A numerical modelling study of coastal flooding |
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| Authors: | Kathleen L McInnes Graeme D Hubbert Debbie J Abbs Steve E Oliver |
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| Institution: | (1) CSIRO Atmospheric Research, PMB#1 Aspendale, Australia, AU;(2) Global Environmental Modelling Systems, Warrandyte, Australia, AU |
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| Abstract: | Summary A coastal ocean model capable of modelling tides, storm surge and the overland flow of floodwaters has been further developed
to include the flux of water from tributaries and the forcing from wave breaking that leads to wave setup in the nearshore
zone. The model is set up over the Gold Coast Broadwater on the east coast of Australia. This complex region features a coastal
lagoon into which five tributaries flow and is subject to flooding from extreme oceanic conditions such as storm surge and
wave setup as well as terrestrial runoff. Weather conditions responsible for storm surge, waves and flooding include cyclones
of both tropical and mid-latitude origin.
Two events are modelled. The first is an east coast low event that occurred in April 1989. This event verified well against
available observations and analysis of the model simulations revealed that wave setup produced a greater contribution to the
elevated water levels than the storm surge. The second case to be modelled was tropical cyclone Wanda, responsible for the
1974 floods. Modelled water levels in the Broadwater were reasonably well captured. Sensitivity experiments showed that storm
surge and wave setup were only minor contributors to the elevated sea levels and their contribution was confined to the earlier
stage of the event before the runoff reached its peak. The contribution due solely to runoff exhibited a tidal-like oscillation
that was 180° out-of-phase with the tide and this was attributed to the greater hydraulic resistance that occurs at high tide.
A simulation of this event with present day bathymetry at the Seaway produced sea levels that were 0.3–0.4 m lower than the
simulation with 1974 bathymetry highlighting the effectiveness of deepened Seaway channel to reduce the impact of severe runoff
events in the Broadwater.
Received October 16, 2001 Revised December 28, 2001 |
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