§ 72-779. Performance, review and design standards.

(a)

Performance standards.

(1)

For applications for a lesser or a standard development, the following performance standards shall be followed in the design of the project:

a.

Stormwater runoff shall be subjected to best management practice prior to discharge into natural or artificial drainage systems. "Best management practice" shall mean a practice or combination of practices determined by the DRC to be the most effective, practical means of preventing or reducing the amount of pollution generated by the project to a level compatible with Florida water quality standards found in chapter 17-3, Florida Administrative Code.

b.

1.
No site alteration shall cause siltation of wetlands, pollution of downstream wetlands or reduce the natural retention or filtering capabilities of wetlands.

2.

No site alteration shall allow water to become a health hazard or contribute to the production of mosquitoes.

3.

All site alteration activities shall provide for such water retention and settling structures and flow attenuation devices as may be necessary to insure that the foregoing standards and requirements are met.

c.

Design of water retention or detention structures and flow attenuation devices shall be subject to the approval of the CDE pursuant to the standards hereof. Detention structures shall be designed to release runoff to the downstream drainage system over a period of time so as not to exceed the capacity of the existing downstream system. Under no case shall open retention areas (ponds, etc.) have side slopes steeper than four horizontal to one vertical (4:1) to a depth of two feet of water at seasonal low pond elevation, at which point the side slope may be increased to two horizontal to one vertical (2:1). Retaining walls may be utilized to accommodate field conditions.

In order to maintain good water quality in stormwater management detention ponds and maximize the provision of fish and wildlife habitat, stormwater management systems with permanently wet detention ponds should be designed, operated and maintained so as to resemble a natural pond to the greatest extent practical. A natural pond design should include: A littoral zone comprised of native emergent and submersed aquatic macrophytic vegetation; a deep open water limnetic zone free of rooted emergent and submersed vegetation; and, where feasible, an upland buffer of native trees, shrubs and under story vegetation in accordance with St. John's River Water Management District requirements.

d.

A positive drainage system shall be provided which will not adversely impact downstream owners or adjacent lands.

e.

Where possible, natural vegetation shall be used as a component of the drainage system. The water table should not be manipulated so as to endanger natural vegetation beneficial to water quality unless natural vegetation can be replanted and survive with a lowered water table condition.

f.

Runoff from higher adjacent lands shall be considered and provisions for conveyance of such runoff shall be included in the drainage plan.

g.

Runoff shall be treated to remove oil and floatable solids before discharge from the site in a manner approved by the CDE.

h.

Erosion by wind or water shall be prevented by the developer throughout the construction process.

i.

Direct discharge to class II waters is prohibited. A workable filter system must be provided prior to any discharge to class II waters.

j.

For the purpose of this division, it is presumed that the lowering of the water table for the purpose of constructing detention/retention basins and for the purpose of permanently protecting road construction does not conflict with the stated objectives of this article if all of the following are met:

1.

The development site is not in an area known to the county, based on data collected and interpreted by the U.S. Geological Survey, the St. Johns River Water Management District, the county and other professional investigators, as important to recharge or to prevention of discharge of the Florida aquifer.

2.

The proposed lowering of the water table shall be over no more than 15 percent of the site to a depth of five feet below the surface of the existing undisturbed ground, or an equivalent volume, said area to be measured at the overflow elevation of the retention area(s).

3.

If ditches, underdrains or similar devices are used to lower the water table, the lateral volumetric effect will be calculated, and the volume will be deducted from that allowed for retention areas.

4.

The high-water table may be lowered up to two feet below the undisturbed ground in the vicinity of roads for the purpose of protecting the subbase and base of the roadway and/or for the purpose of preventing mosquito production in the roadside swales.

5.

The lowering of the water table has no adverse affect on wetlands as defined herein.

6.

The lowering of the water table does not increase flows to the detriment of neighboring lands.

(2)

For applications for a lesser development, the following additional performance standards shall be followed in the design of the project:

a.

The minimum volume of retention to be provided shall be equivalent to one-half inch of depth over the entire project area. For certain soil conditions or groundwater table conditions which do not permit the percolation of this volume within the five days following a storm event, the county engineer may approve detention with filtration systems in lieu of retention.

(3)

For application for a standard development, the following additional performance standards shall be followed in the design of the project:

a.

[ Retention standards. ] The discharge hydrograph produced for the developed or redeveloped site shall not exceed, in terms of peak flow and total volume, the hydrograph produced by conditions existing before any development occurred on-site for a 24-hour, 25-year frequency storm, unless the intent of this recharge provision will be met through detention of the difference between said volumes, in which case said volume difference may be released over not less than a 24-hour, nor greater than a 72-hour period of time. However, the design standards for wet retention areas, when approved by the CDE shall prevail. This requirement may be waived by the CDE for sites consisting predominately of poorly drained soils having permanently and naturally impaired recharge potentials. In addition, the cumulative impact of the outflow hydrograph on downstream flow shall be considered. Runoff rates and volumes resulting from the project, in excess of existing amounts, shall be accommodated on-site. Off-site retention may be permitted if, in the opinion of the CDE, the recharge requirements of this division are met.

b.

Runoff computations. Runoff computations shall be based on the most critical situation (rainfall duration, distribution and antecedent soil moisture condition) and conform to acceptable engineering practices using rainfall data and other local information applicable to the affected area.

c.

Closed basins : The discharge hydrograph produced for the developed or redeveloped site shall not exceed, in terms of peak flow and total volume, the hydrograph produced by conditions existing before any development occurred on site for a 24-hour, 100-year frequency storm.

(b)

Review standards. The CDE in reviewing and/or approving the application shall consider, where appropriate, the following minimum standards:

(1)

The characteristics and limitations of the soil at the proposed site with respect to percolation and infiltration;

(2)

The existing topography of the sites and the extent of topographical changes after development;

(3)

The existing vegetation of the site, the extent of vegetational changes after development and the threat posed to vegetation endangered or indigenous to wetlands;

(4)

The plans and specifications of structures or devices the applicant intends to employ for on-site stormwater retention/detention with filtration, erosion control and flow attenuation;

(5)

The effect the proposed stormwater management system will have upon mosquito breeding habitat;

(6)

The adequacy of easements for drainage systems in terms of both runoff conveyance and maintenance;

(7)

The method of handling upland flow which presently discharges through the site;

(8)

The effectiveness of wind and water erosion control measures during construction;

(9)

Standards and requirements of any other governmental jurisdiction;

(10)

The maintenance entity responsible for upkeep of the system upon its completion;

(11)

The continuity of phased projects; phased projects will require the submission of an overall plan for the applicant's total land holdings;

(12)

The existing hydrologic cycle of the proposed site and the impact of the proposed alterations on the existing hydrologic cycle;

(13)

The impact the proposed project will have on the natural recharge capabilities of the site; and

(14)

The impact the proposed project will have on downstream water quantity and quality and specifically the potential for downstream flooding conditions.

(c)

Design standards.

(1)

Open swales, ditches or other waterways shall require complete engineering data showing the adequacy of design and the effect within the particular drainage area to the satisfaction of the CDE. The cost of designing and installing drainage systems shall be borne by the developer.

(2)

Pipe shall be either class 3 reinforced concrete with patented rubber gasketed joints, fully asphalt-coated corrugated steel pipe of appropriate highway gauge, ADS, PVC, elliptical concrete pipe or other type approved by the CDE. Subject to acceptable soil and groundwater conditions, corrugated aluminum pipe may be considered, provided the minimum cover from top of pipe to the top of subgrade at any point under a roadway shall be equal to the diameter of the pipe, but, in no case, less than 24 inches. In all other locations, the minimum cover shall be equal to the diameter of the pipe, and shall depend upon location and type of pipe.

(3)

Sizes of drainage culverts, ditch sizes and inlet spacings shall be derived from computations required and shall be submitted to the CDE for approval.

(4)

In cases where there is a prevalence of soils that exhibit adverse water table characteristics, underdrains and/or fill or other acceptable alternative that will provide necessary measures to maintain the structural integrity of the road will be required. The determination of need shall be made by reference to applicable portions of the most recent edition of the Soil Survey and Supplement for Volusia County, Florida, as prepared by the U.S. Department of Agriculture, Natural Resource Conservation Services, or whatever subsequent authoritative soil survey may be published for Volusia County after adoption of these regulations, or according to information generated by developers.

(Ord. No. 90-4, § VI, 1-18-90; Ord. No. 96-32, §§ LXIV—LXVI, 12-19-96; Ord. No. 2006-02, § II, 2-2-06; Ord. No. 2008-25, § III, 12-4-08)