SEDIMENT TRANSPORT PROCESSES IN A WEST-CENTRAL FLORIDA OPEN MARINE MARSH TIDAL CREEK - THE ROLE OF TIDES AND EXTRA-TROPICAL STORMS

The extensive open marine marshes on Florida's Gulf of Mexico coast co nstitute one of the largest continuous coastal marsh systems in the U. S.A. and are characterized by (1) the absence of an apparent modem or relict sediment supply, (2) a thin 1-2 m sediment veneer overlying hig hly karstified bedrock and (3) both low wave and low tidal energy regi mes. More importantly, the Florida open marine marsh system appears to be keeping pace with current rates of sea-level rise in spite of a li mited inorganic sediment supply and low tidal energies. Although the m agnitudes and directions of suspended solid transport and the processe s controlling these transports have been rigorously documented for oth er U.S.A. marsh systems, they have not been documented in the Florida marsh system. Total suspended solid (TSS) concentrations, current spee ds and water levels were monitored in Cedar Creek, Florida, so that th e TSS loads could be calculated and the processes exerting control ove r material exchange could be determined. Both TSS concentration and lo ad are modulated by spring/neap variations and time-velocity asymmetri es in the tidal currents. Concentrations at the creek mouth increase b y as much as two orders of magnitude during strong wind events due to the presence of waves; however, large net sediment loads appear to be related to the coupled effects of waves and large tidal prisms. Waves initially mobilize sediments in the adjacent embayment but increased t idal prisms, and the associated higher velocities, are requisite for t ransport of this material further into the creek. Large tidal prisms m ay be the result of astronomically high tides or meteorologically forc ed tides. In Cedar Creek, the most important meteorological events aff ecting sedimentary processes are extra-tropical storms. This is becaus e they occur at much higher frequencies than tropical storms and hurri canes, even though the latter are more potent and potentially could tr ansport greater amounts of material. This study identifies the importa nt processes controlling suspended solid transport in the broad expans es of Juncus roemerianus dominated marsh adjacent to the large arcuate embayments prevalent along the west-central Florida marsh coast as de scribed by Hine and Belknap (1988). The processes exerting control ove r sediment transport in the Cedar Creek drainage basin are similar to those documented in other marsh systems. (C) 1995 Academic Press Limit ed