(A) General. The drainage structures and devices required by this chapter must conform to the provisions of this section as well as recognized principles of hydraulics.
(B) Disposal. Drainage facilities must be designed to carry surface waters to the nearest practical street, storm drain, or natural watercourse approved by the City Engineer or Building Official or other appropriate governmental agency as a safe place to deposit such waters. Desilting basins, filter barriers or other methods, as approved by the City Engineer or Building Official, must 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 a similar energy dissipator may be required.
(C) Site drainage. Graded building sites (building pads) must have a minimum slope of 2% toward a public street or drainage structure approved to receive storm waters. A lesser slope may be approved by the City Engineer or Building Official for sites graded in relatively flat terrain, or where special drainage provisions are made, when the City Engineer or Building Official finds such modification will not result in unfavorable drainage conditions. The grading must provide for drainage around proposed buildings and their appurtenances.
(D) Drainage terraces required. All cut or fill slopes steeper than three horizontal to one vertical must have drainage terraces. For slopes not steeper than three horizontal to one vertical, the City Engineer or Building Official may require a drainage and terrace design to be submitted. Suitable access to permit proper cleaning and maintenance must be provided for all drainage terraces. Cut or fill slopes more than 30 feet in height must have drainage terraces provided vertical intervals not exceeding 25 feet except that where only one terrace is required, it must be at midheight. Such terraces must be not less than eight feet in width (measured horizontally from the outside edge). When the total slope height exceeds 100 feet, one terrace near midheight must be not less than 20 feet in width (measured horizontally from the outside edge). In lieu of the above, for cut and fill slopes greater than 120 feet in height, the applicant may submit a drainage and terrace design by a civil engineer to be approved by the City Engineer or Building Official.
(E) Drainage terraces construction. Drainage terraces must have a longitudinal grade of not less than 5% nor more than 12% and a minimum depth of one foot at a flow line. There must 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. Such terraces must be paved with concrete not less than three inches thick reinforced with 6-inch x 6-inch No. 10 x No. 10 welded wire fabric or equivalent reinforcing centered in the concrete slab. Drainage terraces exceeding eight feet in width need only be so paved for a width of eight feet provided such pavement provides a paved channel at least one foot in depth. Downdrains or drainage outlets must be provided at approximately 300 foot intervals along the drainage terrace or at equivalent locations. Downdrains and drainage outlets must be of approved materials and of adequate capacity to convey the intercepted waters to the point of disposal as defined in subsection (B) of this section.
(F) Overflow protection. Berms, swales or other devices must be provided at the top of cut or fill slopes to prevent surface waters from overflowing onto the damaging face of the slope. Gutters or other special drainage controls must be provided where the proximity of runoff from buildings or other structures is such as to pose a potential hazard to slope integrity. Swales used for slope protection must conform with subsection (H) of this section. Berms used for slope protection must be at least 12 inches above the level of the pad and must slope back at least four feet from the top of the slope.
(G) Subsurface drainage. Cut and fill slopes must be provided with subsurface drainage as necessary for stability. Any required subsurface drainage facilities will be passive in design and require no ongoing monitoring to insure site stability.
(H) Interceptor drains. Paved interceptor drains must be installed along the top of all cut slopes where the height of the cut is greater than five feet measured vertically. Interceptor drains must be paved with a minimum of four inches of concrete or granite and reinforced as required for drainage terraces. They must have a minimum depth of 12 inches and a minimum paved width of 36 inches measured horizontally across the drain. The side slope of interceptor drains must not be steeper than 1-1/2:1. The slope of the drain must be approved by the City Engineer or Building Official.
(I) Drainage guidelines. All drainage devices which collect from the slopes must 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 must be non-centralized to avoid a repetitive pattern. Where feasible, underground drains must be utilized.
(J) Cross lot drainage device maintenance. All cross lot drainage devices not eligible for transfer to a flood control district or similar entity must be maintained by the owner or a private entity such as a homeowners association.
(Ord. 1103, passed 3-7-05)