On the Problem of Modeling the Boat Wake Climate; the Florida Intracoastal Waterway

Abstract:

The wave climate created by boat traffic associated with accelerating coastal development has a significant impact on the health of coastal ecosystems. The transient wave activity created by boat traffic generates intermittent bursts of higher flow velocities, accelerations, and stresses on the bed, vegetation, and both bivalve and coral reefs. Understanding, modeling and forecasting the long term effects of the boat-wave climate is a challenging problem for traditional high-resolution, phase-resolving numerical modeling. The approach presented in this paper consider this challenge taking into account the stochastic component of the wake climate. Analysis of the linear and nonlinear characteristics of wakes observed in the Florida Intracoastal Waterway are carried out. The numerical analysis is conducted using the open-source FUNWAVE-TVD model, a phase-resolving nearshore numerical wave model that solves fully-nonlinear Boussinesq-type wave equations which use a combined finite-volume and finite-difference method. The wake-parameter space of two based on Froude numbers (depth- and length-based) defined by a simplified linear theoretical model are considered through the simulations. The performance of the model, evaluated for the range of Froude numbers observed in the field, is excellent if the wake field is weakly dispersive and the problem is completely specified, e.g., in the case of analytical linear wakes, or for low length-based Froude numbers, corresponding to large container ships generating relatively long waves. The model is challenged by the short-wave field of the wakes generated by small slow boats. However, the numerical simulations suggest the problem is not severe, as it is typically confined to the deeper water domain, where wave evolution is linear and can be handled, for example, by using a linear fully dispersive model. The model describes well the shallow-water nonlinear wake shoaling across all wake populations, which is essential for modeling wake-induced sediment transport processes and associated erosion of coastal wetlands and reefs.