§ 34-5. General standards for commercial, mixed-use and all non-single family or non-duplex residential development, including multifamily development.

(a)

Redevelopment of property with existing commercial use, mixed land uses or residential uses other than single-family or duplex residential uses does not require submission of a stormwater plan under the following circumstances:

(1)

The redevelopment is consistent with the zoning regulations of chapter 48 of this Code relating to redevelopment and nonconformities;

(2)

The redevelopment does not result in a net gain in built upon area;

(3)

The redevelopment does not include the importation of any fill material; or

(4)

The redevelopment includes a stormwater retrofit associated with flood mitigation property improvements which limits the importation of earthen fill material to no greater than 12 inches in depth.

(b)

All redevelopment of property with commercial uses, mixed land uses or residential uses other than single-family or duplex residential uses resulting in a net gain in built upon area requires submission of a stormwater plan showing that the stormwater runoff generated by the increase will be directed into an approved stormwater management system designed to accommodate 4.3 inches of rainfall and that any best management practices constructed for the additional runoff comply with the same commercial standards established in subsection (c), below.

(c)

All other development or redevelopment of property with commercial uses, mixed land uses or residential uses other than single-family or duplex residential uses requires submission of a stormwater plan showing that the development will meet or exceed the following standards:

(1)

All runoff from the project's built-upon area must be directed into an approved stormwater management system designed to accommodate the volume of runoff generated by a 4.3-inch design storm.

(2)

Infiltration systems shall provide a minimum of one foot of vertical clearance from the seasonal high water table and must be located in soils classified as sandy texture soils with a minimum infiltration rate of 0.52 inches per hour. Infiltration systems shall maintain a maximum retention time of five days for the 4.3-inch design storm.

(3)

Wet retention systems shall maintain a minimum retention time of 48 hours and a maximum retention time of five days for the 4.3-inch design storm.

(4)

Overflows and discharges from best management practices shall discharge to an established drainage outfall or drainage way which is maintained by a government entity or the subdivision homeowner's association or as approved by the town or other appropriate federal, state or local entity.

(5)

All required state and federal permits shall be acquired prior to the establishment of a discharge into a drainage way. In no instance shall the system discharge to adjoining private property without the written consent of the adjoining property owner, establishment of appropriate easements, and filing of maintenance agreements with the town.

(6)

Fill shall not be permitted to exceed base flood elevation except in cases where it is placed directly beneath a slab that is designed to meet the regulatory flood protection elevation as defined in town Code section 22-32. In these instances, fill may exceed the base flood elevation by up to 12 inches to support a turn-down or thickened edge slab or beneath a slab that is supported by a ring-wall style foundation. Fill placed above the base flood elevation shall not extend beyond the outside edge of the slab. In areas in which there is no base flood, fill shall not exceed the amount required for wastewater permits required by the Dare County Health Department, or two feet above pre-development surface elevation, whichever is higher.

In no case shall fill be placed or a lot be graded such that off-site drainage patterns are altered to direct stormwater runoff onto another property unless part of an approved plan with appropriate agreements or easements.

(7)

Copies of operations and maintenance agreements must be filed with the town prior to the issuance of the certificate of compliance.

(8)

During construction, to prevent adverse effects onto adjoining properties or rights-of-way, temporary and/or permanent runoff control measures shall be installed after placement of fill. This can be achieved via implementation of:

a.

Installation of earthen diversion berms along the periphery of the property, or

b.

Installation of permanent stormwater control measures which shall be maintained and kept operational for the duration of construction, or

c.

Other approved methods of erosion and stormwater control measures.

(9)

On-site permanent runoff control measures shall be installed, in conjunction with other on-site stormwater management practices, to intercept rainfall runoff from driveways that are sloped or graded towards the street or right-of-way. On-site permanent runoff control practices include, but are not limited to, slotted drains, driveway speed bumps or other approved methods of diverting, collecting and managing on-site runoff.

(d)

Allowance for partial, temporary retention of stormwater within parking lots on all commercial sites:

(1)

Up to 20 percent of a site's parking area may retain runoff up to 48 hours after a 4.3-inch rainfall event, so long as:

a.

Handicap parking shall not be affected.

b.

Drive aisles, fire lanes, loading zones, ingress and egress facilities, traffic ways, pedestrian ways and other site access features shall not be affected.

c.

No impacts of stormwater shall be allowed to entities other than parking spaces and stormwater BMPs.

(e)

Allowance for stormwater control and conveyance facilities built by others on town rights-of-way or on adjacent or town owned properties upon approval of the board of commissioners.

(1)

If as part of development or redevelopment there is an opportunity to improve, mitigate or correct a drainage problem caused by stormwater runoff from the site under review, the board of commissioners may approve stormwater management improvements outside of the subject property boundary if:

a.

An encroachment agreement and/or easement is put in place to allow for construction and use of the stormwater management improvements; and

b.

A maintenance agreement is filed with the town establishing maintenance responsibilities and enforcement methods.

(Ord. No. 15-06-016 , Pt. I, 6-3-2015; Ord. No. 15-10-035 , Pt. I, 10-7-2015; Ord. No. 17-12-020 , Pt. I, 12-6-2017)