(A) The requirement for runoff volume match serves to control and treat the runoff volume generated from the built-upon area, and helps to maintain the predevelopment hydrology of the project site. Within the Coastal Counties, the definition of runoff volume match depends upon the project location:
(1) For projects that drain to SA waters, runoff volume match means the annual runoff volume after development shall not be more than 5% higher than the annual runoff before development.
(2) For projects that drain to other Coastal County waters, runoff volume match means the annual runoff volume after development shall not be more than 10% higher than the annual runoff before development.
(B) Within the Coastal Counties, the design storm used to determine the runoff volume also depends upon the project location:
(1) For projects that drain to SA waters, the design storm is the one-year, 24-hour storm.
(2) For projects that drain to other Coastal County waters, the design storm depth is 1.5 inches.
(C) Projects meeting the definition of runoff volume match do not need to further address nutrient export or treatment.
(D) All projects shall meet the stormwater system minimum design requirements set forth in 15A NCAC 02H.1003. All engineered stormwater controls will meet the standards set in the Design Manual and the State's Minimum Design Criteria, 15A NCAC 02H.1050 through .1062.
(E) All project designs shall incorporate vegetated setbacks, dispersed flow, vegetated conveyances and curb outlet systems.
(F) High-density projects shall be designed to control and treat the volume of runoff generated from all built-upon area in one or more Primary SCMs, using the appropriate design storm based on the project location and receiving water. High- density projects that drain to SA waters are subject to more stringent standards as indicated in the Design Manual.
(G) Low-density projects are not required to be equipped with engineered stormwater controls in exchange for limiting the built-upon area, maximizing dispersed flow and ensuring that stormwater conveyances are vegetated.
(Ord. 23-O-07, passed 4-10-2023)