Intertidal Marsh Suspended Sediment Transport Processes, Terrebonne Bay, Louisiana, U.S.A.

Abstract

This study examines the transport processes of suspended sediment from a tidal creek/bayou onto its adjacent salt marsh in a shallow estuary with negligible freshwater inflow near Terrebonne Bay, Louisiana. Water depth, flow velocity, water temperature and salinity in a tidal bayou, and wind speed and direction nearby were measured. Water samples were collected from the bayou bank to the marsh interior at eight locations 8.5 meters apart over a tidal cycle during normal spring tides. Total suspended sediment and inorganic sediment concentrations were analyzed in the laboratory. Results from statistical methods showed that, under the normal tidal inundations, sediment concentrations decreased from bayou bank to marsh interior during flood tides. During ebb tides, sediment concentrations varied less significantly and only slightly with the distance from the bayou bank and were lower than those during flood tides. These results indicate that marsh surface sedimentation is still an active process in marshes of south Louisiana. During strong southerly winds, inorganic suspended sediment concentrations in the bayou were much higher than those in the marsh. During partial inundation and strong northerly winds, inorganic sediments in the marsh were higher than those in the bayou. This suggests that recently deposited sediment on the marsh may occasionally be resuspended and eroded. However, our computations of flow friction velocity and bottom shear stress showed that tidal currents alone in the marsh were insufficient to resuspend the deposited sediment.