14.40.130 Terracing.
A. General. Unless otherwise indicated on the approved grading plans, terracing and related drainage shall conform to the provisions of this section for cut or fill slopes steeper than three horizontal to one vertical.
B. Terrace.
1. 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 permit authority. Suitable access shall be provided to permit property cleaning and maintenance.
2. Swales or ditches on terraces shall have a minimum gradient of five percent and must be paved with reinforced concrete not less than three inches in thickness or an approved equal paving. They shall have a minimum depth at the deepest point of one foot and a minimum paved width of five feet.
3. A single runoff 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 of Drainage.
1. All drainage facilities shall be designed to carry water to the nearest practicable drainage way approved by the permit authority. Erosion of ground in the area of discharge shall be prevented by installation of nonerosive down drains or other devices.
2. Building pads shall have a drainage gradient of two percent toward approved drainage facilities. The permit authority may approve alternate gradients using the variance process adopted by GHMC 12.16.010.
3. 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.
c. No existing slope faces, which have a slope face steeper than 10 horizontally to one 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 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 building official. (Ord. 1169 § 4, 2009).