Target Completion Date: December 31, 2025 Environment, Planning, and Economics
In-stream construction activities involve the use of temporary enclosures that exclude water from the construction site. Cofferdams are one of the most common methods used by VDOT to enclose an area for the purpose of pumping out water and allowing work to be conducted in the dry. Properly designed cofferdams are effective at keeping sediment out of the adjacent waterbody during construction. The construction and removal of cofferdams, however, create some degree of sediment release as a result of unavoidable streambed disruptions. Some of VDOT’s in-stream construction activities take place in areas that may contain suitable habitat for freshwater mussel species, many of which are listed as state or federally threatened or endangered. To reduce potential impacts to mussels, VDOT and regulatory agencies coordinate with regard to area of impact determinations and associated stream surveys requirements. However, agencies lack the empirical data on which these decisions are based. This study will include evaluating stream data collected at in-stream construction sites for the purpose of informing decisions associated with protecting sensitive species. Specifically, turbidity and suspended sediment data will be collected at defined distances upstream and downstream of project sites before, during, and following cofferdam construction and removal. The findings from this research will provide a better understanding of the intensity, duration, and transport distances of sediment associated with the construction and removal of cofferdams and may result in refined distance requirements for habitat assessments and surveys. Study outcomes may also lead to a reduced frequency of consultations with regulatory agencies, thereby saving VDOT staff time and costs associated with coordination and survey work.
Last updated: December 10, 2023