RAPID: Collecting post-hurricane Helene sediment samples in the Congaree National Park, South Carolina, to constrain floodplain-wide deposition of sand and mud

Predicting sediment fate and transport over floodplains remains a challenge notwithstanding recent advances in the study of floodplain hydrology and sedimentation. This is in part associated with difficulties in modeling flow over complex topography, and in part due to the lack of a framework to quantify transport, erosion and deposition of sediment in the silt/clay range.

The most recent Congaree River flood caused by hurricane Helene between September 27th and October 5th, 2024, represents a unique opportunity to characterize floodplain sedimentation over the ~100 square kilometer forested floodplain of the Congaree National Park, SC, and link it to hydraulic characteristics of a major flood. Characterizing how the spatial distribution of floodplain deposits after a major flood may vary with hydraulic characteristics of main channel flow has direct applications to determine fluxes of fine sediment and nutrients for ecosystem management and develop fate and transport models for particles and contaminants.

This project will provide research opportunity to two early career principal investigators and will also provide training and mentorship for both undergraduate and graduate students.

The investigators will compile a dataset quantifying the spatial distribution of floodplain sedimentation rates and grain sizes after a major flood in a natural setting. The integration of floodplain sampling with data collected at U.S. Geological Survey gages will allow the team to identify links between floodplain sedimentation patterns and hydraulic characteristics of main channel flow.

In floodplain sedimentation models, flow hydraulics is generally simplified as a step function, that is, flow above and below bankfull, and sediment is described in terms of two grain sizes, bed material and wash load. It has been long recognized that floodplain sedimentation is not as simple, due to uneven development of natural levees, complex floodplain topography and a network of floodplain channels and connected depressions carrying water and sediment into the floodplain interior.

The field work in this project will provide critical evidence to constrain the role of floodplain channels in the dispersal of water, bed material (sand for the Congaree River) grain sizes, as well as and wash load (mud), at floodplain scale. This will help advance our understanding of floodplain hydrology and sedimentation.

This project is jointly funded by the Division of Earth Sciences and the Established Program to Stimulate Competitive Research (EPSCoR).

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.