Temporal and Spatial Variations of Flow Patterns At Two Interactive Tidal Inlets, New Pass And Big Sarasota Pass, Florida

Big Sarasota Pass and New Pass are located along the low-energy, microtidal, west-central Florida coast. The two inlets are closely spaced, about 3 km apart, and connect the Gulf of Mexico to the southern part of Sarasota Bay. Big Sarasota Pass is characteristic of a long and curved channel with large offset between the protruding southern Siesta Key and northern Lido Key. New Pass has a short and straight channel with minimal offset. Both inlets are stabilized by seawalls along the south side preventing further migration induced by the net southward longshore sediment transport. No jetties were constructed at the entrances of these mixed-energy tidal inlets, which have large and dynamic ebb-tidal deltas. In this study, detailed tidal flow patterns across the channels were measured simultaneously at the two inlets over a 2-month period, using two H-ADCP current meters. The flow patterns are also simulated using a 2-D depth-averaged numerical tidal circulation model. The objectives of this study are to investigate the interactions between the two closely spaced inlets and the relationship between tidal flow patterns, meteorological effects, and the sedimentation patterns in the vicinity of the inlets. The study area is characteristic of a mixed tidal regime. The spring tide is typically diurnal with a range of roughly 0.8 m, while the neap tide is semi-diurnal with a range of 0.3 to 0.4 m. Although the range of the semi-diurnal neap tide is about half of the diurnal spring tide range, the measured tidal flow velocities are largely similar because of the comparable rate of water-level change. The maximum ebb flow is typically faster than the flood flow. Neap tide conditions generated the greatest current velocities at both inlets, exceeding 1.6 m/s during the ebbing tide. Near the entrance at both inlets, the flood current is mostly uniform across the entire channel, while the ebb current tends to concentrate in a particular portion. These flow patterns are closely related to the sedimentation and erosion pattern. The measured flow patterns compared well with modeled patterns. The tidal flow patterns are significantly influenced by meteorological conditions such as the passages of cold fronts, which provides a challenge for the numerical modeling.