A. Purpose: It is the intent of this section to recognize that certain areas of the city are characterized by steep terrain, native vegetation, natural drainage courses and other physical features, and to establish standards of development for these areas that help to protect the public health, safety and welfare by minimizing potential for erosion, sedimentation, flooding and landslides, while at the same time protecting and enhancing the visual quality of the city's natural landscape. Specific regulations and guidelines are intended to address the following:
1. To protect the public and property from hazards and problems associated with storm water runoff, flooding and erosion.
2. To minimize the threat and consequential damage of landslides in hillside areas.
3. To minimize the threat and consequential damage of fire in hillside areas.
4. To control and minimize the infestation of noxious weeds into the community and outlying neighboring areas.
5. To control and mitigate dust and other nuisances that may have adverse affects on neighboring properties and the air quality of the community.
6. To provide for safe and efficient pedestrian and vehicular access and circulation, including transportation linkages to outlying areas.
7. To enhance the visual and aesthetic quality of the city through the use of grading, revegetation and development techniques that help to improve the appearance of slopes exposed to roadways, preserve prominent natural features and vistas and provide for adequate open space in hillside areas.
8. To offer, promote and encourage a variety of alternative development designs and concepts appropriate for hillside areas.
B. Definitions:
AVERAGE SLOPE: Average slope shall mean and be determined by the use of the following formula:
AS = .00229 (I) (L)
A
AS = Average slope in percent.
.00229 = The conversion factor of square feet to acres.
I = Contour interval in feet. The contour interval may not exceed ten feet (10').
L = Summation of the length of all contour lines, in feet, within the parcel.
A = Total number acres in the parcel.
BUILDABLE LOT AREA: That portion of land within a lot or development site, exclusive of building setback area, and manufactured or natural slope area in excess of thirty percent (30%) gradient.
CAP: A concrete or cement feature placed on top of a wall that promotes watershed and limits infiltration of water into concrete cells.
CLEARING: The removal of vegetation and topsoil or other surface materials from a site.
CONSTRUCTION: Any grading or clearing of land, installation of improvements, erection or placement of structures, or assembly of equipment or materials to be used in any of those activities.
CUT: The removal of earth material by artificial or mechanical means.
DEVELOPMENT: Any construction or any division of land.
EROSION: The process whereby soil particles are detached and transported by water, wind, ice or gravity.
EXCAVATION: The mechanical removal of earth material.
FILL: The deposit of earth material by artificial or mechanical means.
GRADIENT: The vertical rise of a slope over a horizontal distance, expressed as a percentage (rise over run).
GRADING: Any excavating, cutting, filling or other earth moving operation.
HILLSIDE AREA: Any parcel having an average slope of fifteen percent (15%) or greater.
IMPERVIOUS SURFACE: Roads, buildings, tennis courts, roofs, driveways, patios, decks, parking lots and other similar water shedding surfaces.
MANUFACTURED SLOPE: Any slope created through cut, fill or excavation and which is steeper than 5:1.
NATURAL SLOPE: The form of the land surface within a hillside area as it exists before clearing or grading.
NATURAL VEGETATION: Plant materials which exist on the site before clearing or grading.
OPEN SPACE: Land area which is not covered by buildings, parking lots, accessory structures or other similar impervious surfaces.
RETAINING WALL HEIGHT: The vertical height as measured from the lowest finished grade to the top of the retaining wall.
REVEGETATION: The stabilization of disturbed or graded soils after construction by replanting with indigenous plant species or other drought tolerant, low water consumptive plant materials appropriate for the climatic zone.
RUNOFF: That part of precipitation which flows over the land without filtering into the soil.
SEDIMENTATION: The process of depositing soil particles detached and transported by erosion.
SLOPE: A natural slope or manufactured slope steeper than 5:1.
C. Development Standards:
1. Slopes Adjacent To Streets And Roadways:
a. Manufactured slopes shall not be steeper than 3:1.
b. Maximum continuous slope height shall not exceed twenty feet (20'). Continuous slope heights may be broken by bench areas having a minimum horizontal dimension of not less than ten feet (10'); and provided said bench areas are placed within the middle one-third (1/3) of the slope.
c. Retaining wall heights shall not exceed ten feet (10').
d. No slope or retaining wall may be placed or constructed in a street right of way.
e. No retaining wall may be placed or constructed within a public utility, access or drainage easement which abuts a public street right of way.
f. Slopes five feet (5') or less in height shall observe a two and one-half foot (21/2') setback from the back edge of sidewalk. Slopes greater than five feet (5') in height shall observe a five foot (5') setback from the back edge of sidewalk.
g. Retaining walls adjacent to streets and roadways must be capped with an architecturally compatible concrete or cement material.
h. Guard railings, when required by the uniform building code, shall be installed on the top of any retaining wall.
i. All manufactured slopes adjacent to streets and roadways shall be subject to an erosion control and revegetation program.
2. Other Interior Slopes:
a. Manufactured slopes shall not be steeper than 2:1.
b. Maximum continuous slope height shall not exceed thirty feet (30'). Continuous slope heights may be broken by bench areas having a minimum horizontal dimension of not less than fifteen feet (15'); and provided said bench areas are placed within the middle one-third (1/3) of the slope.
c. Retaining wall heights for walls abutting interior property lines shall not exceed six feet (6'). Retaining wall heights for other walls shall not exceed twenty feet (20').
d. Retaining walls greater than six feet (6') in height shall observe an interior property line setback equivalent to the height of the retaining wall.
e. The toe of any slope shall observe an interior property line setback equivalent to one-half (1/2) of the height of the slope.
f. The top of any slope shall observe an interior property line setback equivalent to one-fifth (1/5) of the height of the slope.
g. All manufactured interior slopes shall be subject to an erosion control and revegetation program.
3. Lot Dimensions:
a. For all residential zoning districts subject to a six thousand (6,000) square foot minimum lot size or greater, a minimum buildable lot area of three thousand (3,000) square feet shall be required.
b. For hillside area subdivisions, minimum residential lot size shall be ten thousand (10,000) square feet, exclusive of any manufactured slope area contained within the lot.
c. For hillside area subdivisions, minimum interior side yard setbacks shall be ten feet (10').
4. Exceptions:
a. Manufactured slopes intended and designed to be located within a public street right of way and associated with the construction or widening of the roadway or other related public improvements.
b. Minor deviations from maximum manufactured slope heights associated with rounding, meandering or blending tops or bottoms of slope sections with adjacent ungraded areas.
5. Modification Of Standards: Regulations contained within this section may be varied or modified by the planning commission, where just cause and circumstance warrants, in conjunction with a review of a conditional use permit, subdivision preliminary plat, final plat or an application for site plan review, pursuant to subsection 3-2-3C6 of this chapter.
D. Erosion Protection, Slope Stabilization, Slope Revegetation: Any development requiring a grading permit shall be required to submit a specific area restoration and landscape plan to address erosion, slope stabilization and revegetation for the review and approval of the engineering and planning departments.
1. Slopes Adjacent To Streets And Roads:
a. Landscaping improvements shall be required to include the following material: ground cover consisting of plant material, appropriate seed mix or landscape rock, gravel or comparable material; shrubs, consisting of not less than one minimum two (2) gallon sized planting for each fifty (50) square feet of slope area; trees consisting of not less than one minimum fifteen (15) gallon sized planting for each one thousand (1,000) square feet of slope area. (Note: Tree plantings may be clustered.)
b. Installation of permanent irrigation system.
c. Slope revegetation permanently established.
2. Interior Slopes:
a. Installation of appropriate seed mix with jute mat, or installation of rip rap, landscape rock, gravel or comparable material.
b. Satisfy uniform building code requirements for paved interceptor drains and terrace swales.
c. Drains down the face of slopes are to be discouraged; but, if used, are to include rip rap or concrete three feet (3') wide by one foot (1') deep, or other acceptable means. Thickness and size of rip rap or concrete is to be based on water velocity.
d. Application of seed mix during fall months (September through December) with or without installation of an irrigation system.
e. Slope revegetation permanently established.
3. Nonslope Areas Affected By Clearing, Grading Or Excavation In Excess Of One Acre:
a. Installation of native grass mix (crested wheat).
b. Installation of temporary irrigation system or application of seed mix during fall months (September through December) without installation of irrigation system.
c. Revegetation permanently established on affected areas.
4. Performance Guarantee:
a. Revegetation of slopes and other areas affected by clearing, grading or excavation are considered permanently established when more than fifty percent (50%) of area coverage has been achieved.
b. Revegetation of slopes and other areas affected by clearing grading or excavation must be permanently established in accordance with one of the following time frames:
(1) Prior to final occupancy of the building or premises.
(2) Within two (2) years after issuance of final occupancy of the building or the premises subject to execution of a performance agreement with the city to include bonding or other form of security to guarantee completion of the required work.
(3) Prior to final certification of grading compliance.
(4) Within two (2) years after completion of grading activity subject to execution of a performance agreement with the City to include bonding or other form of security to guarantee completion of the required work.
E. Development Guidelines: The following items are recommended guidelines and standards to help achieve the purpose of this section:
1. Locate property lines at tops of slopes, when feasible.
2. Vary steepness of the slope.
3. Meander tops and toes of slopes.
4. Round and blend top and bottom sections of slopes with adjacent ungraded area.
5. Lay back top one quarter section of the slope.
6. Use of terracing and retaining or slough walls when appropriate.
7. Establish thirty foot (30') fire protection zone surrounding all combustible structures in hillside areas.
8. Fire protection zones should include fire resistant landscaping and/or hardscape material.
9. Increase side yard building setbacks in hillside subdivisions to fifteen feet (15').
10. Minimize steepness of slopes adjacent to streets as a means of improving access for emergency and fire personnel.
11. Recommend and encourage the installation of drought tolerant, low maintenance ground cover, shrubs and trees in combination with installation of a permanent drip type irrigation system to promote low water usage. (Ord. 579, 2-26-2002)