State of Colorado) and the County are utilized.

(j) Exceptions

Construction of non-motorized, public trails on land owned or held in easement by a public or non-profit organization shall be reviewed through the Site Plan process, but shall be exempt from the standards for development in geologic hazard areas, provided that such trails shall be subject to any other applicable regulations of this Land Use Code and the following provisions:
1. No non-motorized, public trail shall be permitted in a geologic hazard area that would subject occupants or users of the area to hazardous conditions; create or worsen such conditions affecting other developments, activities and lands; subject other persons or the County to dangers or expenses required to mitigate such hazardous conditions, respond to emergencies created by such conditions or rehabilitate the improvements, activities and lands.
2. All non-motorized, public trails in geologic hazard areas shall avoid avalanche hazard areas, and shall be constructed in such a manner as to mitigate the hazard to public health and safety or to property due to geologic hazards.

Code repealed and reenacted Ord. No. 14-D, 2006 - § 7-20-50 (part) Ord.032-13, 12-18-13

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7-20-50 Geologic Hazards

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