(A) General. Unless otherwise indicated on the approved plan, drainage facilities and terracing shall conform to the provisions of this section for cut or fill slopes.
(B) Terraces. Terraces at least 6 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 1 terrace is required, it shall be at the mid-point of the vertical height. For cut or fill slopes greater than 60 feet and up to 120 feet in vertical height, 1 terrace at approximately midheight 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 a licensed geotechnical engineer and reviewed by the city. Suitable access shall be provided to permit proper cleaning and maintenance. Swales or ditches on terraces shall have a minimum gradient of 5% and must be paved with reinforced concrete not less than 3 inches in thickness or an approved equal paving. They shall have a minimum depth at the deepest point of 1 foot and a minimum paved width of 5 feet. A single run of swale or ditch shall not collect runoff from a tributary area exceeding 13,500 square feet (projected) without discharging into a down drain.
(C) Subsurface drainage. Cut and fill slopes shall be provided with subsurface drainage as necessary for stability.
(D) Disposal.
(1) All drainage facilities shall be designed to carry waters to the nearest practicable drainageway approved by the city for the deposit of such waters. Erosion of ground in the area of discharge shall be prevented by installation of non-erosive down-drains or other devices. Building pads shall have a drainage gradient of 2% toward approved drainage facilities, unless waived by the city.
(2) The gradient from the building pad may be 1% where the following conditions exist throughout the site:
(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;
(c) No existing slope faces, which have a slope face steeper than 10 horizontally to 1 vertically, have a vertical height in excess of 10 feet.
(E) Interceptor drains. Paved interceptor drains shall be installed along the top of all cut slopes where the tributary drainage area above slopes towards the cut and has a drainage path greater than 40 feet measured horizontally. Interceptor drains shall be paved with a minimum of 3 inches of concrete or granite 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.
(Prior Code, § 4.06)