All storm drainage installation and systems shall comply with the requirements of this Article.
A. Drainage Required. An adequate drainage system, including necessary ditches, pipes, culverts, drains, inlets, bridges, etc., shall be provided for the proper drainage of all surface water.
B. Stormwater Management Plan.
- Plan Required. All persons proposing development or construction in the city shall prepare a stormwater management plan.
- Approval Required. No final subdivision plat shall be approved and no development or building permit shall be issued until and unless the stormwater management site plan has been reviewed and approved by the Engineering Director, except as exempt below.
- The stormwater management standards listed below are required for any new development and/or redevelopment site that meets one or more of the following criteria:
- New development that creates, or adds 5,000 square feet or greater of impervious surface, or that involves land disturbing of 5,000 square feet or greater or,
- Redevelopment that creates, replaces or adds 5,000 square feet or greater of new impervious surface, or that involves land disturbing activity of one acre or more, including projects less than one acre if they are part of a larger common plan of development or sale, or,
- Any commercial or industrial new development or redevelopment, regardless of size, with a SIC or NAICS that requires coverage under the State of Georgia's NPDES Industrial Stormwater Discharge Permitting Program, or a hotspot use as defined below.
- Redevelopment sites that involve land disturbing of 5,000 square feet or greater, but less than one acre.
- For the purposes of engineering calculations, replacement of impervious surface shall assume that the site's predevelopment state is "pasture in good condition" or equivalent.
- These standards will be required of all land disturbing plan applications initially received after January 1, 2016.
- For sites that meet one or more of the above criteria, the permittee shall ensure that the following minimum standards are incorporated into the site plan:
- Stormwater Runoff Quality/Pollutant Reduction. Stormwater runoff shall be adequately treated prior to discharge. The stormwater management system shall be designed to remove at least 80 percent of the average annual post-development total suspended solids (TSS) load or equivalent as defined in the Georgia Stormwater Management Manual. Compliance with this performance standard is presumed to be met if the stormwater management system is sized to capture and treat the water quality volume, which is defined as the runoff volume resulting from the first 1.2 inches of rainfall from a site.
- Stream Channel/Aquatic Resource Protection. Steam Channel and/or Aquatic Resource Protection shall be provided by using the following approaches: 1) 24-hour extended detention storage of the 1-year, 24-hour return frequency storm event; 2) erosion prevention measures such as energy dissipation and velocity control; and 3) preservation of the applicable stream buffer.
- Overbank Flood Protection. Downstream Overbank Flood Protection shall be provided by controlling the post-development peak discharge rate to the predevelopment rate for the 25-year, 24-hour storm event.
- Extreme Flood Protection. Extreme Flood Protection shall be provided by controlling the 100-year, 24-hour storm event such that flooding is not exacerbated.
D. Definitions. The following terms have special meaning as used in this Article:
- New development is defined as land disturbing activities, structural development (construction, installation or expansion of a building or other structure), and/or creation of impervious surfaces on a previously undeveloped site.
- Redevelopment is defined as structural development (construction, installation or expansion of a building or other structure), creation or addition of impervious surfaces, replacement of impervious surface not part of routine maintenance, and land disturbing activities associated with structural or impervious development. Redevelopment does not include such activities as exterior remodeling.
- A hotspot is defined as a land use or activity on a site that produces higher concentrations of trace metals, hydrocarbons or other priority pollutants than are normally found in urban stormwater runoff. Examples of hotspots include gas stations, vehicle service and maintenance areas, salvage yards, material storage sites, garbage transfer facilities, and commercial parking lots with high-intensity use.
E. Exemptions. The following development activities are exempt from the minimum stormwater management standards:
- Individual single-family residential lots. (Single-family lots that are part of a subdivision or phased development project are not exempt from the minimum standards); and
- Additions or modifications to existing single-family structures.
F. Additional Requirements.
- New development or redevelopment in critical or sensitive areas, namely watersheds that contribute to Columbus's drinking water source, Lake Oliver, or watersheds listed on the most current 303(d) Impaired Waters list, published by the Georgia Environmental Protection Division, may be subject to additional performance and or regulatory criteria. Furthermore, these sites may be required to utilize or restrict certain structural controls in order to protect a special resource or address certain water quality or drainage problems identified for a drainage area/watershed.
- This requirement for additional Best Management Practices (BMPs) or restriction of the use of certain BMPs will be at the discretion of the Director of Engineering or his/her designee on a case-by-case basis.