Weddington Subdivision Flood Study & Culvert Design – WithersRavenel

Weddington Subdivision Flood Study & Culvert Design

About This Project

Located off Green Level West Road in Apex, Weddington Subdivision is transected along its southeast edge by an unnamed tributary to White Oak Creek. While White Oak Creek is a FEMA-studied stream with established base flood elevations (BFEs), the tributary had not been studied prior to development of the subdivision and therefore had no published floodplain or BFEs.

WithersRavenel completed a flood study that included the hydrologic and hydraulic analysis and modeling of the tributary, the approximately 330-acre drainage area associated with the development, and the backwater expected from flooding within White Oak Creek. The model was used to iteratively design a road crossing and associated culverts as well as a greenway crossing so as not to adversely impact the proposed lots or existing adjacent properties.

Due to the relatively wide and shallow nature of the tributary channel and overbanks, the road crossing consisted of a single culvert within the stream channel to provide aquatic passage and an aluminum box culvert in the overbanks. This allowed for the necessary utility relocations and minimized the stream impacts associated with the crossing while preventing the access road from overtopping in a 100-year storm event. The greenway trail crossing consisted of approximately 950 feet of boardwalk elevated above the BFE.

The flood study model was also used to determine that the proposed development would have no adverse impacts on the Green Level West Road crossing up-stream of the development or on the established BFEs for White Oak Creek.