Manakin-Sabot, VA: James River Wetland Mitigation Landbank, Manakin-Sabot, Virginia
Project involved converting a cultivated section of farmland into a 150-acre wetland mitigation landbank. The site bordered to the south by the James River and to the west by Genito Creek, lies within the floodplain of the James River. Converting the site into a wetland required extensive earthwork and grading of the entire 150 acres of land. In total, approximately 150,000 cubic yards of soil were moved to create ponds, channels and uplands. Common phasing of the project included topsoil stripping, relocation of silty/clayey loam material, and in a few designated areas, over excavation and removal of sandy soils, followed by topsoil replacement. The sandy soil, as well as any extra silty/clayey loam material requiring relocation, was placed along the banks of the James River and Genito Creek creating an area known as the riparian buffer. The buffer is several feet higher than the inner wetland region and was designed to control water inflow/outflow for the site. The final phasing of the project included stream restoration and seeding. Twelve water control structures were also installed at specific locations along the streams to control discharge from pond regions.
Equipment used to perform the soil excavation and relocation included self-loading pans, as well as excavators and trucks. Due to moist weather conditions most of the fine grading work was performed using (six-way blade) bulldozers.
Grading was controlled by using several types of grade lasers, including both flat and dual slope lasers. Targets were attached to the equipment and set to grade for each varying region. Extensive QA/QC was performed throughout the project using conventional survey equipment, such as a total station transit, to layout perimeters of ponds and uplands as well as for grade verification and data collection. Grading tolerances, as stated in the specifications, were within +/- 0.1 ft.
Challenges included an extremely tight construction schedule, inclement weather conditions and a major flood event. The project was completed on time and on budget.