§ 6.06.104. Storm drains.

1.

Design frequency: Storm drains shall be designed to convey flow with a ten-year design frequency.

2.

Hydrologic analysis: The rational method shall be used for hydrologic calculations relating to storm drains. A minimum time of concentration of ten minutes shall be used.

3.

Hydraulic analysis: Hydraulic calculations shall be based on open channel and pressure flow as appropriate.

a.

All storm drain designs incorporating curb inlets shall demonstrate that the hydraulic grade line remains below the theoretical gutter elevation.

b.

Temporary ponding or overload will be permitted for ditch bottom inlets provided the entire ponded area is contained within the drainage or right-of-way easements and land values are not affected.

c.

Friction losses and minor energy losses such as entrance, exit, junction, expansion and contraction losses shall be considered.

4.

Pipe slopes: To avoid the accumulation of debris and lower maintenance requirements, the minimum physical pipe slope shall be that which will produce a velocity of 2.5 ft./s applying Manning's Equation to the pipe flowing full. An exception may be made, at the discretion of the county engineer, for equalizer pipes.

5.

Spacing of curb inlets: Maximum spacing for curb inlets shall be based on the width of spread. Width of spread shall not exceed one-half of the travel lane adjacent to the gutter for a rainfall of four inches per hour. If spread computations permit, the maximum spacing for inlets shall be 500 feet.

6.

Placement of inlets: Inlets shall be placed at all low points in the gutter grade, and as appropriate at intersections, median breaks, and on side streets where drainage could adversely affect the safety of vehicular or pedestrian movements within the roadway intersection.

7.

Gutter grade: The minimum allowable gutter grade shall be 0.3 percent.

8.

Maintenance access: The maximum length of pipe allowed without a maintenance access structure such as a manhole or inlet is 500 feet.

9.

Minimum pipe cover: Unless otherwise approved, minimum pipe cover shall be 18 inches measured from the outside top of pipe to the top of the roadway base at any point in the roadway cross-section.

10.

Minimum pipe size: The minimum allowable pipe diameter for storm drains shall be 18 inches or the equivalent section for arch or elliptical pipe, unless otherwise approved by the county.

11.

Materials: Accepted materials for piping and structures are those included on the approved FDOT materials list. Piping within public right-of-way shall be reinforced concrete unless approved otherwise by the county engineer.

(Ord. No. 11-01, § 2, 1-18-11)