Article 5 — SLOPE DRAINAGE — Oakley Municipal Code

§ 6.9.502. General Provisions.¶

Terracing and the associated drainage facilities are prohibited except for special circumstances as determined by the City Engineer. When permitted, these facilities shall conform to the following specifications unless shown otherwise on the approved grading plan:

a. When cut or fill slopes greater than 30 feet in height are authorized, drainage collection and slope stability devices shall be incorporated in accordance with City standards.
b. On manufactured slopes greater than 30 feet in height drainage collection and slope stability devices shall have a minimum gradient of 2% and must be paved with reinforced concrete, or approved equivalent.
c. Run-off shall not be collected from a tributary area exceeding 13,500 square feet without discharging into a system (ditch or pipe) approved by the City Engineer.
d. Cut and fill slopes shall be provided with approved subsurface drainage as necessary for stability and protection of adjacent properties from the influence of groundwater. The design of such facilities shall be contained in the approved preliminary (initial) soil engineering or engineering geology report and/or shall appear on the approved grading plan pursuant to the approval of the soil engineer and the engineering geologist (if applicable).
e. Subsurface drainage facilities shall be installed beneath all fills and where natural and artificially introduced ground water affects, or is likely to affect, the project in a potentially unstable, hazardous or otherwise deleterious manner.
f. All drainage facilities shall be designed to carry waters to the nearest approved drainage system.
g. Where surface waters are to be conducted or directed onto adjacent property in an unnatural manner, the applicant shall obtain written permission from the adjacent property owner accepting the surface waters prior to issuance of a grading permit.
h. Building sites shall have a sheet flow drainage gradient of 2% minimum from the structure toward approved swales or drainage facilities, unless otherwise waived by the Chief Building Official. The maximum drainage gradient of an earth swale shall be 4%.
i. Grading of future building sites under a preliminary grading permit for the purpose of lot sales shall have a sheet flow drainage gradient of 2% toward approved drainage facilities. The City Engineer may reduce this minimum gradient to 1% upon the written request of the applicant of his/her agent, providing the applicant demonstrates the following:
- 1. Finish grades for drainage of building sites can be constructed in accordance with the requirements of this subsection without importing additional fill; and
- 1. Sufficient approved swales or drainage facilities are constructed to prevent water from ponding on any lot supported by a natural slope.
j. Finish grades, other than those detailed in subsections (b), (h) and (i) of this section, shall conform to the following minimum drainage gradient standards:

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City of Oakley, CA

PUBLIC WORKS REGULATIONS

§ 6.9.502

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Surface Condition/Flow Type Minimum Gradient
1) Earth swales 1.0%
2) Earth (sheet flow) 1.0%
3) Asphalt pavement (sheet flow) 1.0%
4) Concrete drain in earth area 1.0%
5) Concrete gutter in asphalt paved area 0.5%
6) Concrete pavement (sheet flow) 0.5%
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k. Approved interceptor drains shall be installed along the top of all manufactured slopes unless waived by the City Engineer.
l. Slopes flatter than 3:1 shall be re-vegetated, interceptor and subdrain systems installed as required by the City Engineer, and have appropriate setbacks as defined in the current Uniform Building Code (UBC) and sediment collection areas at the base of the slope.

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City of Oakley, CA

PUBLIC WORKS REGULATIONS

§ 6.9.602

§ 6.9.612