Implementing Diverse Bank Stabilization Measures To Contain and Capture Lead-Contaminated Sediment

Three bank sites were stabilized on a small river using weirs, longitudinal peaked stone toe protection (LPSTP), and rootwad revetment. These stabilization features prevent additional erosion, but also help capture suspended sediment. A creek outlet within the project area was also relocated to a more natural orientation that allows for the efficient transfer of sediment into and through the river.

The Southeast Missouri Lead District was the world leader in lead production for nearly 100 years, until the early 1970’s. Mining operations introduced gravel, sand, and silt-sized waste material into the Big River. This waste is periodically transported downstream by elevated flows, and most affected areas are now encompassed by a U.S. Environmental Protection Agency (USEPA) superfund site. U.S. Army Corps of Engineers (USACE) entered into a cost-share agreement with USEPA to design and construct a series of bank stabilization features in a highly erosive reach. These features will prevent additional erosion of legacy mine waste sediment that has deposited onto the floodplain during elevated flows for over 100 years.

The overall site design was informed by depth, velocity, and shear outputs from a 2D HEC-RAS model of the reach.

The creek outlet relocation involved reorienting the creek into a former creek channel that was serving as a high flow outlet, and constructing a small, reinforced earthen dam in the existing main creek channel. The upstream bank in the river is protected using longitudinal peaked stone toe protection (LPSTP) that is offset from the eroding bank by a significant distance. The edge of the LPSTP functions to reposition the main channel thalweg into a more efficient and natural planform geometry. The area between the LPSTP and the eroding bank has tie-backs to form depositional zones. The middle bank of the river is protected using traditional weirs. A small section of LPSTP on the downstream edge of this bank maintains the river’s transition into the downstream bank. The downstream bank is protected using a combination of riprap and rootwad revetment, tied into a low constructed floodway. All four of the areas on this site had unique challenges ranging from philosophical to geometric in nature. As constructed, all four of the areas are providing valuable lessons that both affirm and challenge some of the design assumptions. After a few substantial floods, monitoring efforts have identified a few areas that need improvement and will be addressed through adaptive management, including:

a bank segment that is being eroded by overtopping flow, which if allowed to continue could negatively impact overall site function, a stabilization feature that is scalloping unexpectedly, which if allowed to continue could result in failure of the whole feature, and a designed depositional area that is net erosional.