§ 6.06.101. Retention and detention facility design features.

In addition to the quantity and quality criteria established by this ordinance, stormwater ponds shall be designed, constructed and maintained in accordance with the following design features:

1.

Detention and retention areas shall meet all criteria established by FDEP relating to the design, construction and maintenance of stormwater management facilities, including but not limited to guidelines for littoral shelf, permanent pool, and recovery of treatment volume.

2.

Detention and retention areas shall be designed, where possible, so that shorelines are sinuous rather than straight and so that the length of shoreline is maximized, thus providing aesthetic benefits and offering more space for the growth of littoral vegetation.

3.

The banks of detention and retention areas shall slope at a grade of 3:1 or flatter to the bottom of a dry facility or to a depth of three feet below the normal water level of a wet facility. No slope for berms or swales shall be constructed steeper than 3:1.

4.

In residential areas, a perimeter fence with a minimum height of six feet shall be provided around all retention and detention areas with side slopes steeper than 3:1 or on any retention or detention area with a depth greater than four feet measured from the top of berm to the bottom of the area. Gates for maintenance access shall be placed in locations accessible to maintenance vehicles.

5.

In single-family detached residential developments with densities of four or more units per acre, retention/detention areas should be located adjacent to roadways for easy access and maintenance and not be situated behind backyards.

6.

When retention and detention areas are not accessible directly from the road right-of-way, a 20-foot access easement shall be provided.

7.

Retention and detention areas shall be designed with access for maintenance located within the boundaries of the facility and adjacent to the top of bank. The access way shall have a minimum width of 15 feet, maximum cross slope of 8:1, and provide access around the facility. Commercial, condominium, and apartment projects shall demonstrate adequate access at the inside top of bank for maintenance.

8.

Retention/detention areas should not back-up into parking areas in order to meet stormwater storage requirements.

9.

Specific cross-sections of each swale and each retention area shall be provided on the drainage plans. The cross-sections shall show top and bottom widths, top and bottom elevations, side slopes, and water table elevation (seasonal high) at the location of cross-section.

10.

Corners of ponds shall be rounded and increase in diameter consistent with the side slope ratio starting with a minimum radius of three feet at the toe of the slope.

11.

Retention and detention areas shall be constructed with freeboard above the maximum design stage at a minimum depth equal to 20 percent of the depth required to retain or detain the critical design storm event. The maximum depth of freeboard required shall not exceed one-foot of freeboard above the maximum design stage. For the purpose of this design requirement, freeboard shall be defined as available storage volume above the maximum design stage and below the top of the stormwater area berm.

12.

Retention and detention areas that incorporate an earthen berm constructed above natural ground shall provide a minimum berm top width of 30 inches with an associated maximum berm height of two feet. Berms designed to be taller shall increase at a ratio no less than 30 inches horizontal to two-foot vertical.

13.

Slopes that do not meet the minimum standards provided in this section shall be protected by fences or other barriers in conformity with the Florida Building Code.

14.

Retention and detention areas shall be designed such that no individual lot lines cross the facilities.

15.

A minimum setback of five feet shall be provided between top of bank of retention/detention areas and property lines, fences, and building structures.

16.

All swales and retention/detention area side slopes shall be sodded.

17.

Stormwater collection systems (excluding backyard collection systems) and cross drains shall be designed with pipe of 18-inch minimum diameter.

18.

Connections to stormwater facilities (inlets, structures, piping, and basins) shall only include elements intended for stormwater treatment or conveyance. Any connection or discharge to a stormwater system that is illicit shall be prohibited.

(Ord. No. 11-01, § 2, 1-18-11)