The City deems it important to the peace, health, safety, and welfare of the inhabitants of Centerville that the steep slopes and hillsides of the City be protected to insure that urban development in these sensitive areas be guided in a manner that will minimize the potential for flooding, erosion, and other environmental hazards and will protect the natural scenic beauty of the foothills.  The objectives to be achieved by the use of the Hillside Overlay Zone shall include but not be limited to the following:

1. A minimum amount of grading and earthwork.
2. Retention of trees and other native vegetation (except in those cases where a high fire hazard results) which stabilizes steep hillsides, retains moisture, prevents erosion and enhances the beauty of the natural landscape.
3. Design and construction of roads, where necessary, in such a way as to minimize scars from cuts and fills and to avoid permanent scarring of hillsides.  Design of roads so as to make them easily accessible to fire protection, snow removal, and emergency vehicles.
4. Placement of building sites in such a manner as to permit ample room for adequate landscaping, surface drainage, parking between and around the buildings, and utility serviceability.
5. Grading which will eliminate sharp angles at the top and at the toe of cut and fill slopes, both with respect to building sites and to road cross-sections.
6. Street rights-of-way and grades, lot layouts and structure designs which will aid the objective of reducing excavation and natural topographic disturbance.
7. Low density development, cluster-type development or similar concepts that will minimize as far as possible construction on steep or dangerous terrain.
   
8. Early temporary or permanent planting, or both, wherever appropriate to maintain necessary cut and fill slopes, stabilizing them by plant roots and concealing the raw soil from view.
9. The preservation of natural features, wildlife habitat and open space.
10. Regard for the view of the hillside as well as the view from the hillsides.

1. The regulations contained in this Chapter shall apply to all lands in the City that lie within the area designated as the Hillside Overlay Zone, on the Zoning Map.  The Hillside Overlay Zone is applied in addition to the provisions of the underlying zone designation.
2. This Chapter makes additional provisions to those provided in CMC 15 (Subdivisions) and in other chapters of this Title.  In the event of conflict, the more restrictive provisions shall apply.

1. Subdivisions and PUD's. Proposals for subdivision or PUD development within the Hillside Overlay Zone shall comply with all provisions regarding the same as set forth in CMC 15 (Subdivisions) and all additional requirements set forth herein.  All concept plans, preliminary plats and final plats for any proposed subdivision or PUD development within the Hillside Overlay Zone may be approved by the City Council after recommendation of the Planning Commission and City Engineer.
2. Conceptual Approval. In addition to the requirements set forth in CMC 15 (Subdivisions) proposals for concept approval of a subdivision or PUD within the Hillside Overlay Zone shall include the following:
   1. Location of the proposed Planned Unit Development, or Subdivision, with identification of abutting streets.
   2. A slope district map reflecting existing slope conditions prior to development at a scale of 1" = 100' and an estimate of the average slope of the proposed development.
   3. A topographic contour map, tied to a land base survey, delineating areas within the development site with slopes of less than 10%, areas between 10% and 20%, areas between 21% and 30%, and areas greater than 30%, shall be designated topographic contours at two foot intervals for slopes up to 20% and five foot intervals for slopes greater than 20%.
   4. The total acreage, number of lots and proposed total density and slope district density for residential developments.
   5. The location and approximate size of the proposed lots. 
   6. A general street location, width, and grade of all proposed streets and radius of any cul-de-sac.
   7. Location of existing or proposed schools, churches, or parks.
   8. Location of known hazards (i.e., faults, drainage, rock fall, landslide, slump, etc.).
   9. Soil type and general description of soil types to a depth of five feet.
   10. Land use data, (i.e., the amount of residential land, transportation land, etc.), by acreage and percent.
   11. Existing vegetation-type map.
       
3. Preliminary Approval. In addition to the information as required for preliminary approval under CMC 15 (Subdivisions), proposals for preliminary approval of a subdivision or Planned Unit Development in the Hillside Overlay Zone shall be required to include the following.  All reports submitted herein, shall be prepared by persons or firms either licensed to practice their specialty or expertise in the State of Utah, if such license for practice is required, or by one having demonstrable expertise in such field of practice if such license is not required.
   1. Soil Characteristics Report. This report shall contain data regarding the nature, distribution, and strength of soils within the project area to a depth of five feet; the soil report shall include:
      1. Unified classification of all soils with an estimate of susceptibility to erosion, location of clays, liquid limit, shrink-swell potential, and general suitability for development shall be defined.
      2. Estimate of the normal highest elevation of the seasonal high water table.
      3. Flood history and potential.
      4. Proximity to known Flood Plain Areas and Drainage Channels.
      5. Topographic contours.
   2. Vegetation Report. This report shall include a slope stabilization and revegetation report which shall include:
      1. Location and identification of existing vegetation.
      2. The vegetation to be removed and the method of disposal.
      3. The vegetation to be planted.
      4. Slope stabilization measures to be installed including but not limited to erosion control blankets.
      5. Analysis of the environmental effects of such operations including effects on slope stability, soil erosion, water quality, fish and wildlife, and fire hazard.
      6. Topsoil stockpile areas will be designated.
      7. Solar orientation is recommended for review.
   3. Geologic Conditions Report. This report shall include the following information: 
      1. Definition of any zones of deformation with respect to active faults and other mass movements of soil and rock.
      2. Identification of anomalies of the terrain or characteristics of the geological materials which would have any potential impact upon the use of the site.
      3. Determination of ground water characteristics.
      4. Depth to bedrock and geological evaluation to a minimum of 10 feet.   
      5. Written recommendations for construction of proposed improvements to avoid impact of any potential geologic hazards.
   4. Grading and Drainage Report. The application for preliminary approval shall include a storm water management and erosion and grading plan describing the methods by which surface water, natural drainages, flooding, erosion and sedimentation loss will be controlled during and after construction. The plan shall include the following information.
      1. The grading plan shall show present topography to include elevations, lines and grades including the location and depth of all proposed fills and cuts of the finished earth surfaces using a contour interval of five feet or less. Access or haul road location, treatment and maintenance requirements shall be included.
      2. An appropriate scale shall be used which most clearly presents the proposed action, generally 1" = 100' or larger.
         
      3. The proposed area to be graded shall be clearly delineated on the plan and the area amount stated in square feet.
      4. All calculations and proposed details used for design and construction of debris basins, impoundments, diversions, dikes, waterways, drains, culverts and any other water management or soil erosion control measures shall be shown. Calculations shall employ predictions of soil loss sheet erosion using the Universal Soil Loss Equation or appropriate equivalent.  Equations should include factors of:
         1. Rainfall intensity and energy
         2. Soil erodibility
         3. Land slope and length of slope or topography
         4. Condition of the soil surface and land management practices in use
         5. Surface cover; grass, woodland, crops, pavements, etc.
         6. Methods intended to be employed to control increased erosion during construction phase. 
4. Final Approval. To ensure proper development of subdivisions and PUD's within the Hillside Overlay Zone and compliance with hillside standards, final approval shall be required by the Planning Commission and City Council. The application for final approval shall include the information required in CMC 15 (Subdivisions) and any other requirements imposed by the Planning Commission or City Council as required to meet applicable provisions of this Chapter. Application for final approval shall include, along with improvement drawings, spot elevations on all lot corners or contour grading plans of all lot frontages. The Planning Commission or City Council may require the staking of lots to ensure compliance with development standards.
5. Single-Family Dwellings and Accessory Buildings. Proposals for approval of single-family dwellings or accessory buildings upon a lot or parcel within the Hillside Overlay Zone shall be required to file a plot plan drawn to a scale of at least 1" to 10' which plot plan shall show lot lines, existing and proposed contours at two foot intervals, location of proposed dwelling unit, walks, driveways, patio areas, and vegetative, drainage, and erosion controls.  Plot plans shall be reviewed and approved by the City Engineer and the Zoning Administrator. Additional reports as set forth herein may be required by the Zoning Administrator and reviewed by the Planning Commission and/or City Council for approval when deemed appropriate by the Zoning Administrator.
6. Approval Condition.  No grading, construction, or development shall be conducted within the Hillside Overlay Zone and no building permit shall be issued until final plat approval has been granted by the City Council for subdivision or PUD development or until final plot plan approval has been granted by the Zoning Administrator for a single-family dwelling unit on a parcel or lot within the Hillside Overlay Zone. The approved plot plan for single-family unit on a parcel or lot shall be attached to the building permit for the same.
   

1. Requirements for all Lots. Every lot in the Hillside Overlay Zone shall have at least 5,000 square feet of contiguous space which has a slope of less than 30%. This space may be no less than 50 feet wide at any given point. This buildable area must be undisturbed or virgin slope.  Certain limited hillside areas may be considered as either natural or man-made "anomalies" such as gravel pit operations or other artificial disturbances based upon size, location, and history of slope, and may be included within the buildable area as may be recommended by the Planning Commission. Lots shall allow dwelling structures to be located within 250 feet of a public street. All main and accessory buildings shall be built on the buildable area.
2. Density for Single-Family Lots. The minimum lot size and yard requirements of the underlying zone shall apply to all lots in the Hillside Overlay Zone. In residential zones, all lots located within slope areas greater than 10% and less than 15% shall require a minimum of 80 feet at the setback line, and all lots within slope areas of 15% or greater shall require a minimum lot width of 100 feet at the setback line.  In agricultural zones, all lots located within slope areas greater than 10% and less than 15% shall require a minimum lot width of 100 feet at the setback line, and all lots within slope areas of 15% or greater shall require a minimum lot width of 125 feet at the setback line.
3. Lot Density for Planned Unit Developments and Dwelling Groups. The density limitations for the underlying zone shall apply except where, under a conditional use permit, the Planning Commission determines that additional buildable area, lot size, yard requirements or other condition is needed. All buildings shall be built on the buildable area. All dwelling units shall be built within 250 feet of a public street, or private street that has been approved by the Planning Commission.  Dwellings and accessory structures may not occupy more than 40% of the lot area in any hillside area.
4. Maximum Impervious Material Coverage. Except as otherwise provided herein, the maximum allowable coverage of a lot in the Hillside Overlay Zone by impervious material shall be 40% of the total lot area, or 5,000 square feet, whichever is less. The maximum allowable impervious material coverage of a lot may be allowed to exceed 5, 000 square feet as an exception upon recommendation of the City Engineer and approval of the applicable land use authority for the subject application (i.e. subdivision, site plan, or building permit), as follows:
   
   1. Lots less than 10% slope may increase 60%
      
   2. Lots 10% to 14% slope may increase to 55%
      
   3. Lots 15% to 19% slope may increase to 50%
      
   4. Lots 20% to 24% slope may increase to 45%
      
   5. Lots 25% to 29% slope are limited to 40%
      
5. Maximum Impervious Material Exception. Any applicant seeking an exception to exceed 5, 000 square feet of impervious material coverage per lot shall be required to provide on-site detention/retention as required by local or state statutes and appropriately sized outflow orifice plates for the additional impervious area (over 5, 000 square feet) in accordance with City Engineer recommended detention/retention volume calculations for a 25-year storm event. The applicant shall be required to provide engineered drawings and specifications for the proposed detention/retention and drainage to qualify for the exception. Upon acceptance and approval of the engineering documents, the applicant shall enter into a maintenance agreement, as deemed acceptable by the City. Such maintenance agreement shall be recorded against the subject property as a condition of granting an increase impervious material allowance. For purposes of calculating the permissible lot coverage percentage, lot areas that exceed 30% slope shall be excluded and shall not be used in calculating the allowable impervious coverage area.
6. Front Yard Setback. The minimum front yard setback in the Hillside Overlay Zone may be reduced to not less than 20 feet, provided the average slope of the lot exceeds 20% as recommended by the City Engineer.
   

1. Scope. The development standards and provisions set forth in this Section shall be required in connection with all building and construction in the Hillside Overlay Zone.
2. Drainage and Erosion. The area of the watershed shall be used to determine the amount of storm water runoff generated before and after construction.
   1. The "Rational Method" or other storm water computation method as approved by the City Engineer shall be used in computing runoff. The basic formula for the "Rational Method" is:
      
      Q = CIA in which:
      Q = Runoff in cubic feet per second (c.f.s.)
      C = Coefficient of runoff or the portion of storm water that runs off a given area.
      
      The following are typical examples of land use ranges for C value. The actual C value used shall be approved by the City Engineer.
      
      

      Type of Development	Runoff Coefficient
      Industrial & Commercial	.80 — .90
      Residential	.30 — .40
      Parks	.15 — .25
      Agricultural	.10 — .20

      I = Average rainfall intensity during time of concentration for 10 year return period in inches per hour. The time of concentration shall be defined as the time required for water to flow from the most remote point of the section under consideration.
      
      A = Drainage area in acres.
      
      
   2. Maps of the development site at the scale of 1" = 200' shall be provided by the developer to the City Engineer defining the boundaries of any 100 year flood plain and the limits of the watershed.
   3. Lots shall be arranged so as to insure adequate setbacks from drainage channels. The 100 year storm shall be that basis for calculating setbacks. All structures shall comply with CMC 9.8 (Flood Damage Prevention).
   4. Facilities for the collection of storm water runoff shall be required to be constructed on development sites and according to the following requirements:
      1. Such facilities shall be the first improvements or facilities constructed on the development site.
      2. Such facilities shall be designed so as to detain safely and adequately the maximum expected storm water runoff for a 10 year storm, not to exceed 0.2 cubic feet per second per acre or at a flow rate higher than the flow rate before construction, whichever is less, on the development site, for a sufficient length of time so as to prevent flooding and erosion during storm water runoff flow periods. 
         
      3. Such facilities shall be so designed as to divert surface water away from cut faces or sloping surfaces of a fill.
      4. The existing natural drainage system will be utilized to the extent possible in its unimproved state.
      5. Where drainage channels are required, wide shallow swales lined with appropriate vegetation shall be used instead of cutting narrow, deep drainage ditches.
      6. Flow retarding devices, such as detention ponds and recharge berms, shall be used where practical to minimize increases in runoff volume and peak flow rate due to development. Areas which have shallow or perched groundwater or areas that are unstable must be given additional consideration.
   5. Construction on the development site shall be of a nature that will minimize the disturbance of vegetation cover.
   6. Erosion control measures on the development site shall be required to minimize the increased solids loading in runoff from such areas. The detailed design system to control storm water erosion during and after construction shall be contained in the Grading and Drainage Report described in CZC 12.42.030.
3. Grading, Cuts, Fills, Vegetation and Revegetation.
   1. The developer/builder is responsible for interim stabilization of all disturbed areas during the period of construction to prevent erosion off-site effects and for final stabilization once construction is completed.
   2. Exposed unstable surfaces of an excavation or fill shall not be steeper than one vertical to two horizontal (1:2), unless stabilized by approved means.
   3. All fill slopes shall be located so that settlements, slidings, or erosions shall not damage or cover streets, curb, gutter, sidewalks or buildings.
      
   4. All fill and degrees of compaction shall comply with the standards of the Construction Codes. 
   5. The top and bottom edges of slopes caused by an excavation or fill up to 10 vertical feet shall be at three horizontal feet from any public right-of-way line.
   6. The maximum vertical height of all cuts or fills shall be 10 feet.  Fills for slumps or other natural depressions may exceed 10 feet with Planning Commission approval.
   7. All structures except retaining walls or soil stabilization improvements shall have a setback from the crest of the fill or base of the cut of a minimum distance equal to the depth of the fill or the height of the cut, unless a structurally sound retaining wall is built for the cut or fill slope. Retaining walls may be a part of the dwelling unit. 
   8. Retaining walls shall be used to retain existing slope or graded slope as may be approved by the City Engineer. The height of necessary and approved retaining walls shall be a maximum of eight feet. Extensive "rear yard" retaining walls built for the purpose of leveling a yard by backfilling, are expressly prohibited.
      
   9. All areas of development sites cleared of natural vegetation in the course of construction of off-site improvements shall be replanted with vegetation which has good erosion control characteristics.
   10. New plantings shall be protected with mulch material and fertilized when in conjunction with planting and watering schedule.
   11. Persons or firms having expertise in the practice of revegetation (i.e., licensed landscape architects or nurserymen) shall supervise the planning and installation of revegetation cover for the total development site.
   12. Vegetation shall be removed only when absolutely necessary (e.g., for the construction of buildings, roads and filled areas), as approved by the City Engineer.
   13. Where permanent roads or roadbeds are to be used during construction and storm water inlets have already been installed, they shall be protected to prevent sediment laden water entering the storm water system.
4. Geology.
   1. Structures may not be built within a minimum of 50 feet of a center line of a zone of deformation with respect to known active faults.  The Planning Commission may reduce the required setback provided herein from faults that are determined to be secondary, or a lesser significant classified deformation area, upon receiving recommendation from the City Engineer and based upon a geotechnical/geologic report submitted by the applicant. In no event shall the fault line setback be reduced to less than 30 feet from the center line of the fault or zone of deformation.  If reduction is approved, a plat note and delineation of the fault line and deformation area shall be provided on the subdivision plat. The Planning Commission may also require a notice of geologic hazard and/or a waiver of liability agreement to be provided by the applicant in a form acceptable to the City. The zone of deformation is defined as area of variable width adjacent to a fault where it is determined that ground rupture is likely to occur. A greater setback may be required by the City where deemed necessary to protect public health and safety. Off-site improvement design will be reviewed and approved or denied by the City Engineer.
   2. No structures or off-site improvements shall be allowed on any area known to be an active landslide area, verified by the City Engineer or State Geologist.
   3. Problems associated with development on or near perched ground water and shallow ground water must be mitigated.
   4. No structures shall be allowed in any rockfall zone.  Off-site improvements may be allowed through special approval by the Planning Commission.
5. Fire Protection.
   1. Areas without a recognized water supply should meet special requirements and may be approved on an individual basis.
   2. All water, sewer and utilities must be installed in accordance with CMC 15 (Subdivisions).
   3. Each development site proposal and building permit application for private lots, where the front setback is greater than 50 feet, shall be reviewed by the South Davis Metro Fire District to determine whether it complies with the Fire Code and applicable Construction Codes, but not limited to, provisions regarding Access Roadways for Fire Apparatus. Developments which do not comply with Fire Code or applicable Construction Codes as determined by the South Davis Metro Fire District, shall not be approved.
6. Street and Ways.
   1. The City Standards and Specifications for streets shall apply to all development in the Hillside Overlay Zone, except where conditions related to proper development of hillside areas necessitate altering these standards as described below and elsewhere in this Title. Any such exception must be approved by the City Council upon recommendation of the Planning Commission and City Engineer.
   2. Streets, roadways and private access ways shall follow as nearly as possible the natural terrain and shall not cross slopes greater than 30% unless so recommended by the City Engineer and approved by the Planning Commission.
   3. Design Requirements:
      
      

      Exception	Normal	Permissible
      Minor road and turn cul-de-sac right-of-way width	50' minimum	40' minimum except
      Minor road and cul-de-sac length	400' maximum	600' maximum
      Minor road and sidewalk cul-de-sac radius	50' minimum	40' minimum if sidewalk and parkstrip improvements are waived
      Construction Details	City Standards	Alternates for Slopes
      Horizontal Curve	100' minimum C over L radius	75' minimum C over L radius
      Vertical Curve	300' minimum slight distance	200' minimum slight distance
      Road Grade	12% maximum	As provided hereafter
      Driveway	12% maximum	As provided hereafter

   4. Although minimum rights-of-way may be reduced to 40 feet, all fill slopes must be contained within the right-of-way.
   5. Points of access shall be provided to all developed and non-developed acres for emergency and fire fighting equipment.  Double access points shall be encouraged and shall be required for developments in excess of 20 lots.
   6. Development sites which are located near well established canyon trails will provide reasonable access to those trails. Parking areas may be required by the Planning Commission at trail heads.
   7. The maximum amount of impervious surface for streets and ways shall be 20% of the entire development site.
   8. Variations of the street design standards developed to solve special hillside visual and functional problems may be presented to the Planning Commission for consideration. Examples of such variations may be the use of split roadways to avoid deep cuts, one-way streets, modifications of surface drainage for curb, gutter and sidewalk design and other innovative designs for hillside development.
      1. The maximum grade of such streets or rights-of-way shall be 12% except as hereafter provided.
      2. The City Council after receiving a recommendation from the Planning Commission may grant approval for the construction of such streets or rights-of-way having a grade exceeding 12%, but the grade of such streets shall not, in any event, exceed 15% for a distance of more than 200 feet.
      3. Roads shall be designed to meet the road base, asphalt, and compaction standards set forth in the City Standards and Specifications.
7. Architectural Design.
   1. The design of buildings proposed for construction in the Hillside Overlay Zone is encouraged to be visually compatible with the natural beauty of the foothills and canyon areas. The use of building materials in colors that will blend harmoniously with the natural settings is suggested.
   2. The Planning Commission may review the design and comment on the specified exterior materials and colors for all structures other than single-family dwellings. Prohibition of cedar shake roofing materials, the installation of chimney screens and sprinkling systems, as well as other fire protection measures may be required by the Planning Commission as may be recommended by the South Davis Metro Fire District.
   3. All fences located on slopes of 30% or greater shall be dark brown or black vinyl coated chain link fence to blend in with the native landscaping. The following types of fences shall be prohibited from 30% slopes: uncoated chain link, masonry, block, wood, vinyl, or other sight obscuring materials. All fences on lots within the Hillside Overlay Zone shall conform to other fence regulations with respect to setback and height, as provided in this Title.
8. Completion of Improvements. All public improvements, utilities, and other on-site or off-site improvements required to be completed by developer or property owner prior to obtaining a building permit must be completed within 18 months from the effective date of final approval. All on-site and off-site improvements shall be completed in accordance with the development site approval and applicable Centerville Municipal Ordinances.
   
9. Bond. In addition to the provisions requiring the posting of a bond as set forth in CMC 15 (Subdivisions), the developer or property owner may be  required by the City Council (as a condition to receiving a building permit) to guarantee the completion of revegetation projects, the stabilization of grading sites, cuts and fills and construction of storm water runoff facilities, and the construction of recreation space as required in this Section. If such bond is required, it shall be in an amount equal to the cost of construction of such projects as determined by the City. 
   
10. Earthquake and Natural Hazard Acknowledgment. All owners of lots in the Hillside Overlay Zone must sign an acknowledgment of hazards and risk associated with land use in this area prior to the issuance of a building permit for any dwelling or accessory building.