Chapter 83.08 — HILLSIDE GRADING STANDARDS

This Chapter establishes regulations for development within hillside areas to:

• (a) Facilitate appropriate hillside development through standards and guidelines for hillside areas.

• (b) Ensure that development in the hillside areas is designed to fit the existing landform.

• (c) Preserve significant features of the natural topography, including swales, canyons, streams, knolls, ridgelines, and rock outcrops.

• (d) Provide a safe means of ingress, egress and traffic flow for all forms of permissible traffic within hillside areas.

(e) Provide alternative approaches to conventional grading practices by achieving development intensities that are consistent with the natural characteristics of hillside areas (e.g., land form, scenic quality, slopes, and vegetation).

(f) Encourage the planning, design, and development of sites that provide maximum safety with respect to fire hazards, exposure to geological hazards, drainage, erosion and siltation, and materials of construction; provide the best use of natural terrain; and to discourage development that will create or disproportionately increase fire, flood, slide, or other safety hazards to public health, welfare, and safety.

(Ord. 4011, passed - -2007)

(a) Slope Gradient of 15 Percent or Greater. The standards contained in this Chapter apply to all uses and structures within areas having a natural slope gradient of 15 percent or greater over the area being graded and requiring a Grading Permit. For the purpose of this Chapter, slope shall be computed as set forth in § 83.08.040(b) for the area being graded before grading is commenced.

(b) Site Conditions Requiring Hillside Grading Review. If the slope gradient is 15 percent or greater and if any one of the following thresholds applies on a particular site meeting the criteria set forth in Subdivision (a) above, a full analysis and compliance with this Chapter shall be required and a Hillside Grading Review shall be conducted in compliance with § 83.08.030 (Hillside Grading Review):

(1) The volume of proposed grading is more than 500 cubic yards per lot or more than a total of 2,000 cubic yards for the total project.

(2) If retaining walls or the proposed cut or fill slopes greater than 15 feet in height will be visible and exposed to permanent public view or will be adjacent to designated open space or public lands.

(3) The width of proposed cut or fill slopes is greater than 75 feet in the Valley and Mountain Regions and 150 feet in the Desert Region as measured at the widest point of the slope.

(4) The area of proposed disturbance is more than 50 percent of the site area, or the proposed disturbed area exceeds 10,000 square feet, whichever is less.

(Ord. 4011, passed - -2007; Am. Ord. 4043, passed - -2008)

A subdivision, land use permit, or Building Permit application for a site or development that meets or exceeds the thresholds in § 83.08.020 (Applicability) shall require a Hillside Grading Review.

(a) Procedure. The review shall be conducted concurrently with any required discretionary review or in

conjunction with an application for a Grading Permit for any project that meets or exceeds the thresholds listed in §

(b) Submittal Requirements. An application for a Hillside Grading Review shall require the following documents, reports, maps and such others as determined appropriate by the Director. Exceptions to the filing requirements shall require a written justification supported by factual information submitted to the Director for consideration. Some of the required submittals listed below may be displayed on a single map or plan.

(1) Natural Features Map. A natural features map shall identify all existing slope banks, ridgelines, canyons, natural drainage courses, Federally recognized blue line streams, rock outcroppings, and existing vegetation. When a geology report is required, landslides and other existing geologic hazards shall also be depicted.

(2) Grading Plan. A conceptual grading plan shall include the following items:

(A) A legend with appropriate symbols shall include the following items: change in direction of drainage, elevation of regulated trees subject to the provisions of § 88.01.070(b) (Regulated Trees), estimated volumes proposed to be cut and/or filled, finished floor elevations, high point, low point, pad elevations, spot elevations, top of curb, and top of wall;

(B) A separate map, with proposed fill areas colored in green and cut areas colored in red, with areas where cut and/or fill exceed depths established in compliance with this Chapter. If custom foundations are proposed, this shall be noted on the map. Additionally, the area of cut and/or fill, calculated as a percentage of the total surface area of the site, shall be included on the plan; and

(C) Contours for existing and natural land conditions and proposed work. Existing contours shall be depicted with a dashed line with every fifth contour line darker; and proposed contours shall be depicted similarly with solid lines. Contours shall be shown at maximum five-foot intervals above 20 percent slope.

(D) For the efficient use of water, grading of the project site shall be designed so that soil erosion, runoff, and water waste are minimized. As part of the landscape document package, if a project’s grading exceeds 100 cubic yards, then the project developer shall submit the most recent rough and/or precise grading plan(s) that have been prepared and signed by a licensed professional.

(3) Drainage Map. A conceptual drainage and flood control facilities map describing planned drainage improvements.

(4) Slope Analysis Map. A slope analysis map for the purpose of determining the amount and location of land as it exists in its natural state falling into each slope category as specified in this Subdivision. This map shall be prepared and signed by a registered civil engineer or licensed land surveyor, and shall have a scale of not less than one inch to 100 feet and a contour interval of not more than two feet, provided that the contour interval may be five feet when the slope is more than 20 percent. A scale of not less than one inch to 200 feet may be used for developments greater than 100 acres in size. This map shall show the closest structures on all contiguous properties. It shall delineate slope bands in the range of zero to less than 15 percent, 15 to less than 30 percent, 30 percent to less than 40 percent, and 40 percent or greater. Also included shall be a tabulation of the land/area in each slope category specified in acres.

(5) Slope Profiles. A sufficient number of slope profiles shall be provided as required by the Director to clearly illustrate the extent of the proposed grading. The slope profiles shall:

(A) Be drawn at the same scale and indexed, or keyed, to the grading plan, and project site map.

(B) Show existing and proposed topography, structures, and infrastructure. Proposed topography, structures, and infrastructure shall be drawn with a solid, heavy line. Existing topography and features shall be drawn with a thin or dashed line.

(C) The slope profile shall extend far enough from the project site boundary to clearly show impact on adjacent property, within at least 150 feet.

(D) The profiles shall be drawn along those locations of the project site where:

(I) The greatest alteration of existing topography is proposed;

• (II) The most intense or dense development is proposed;

• (III) The site that is most visible from surrounding land uses; and

• (IV) At all site boundaries illustrating maximum and minimum conditions.

(E) At least two of the slope profiles shall be roughly parallel to each other and roughly perpendicular to existing contour lines. At least one other slope profile shall be roughly at a 45-degree angle to the other slope profiles and existing contour lines.

(6) Slope Design. Slopes with a 5:1 ratio or greater; cut slopes with a five-foot vertical height or greater; and fill slopes with a three-foot vertical height or greater shall be protected against damage from erosion. In addition to the stabilizing mulch, drought-tolerant plant material and hardscape features shall be utilized on slopes to promote water retention and erosion control. Decorative boulders and other suitable hardscape materials may be utilized on slopes, but the dominant visual character of the slope shall be made up of drought-tolerant plant materials. Shrubs shall be used in combination with lateral spreading groundcovers; trees shall be used where slope exceeds 15 feet vertical height. Trees and shrubs shall be planted in visually attractive groupings that provide a more natural appearance.

itable hardscape materials may be utilized on slopes, but the dominant visual character of the slope shall be made up of drought-tolerant plant materials. Shrubs shall be used in combination with lateral spreading groundcovers; trees shall be used where slope exceeds 15 feet vertical height. Trees and shrubs shall be planted in visually attractive groupings that provide a more natural appearance.

(7) Dust Control. If grading takes place, a dust control plan shall be submitted for review. All grading and dust control measures shall be conducted in compliance with the provisions of Chapter 88.02 (Soil and Water Conservation).

(Ord. 4011, passed - -2007; Am. Ord. 4400, passed - -2021)

(a) Landform Grading and Revegetation Standards. Incorporation of the basic principles of the landform grading and revegetation concept in the design and construction of hillside development projects shall be required so that they will be in harmony with the natural topography and reflect existing plant distribution patterns. The general principles of landform grading and revegetation include the following elements:

(1) The basic land plan flows with the natural topography rather than against it. This means that street patterns and building pad configurations follow the underlying topographic features rather than cutting across them.

Figure 83-6 Development Follows Natural Topography

(2) Manufactured Sites.

(A) All manufactured cut and fill slopes exceeding 15 feet in height, which will be either exposed to permanent public view or are adjacent to environmentally sensitive areas, shall be designed with features characteristic of natural slopes so that their ultimate appearance will resemble a natural slope. This shall include slopes along streets and highways, slopes adjacent to parks, schools, open spaces, and other public facilities, and other prominent and highly visible slopes. See Figure 83-7.

(B) Side setback slopes and rear setback slopes, less than 25 feet in height, need not have landform design applied.

(C) Slope drainage devices (i.e., down drains and interceptor drains) shall be designed so that they are built into the natural slope features and become hidden from view.

Figure 83-7 Characteristics of Manufactured Slopes

(3) When not otherwise required, terracing and the associated concrete drainage devices (i.e., terrace drains, down drains, and interceptor drains) distract from efforts to give cut and fill slopes a natural appearance and are therefore discouraged.

(4) Landscaping shall be applied in patterns resembling native plant distribution. See Figure 83-8.

Figure 83-8 Patterns of Landscaping

(b) Slope Analysis.

(1) Calculating Average Slope. Use one of the following formulas or an acceptable alternative approved by the Director that would accurately portray the steepness of areas throughout the site that are proposed for development and preservation in open space to calculate the weighted average natural slope by slope category for the entire project site and the weighted average for the area to be graded:

(2) Slope Categories. Table 83-8 (Slope Categories) provides standards for hillside slopes in areas that will not be landform graded. These standards ensure that development will complement the existing character and topography of the land. The standards for one category may be applied to limited portions of the site in an adjacent category when a project is developed on a site with more than one slope category. The maximum allowable density for residential projects shall be determined by the formulas contained in § 84.18.030 (Development Standards) or in § 82.13.050 (General Development Standards) if the project is located within the FS Overlay.

Table 83-8

(c) Grading.

• (1) Grading Standards.

• (A) Cut and fill slopes shall not be created greater than 50 percent (2:1).

(B) Where cut or fill conditions are created, slopes shall be varied rather than left at a constant angle that may be unstable or create an unnatural, rigid, “engineered” appearance. See Figure 83-9.

Figure 83-9 Variations in Cut and/or Fill Slopes

(C) The toe and crest of any slope in excess of ten feet in vertical height shall be rounded with vertical curves of radii no less that five feet and designed in proportion to the total height of the slope.

(D) A manufactured slope bank shall not exceed 30 feet in vertical height unless no feasible alternative exists or unless grading can be significantly reduced by increasing slope height. However, the use of an alternative design is strongly recommended as the desirable approach in reducing grading and slope height. Any bank exceeding 25 feet in height, regardless of length, shall have variable gradients.

(E) Grading shall be phased so that prompt revegetation or construction will control erosion. Where feasible, only those areas that will be built on, resurfaced, or landscaped shall be disturbed. Topsoil shall be stockpiled during rough grading and used on cut and fill slopes whenever feasible. Revegetation of cut and fill slopes shall occur within three months of grading completion.

(F) Grading operations shall be prohibited during the rainy season, October 15 to April 15, unless adequate erosion control measures are implemented as approved by the Director to control run-off and retain sediment on-site. (G) Retaining walls associated with lot pads shall not exceed four feet in height, where they will be visible to the public. Where an additional retained portion is necessary due to unusual or extreme conditions (i.e., parcel configuration, steep slope, or road design), the use of terraced retaining structures shall be considered on an individual parcel basis and shall only be allowed where landscaping is provided between the walls to soften the overall

appearance. Terraced walls shall be separated by a minimum of three feet with appropriate landscaping. No more than three terraced or stepped walls shall be permitted without obtaining a Variance for more. Terraced retaining walls shall not be used as a typical solution within a development and shall be limited to the minimum required subject to approval of the Director.

(H) Parcel lines shall be placed two feet beyond top of major slope areas within public view corridors to help ensure their maintenance by the downhill owner.

(I) Where feasible, graded areas shall be designed with manufactured slopes located on the uphill side of structures, thereby hiding the slope behind the structure. See Figure 83-10.

Figure 83-10 Manufactured Slopes Located at Rear of Lot

(J) On parcels sloping with the street and other configurations not addressed above in this Subdivision (1), one retaining wall, not to exceed 42 inches in height, may be used in a side setback where necessary. See Figure 83-11. Figure 83-11 Retaining Walls for Side Setbacks

(2) Drainage Standards.

(A) Debris basins, riprap, and energy dissipating devices shall be provided where necessary to reduce erosion when grading is undertaken. Except for necessary flood control facilities and road and utility crossings, significant natural drainage courses shall be protected from grading activity. In instances where crossing is required, a natural crossing and bank protection shall be preferred over steel and concrete systems, where such crossing is feasible. Where brow ditches are required, they shall be naturalized with plant materials and native rocks.

(B) Terrace drains shall follow landform slope configuration. Down drains shall not be placed in exposed positions. Down drains shall be hidden in swales diagonally or curvilinearly across a slope face. In this manner they

shall be built into the overall landform of the slope. See Figure 83-12.

Figure 83-12 Drains Follow Topography This

Not This

(C) Building Permits and Grading Permits shall not be issued for construction on any site without an approved location for disposal of runoff waters, (i.e., a drainage channel, public street or alley, or private drainage easement).

(D) The use of cross lot drainage shall be subject to the Director’s review and may be approved after demonstration that this method will not adversely affect the proposed parcels or adjacent properties, and that it is absolutely required in order to minimize the amount of grading that would result with conventional drainage practices. Where cross lot drainage is utilized, the following shall apply:

(I) One parcel may drain across another parcel if an easement is provided either within an improved, open V- swale gutter that has a naturalized appearance or within a closed drainage pipe that should be a minimum 12 inches in diameter. This drainage shall be conveyed to either a public street or to a drainage easement. The easement width shall be determined on an individual basis and shall be dependent on appropriate hydrologic studies and access requirements.

(II) On-site drainage shall be conveyed in an improved, open V-swale gutter that has a naturalized appearance, or within an underground pipe as determined on an individual basis and shall be dependent on appropriate hydrologic studies and access requirements.

(E) Slope drainage on graded slopes should be regulated per the California Building Code.

(F) Natural drainage courses shall be preserved and enhanced to the extent feasible. Rather than filling them in, drainage features shall be incorporated as an integral part of the project design.

(3) Access, Trails, and Roadway Standards.

(A) Driveway grades up to a maximum of 20 percent shall be allowed and shall be aligned with the natural contours of the land. Proper design considerations shall be employed (i.e., vertical curbs and parking landings). Parking landings shall be utilized on all driveways over ten percent in grade.

(B) Where retaining walls are necessary adjacent to roadways or within street setbacks, they shall be limited to three feet in height where they will be visible from the street in order to avoid obstruction of motorists’ and pedestrians’ field of view and to create an aesthetically pleasing streetscape. No more than four terraced or stepped retaining walls shall be utilized. Walls shall be separated by a minimum of three feet and include appropriate landscaping.

Figure 83-13 Retaining Walls Along Streets and in Setbacks

(C) Roadways and Driveways Shall Conform to the Natural Landform, Where Feasible. They shall not greatly alter the physical and visual character of a hillside by creating large notches in ridgelines, defining wide straight alignments, or by building switch-backs on visually prominent hillsides. Split sections and parking bays shall be utilized in the layout of hillside streets.

(D) Where Road Construction Is Allowed in Hillside Areas, the Extent of Vegetation Disturbance and Visual Disruption Shall Be Minimized by the Combined Use of Retaining Structures and Regrading to Approximate the Natural Slope. The following techniques shall be used where feasible:

(I) Utilize landform revegetation planting in order to create a natural appearance and provide a sense of privacy.

(II) Reduce the visual and safety impacts by use of terraced retaining walls and landscaping.

(III) Split roadways increase the amount and appearance of landscaping and the median can be used to handle drainage.

• (4) Site Design.

(A) The dimensions of a structure parallel to the direction of the slope shall be maximized in order to limit the amount of cutting and filling and to better fit the structure to the natural terrain. See Figure 83-14.

Figure 83-14 Streets and Lots Follow Contours

(B) Design of building sites shall be sensitive to the natural terrain. Structures shall be located in ways that minimize grading and preserve natural features (i.e., knolls or ridgelines). See Figure 83-15.

Figure 83-15 Preserve Natural Features

(C) Projects shall incorporate variable setbacks, multiple orientations, and other site planning techniques to preserve open spaces, protect natural features, and offer views for residents.

(5) Landscaping Standards. In addition to the requirements in Chapter 83.10 (Landscaping Standards) the following standards shall apply to hillside development subject to the requirements of this Chapter:

(A) Native or naturalized plants or other plant species that blend with the landscape shall be utilized in all areas with required planting.

• (B) Fire retardant plant materials shall be utilized.

(C) A permanent landscape and irrigation system, for purposes of establishing and maintaining required planting, shall be installed on all slopes. The emphasis shall be toward using plant materials that will eventually need minimal irrigation. Water and energy conservation techniques shall be utilized, including drip irrigation, reclaimed water, and xeriscape. Within the Desert Region, if a natural landscape palette is selected, permanent irrigation need not be provided if it is demonstrated to the satisfaction of the Director that permanent irrigation is unnecessary. Drip irrigation need not be provided for landscape palettes where such a system would not be water-efficient. Reclaimed water need be used only in situations where it is available at the site.

(D) Landscaping shall be used to screen views of downslope building elevations. When the structure height exceeds 20 feet from finished grade on a downslope, additional landscaping shall be required and a landscaping plan shall be submitted for review with the submittal package.

(E) Slopes with required planting shall be planted with informal clusters of trees and shrubs to soften and vary the slope plane. Where required by the County, jute netting or similar material shall be used to help stabilize planting and minimize soil erosion.

(F) Native vegetation shall be retained and supplemented within undeveloped canyons and along natural drainage courses as allowed by State and Federal resource agencies (e.g., State Department of Fish & Game, U.S. Fish and Wildlife, U.S. Army Corps of Engineers, etc.).

(G) Landscaping shall become a “revegetation” process and be applied in patterns that occur in nature: Trees and shrubs shall be concentrated largely in concave areas, while convex portions shall be planted mainly with groundcovers.

(Ord. 4011, passed - -2007; Am. Ord. 4043, passed - -2008; Am. Ord. 4334, passed - -2017)