Glenn County Municipal Code § 15.65 Drainage 15.65.010 General Requirement 15.65.020 Easements 15.65.030 Drainage…

All subdivisions shall be protected from flood hazard and inundation by storm waters originating without and within the proposed subdivision. The design and construction of drainage facilities shall be such that water courses traversing the subdivision and water emanating from within the subdivision will be carried through and off the subdivision without injury to improvements, residential sites, or adjacent properties. Drainage waters shall not be discharged onto existing county rightsof-way except in manner approved by the public works director. All proposed subdivisions, whether or not they front on existing county rights-of-way, shall meet the minimum requirements of this chapter. (Ord. 1183 § 2, 2006)

1. Drainage facilities shall be located in a dedicated public street, road or lane, or within a public drainage easement. Necessary dedications shall be accomplished on the parcel or final map or by grant deed. The county shall not accept the maintenance of drainage facilities which are not located in a public right-of-way. Dual use of easements shall not be approved unless it can be demonstrated to the satisfaction of the public works director that dual use will not be conflicting.

2. The minimum width of any drainage easement for a closed conduit system shall be twelve feet and the minimum width for any open conduit system shall be twenty feet. For any conduit exceeding thirty inches in diameter, with more than one manhole or more than one turning structure, a twelve-foot width service road shall be improved and dedicated. (Ord. 1183 § 2, 2006)

1. Drainage systems and all bridges shall be designed to pass a one hundred-year frequency flood without damage to the structure or adjacent property, except that drainage systems draining an area smaller than one square mile may be designed for ten-year frequency floods if ponding due to the one hundred-year flood will not cause damage.

2. Drainage systems under driveway entrances shall be adequate to carry the design flow but shall not have less than a twelve-inch inside diameter. The minimum slope shall be one percent where practical. Drainage systems crossing streets shall be of a size adequate to carry the design flow but shall not have less than a fifteen inch inside diameter for concrete and an eighteen-inch inside diameter for C.M.P. Drainage systems for use outside the public right-of-way may be of any approved type and strength to meet field conditions, but shall not have less than a twelve-inch diameter. All pipe in the right-of-way shall be designed to standard H-20 live load and shall have a design life of twenty-five years.

3. Debris control, location and slope of culverts, entrances and endwalls, shall be in accordance with the recommendations of “California Culvert Practice.” (Ord. 1183 § 2, 2006)

1. All open ditches having a top width of ten feet or more shall be designed in an easement wide enough to allow motor vehicles on one side of the open ditch. The access shall be at least ten feet wide. This requirement may be waived by the public works director when, in his or her opinion, access will not be needed for future maintenance and when, in the opinion of the health officer, access is not needed for mosquito control.

2. New unlined drainage facilities or relocated natural drains may not be installed closer than fifty feet to existing or proposed leach lines. The gradient for earth ditches shall not exceed 4 percent nor be less than 0.1 percent. Earth ditches shall not be permitted if water therein could reach erosive velocities. The gradient for lined or paved ditches and gutters shall be not less than 0.20 percent, unless specific written approval is granted by the public works director. (Ord. 1269 § 10, 2018; Ord. 1183 § 2, 2006)

Whenever water is discharged from a subdivision where the method of discharge or the quantity has been changed, a “Drainage Release”, approved by the county counsel, shall be filed with the public works director prior to approval of the construction plans. (Ord. 1183 § 2, 2006)

Valley gutters, where feasible, are preferred for driveways and may be used for local streets where it can be shown that underground conduits cannot feasibly or reasonably be installed. Valley gutters will not be permitted across major or collector roads, except at intersections. (Ord. 1183 § 2, 2006)

Alternative methods of analysis and solution of drainage problems may be used in lieu of the requirements of this chapter when, based upon accepted engineering principles, they achieve the results of Section 15.65.010. Such deviations of the requirements herein may be accomplished only upon the consent of the public works director without complying with the provisions of Chapter 15.28. (Ord. 1183 § 2, 2006)