Monitoring Processes and the Fate of a Sediment Mound at the Cape Fear River USACE Field Research Facility
CHL


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Engineering & Science Partners
Experimental Mixed-Sediment Mound
Monitoring Program, Cape Fear, NC
US Army Corps of Engineers,   Engineer Research and Development Center,
Coastal & Hydraulics Laboratory,   Dredging Operations and Environmental Research
Description
The US Army Corps of Engineers (USACE), Engineer Research and Development Center (ERDC), Coastal and Hydraulics Laboratory (CHL), Dredging Operations and Environmental Research (DOER) program has constructed a mixed-sediment mound at the Offshore Dredge Material Disposal Site (ODMDS) approximately four miles (7 Km) south of the mouth of the Cape Fear River, North Carolina. The objectives of the DOER Mound study include the following:
  1. Document the fate of the mound, particularly the erodability of the mixed sediment composition
  2. Investigate the generation of turbidity associated with the mound
  3. Document sediment characteristics over the long term
Purpose
Beneficial use of dredged material is a priority for the USACE. Placement of dredged material as nearshore berms could provide for shorline stability and greatly reduce the cost of transporting the material much further offshore. Some questions remain, however, prior to implementation of nearshore mounds when mixed sediments are being dredged. Do the fines actually winnow out as has been hypothesized, leaving beach quality sediment that will move onshore? Are there turbidity levels associated with the presence of the mound that can have adverse effects on fish or habitat?
Program Benefits
This study is important to ERDC CHL for model development and dredging operations implimentation. Models are being developed that can predict the fate of nearshore mounds. Improved accuracy and calibration of these models necessitates an understanding of the processes and associated response of the sediments. The value of this project is considered very high and consistent with operational-research initiatives of the USACE. To achieve the study objectives, the USACE Field Research Facility (FRF) has been asked to help design the study and implement the field-monitoring program.

Monitoring Tasks

  1. Fixed instrument installations on the mound to measure sediment transport parameters
  2. Directional wave spectra and vertical current profile measurements inshore, offshore, and on the mound.
  3. Repetitive high-resolution bathymetric and sub-bottom surveys
  4. Concentration validation to determine size distribution of materials in water