Astronomic tides and nonlinear tidal dispersion for a tropical coastal estuary with engineered features (causeways): Indian River lagoon system.

Abstract Astronomic tides and nonlinear tidal dispersion were assessed for the Indian River lagoon system, a tropical coastal estuary (located in central east Florida) with engineered features (causeways). The four inlets, which choke the tides entering the system, together with the expansive size and shallowness of the estuary (and the associated energy dissipation) are the prominent mechanisms leading to the microtidal environment of the lagoon. Inside the shallows, there are 12 causeway abutments that cause a compartmentalization of the waters into separate basins, whereby the causeway openings act mechanistically as acceleration-inducing throttles to promote local regions of high kinetic energy (velocities). The causeways lead to a furthered decay of tidal amplitudes, phase lags in the tides and an enhanced generation of harmonic overtides and tidal residuals relative to the natural domain (i.e., fully open—no causeways). Numerical modeling of astronomic tidal flows (Advanced Circulation—ADCIRC) employed an unstructured, triangular mesh that resolved the entire scale of the lagoonal system with element sizes of 10–100 m and captured its many intricate domain features, including: the causeways in Indian River lagoon proper and Banana River lagoon; over 150 km of sinuous channels in Mosquito lagoon; and the hydraulic connections of the individual lagoons—one of which, Haulover Canal, is only 55 m wide. The model performed well with an index of agreement of (on average) 94% when compared with tidal data from 23 stations located throughout the system. Tides in the shallows are small at just millimeters in range; the model captured the tidal signal at the stations located there with an index of agreement of (at worst) 79%. Considering previous tidal studies of the Indian River lagoon system and tropical coastal estuaries in general, this level of domain definition and model validation of astronomic tide behavior is unprecedented and provides a benchmark for numerical simulation of lagoonal tidal flow. [ABSTRACT FROM AUTHOR]