Morphodynamics of an anthropogenically altered dual-inlet system: John's Pass and Blind Pass, west-central Florida, USA

The morphodynamics of the John's Pass–Blind Pass dual inlet system were investigated based on hydrodynamic and morphology measurements, and numerical modeling. The co-existence of the dual inlets is realized by the dominance of mixed-energy John's Pass in terms of tidal prism and size of the ebb delta and the artificial maintenance of the wave-dominated migratory Blind Pass. Due to the secondary role of Blind Pass, the aggressive anthropogenic activities there do not seem to have a significant influence on the morphodynamics of John's Pass. On the other hand, the opening (in 1848) and subsequent evolution of John's Pass had substantial influence on Blind Pass, causing it to migrate rapidly to the south. In addition, anthropogenic activities had much more influence on the morphodynamics of the secondary Blind Pass than that of the dominating John's Pass.Results from numerical modeling provide a semi-quantitative understanding of the hydrodynamics and morphodynamics of John's Pass and Blind Pass in association with cold front passages, which have substantial influences on inlet morphology. Two large eddies are modeled from the interactions between the southward longshore current and John's Pass ebb and flood flow, respectively. These eddies are closely related to the morphodynamics of the channel margin linear bar and longshore transport divergence at the downdrift side. Both are key features of a mixed-energy inlet. The shallow water and wave-breaking-induced longshore current and elevated sediment suspension along the ebb delta terminal lobe provide the pathway for sediment bypassing. The morphodynamics of Blind Pass are dominated by wave forcing. The weak ebb jet is not capable of forming a sizable ebb delta and tends to be deflected by the strong longshore current, causing elevated longshore transport along the downdrift beach. The 90-degree turn of the inlet, which is common for wave-dominated migratory inlets, results in weak ebb flushing along the updrift (north) side of the inlet, and is responsible for the alongshore migration of the inlet before the artificial stabilization and sedimentation along the northern side of the inlet following stabilization.

Research Highlights
► In this study, we investigate the morphodynamics of a dual-inlet system based on field measurements and numerical modeling.
► The co-existence of the dual inlets is realized by the dominance of one inlet and the artificial maintenance of the other.
► The morphodynamics of the two inlets are strongly controlled by winter cold front passages.
► Large eddies are modeled from the interaction between wave-driven longshore current and tidal flow.
► The eddies and elevated sediment suspension by breaking waves are key factors controlling the inlet morphology.