This project stabilized two sections of the stream channel within the Hammond Hills residential area on Fort Bragg, North Carolina. The stream channel was stabilized in 2009 and 2010 using natural design methodologies, but since that time, the two sections of the stream channel have eroded resulting in concerns about the hydraulic characteristics of the stream channel and stability of the stream banks and associated features.
Project Site #1 is located north of Bastogne Drive and west of Viking Court where a 72-inch diameter culvert collects storm water runoff from Bastogne Drive and discharges storm water at the head of the armored Hammond Hills urban storm water channel. The stream channel downstream of the culvert was armored with concrete bags and large rip rap to prevent erosion and to a large extent, the existing erosion control measures were functioning properly. However, during larger storm events, the runoff flows have created a storm surge pool at the pipe outlet, at the base of the concrete end wall, and erosion of the stream banks downstream. In addition to creating erosion in the stream channel and along the stream banks, this overflow has resulted in some erosion beneath and atop the culvert end wall leading to concerns about the stability of this structure.
Project Site #2 is approximately 1,300 feet from downstream from Project Site #1 along the natural channel and flows through a structure under Viking Court. Most of this stream channel appears to be stable and not eroded. At Project Site #2, the stream course had been redirected by recent storm water flows, resulting in dislocation of previously installed erosion control stone and large log vanes. The log vanes were installed as an erosion control device by others several years ago. The dislocation of these measures has resulted in severe erosion of the north stream bank and minor erosion of the south bank at the same location. This erosion is affecting the structural stability of the stream bank and has resulted in both failure of portions of the bank and deposition of eroded soil downstream of the primary failure location.
The scope of work was to design repairs to the stream channel and banks at both project sites. At Project Site #1 we armored and stabilized the culvert headwall, created an armored plunge pool at the culvert outfall, and armored the stream channel and banks immediately downstream of the culvert outfall with gabion baskets, rip rap, or similar materials. At Project Site #2, we reshaped the eroded stream bank and install hardened structures using gabion baskets to stabilize the storm water channel. Also, the existing wood log vane was removed and a boulder vane installed in its place. In addition to the armoring, vegetation was re-established along portions of the re-constructed stream banks.