News - Knob Hill Drive, Clemmons, NC Stream Restoration Project
Constricted outlet before construction
February 28, 2012 – JEWELL Engineering Consultants recently completed the stream restoration on an empty residential lot in the Village of Clemmons. A hydraulic and hydrologic review was performed by JEWELL and it was determined that the existing culvert under Knob Hill Drive did not have adequate capacity in this established residential area. In order to modify the culvert in the future, the discharge outlet would need to be capable of handling the discharge. The existing 66-inch RCP flowing under Knob Hill Drive discharges to an open lot where the drainage channel had been modified such that the normal flow from the pipe could not flow without overtopping the property both upstream and downstream of Knob Hill Drive. The Village decided to provide an environmentally improved solution while solving the drainage insufficiencies.
JEWELL developed a stream restoration plan for the site. The plan included removing 2 sections of 66-inch RCP, designing a stilling basin to receive discharge from the 66-inch RCP, removing miscellaneous disconnected 48-inch RCP sections in the lot and adding a new meandering stream channel with vegetation to tie into an existing channel at the downstream property line. Grading was used to create the stream channel and provide a flood plain for high flows. Both 401 and 404 permits from NC DENR DWQ and USACE were obtained before construction commenced.
Completed project with headwall and natural channel
Construction began with the installation of a temporary pump around system and diversion channel for the continuous flow discharging from the existing 66-inch RCP outlet. Once the RCP outlet was modified, the stilling/dissipater basin excavation began and a substantial amount of rock was encountered. Much of it was removed off-site and some was retained for creating in-stream structures. The stream channel alignment was excavated, rock structures were installed and coir matting was placed on the stream banks. Excavation was delayed due to excessive precipitation, but the stream was finished in mid-summer except for planting of tree and brush vegetation. The headwall was constructed of segmental blocks. This would provide a pleasing headwall wingwall view for the neighbors, but also allow portions of the wall to be disassembled and reassembled later with the addition of future culverts to provide the required capacity for the 25-year precipitation event.