(A) Purpose. The storm water management regulations of this section shall protect, maintain and enhance the public health, safety, environment and general welfare by establishing minimum requirements and procedures to control the adverse effects of storm water runoff associated with new development. Proper management of storm water runoff will protect property, control stream channel erosion, prevent increased flooding associated with new development, protect floodplains, wetlands, water resources, riparian and aquatic ecosystems and otherwise provide for environmentally sound use of the town’s natural resources. These regulations create standards for post development levels of run off in addition to construction run off regulation that are governed by the Department of Environment and Natural Resources as part of the soil erosion control permit. All storm water best management practices planned, designed and implemented under the authority of this chapter shall conform to the standards adopted by NCDENR in the latest Storm Water Best Management Practices Manual. Access to this manual can be found at http://portal.ncdenr.org/web/lr/bmp-manual. Where contradiction exists between the manual and this chapter, the stricter of the two shall prevail.
(B) Definitions. For the purpose of this section, the following definitions shall apply unless the context clearly indicates or requires a different meaning.
APPLICANT. An owner or developer of a site who executes the storm water permit application.
BIO-RETENTION BASIN. The use of plants and soils for removal of pollutants from storm water runoff via adsorption, filtration, sedimentation, volatilization, ion exchange and biological decomposition. In addition, BIO-RETENTION provides landscaping and habitat enhancement benefits.
CONNECTION. Any ditch, pipe or other device for the diversion or transmission of storm drainage, which will in any way affect the operation or maintenance of the drainage ways.
CONVEYANCE. Any feature of the landscape or earth, human-made or natural, which carries water in a concentrated flow.
DETAIN. To store and slowly release storm water runoff following precipitation by means of a surface depression or tank and an outlet structure.
DEVELOPMENT. Any land disturbing activity which adds to or changes the amount of impervious or partially pervious cover on a land area or which otherwise decreases the infiltration of precipitation into the soil, other than a rebuilding activity that does not qualify as redevelopment.
DRAINAGE STRUCTURES. Shall include swales, channels, storm sewers, curb inlets, yard inlets, culverts and other structures designed or used to convey storm water.
DRY EXTEND DETENTION BASIN. A dry extended detention basin temporarily stores incoming storm water, trapping suspended pollutants and reducing the peak discharge from the site.
GRASSED SWALE. A water quality grassed swale is a shallow open-channel drainage way stabilized with grass or other herbaceous vegetation that is designed to filter pollution.
LAND DISTURBING ACTIVITY. Any use of, or operations on, the land by any person in residential, industrial, educational, institutional or commercial development, including road construction and maintenance, that results in a change in the natural cover or topography.
TEN-YEAR, 24-HOUR STORM. The surface runoff resulting from a 24-hour rainfall of an intensity expected to be equaled or exceeded, on average, once in ten years and with a duration of 24 hours.
RAIN GARDEN. A rain garden is a planted depression allows rain water runoff from impervious urban areas, like roofs, driveways, walkways, parking lots and compacted lawn areas, the opportunity to be absorbed.
RETAIN. To capture and hold storm water runoff following precipitation by means of surface depression allowing the water to infiltrate into the soil, thus reducing the hydrologic and pollution impacts downstream.
STORM WATER. Any surface flow, runoff and drainage consisting entirely of water from rainfall events.
STREAM. A watercourse that collects surface runoff, minor waterway leading to a river.
VELOCITY. The average velocity of flow through the cross-section of the main channel at the peak flow of the storm of interest.
WET DETENTION BASIN. A storm water management facility that includes a permanent pool of water for removing pollutants and additional capacity above the permanent pool for detaining storm water runoff.
(C) Applicability and exemptions.
(1) The storm water management regulations of this section apply to the following activities:
(a) All new commercial development or expansions of commercial/industrial development that create an additional 2,000 square feet of impervious surface.
(b) All major subdivisions and planned residential developments with land disturbance over one acre, that will require a soil and erosion control plan.
(2) The following activities will be exempt:
(a) Any development in which the owner has accrued a vested right prior to adoption of these regulations;
(b) Redevelopment or expansions on existing residential lots, if the increase in the additional impervious surface created is less than 3,000 square feet;
(c) Minor subdivisions and minor subdivisions for heirs;
(d) Single-family residential development when total land disturbance of less than one acre takes place;
(e) Agricultural and forestry activities as defined by general statutes; and
(f) Activities for which a permit is required under the Mining Act, being G.S. Ch. 74, Art. 7.
(D) Design standards.
(1) Design standards are established for the purpose of promoting sound development practices which respect, preserve and enhance the town’s watercourses and are not intended to prohibit the use of innovative and alternative techniques which can be demonstrated to have the potential for successfully achieving the objectives stated in division (A) above. All storm water best management practices planned, designed and implemented under the authority of this chapter shall conform to the standards adopted by NCDENR in the latest Storm Water Best Management Practices Manual. To access this manual: http://portal.ncdent.org/web/lr/bmp-manual. Where contradictions exist between the manual and this chapter, the town ordinance shall supersede the NCDENR document.
(2) The measures shall control and treat the difference in storm water runoff volume leaving the project site between the pre- and post-development conditions for, at a minimum, the ten-year, 24-hour storm.
(3) The design of drainage facilities in flood hazard areas shall be consistent with the requirements of Ch. 150 of this code of ordinances. No storm water controls shall be allowed within the floodway unless a no rise certification from a licensed engineer or a CLOMR and LOMR are obtained from FEMA.
(4) Runoff calculations shall be based on full potential development of the project to the extent allowed by the current zoning and subdivision regulations. A full set of design calculations, plans, hydrographs and other supporting documents shall be submitted to the town to demonstrate compliance with this chapter. The aforementioned plans must be sealed by a licensed North Carolina professional engineer.
(5) Storm water controls that drain in whole or part to designated trout waters as defined by the state’s Environmental Management Commission shall be designed and shall implement the best storm water management practices that do not result in a sustained increase in the receiving water temperature, while still meeting the other requirements of this chapter. It is the applicant and the engineer’s responsibility to demonstrate that this requirement can be met based on the proposed BMP and design.
(E) Design standards for water detention.
(1) This shall be accomplished under the guidelines as follows.
(a) Wet detention basins shall maintain a permanent pool of water, sufficiently deep to function as open waterbody.
(b) Ponds should be engineered to maximize the theoretical detention time and avoid flow short-circuiting. Basic considerations for the installation of detention basins are location, hydraulic inflow rate, hydraulic residence time, permanent pool size and maintenance.
(c) Design shall include mechanisms to:
1. Promote settling of suspended particulates;
2. Biological uptake of pollutants; and
3. Decomposition of pollutants and plant nutrients.
(d) Pond shape, depth and surrounding fringe areas must be considered to maximize effectiveness of basin.
(e) Marsh plants shall be included around this fringe area to help remove pollutants, provide habitat, hide debris and improve the look of an otherwise unsightly area.
(f) Dry extended detention basins provide fewer hazards to the public due to the absence of a permanent pools.
(g) Rain Gardens and grassy swales reduce run-off by allowing storm water to soak back into the ground with the use of natural plants that also absorb the water and hold it until it can be released slowly back into the ground.
(2) Maintenance of wet retention ponds should be minimal if designed correctly. However, non-organic debris shall be removed on a regular basis.
(3) Maintenance of any storm water measures will be overseen by a property owners association (or equivalent) if required as a part of a planned residential development approval. Failure to maintain storm water development systems may result in a violation of this chapter and will be subject to penalties as outlined in § 152.999 of this chapter.
(F) Notice of violation and penalty. Failure to design storm water development systems or maintain these systems may result in a violation of this chapter and will be subject to penalties as outlined in § 152.999 of this chapter.
(Ord. passed 3-14-2005; Ord. passed 5-14-2007; Ord. passed 7-14-2008; Ord. passed 4-12-2010; Ord. passed 10-10-2016; Ord. passed 3-14-2019, § 313)