§ 50-131. Stormwater management measures (mandatory).

(a)

Stormwater management measures may include both structural and nonstructural elements. Natural swales and other natural runoff conduits shall be retained where practicable.

(1)

Structural stormwater controls. All structural stormwater management facilities shall be selected and designed using the appropriate criteria from the Georgia Stormwater Management Manual. All structural stormwater controls must be designed appropriately to meet their intended function. For other structural stormwater controls not included in the Georgia Stormwater Management Manual, or for which pollutant removal rates have not been provided, the effectiveness and pollutant removal of the structural control must be documented through prior studies, literature reviews, or other means and receive approval from the manager before being included in the design of a stormwater management system. In addition, if hydrologic or topographic conditions, or land use activities warrant greater control than that provided by the minimum control requirements, the manager may impose additional requirements deemed necessary to protect upstream and downstream properties and aquatic resources from damage due to increased volume, frequency, and rate of stormwater runoff or increased nonpoint source pollution loads created on the site in question.

Applicants shall consult the Georgia Stormwater Management Manual for guidance on the factors that determine site design feasibility when selecting and locating a structural stormwater control. All stormwater management measures shall be designed in accordance with the Georgia Stormwater Management Manual.

(2)

Stormwater credits for nonstructural measures. The use of one or more site design measures by the applicant may allow for a reduction in the water quality treatment volume required under subsection 50-132(a) and further specified in the Georgia Stormwater Management Manual. The applicant may, if approved by the manager, take credit for the use of stormwater better site design practices and reduce the water quality volume requirement. For each potential credit, there is a minimum set of criteria and requirements which identify the conditions or circumstances under which the credit may be applied. The site design practices that qualify for this credit and the criteria and procedures for applying and calculating the credits are included in the Georgia Stormwater Management Manual.

(3)

Drainage system guidelines. Stormwater conveyance facilities, which may include but are not limited to culverts, stormwater drainage pipes, catch basins, drop inlets, junction boxes, headwalls, gutter, swales, channels, ditches, and energy dissipaters shall be provided when necessary for the protection of public right-of-way and private properties adjoining project sites and/or public right-of-ways. Stormwater conveyance facilities that are designed to carry runoff from more than one parcel, existing or proposed, shall meet the following requirements:

a.

Methods to calculate stormwater flows shall be in accordance with the manual;

b.

All culverts, pipe systems and open channel flow systems shall be sized in accordance with the stormwater management plan using the methods included in the manual; and,

c.

Design and construction of stormwater conveyance facilities shall be in accordance with the criteria and specifications found in the manual.

(4)

Dam design guidelines. Any land disturbing activity that involves a site which proposes a dam shall comply with the Georgia Safe Dams Act and Rules for Dam Safety as applicable and with the county development standards and specifications as applicable. No residential lots shall be platted on a dam. No house or other habitable structure shall be permitted on a dam. If an existing house on a dam predating this ordinance becomes substantially damaged, it shall not be permitted for reconstruction on the dam.

(5)

Donation or dedication of property for water quantity and water quality purposes. The donation or dedication of land (floodplain or non-floodplain) for stormwater quantity or quality requirements may be accommodated by administrative variance, if so requested by the owner. Any required setbacks or minimum lot sizes affected by the donation or dedication of land (floodplain or non-floodplain) for stormwater quantity or quality requirements may be administratively varied. The owner shall make the request to the director of the community development agency and the request shall be processed in accordance with section 134-35, except that the variance may equal up to 100 percent of the existing requirements. The use of administrative variances for the donation or dedication of property for water quantity and water quality purposes shall not allow for an increase development density above that permitted by the underlying zoning. Any administrative variance for the donation or dedication of property for water quantity and water quality purposes shall be reported to the district commissioner.

(b)

All stormwater management measures shall be designed in accordance with the manual.

(Ord. of 9-28-93; Code 1977, § 3-22.5A-16; Ord. of 4-13-04; Ord. of 1-24-06; Ord. of 2-27-07)