Pilot Bank

DURATION: September 2009 - November 2009

STATUS: completed

RIVERBANK LOCATION: Immediately downstream of the former DuPont Waynesboro plant on the east riverbank across from Constitution Park and upstream of Rockfish Run

RIVERBANK LENGTH: 500 feet

ESTIMATED MERCURY INPUT FROM ERODING BANKS: 7.3%

OUTCOME:

Since it was constructed, the Pilot Bank has withstood high river flows during large storms. The trees on the bank have matured and provide a buffer between the river and floodplain. On the slope of the bank, the coconut mesh fabric has degraded as designed, and the woody shrubs and grasses have taken root and provide strength and stability.

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The Science Team constructed the Pilot Bank to test whether riverbank stabilization is effective in reducing the amount of mercury-impacted soil that enters the river and enhancing the aquatic habitat and riparian zone, which is the interface between the land and the river.

The Department of Game and Inland Fisheries provided input on the design of the Pilot Bank, which was constructed in seven basic steps:

Clear the vegetation to prepare the area for construction. At the Pilot Bank, a lot of the vegetation that was removed consisted of non-native plants or bushes and trees that were too large to be supported by the riverbank.
Create a coffer dam of sand bags in the river to protect the work area and isolate the construction area from the main flow of the river.
Place rocks at the base of the bank to buffer the shear stresses of the river and protect the riverbank from eroding in the future.
Place tree logs in the rocks for fish habitat.
Install coconut mesh, fabric-encapsulated soil tiers on the riverbank slope.
Seed the tiers with grasses, and plant native, woody shrubs like elderberry and willow.
Plant native trees like sycamore, red maple, hackberry, and sumac on top of the riverbank.

To test if the stabilization was effective, the Science Team measured mercury levels in water and river sediment and aquatic organisms before and after construction. The results were positive and provided the support to continue bank stabilization activities at other locations.

Monitoring Data

Mercury concentrations in sediment, pore water, and Asiatic clam samples collected along the Pilot Bank have steadily declined following the completion of the project in 2009. In fact, inorganic mercury concentrations in pore water have decreased by more than 90% in this time.