Suchergebnisse

Abstract. Many previous modelling studies have considered
storm-tide and riverine flooding independently, even though
joint-probability analysis highlighted significant dependence between
extreme rainfall and extreme storm surges in estuarine environments. This
study investigates compound flooding by quantifying horizontal and vertical
differences in coastal flood risk estimates resulting from a separation of
storm-tide and riverine flooding processes. We used an open-source version
of the Delft3D model to simulate flood extent and inundation depth due to a
storm event that occurred in June 2016 in the Shoalhaven Estuary,
south-eastern
Australia. Time series of observed water levels and discharge measurements
are used to force model boundaries, whereas observational data such as
satellite imagery, aerial photographs, tidal gauges and water level logger
measurements are used to validate modelling results. The comparison of
simulation results including and excluding riverine discharge demonstrated
large differences in modelled flood extents and inundation depths. A flood
risk assessment accounting only for storm-tide flooding would have
underestimated the flood extent of the June 2016 storm event by 30 %
(20.5 km2). Furthermore, inundation depths would have been
underestimated on average by 0.34 m and by up to 1.5 m locally. We recommend
considering storm-tide and riverine flooding processes jointly in estuaries
with large catchment areas, which are known to have a quick response time to
extreme rainfall. In addition, comparison of different boundary set-ups at
the intermittent entrance in Shoalhaven Heads indicated that a permanent
opening, in order to reduce exposure to riverine flooding, would increase
tidal range and exposure to both storm-tide flooding and wave action.