(1) General. Unless otherwise indicated on the approved grading plan, drainage facilities and terracing shall conform to the provisions of this Chapter for cut or fill slopes steeper than one (1) unit vertical in three (3) units horizontal (33.3% slope).
(2) Terrace. Terraces at least six feet (6') (1829 mm) in width shall be established at not more than thirty foot (30') (9144 mm) vertical intervals on all cut or fill slopes to control surface drainage and debris except that where only one (1) terrace is required, it shall be at midheight. For cut or fill slopes greater than sixty feet (60') (18 288 mm) and up to one hundred twenty feet (120') (36 576 mm) in vertical height, one (1) terrace at approximately midheight shall be twelve feet (12') (3658 mm) in width. Terrace widths and spacing for cut and fill slopes greater than one hundred twenty feet (120') (36 576 mm) in height shall be designed by the civil engineer and approved by the Building Official. Suitable access shall be provided to permit proper cleaning and maintenance.
Swales or ditches on terraces shall have a minimum gradient of five percent (5%) and must be paved with reinforced concrete not less than three inches (3") (76 mm) in thickness or an approved equal paving. They shall have a minimum depth at the deepest point of one foot (1') (305 mm) and a minimum paved width of five feet (5') (1524 mm).
A single run of swale or ditch shall not collect runoff from a tributary area exceeding 13,500 square feet (1254.2 m2) (projected) without discharging into a down drain.
(3) Subsurface drainage. Cut and fill slopes shall be provided with subsurface drainage as necessary for stability.
(4) Disposal. All drainage facilities shall be designed to carry waters to the nearest practicable drainage way approved by the Building Official or other appropriate jurisdiction as a safe place to deposit such waters. Erosion of ground in the area of discharge shall be prevented by installation of nonerosive downdrains or other devices.
Building pads shall have a drainage gradient of two percent (2%) toward approved drainage facilities, unless waived by the Building Official.
Exception: The gradient from the building pad may be one percent (1%) if all of the following conditions exist throughout the permit area:
(a) No proposed fills are greater than ten feet (10') (3048 mm) in maximum depth.
(b) No proposed finish cut or fill slope faces have a vertical height in excess of ten feet (10') (3048 mm).
(3) No existing slope faces steeper than one (1) unit vertical in ten (10) units horizontal (ten percent (10%) slope) have a vertical height in excess of ten feet (10') (3048 mm).
(5) Interceptor drains. 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 forty feet (40') (12 192 mm) measured horizontally. Interceptor drains shall be paved with a minimum of three inches (3") (76 mm) of concrete or gunite and reinforced. They shall have a minimum depth of twelve inches (12") (305 mm) and a minimum paved width of thirty inches (30") inches (762 mm) measured horizontally across the drain. The slope of drain shall comply with the requirements found in the current edition of the International Building Code and be approved by the Building Official.
Ord. No.97-35, Recodified, 6/19/1997
Ord. No. 03-31, Enacted, 9/4/2003