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(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.
(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.
(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.
(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:
Weighted Average Slope = 0.002296 IL/A
Contour interval in feet
Summation of length of all contours in feet
Area in acres of parcel being considered (minimum area to be considered shall be 10,000 square feet)
Weighted Average Slope = 100 IL/A
Contour interval in feet
Summation of length of all contours in feet
Area in square feet of parcel being considered (minimum area to be considered shall be 10,000 square feet)
(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.
Weighted Average Natural Slope Gradient
15 percent to less than 30 percent
Structures shall conform to the natural topography and natural grade by using appropriate techniques, including stepped or split-level foundations, stem walls, stacking, and clustering. Walls shall be as natural appearing as possible. Conventional grading may be considered for limited portions of a project when its plan includes special design features, extensive open space, or significant use of greenbelts.
30 percent to less than 40 percent
Development within this category shall be restricted to those sites where it can be demonstrated that safety will be maximized while environmental and aesthetic impacts will be minimized. Use of large parcels, variable setbacks, and variable building structural techniques (e.g., stepped foundations) shall be expected. Extra erosion control measures may be included as conditions of approval.
40 percent and greater
This is an excessive slope condition. Pad grading shall not be allowed. Grading for driveways and roads shall be reviewed through the Minor Use Permit application process.
(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.
(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.
(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.
(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.
(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.
(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.
(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.
(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)