Any changes in private drainage that flows into or across the county right-of-way shall be subject to these regulations and specifications.
(A) Increased runoff due to new construction.
(1) Whenever private drainage is changed such that an increased amount of surface runoff is directed to an existing county right-of-way a certified drainage design may be required by the County Engineer. This will be provided prior to the issuance of the required permit for construction within the county right-of-way. If it is determined by the County Engineer that the change in runoff will adversely affect the roadway he may require the runoff to be detained on site and released at a rate similar to that which previously existed. If an acceptable rate of runoff can be provided by enlarging an existing through structure, the County Engineer may so direct. The cost of this improvement shall be bore by the party responsible for the increase in runoff.
(2) In addition necessary precautions shall be taken to prevent an excess of silts and fines from entering the roadside drainage.
(B) Driveways and entrances.
(1) A determination of the necessity of placing culverts at all driveways and entrances shall be determined following site investigation by the County Highway Department. The Highway Department may consult with the County Engineer in making any determinations under this section. If following this investigation it is determined that the placement of a culvert is necessary due to drainage and other considerations set forth then the following specifications shall apply:
(a) The minimum length of culvert shall be 20 feet. Longer lengths may be required due to the nature of the site, drainage, storm water flow, and the nature of the driveway being constructed.
(b) Diameter of the culvert shall be specified by the Highway Department based upon consideration of the amount of storm water flow.
(c) Culverts shall be constructed of corrugated steel, aluminum pipe, concrete pipe, or plastic pipe (smooth interior only) with said materials being subject to approval of the Highway Department based upon consideration of the site, drainage, storm water flow, and the nature of the driveway being constructed.
(d) Minimum cover over the culvert shall be eight inches of aggregate or such additional amount as may be determined appropriate by the Highway Department in consideration of the nature of the site, drainage, storm water flow, and nature of the driveway being constructed.
(e) No headwalls or other obstructions over four inches in height shall be allowed on the county right-of-way. The culvert is to be installed at the centerline of the ditch.
(2) Temporary construction drives shall be graded lower than the pavement of any adjacent roadways so as not to permit water to pond on said roadway. Culvert installation in accordance with these specifications must be completed before a certificate of occupancy permit may be issued by the County Building Department. The Building Department shall conduct any final inspections regarding the specifications set forth in this section.
(C) New roadways.
(1) Certified design. All elements of storm drainage shall be designed by a certified professional. This includes all pipes, ditches, temporary or permanent storage basins, inlet sizes and spacing, as well as, any other drainage related feature. Design plans shall show all drainage elements with design calculations submitted at the time of plan submittal. Plans shall show drainage flow directions.
(2) Roadside swales. Roadside swales for new construction shall be constructed as shown in the typical section. Swales having a grade of 3% to 5% shall have a three-foot sod bottom. Swales having a slope in excess of 5% shall have a concrete gutter, constructed in accordance with the standard specifications. Riprap ditches may be allowed in lieu of concrete gutter if appropriately designed. Outlets of all drainage structures shall be protected from erosion by approved means.
(3) Large drainage structures. Culverts, bridges and other drainage structures larger than 60 inches in diameter shall require special approval as to design, location and construction.
(4) Edge drains. Pavements constructed on 3% or more grade or along side of a hill where finish grade is 15 feet or more below the surrounding hill side shall require four-inch edge drains. This shall be on both sides on steep grades and on the up-hill side only on hillsides. These shall be constructed in accordance with the standard specifications. See under drain detail.
(5) Cross culverts. All cross culverts shall extend from center to center of ditch and shall be sized according to a certified drainage plan. Connections of two or more sections of pipe shall be with a pre-manufactured banding device. Cross culverts shall require end sections.
(6) Materials. Storm drainage materials shall meet the requirements of the standard specifications.
(7) Erosion control. Precautions shall be taken during construction to prevent erosion as directed by the County Engineer. These shall include straw bales, silt basins, silt fence or other measures as required to prevent excess erosion from the right-of-way.
(BC Ord. 9-1997, passed 6-2-97)