In order to mitigate the impacts associated with the Main Post Infrastructure Project, TMG’s joint venture entity, AKHI Construction, was engaged to provide stream restoration activities along ~1,260 LF of a perennial stream channel located upstream from Pohick Road and downstream of the outfall of an existing 4 foot by 4.5-foot culvert. The overall project, totaling 1,410 LF of stream restoration, utilized natural channel design (NCD) techniques to develop a stable channel cross section, longitudinal profile and planform geometry for a degraded stream channel.
Mother Nature made the first phases of the restoration nearly impossible to complete. The streambed itself was to serve as the access road, but with spring rains that seemed to have no end, seepage from ground water actually exceeded the normal flow conditions of the stream, making traversing the bed almost totally unmanageable. Finally, work was able to get underway. Restoration activities along approximately 220 LF of two, nearby intermittent stream channels were also covered by this task order. In preparation for these activities, approximately 170 LF of existing 12-inch ductile iron pipe (DIP) was removed and replaced with new, Class 53 DIP. Running around the clock, an intricate system of pumps facilitated the installation of the pipe by stemming the constant flow of water coming from the bank, surface runoff, and the stream itself. Once complete, the waterline service was tied back in.
Ancillary work included the demolition and removal of existing drainage culverts (two 48” RCP) located within the existing perennial channel at Pohick Road; the excavation of a 30 LF, three-foot deep swale at Old Pohick Road, including the creation of a six-foot high imbricated stone wall embedded with downstream soil; removal of a log cribbing structure and placement of another imbricated rock system; the replacement of unsuitable streambed material with reinforced bedding material; sloughing and removal of unsuitable embankment material and replacement with Class 2 riprap and filter fabric; and significant streamside/riparian buffer planting. In addition, hardwood trees, hewn on-site, were cut to length and used throughout the length of the streambed as in-stream habitat logs.