(A) The purpose of this chapter is to:
(1) Mitigate damage to property caused by flooding;
(2) Reduce pollutants and ecological hazards;
(3) Reduce existing and future maintenance of, and capital expenditures for, stormwater drainage systems;
(4) Cooperate in the coordination of related goals expressed by state and federal regulations and that require certain actions with regard to but not limited to stormwater management, soil erosion and sedimentation control and floodplain management;
(5) Guide growth in an orderly manner consistent with the Kill Devil Hills Land Use Plan; and
(6) Encourage nonconforming sites to comply as much as practicable when a change of use or alteration occurs.
(B) All commercial development (new or substantial improvements) and one or two-family dwellings greater than 6,000 square feet lot coverage (new or substantial improvements) shall provide a comprehensive plan for the proper drainage of all surface water to systems on and off the property in question. The design criteria as stated in the following divisions or that as may be specified by state or federal agencies, whichever is the most restrictive, will be used. Every reasonable effort will be made to retain a maximum of the runoff on site to the extent feasible and practical. The Stormwater Management Plan shall be certified by a North Carolina registered design professional for compliance to requirements of this section.
(C) All surface water drainage into the site being developed or generated on said site must be accommodated in accordance with these guidelines. All surface water drainage leaving the site shall be channeled to points of approved discharge, including but not limited to, a natural or man-made watercourse, a lake, pond, ditch, stormwater drainage system, or other appropriate and approved points of discharge. Filling of a natural or man-made watercourse, lake, pond, ditch, stormwater drainage system is hereby permitted if it meets the following requirement: A plan must be submitted to the town sealed by North Carolina Licensed Engineer demonstrating that such project will not diminish the town's ability to manage stormwater.
(D) No surface water shall be channeled or directed into a sanitary sewer or septic tank system. Distances between open ditches and septic tank systems must be specified on the plans and approved by the Dare County Sanitarian. This approval must be obtained by the developer prior to approval of the drainage system by the town.
(E) For management and control of stormwater runoff, techniques such as but not limited to retention, detention and infiltration systems will be used.
(F) The drainage design criteria for open and closed drainage systems shall conform to generally accepted stormwater engineering practices.
(G) Development plans shall show the flow direction of stormwater on and off the property; size, slope, invert and rim elevations of system components; and ditch cross sections in the vicinity of the development and/or to a distance as is necessary to evaluate the impact of runoff to existing surface water drainage systems.
(H) Drainage calculation, drainage area maps, flood routing calculations, infiltration calculations, storm sewer back water curve calculations and other information that may be required from time to time shall accompany or be a part of site plans submitted.
(I) Estimated runoff calculations may be computed by the Rational Method (Q=CIA) (see below) or other approved methodologies. Sizing of structures will be based on the Manning Equation. Culverts shall be evaluated for inlet and outlet control as necessary.
(1) Q means flow in cubic feet per second.
(2) C means runoff coefficient.
(3) I means rainfall intensity in inches per hour.
(4) A means drainage area in acres.
(J) Systems shall be designed to retain, as a minimum, runoff expected from a ten-year, two-hour storm (4.3 inches of rainfall). There may be some situations which would warrant a different requirement due to the size of the system. The design engineer will contact the town planning staff in the preliminary design stages to determine if a change is warranted.
(K) A modified rational method hydrograph procedure may be used in sizing retention and detention systems for sites up to one acre in size. For sites greater than one acre, a runoff hydrograph shall be computed using the tabular method as defined in the most recent edition of SCS TR-55 or other accepted engineering analysis.
(L) All underground storm sewers, open drainage ways and related structures shall be constructed to the applicable provisions of the most recent edition of Roadway Standard Drawings and Standard Specifications for Road and Structures produced by the North Carolina Department of Transportation.
(M) During the construction, preparation, arrangement and installation of improvements and facilities in developments, the developer shall maintain each stream, creek, ditch or channel contiguous to or located within the subdivision in an unobstructed state and shall remove from such watercourses and the banks of the watercourses all debris, logs, timber and other accumulations that would, in time of flood, clog or dam the passage of waters in their downstream course. Installation of appropriately sized conduits, culverts, bridges or other required structures shall not be constructed in a way which will obstruct the flow of drainage.
(N) During the development of a site, the person conducting the land-disturbing activity shall install and maintain all temporary and permanent erosion and sedimentation control measures as required by the approved plan or any provision of this chapter, the Act or any order adopted pursuant to this chapter or the Act. After site development, the landowner or person in possession or control of the land shall install and/or maintain all necessary permanent erosion and sedimentation control measures, except those measures installed within a road or street right-of-way or easement accepted for maintenance by a governmental agency.
(O) Whenever the town determines that significant sedimentation is occurring as a result of land-disturbing activity, despite application and maintenance of protective practices, the person conducting the land-disturbing activity will be required to and shall take additional protective action.
(P) In all cases, including one- and two-family dwellings, the developer shall be required to provide culvert pipes, swales, any improvements in the adjoining right-of-way and other related drainage improvements as required by the Public Services Department. Such improvements must be in place and inspected for compliance and completion by the Public Services Department before a Certificate of Occupancy is issued.
(Q) Stormwater management maintenance. To ensure the proper operation, the owner shall be responsible for the operation and maintenance of all required stormwater management features:
(1) All features of the approved stormwater management plan must be regularly maintained and repaired as necessary in order for the system to function as originally designed and shall comply with the criteria of the North Carolina Division of Water Quality Stormwater Design Manual (current edition).
(Ord. 91-08, passed 11-18-91; Am. Ord. 01-02, passed 2-28-01; Am. Ord. 02-08, passed 6-10-02; Am. Ord. 14-09, passed 5-12-14; Am. Ord. 17-9, passed 9-11-19; Am. Ord. 18-4, passed 6-14-21)