Tidal Motion in a Complex Inlet and Bay System, Ponce de Leon Inlet, Florida

Abstract

Tidal motion and inlet processes were investigated in Ponce de Leon (Ponce) Inlet, Florida and its bay channels through a 10-week data-collection campaign and two-dimensional numerical simulation modeling. Water level and current were measured at six locations spanning the ebb shoal, inlet, and bay channels. Measurements revealed that the inlet was flood dominated during the data-collection period. The flood dominance may have been enhanced by a net influx of water during the measurement period, which was captured at two measurement stations in the bay channels located 5 km away from the inlet.

Scour, erosion, and sedimentation are problems faced at Ponce Inlet, and calculations suggest tide-related circulation patterns contribute to problematic hot spots. Scour along the north jetty may be most active on the ebb tide, when the strongest flows oriented parallel to the jetty are present. Erosion on the north interior spit owes to a bend in the inlet that forces the strong flood current to impinge on the spit shoreline. Progradation of the south spit into the inlet is a product of the curvature of the spit that creates a region of relatively weak current in the southern portion of the inlet. Deposition may therefore occur on both flood and ebb tidal cycles. Tidal attenuation was calculated along a 7 km transect from the ebb shoal, through the inlet, and south along the Indian River North. Attenuation of the M2 tide (water level) was estimated to be 1.1 cm/km along the unimpeded reach of the transect extending south from the ebb shoal to just north of a bridge. At the bridge, the attenuation was increased to 55 cm/km, a decay that is 50 times greater than in the unimpeded channel. The bridge was found to contribute to 56% of the tidal-amplitude reduction between the ebb shoal and the bridge.