Chapter 17.87
DRAINAGE AND TERRACING
Sections:
17.87.010 Drainage and Terracing Provisions.
17.87.020 Slope Planting and Erosion Control.
17.87.010 Drainage and Terracing Provisions.
A. General. Unless otherwise recommended by a civil engineer and approved by the City Engineer, drainage facilities and terracing shall be provided in accordance with the requirements of subsection (B) of this section for all cut and fill slopes three (3) units horizontal to one (1) unit vertical (thirty-three percent (33%) slope) and steeper.
For slopes flatter than three (3) units horizontal to one (1) unit vertical (thirty-three percent (33%) slope), but steeper than five (5) units horizontal to one (1) unit vertical (twenty percent (20%) slope), a paved swale or ditch shall be installed at thirty (30) foot vertical intervals to control surface drainage and debris. Swales shall be sized based on contributory area and shall have adequate capacity to convey intercepted waters to the point of disposal as defined in subsection (D) of this section. Swales must be paved with reinforced concrete measuring not less than three (3) inches in thickness, reinforced with six (6) inch by six (6) inch, No. 10 by No. 10 welded wire fabric or equivalent, as approved by the City Engineer. Swales must have a minimum flow line depth of one (1) foot and a minimum paved width of eighteen (18) inches. Swales shall have a minimum grade of not less than five percent (5%). There shall be no reduction in grade along the direction of flow unless the velocity of flow is such that slope debris will remain in suspension on the reduced grade.
B. Drainage Terraces. Drainage terraces at least eight (8) feet in width (measured horizontally from the outside edge) shall be established at not more than twenty-five (25) foot vertical intervals on all cut or fill slopes more than thirty (30) feet in height to control surface drainage and debris. When only one (1) terrace is required, it shall be at mid-height. For cut or fill slopes greater than one hundred (100) feet and up to one hundred twenty (120) feet in vertical height, one (1) terrace at approximately mid-height shall be twenty (20) feet in width. Terrace widths and spacing for cut and fill slopes greater than one hundred twenty (120) feet in height shall be designed by the civil engineer and approved by the City Engineer. Suitable access shall be provided to permit proper cleaning and maintenance.
Drainage swales on terraces shall have a longitudinal grade of no less than five percent (5%) and no more than twelve percent (12%) and a minimum depth of one (1) foot at a flow line. There shall be no reduction in grade along the direction of flow unless the velocity of flow is such that the slope debris will remain in suspension on the reduced grade. Drainage swales must be paved with concrete not less than three (3) inches thick reinforced with six (6) inch by six (6) inch, No. 10 by No. 10 welded wire fabric or equivalent reinforcing centered in the concrete slab or an approved equal paving. Drainage terraces exceeding eight (8) feet in width need only be so paved for a width of eight (8) feet provided such pavement provides a paved swale of at least one (1) foot in depth. Downdrains or drainage outlets shall be provided at approximately three hundred (300) foot intervals along the drainage terrace or at equivalent locations. Downdrains and drainage outlets shall be of approved materials and of adequate capacity to convey the intercepted waters to the point of disposal as defined in subsection (D) of this section.
Subgrade shall be approved in writing for line and grade by the civil engineer and approved in writing by the geotechnical engineer stating that the subgrade is firm and unyielding and void of expansive materials prior to concrete placement.
C. Interceptor Drains and Overflow Protection. Berms, interceptor drains, swales, or other devices shall be provided at the top of cut or fill slopes to prevent surface waters from overflowing onto the damaging face of the slope. Berms used for slope protection shall not be less than twelve (12) inches above the level of the pad and shall slope back at least four (4) feet from the top of the slope.
Interceptor drains shall be installed along the top of all graded slopes where the height of the cut is greater than five (5) feet in height, measured vertically, receiving drainage from a slope with a tributary width of greater than thirty (30) feet, measured horizontally. They shall have a minimum depth of one (1) foot and a minimum width of three (3) feet. The slope shall be approved by the City Engineer, but shall not measure less than two percent (2%). Interceptor drains shall be paved with a minimum of three (3) inches of concrete or other materials as approved by the City Engineer and reinforced as required for drainage terraces.
Gutters or other special drainage controls shall be provided where the proximity of runoff from buildings or other structures is such as to pose a potential hazard to slope integrity.
D. Disposal. All drainage facilities shall be designed to carry surface waters to the nearest practical street, storm drain, or natural watercourse, or drainage way approved by the City Engineer or other appropriate governmental agency; provided, that the discharge of such waters at that location will not create or increase a hazard to life or property. Erosion of the ground in the area of discharge shall be prevented by installation of nonerosive down drains and/or other devices. Desilting basins, filter barriers or other methods, as approved by the City Engineer, shall be utilized to remove sediments from surface waters before such waters are allowed to enter streets, storm drains or natural watercourses. If the drainage device discharges onto natural ground, riprap or similar energy dissipaters may be required.
Graded building sites (building pads) shall have a minimum slope of two percent (2%) toward a public street or drainage structure approved to receive stormwaters unless otherwise directed by the City Engineer. A lesser slope may be approved by the City Engineer for sites graded in relatively flat terrain, or where special drainage provisions are made, when the City Engineer finds such modification will not result in hazard to life or property. The grading shall provide for drainage around proposed buildings and their appurtenances.
E. Subsurface Drainage. Cut and fill slopes shall be provided with subsurface drainage as necessary for stability as required by the geotechnical engineering report. Any required subsurface drainage facilities will be passive in design and require no ongoing monitoring to ensure site stability.
F. Drainage Guidelines. All drainage devices which collect from the slopes shall be screened by means of underground pipes, diagonal curvilinear drains, rock-lining, colored concrete or other approved materials to blend with the natural topography in character, color or design. Downdrains shall be noncentralized to avoid a repetitive pattern. Where feasible, underground drains shall be utilized. On hillside projects, all drainage devices shall be consistent with the City’s Hillside Development Guidelines unless special circumstances are established to the satisfaction of the City Engineer.
G. Drainage Across Property Lines. Drainage across property lines shall not exceed that which existed prior to grading. Excess or concentrated drainage shall be contained on site or directed to an approved drainage facility. Erosion of the ground in the area of discharge shall be prevented by installation of nonerosive down drains or other devices.
H. Cross Lot Drainage Device Maintenance. All cross lot drainage devices not eligible for transfer to Los Angeles County Flood District should be maintained by an entity such as a homeowners’ association. (Ord. 13-8 § 4 (Exh. A), 6/11/13)
17.87.020 Slope Planting and Erosion Control.
A. Slopes. The faces of cut and fill slopes shall be prepared and maintained to control erosion. This control shall consist of jute netting, effective planting, erosion control blankets, soil stabilizers, or other means, as approved by the City Engineer. Erosion control for slopes shall be installed as soon as practicable and prior to calling for final inspection.
Exception: Erosion control measures need not be provided on cut slopes not subject to erosion due to the erosion-resistant character of the materials, as approved by the project consultants, to the satisfaction of the City Engineer.
B. Other Devices. Where necessary, check dams, cribbing, riprap, or other devices or methods shall be employed to control any erosion. Also, jute netting shall be immediately installed on any slopes having a vertical height of seven (7) feet or more and steeper than three to one (3:1) horizontal to vertical ratio (H:V) to minimize or control erosion problems.
C. Erosion Control (Slopes Subject to Section 17.51.020). Erosion control for grading where average slopes are greater than ten percent (10%) and involving more than one hundred (100) cubic yards is subject to Section 17.51.020 (Hillside Development). For specific recommendations for phasing the project to promote prompt revegetation, leaving undeveloped pads longer than thirty (30) to ninety (90) days and clearing of brush or vegetation, refer to the Hillside Development Guidelines.
D. Planting (Areas Not Subject to Section 17.51.020). The surface of all cut slopes more than five (5) feet in height and fill slopes more than three (3) feet in height shall be protected against damage by erosion by planting with grass or ground cover plants. Slopes exceeding five (5) feet in vertical height shall also be planted with one (1) gallon minimum sized shrubs, spaces at not to exceed ten (10) feet on centers; and fifteen (15) gallon minimum sized trees, spaced not to exceed twenty (20) feet on centers; or a combination of shrubs and trees at equivalent spacings, in addition to the grass or ground cover plants to the satisfaction of the Director. The plants selected and planting methods used shall be suitable for the soil and climatic conditions of the site.
Plant material shall be selected which will produce a coverage of permanent planting to effectively control erosion. Consideration shall be given to deep rooted plant material needing limited watering, maintenance, high root to shoot ratio, wind susceptibility, and fire-retardant characteristics. All plant materials must be approved by the Director.
Planting may be modified for the site if specific recommendations are provided by both the geotechnical engineer and a landscape architect. Specific recommendations must consider soils and climatic conditions, irrigation requirements, planting methods, fire retardant characteristics, water efficiency, maintenance needs, and other regulatory requirements. Recommendations must include a finding that the alternative planting will provide a permanent and effective method of erosion control. Modifications to planting must be approved by the Director prior to installation.
E. Irrigation. Slopes required to be planted by subsection (D) of this section shall be provided with an approved system of irrigation that is designed to cover all portions of the slope. Irrigation system plans shall be submitted to and approved by the Director prior to installation. A functional test of the system may be required.
For slopes less than twenty (20) feet in vertical height, hose bibs to permit hand watering will be acceptable if such hose bibs are installed at conveniently accessible locations where a hose no longer than fifty (50) feet is necessary for irrigation.
Irrigation requirements may be modified for the site if specific recommendations are provided by both the geotechnical engineer and a landscape architect. Specific recommendations must consider soils and climatic conditions, irrigation requirements, planting types, planting methods, fire retardant characteristics, water efficiency, maintenance needs, and other regulatory requirements. Recommendations must include a finding that the alternative irrigation method will sustain the proposed planting and provide a permanent and effective method of erosion control. Modifications for irrigation systems must be approved by the Director prior to installation.
F. Planting and Irrigation (Areas Subject to Section 17.51.020). Requirements for planting and irrigation in areas subject to Chapter 17.51.020 (Hillside Development) are governed by that ordinance. Recommendations for these areas are also included in the Hillside Development Guidelines.
Plant material shall be selected which will produce a coverage of permanent planting effectively controlling erosion. Consideration shall be given to deep-rooted plant material needing limited watering, to low maintenance during the lifetime of the project, to high root to shoot ratio (weight of above-ground parts versus root system), wind susceptibility and fire-retardant characteristics.
G. Plans and Specifications. Planting and irrigation plans shall be submitted for slopes required to be planted and irrigated by subsections (D) and (E) of this section. Except as waived by the City Engineer for minor grading, the plans for slopes twenty (20) feet or more in vertical height shall be prepared and signed by a civil engineer or landscape architect. These plans must be approved by the City prior to issuance of the grading permit unless other provisions are made to the satisfaction of the City Engineer. The responsibility of maintenance of drainage terrace shall be clearly stated on the grading plan to the satisfaction of the City Engineer.
H. Rodent Control. Fill slopes shall be protected from potential slope damage by a preventative program of rodent control.
I. Release of Security. The planting and irrigation systems required by this section shall be installed as soon as practical after rough grading. Prior to final approval of grading and before the release of the grading security, the planting shall be well established and growing on the slopes and there shall be evidence of an effective rodent control program.
J. Graded and/or landscaped areas within a landscape maintenance district are to be maintained in accordance with the original landscape plans and design concept per the originally approved subdivision or development plans. Any alteration of landscape plans or of areas within a landscape maintenance district must be approved by the Director of Administrative Services per the regular provisions of the grading code. Homeowner encroachments such as fences, block walls, structures, unauthorized plantings, alterations to the irrigation, grading or drainage are not allowed. Any approved alterations must be done by City-authorized crews through an approved City permit. Failure to comply with this section shall constitute a use of land contrary to the provisions of this title and shall be deemed a public nuisance under Title 23. (Ord. 13-8 § 4 (Exh. A), 6/11/13)