(Amended by Ordinance No. 173270, effective May 21, 1999.)
A. General. Unless otherwise indicated on the
approved grading plan, drainage facilities and terracing shall conform to the
provisions of this Section.
B. Terrace. 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 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. Suitable access
shall be provided to permit proper cleaning and maintenance.
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 downdrain.
C. Subsurface drainage. Cut
and fill slopes shall be provided with subdrainage as necessary for stability.
Adequate culverts shall be laid under all fills placed in natural watercourses
and along the flow line of any tributary branches in such a manner that the
hydraulic characteristics of the stream are not adversely altered. In addition,
subdrainage shall be installed if active or potential springs or seeps are
covered by the fill. All culverts/subdrainage shall be installed after the
suitable subgrade preparation. Design details of culverts/subdrainage shall be
shown on each plan and be subject to the approval of the Director and of other
government/private agencies as may be required.
A subdrain system shall be provided for embedded
foundation/ retaining walls and floor slabs where ground water or seepage has a
potential to affect the performance of the structure. The plans shall indicate
1. subdrainage details
with appropriate specifications,
2. location of footing
subdrain/discharge lines and,
3. method of disposal.
In lieu of above, walls/floors may be waterproofed and
designed to resist hydrostatic pressure.
D. Disposal. All drainage
facilities shall be designed to carry waters to the nearest practicable
drainageway or approved stormwater management facility, as approved by the
Director and/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 non-erosive downdrains or other devices.
Building pads shall have a drainage gradient of 2
percent toward approved drainage facilities, unless waived by the Director.
Exception: The gradient from the building pad may be 1
percent if all of the following conditions exist throughout the permit area:
1. No proposed fills are
greater than 10 feet in maximum depth.
2. No proposed finish cut
or fill slope faces have a vertical line in excess of 10 feet.
3. No existing slope
faces, which have a slope face steeper than 10 horizontal to 1 vertical, 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 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 the drain shall be approved by the Director.