MORPHODYNAMICS AND HYDRODYNAMICS OF TWO INTERACTIVE TIDAL INLETS, NEW PASS AND BIG SARASOTA PASS, FLORIDA

The closely spaced and interactive Big Sarasota Pass and New Pass play a crucial role in the densely populated oceanfront community of Sarasota County, Florida. New Pass has a short and straight channel with minimal offset, whereas Big Sarasota Pass is characteristic of a long and curved channel with large offset. Both inlets are stabilized by seawalls along the south side preventing further migration due to the net southward longshore sediment transport. No jetties were constructed at the entrances of these mixed-energy tidal inlets with large and dynamic ebb-tidal deltas. This study examines the interactions of the two inlets and the relationship between tide and wave conditions and the sedimentation/erosion patterns in the vicinity of the inlets. Morphodynamic characteristics were determined through analysis of time series aerial photos since 1943. Detailed tidal flow patterns across the two inlets were measured simultaneously over a 2-month period, using two H-ADCP current meters. In addition, vertical current profiles were measured with a ship-mounted ADCP to study the bottom boundary layer and its relation to sediment grain size and bedforms. The flow patterns are also simulated using CMS-2D, a 2-D depth-averaged circulation model. Based on meteorological data, representative wave events were modeled using STWAVE, a steady state, spectral wave model. The relationship between the morphologic characteristics and the measured and computed hydrodynamic conditions was examined. Both New Pass and Big Sarasota Pass have large and active ebb tidal deltas with substantial southward sand bypassing along the terminal lobe. The bypassing is strongly influenced by the passage of cold fronts. The pathways for sand leaving the updrift beach include both offshore bar and nearshore zone. The downdrift attachment took the form of onshore migration of complex swash bars. Another contributing factor to morphologic change in the system is the addition of sediment to the system due to frequent beach nourishments.