§ 26-166. General requirements.

(a)

Adequate drainage and control of stormwater are an integral and important part of any development. Proper drainage planning shall be considered an essential element of any stormwater concept plan or stormwater management plan submitted to the county. The design and construction of a site shall also follow the rules and regulations found in article XXXIV of Z.R.F.C. and section 26-39 of this Code.

(b)

At the time of the initial submittal to the county with an application for a preliminary plat, every sub-divider or developer shall, at his/her sole expense, be required to submit to the stormwater management section of the department of public works, a stormwater concept plan for review and approval. At the time of the site visit, it shall be determined if drainage studies and reports, design computations, and such other information need to be required to ensure that stormwater originating both from the proposed subdivision or development and lands lying upgradient will be adequately drained and controlled in order to approve the stormwater concept plan. The stormwater concept plan shall be a preliminary drawing of the proposed location of storage facilities, stormwater discharge path of detention/retention pond(s), other downstream and upstream constraints and other matters with potential stormwater implications. Such plans and supplementary information shall be consistent with the requirements of this article, the Z.R.F.C., and the Comprehensive Stormwater Management Design and Criteria Manual.

(c)

Upon approval of the stormwater concept plan and prior to the issuance of any building or land disturbance permits, the subdivider shall, at his/her sole expense, prepare and submit for review and approval by the development services department a stormwater management plan. The stormwater management plan shall detail how post-development stormwater runoff will be controlled or managed and how the proposed project will meet the requirements of this article, including the performance criteria set forth below. This plan shall be in accordance with the criteria established in this section and be prepared under the direct supervisory control of either a registered professional engineer or a registered landscape architect licensed in the State of Georgia. Subsections (3), (4), (5) and (6) shall be prepared under the direct supervisory control of a registered professional engineer, who shall seal and sign the work. Portions of the overall plan may be prepared and stamped by a registered land surveyor licensed in the State of Georgia as appropriate, such as boundary surveys, contour maps, erosion and sedimentation control plans. The stormwater management plan must ensure that the requirements and criteria in this article are being complied with and that opportunities are being taken to minimize adverse post-development stormwater runoff impacts from the development. The plan shall consist of maps, narrative, and supporting design calculations (hydrologic and hydraulic) for the proposed stormwater management system. The plan shall include all of the information required in the stormwater management site plan checklist found in the stormwater design and criteria manual. This includes:

(1)

Common address and legal description of site.

(2)

Vicinity map.

(3)

Existing conditions hydrologic analysis. The existing condition hydrologic analysis for stormwater runoff rates, volumes, and velocities, which shall include: a topographic map of existing site conditions with the drainage basin boundaries indicated; acreage, soil types and land cover of areas for each subbasin affected by the project; all perennial and intermittent streams and other surface water features; all existing stormwater conveyances and structural control facilities; direction of flow and exits from the site; analysis of runoff provided by off-site areas upstream of the project site; and methodologies, assumptions, site parameters and supporting design calculations used in analyzing the existing conditions site hydrology. For redevelopment sites, predevelopment conditions shall be modeled using the established guidelines for the portion of the site undergoing land development activities.

(4)

Post-development hydrologic analysis. The post-development hydrologic analysis for stormwater runoff rates, volumes, and velocities, which shall include: a topographic map of developed site conditions with the post-development drainage basin boundaries indicated; total area of post-development impervious surfaces and other land cover areas for each subbasin affected by the project; calculations for determining the runoff volumes that need to be addressed for each subbasin for the development project to meet the post-development stormwater management performance criteria in section 26-173; location and boundaries of proposed natural feature protection and conservation areas; documentation and calculations for any applicable site design credits that are being utilized; methodologies, assumptions, site parameters and supporting design calculations used in analyzing the existing conditions site hydrology. If the land development activity on a redevelopment site constitutes more than 50 percent of the site area for the entire site, then the performance criteria in Section 26-173 must be met for the stormwater runoff from the entire site.

(5)

Stormwater management system. The description, scaled drawings and design calculations for the proposed post-development stormwater management system, which shall include: a map and/or drawing or sketch of the stormwater management facilities, including the location of non-structural site design features and the placement of existing and proposed structural stormwater controls, including design water surface elevations, storage volumes available from zero to maximum head, location of inlet and outlets, location of bypass and discharge systems, and all orifice/restrictor sizes; a narrative describing how the selected structural stormwater controls will be appropriate and effective; cross-section and profile drawings and design details for each of the structural stormwater controls in the system, including supporting calculations to show that the facility is designed according to the applicable design criteria; a hydrologic and hydraulic analysis of the stormwater management system for all applicable design storms (including stage-storage or outlet rating curves, and inflow and outflow hydrographs); documentation and supporting calculations to show that the stormwater management system adequately meets the post-development stormwater management performance criteria in section 26-173; drawings, design calculations, elevations and hydraulic grade lines for all existing and proposed stormwater conveyance elements including stormwater drains, pipes, culverts, catch basins, channels, swales and areas of overland flow; and where applicable, a narrative describing how the stormwater management system corresponds with any watershed protection plans and/or local greenspace protection plan.

(6)

Post-development downstream analysis. A downstream peak flow analysis which includes the assumptions, results and supporting calculations to show safe passage of post-development design flows downstream. The analysis of downstream conditions in the report shall address each and every point or area along the project site's boundaries at which runoff will exit the property. The analysis shall focus on the portion of the drainage channel or watercourse immediately downstream from the project. This area shall extend downstream from the project to a point in the drainage basin where the project area is 10 percent of the total basin area. In calculating runoff volumes and discharge rates, consideration may need to be given to any planned future upstream land use changes. The analysis shall be in accordance with the stormwater design manual.

(7)

Construction-phase erosion and sedimentation control plan. An erosion and sedimentation control plan in accordance with the Georgia Erosion and Sedimentation Control Act (or reference to the local erosion and sedimentation control ordinance) or NPDES permit for construction activities. The plan shall also include information on the sequence/phasing of construction and temporary stabilization measures and temporary structures that will be converted into permanent stormwater controls.

(8)

Landscaping and open space plan. A detailed landscaping and vegetation plan describing the woody and herbaceous vegetation that will be used within and adjacent to stormwater management facilities and practices. The landscaping plan must also include: the arrangement of planted areas, natural and greenspace areas and other landscaped features on the site plan; information necessary to construct the landscaping elements shown on the plan drawings; descriptions and standards for the methods, materials and vegetation that are to be used in the construction; density of plantings; descriptions of the stabilization and management techniques used to establish vegetation; and a description of who will be responsible for ongoing maintenance of vegetation for the stormwater management facility and what practices will be employed to ensure that adequate vegetative cover is preserved.

(9)

Operations and maintenance plan. Detailed description of ongoing operations and maintenance procedures for stormwater management facilities and practices to ensure their continued function as designed and constructed or preserved. These plans will identify the parts or components of a stormwater management facility or practice that need to be regularly or periodically inspected and maintained, and the equipment and skills or training necessary. The plan shall include an inspection and maintenance schedule, maintenance tasks, responsible parties for maintenance, funding, access and safety issues. Provisions for the periodic review and evaluation of the effectiveness of the maintenance program and the need for revisions or additional maintenance procedures shall be included in the plan.

(10)

Maintenance access easements. The applicant must ensure access from public right-of-way to stormwater management facilities and practices requiring regular maintenance at the site for the purpose of inspection and repair by securing all the maintenance access easements needed on a permanent basis. Such access shall be sufficient for all necessary equipment for maintenance activities. Upon final inspection and approval, a plat or document indicating that such easements exist shall be recorded and shall remain in effect even with the transfer of title of the property.

(11)

Inspection and maintenance agreements. The applicant must execute an easement and an inspection and maintenance agreement binding on all subsequent owners of land served by an on-site stormwater management facility or practice.

(12)

Evidence of acquisition of applicable local and non-local permits. The applicant shall certify and provide documentation to the county that all other applicable environmental permits have been acquired for the site prior to approval of the stormwater management plan.

(d)

The stormwater management plan shall conform to the stormwater concept plan for said development. Such plans and supplementary information shall be consistent with the requirements of this article, the Z.R.F.C., and the Comprehensive Stormwater Management Design and Criteria Manual.

(e)

A developer and his/her professionals should discharge the drainage from their site into a storm conveyance system that is publicly owned and maintained. Every subdivider shall provide, at no cost to the county, an easement up to a maximum width as is necessary to accommodate drainage from a 100-year storm for the purpose of constructing and maintaining the drainage system for the transmission, through the sub-divider's property, of all stormwater generated upstream from the subdivision. Notwithstanding this requirement, any natural drainageway which traverses any sub-divider's property or adjacent properties, shall not be encroached upon or altered so as to render the same less suitable to accept and transport stormwater that has historically flowed through such drainageway. Should a subdivider fail to obtain an off-site easement for the purpose of drainage conveyance, then the design discharge at the outlet facilities of the subdivision shall be limited to the pre-developed conditions for all storm events, including the discharges and velocities, whichever is more restrictive shall apply.

(f)

Site visit. Prior to the submittal of a land disturbance permit, or in connection to the stormwater concept plan, the developer/engineer must contact the department of public works stormwater management section to arrange an onsite evaluation visit. By way of example and not limitation, the visit should include an evaluation of the location of storage facilities, stormwater discharge path of detention/retention ponds, other downstream and upstream constraints and other matters with potential stormwater implications.

(g)

It shall be the responsibility of the developer to demonstrate that the development and/or stormwater conveyance facilities will not cause a violation of local, state, and federal laws or regulations to occur at the time of the application for a land disturbance permit. Evidence that the applicant has complied with requirements to obtain other state and federal permits which may be applicable, such as, but not limited to wetlands (404) permit, NPDES permit, and Metropolitan River Protection Act, must also be supplied to the county as part of the stormwater management plan and study.

(h)

It shall be the responsibility of the developer/engineer to accurately depict the conditions of the site, both onsite and off-site, on the plans submitted to the county that are affected by this article. Any modifications, changes, or construction that occur to the plans or in the field, as a result of having to conform to the county's Storm Drainage Criteria Manual or other criteria found in this article, and the cost to rectify shall be borne entirely by the developer.

(95-0093, art. II, § A, 3-15-95; Ord. No. 08-0194, 2-20-08)