MORPHODYNAMICS OF NEW PASS AND BIG SARASOTA PASS, WEST-CENTRAL FLORIDA, USA

The West-central Florida coastline has 29 barrier islands, 30 tidal inlets, and the most diverse morphology of any barrier system in the world. New Pass and Big Sarasota Pass are situated along this microtidal, low-wave energy coast. The two closely spaced inlets carry a large tidal prism, on the order of 10 million cubic meters each. New Pass inlet has a mixed-energy straight morphology and Big Sarasota Pass has a mixed-energy offset morphology. The objectives of this study are to examine 1) the various factors controlling the morphodynamics of the two inlets, 2) interaction between the inlets and the adjacent beaches, and 3) morphodynamic response of the inlets and the adjacent beach to anthropogenic modifications. Time-series aerial photographs from 1943 to 2006 are digitized and compared. Tidal flow patterns through both inlets were measured using side-looking acoustic Doppler current profilers (H-ADCP).

The sediment bypassing at New Pass can be explained by a modified ebb tidal delta breaching model with the breaching initiated by frequent channel dredging. The sediment bypassing at Big Sarasota Pass is different from that at New Pass, in that it is transported across the entire shallow ebb tidal delta with minor interruptions. This particular morphology has been maintained by natural processes over at least the last 65 years. The shoreline in the vicinity of both inlets fluctuates as much as 200 m in a time scale of only few years. The shoreline fluctuation is controlled by both wave and tide forcing in addition to artificial supply from beach nourishment. The shoreline at the updrift side of New Pass is relatively stable. At the downdrift side the shoreline position fluctuates dramatically depending upon the exact location and timing of the attachment. This is controlled by the timing of the dredging and the timing of the collapse of the downdrift side of the ebb tidal delta. The shoreline in the vicinity of Big Sarasota Pass is substantially influenced by the frequent Lido Key beach nourishment. A considerable portion is transported along the shoreline and deposited at the southern tip of Lido Key. A large portion of the sediment is eventually transported onto the ebb tidal delta. The pattern of downdrift shoreline advance is related to the location and timing of the swash bar attachment.