Fluvial Morphology and Bedform Migration in the Ebb Tidal Dominated Duplin River, Georgia

Abstract:

The Duplin River is an ebb-domintated, salt marsh drainage system west of Sapelo Island, Georgia. With no riverine input, flow in the Duplin is dependent on local surface run off, groundwater discharge and tidal flushing. Repeat multibeam bathymetry surveys within this system provide insight into sediment transport, current dynamics, and the migration of bottom features. Examination of bathymetric changes and the rate of bedform migration can be used to help estimate net sediment transport in fluvial and tidal systems. The swath bathymetry data presented here were collected during December 2009, March 2013, and June 2013 (high and low tide) aboard a small survey vessel, using a pole-mounted Kongsberg EM3002d multibeam bathymetry system. Along-stream profiles from bathymetry data collected during a single spring tidal cycle show little bedform migration, while the more temporally distant profiles record significant shifts in both small (cm-scale) and large (m-scale) bedform position, as well as changes in the morphology of large erosional scour depressions. Previous work has suggested the larger bedforms, which maintain an ebb-oriented geometry through both ebb and flood tide, are indicative of sediment transport rates that are an order of magnitude greater during the ebb tide (Zarillo, 1985). The new data suggest punctuated events, such as storm surges, may also play an important role in the fluvial transport, although more analysis is needed to determine how sediment storage changes in the Duplin river system over multiple tidal cycles. Integration of topographic LiDAR data, vegetation patterns, sediment composition, groundwater inputs and planform river morphology will also provide insight into sediment storage and transport within the system.