Bird-Long Island Management Study Phase 1B: Hydrodynamic Characterizations for Bird/Long Island

Bird-Long Island, located between two channels in the Savannah River, contains cultural resources that are threatened by erosion. This study characterizes the hydrodynamics in the vicinity of the island with field measurements including velocity profiles of the river, long-term current wave profiling measured with Aquadopp current profilers, and short-term water level time series. Numerical simulations are performed using the Coupled-Ocean-Atmosphere-Wave-Sediment Transport (COAWST) model system for the Savannah estuary. The Aquadopp deployments record waves and currents in the Main Channel, the larger and deeper shipping channel north of the island, and the South Channel, the shallower channel south of the island. All data show a significant and consistent response to large vessel traffic. Measured vessel wake reaches up to 2.01 m height in the Main Channel and 0.32 m height in the South Channel. Wake propagates into the South Channel from both ends of the island such that the southwestern shore of Bird-Long Island is impacted by similar waves twice for each vessel passage. An energy contribution analysis is performed to estimate the relative significance to potential shoreline impacts of tidal currents, wind waves, and mid-band frequencies. A water level threshold is applied to isolate energy contributions to periods of time when the eroding scarp is vulnerable to hydrodynamic processes. At the Main Channel site, the percentage energy contributions of tidal currents, wind waves, and mid-band frequencies are 6%, 26%, and 68%, respectively. At the South Channel site, the percentage energy contributions of tidal currents, wind waves, and mid-band frequencies are 38%, < 1%, and 61%, respectively. The mid-band energy is mainly produced by large vessel wake and the seiching it induces. Thus, large vessels are the main source of energy; however, tidal currents have a significant role in the South Channel, and wind waves have a role in the Main Channel.

Language

  • English

Media Info

  • Media Type: Digital/other
  • Edition: Final Report
  • Features: Figures; Photos; References; Tables;
  • Pagination: 115p

Subject/Index Terms

Filing Info

  • Accession Number: 01704428
  • Record Type: Publication
  • Report/Paper Numbers: FHWA-GA-19-1634, Report No. 16-34
  • Contract Numbers: PI# 0015304
  • Files: NTL, TRIS, ATRI, USDOT, STATEDOT
  • Created Date: Apr 19 2019 12:07PM