17.154.190 Drainage and terracing.
(1) Unless otherwise indicated on the approved grading plan, drainage facilities and terracing shall conform to the provisions of this section for cut or fill slopes steeper than one unit vertical in three units horizontal (33.3 percent slope).
(2) Terraces at least six feet in width shall be established at not more than 30-foot vertical intervals on all cut or fill slopes to control surface drainage and debris, except that where only one terrace is required, it shall be at mid-height. For cut or fill slopes greater than 60 feet and up to 120 feet in vertical height, one terrace at approximately mid-height shall be 12 feet in width. Terrace widths and spacing for cut and fill slopes greater than 120 feet in height shall be designed by the civil engineer and approved by the director or city. Suitable access shall be provided to permit proper cleaning and maintenance.
(3) Swales or ditches on terraces shall have a minimum gradient of one-half percent.
(4) Cut or fill slopes shall be provided with subsurface drainage as necessary for stability and proper conveyance of groundwater.
(5) All drainage facilities shall be designed to carry waters to the nearest practicable drainage way in a safe manner approved by the director or city. Outfalls or points of discharge shall be designed using best management practices and construction procedures which prevent or minimize erosion.
(6) Building pads shall have a drainage gradient of two percent toward approved drainage facilities, unless waived by the city. Exception: The gradient from the building pad may be one percent if all of the following conditions exist throughout the permit area:
(a) No proposed fills are greater than 10 feet in maximum depth;
(b) No proposed finish cut or fill slope faces have a vertical height in excess of 10 feet; and
(c) No existing slope faces steeper than one unit vertical in 10 units horizontal (10 percent slope) have a vertical height in excess of 10 feet.
(7) Paved interceptor drains shall be installed along the top of all cut slopes where the tributary drainage area above slopes toward the cut and has a drainage path greater than 40 feet measured horizontally. Interceptor drains, if required, shall be paved with a minimum of three inches of concrete or gunite and reinforced. They shall have a minimum depth of 12 inches and a minimum paved width of 30 inches measured horizontally across the drain. The slope of drain shall be approved by the city. (Ord. 1499 § 10 (Exh. H), 2021).