§ 7.06.05. Stormwater management requirements.

A.

Performance standards. All development must be designed, constructed and maintained to meet the following performance standards:

1.

While development activity is underway and after it is completed, the characteristics of stormwater runoff shall approximate the rate, volume, quality, and timing of stormwater runoff that occurred under the site's natural unimproved or existing state, except that the first one inch or the total runoff of 2.5 times the percentage impervious, whichever is greater, of stormwater runoff shall be retained in an off-line dry or wet retention system or according to other best management practices.

2.

The proposed development and development activity shall not violate the water quality standards as set forth in chapter 17-3, Florida Administrative Code.

3.

All commercial or industrial development shall provide 0.5 inches of stormwater pretreatment in a dry retention area in addition to subsection 1, above.

4.

Dry retention and detention systems shall be designed with the wet season water table at least one foot below the bottom surface of the treatment area.

5.

Wet detention systems shall have water depths no more than ten feet, unless specifically accepted by the county engineer, and side slopes of 4:1 from proposed finished grade to two feet below the control elevation.

B.

Design standards, systemwide. To comply with the foregoing performance standards the proposed stormwater management system shall conform to the following design standards:

1.

Detention and retention systems shall be designed to comply with the appropriate standards set out in the South Florida Water Management District's Permit Information Manual, Volume IV, Management and Storage of Surface Waters.

2.

The proposed stormwater management system shall be designed to accommodate the stormwater that originates within the development and stormwater that flows onto or across the development from adjacent lands.

3.

The proposed stormwater management system shall be designed to function indefinitely if properly maintained and shall comply with subsections 7.06.06(A) and 7.06.06(B) of this Code.

4.

The design and construction of the proposed stormwater management system shall be certified as meeting the requirements of this Code by a professional engineer registered in the State of Florida.

5.

No surface water may be channelled or directed into a sanitary sewer.

6.

The proposed stormwater management system shall be compatible with the stormwater management facilities on surrounding properties or streets, taking into account the possibility that substandard systems may be improved in the future.

7.

The banks of detention and retention areas should be sloped to accommodate, and should be planted with appropriate vegetation.

8.

Natural surface waters shall not be used as sediment traps during or after development.

9.

For aesthetic reasons and to increase shoreline habitat, the shorelines of detention and retention areas shall be sinuous rather than straight.

10.

Water reuse and conservation shall, to the maximum extent practicable, be achieved by incorporating the stormwater management system into irrigation systems serving the development.

11.

Vegetated buffers of sufficient width to prevent erosion shall be retained or created along the shores, banks or edges of all natural or manmade surface waters.

12.

In phased developments the stormwater management system for each integrated stage of completion shall be capable of functioning independently as required by this Code.

13.

All detention and retention basins, except natural water bodies used for this purpose, shall be accessible for maintenance from streets or public rights-of-way.

14.

All drainage systems will provide best management practices (BMP) for water quality.

C.

Design standards, streets and swales.

1.

Valley curb. Valley curb shall be 24 inches wide with a minimum thickness of six inches at the center, with a three-inch rise to the back of the curb and one inch to the pavement edge, 3,000 psi concrete used throughout. Design to be submitted to the county engineer for approval.

2.

Curb and gutter. Curb shall be 12 inches deep, five-inch top width with a six-inch-deep, one-inch-wide reveal on the face. Gutter shall be six inches deep, 18 inches wide with a slope of one inch to one foot, 3,000 psi concrete used throughout. Design to be submitted to the county engineer for approval.

3.

Vertical curb. Vertical curb without gutters shall be six inches wide, 18 inches deep with six-inch curb above pavement, 3,000 psi concrete used throughout. Design to be submitted to the county engineer for approval.

4.

Culvert pipe. Culvert pipe shall be reinforced concrete pipe, asphalt coated corrugated metal pipe, aluminum pipe, or approved equivalent. Culvert pipe not subjected to wheel traffic loads may be of nonreinforced concrete, asphalt coated corrugated metal pipe or such aluminum pipe conforming to specifications of AASHTO.

5.

Headwalls. All culverts under roadways shall have headwalls made of reinforced concrete or concrete block with reinforcement, or other approved structures. Where shallow swale ditches intersect deeper drainage ditches, erosion control shall be provided by use of culvert pipes, concrete swales, sandbag riprap, headwalls with spillways, or other suitable means approved to by the county engineer.

a.

Sandbag riprap. The sandbag riprap mixture shall contain at least one part cement to five parts of clean sand. Construction methods shall comply with FDOT standards until such time as Okeechobee County adopts engineering specifications.

b.

The proposed design of reinforced concrete headwalls shall be submitted for approval of the county engineer.

c.

The proposed design of reinforced concrete block headwalls shall be submitted for approval of the county engineer.

6.

Manholes and junction boxes. All manholes or junction boxes shall be a minimum of four feet inside diameter at the base with straight walls or corbelled a maximum of four inches in one foot, with steps and suitable cover for access. All inverts are to be formed to a minimum of one-half the pipe diameter. Proposed designs shall be submitted for approval of the county engineer.

7.

Catchbasins. All catchbasins shall have a minimum inside area of ten square feet with straight walls and suitable access either through removable grates or manhole covers. Proposed designs shall be submitted for approval of the county engineer.

8.

Valley crossings in streets. Valley crossings in streets shall not be permitted.

9.

Underdrains.

a.

Underdrains for curb and gutter construction. Where road construction incorporates curbs and gutters, underdrains shall be installed if the bottom of the curb is less than 24 inches above the existing water table unless the lack of such underdrains is demonstrated to meet the standard specifications on subsurface drainage of the Okeechobee County department of engineering. The underdrains shall be 18 inches outside of the street line or curb and a minimum of 18 inches below the bottom of the base or curb with a slope to a positive outfall.

b.

Underdrains for roadside swale construction. Where road construction incorporates swale construction, underdrains shall be installed if the water table is less than 24 inches below the invert of the swale unless the lack of such underdrains is demonstrated to meet standard specifications on subsurface drainage of the Okeechobee County department of engineering.

c.

Underdrain specifications. Pipe used for underdrains shall have a minimum diameter of four inches. Suitable plastic, vitrified clay, bituminous fiber, concrete, asphalt coated metal, or other pipes approved by the county engineer. Underdrain pipe construction shall be suitable for the purpose and the rock, slag or other materials used for pipe beds shall be as approved by the county engineer.

10.

Swale ditches.

a.

Swale ditch geometry. Swale drainage will have a maximum side slope of one to four. The minimum shoulder width shall be five ft. on both sides. Ditches shall be located within the rights-of-way, except that provided a backslope of one to four has been allowed for in the right-of-way, a flatter backslope extending beyond the right-of-way may be permitted. Minimum bottom width of swale shall be one foot, minimum depth of swale shall be eight inches.

b.

The minimum road right-of-way where roadside swale drainage is to be employed may be computed by the following formula:

W = P + 2(8D + 1) + 2B

Where:

W	=	Right-of-way width in feet
P	=	Width of paving in feet
B	=	Width of shoulder (berm) in feet
D	=	Maximum depth of swale in feet

 

c.

Swale ditch erosion protection. Swale ditches shall be provided with permanent erosion protection. Such protection may be turf, using an approved type grass, or approved type of pavement liner may be utilized. When turf, using an approved type protection is used, the swale ditches shall be sodded, sprigged or seeded a lateral distance extending from within one foot of the road pavement to the top of the swale ditch backslope. Mulching in accordance with the Okeechobee County department of engineering standards shall be acceptable.

d.

Driveways across swale ditches. Driveways across swale ditches shall be constructed to conform to the swale profile.

e.

Swales for drainage in subdivisions shall have bottoms two feet above high water table.

(Ord. No. 94-8, § 1 (7.06.05), 10-5-94)