Numerical study of the effects of mangrove areas and tidal flats on tides: A case study of Darwin Harbour, Australia

Abstract

The tidal dynamics of Darwin Harbour, Australia, are simulated using a finite volume coastal ocean model. The calibrated model agreed well with the observed sea surface elevation and current velocity. Results indicate that the harbor's hydrodynamics are driven mainly by the tides, with wind and river inputs playing only small roles. The M2 tide is dominant, with amplitude 1.7 m and peak current speed 3.0 m s−1. Sensitivity tests using the model indicate that the mangrove areas and tidal flats play crucial roles in modulating tidal amplitudes and phases in the embayments, especially for the shallow water tides such as M4. Removal of the mangrove areas and tidal flats from Darwin Harbour would dampen the M2 amplitude due to decreased shoaling effects but generate a 75.0% greater M4 amplitude in parts of the harbor. Mangrove areas and tidal flats also affect tidal asymmetry through the changing amplitudes and phases of mainly the M2 and M4 tides. In Darwin Harbour, tidal asymmetry, measured by elevation and current skewness, would increase by up to 100% if the mangrove areas were removed. If the tidal flats were removed as well, the increase would be 120%. Therefore, reclamation of the mangrove areas and tidal flats may cause sediment siltation as a result of increased flood dominance. Although this study is site‐specific, the model and our findings have a wider applicability to the effects of mangrove areas and tidal flats on tides and sediment transport in harbors and estuaries.