A. Compliance Required: 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 six horizontal to one vertical (6:1).
B. Terrace:
1. In order to control surface drainage and debris, terraces at least six feet (6') in width shall be established at not more than thirty foot (30') vertical intervals on all cut or fill slopes. Where only one terrace is required, it shall be established at midheight. For cut or fill slopes greater than sixty feet (60') and up to one hundred twenty feet (120') in vertical height, one terrace at approximately midheight shall be twelve feet (12') in width. Terrace widths and spacing for cut and fill slopes greater than one hundred twenty feet (120') 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.
2. Swales or ditches on terraces shall have a minimum gradient of three percent (3%) and must be stabilized with an approved erosion free channel. Said swales or ditches shall also have a minimum depth at the deepest point of one foot (1') and a minimum width of five feet (5') unless a civil engineer can demonstrate a smaller channel is appropriate. (1978 Code §8-17)
3. The capacity of a swale or ditch shall be adequate to convey the 100-year flood event for the tributary area. (1978 Code §8-17; amd. 1994 Code)
C. Subsurface Drainage: Cut and fill slopes shall be provided with subsurface drainage, where such drainage is reasonably necessary to achieve stability.
D. Disposal:
1. All drainage facilities shall be designed to carry waters to the nearest approved drainageway. Erosion in the area of discharge shall be prevented by installing nonerosive down drains or other devices, as needed.
2. Building pads shall have a drainage gradient of two percent (2%) from the building pad toward approved drainage facilities, unless waived by the building official.
3. The gradient from the building pad may be one percent (1%) if all of the following conditions exist throughout the permit area:
a. Proposed fills are no greater than ten feet (10') in maximum depth.
b. Proposed finish cuts or fill slope faces have a vertical height no greater than ten feet (10').
c. Existing slope faces which have a slope face steeper than ten horizontally to one vertically (10:1) shall have a vertical height no greater than ten feet (10').
E. Interceptor Drains: Interceptor drains shall be installed along the top of all cut slopes where the tributary drainage has been channelized and there is a potential for continued erosion. (1978 Code §8-17)