Coastal inundation is one of the two coastal hazards that we are primarily concerned with when determining coastal risk (the other being coastal erosion). Coastal inundation usually occurs due to an extreme event that produces higher than average water levels. Under the right combination of conditions water can reach elevations much higher than mean sea level (Figure 1.1). This increase in water level only occurs for a short period but it can be sustained enough to cause widespread damage (as evidenced by most flood events).
To help with understanding the potential coastal inundation hazard the likely return interval of extreme water level elevations is often computed where possible. Ideally, the analysis of extreme water levels will include all aspects outlined in Figure 1. This is not always available, however, for the Australian coast there is an online tool that can provide an estimate of extreme water level return intervals that we can use that can provide an estimate for some of the processes outlined in Figure 1 (Canute 3.0).
To visualise the potential impact of extreme water levels on the coast we can use coastal topography and bathymetric data that shows where inundation may occur under different scenarios. A common approach is the “bathtub model” where we simply increase mean sea level on a digital elevation model (DEM) to show where inundation may occur (Figure 2). This is quite a simplistic approach that does not truly reflect reality (it is usually over-predicts the impact of inundation but can underpredict as well) but it is used widely when performing risk assessments. The online tool CoastalRisk allows us to visualise inundation on the coast of Australia using the “bathtub model” approach by raising the water levels on a coastal DEM.
We will use both Canute 3.0 and CoastalRisk to investigate the risk of damaging coastal inundation for Palm Beach, Queensland.
Figure 1. Components that can combine to create high water levels from Vitousek et al. (2017).
Figure 2. Example of a bathtub model of coastal inundation from CoastalRisk.
Canute 3.0 (https://shiny.csiro.au/Canute3_0/) provides an analysis of the potential return interval of extreme water levels. It uses both coastal wave conditions and future sea level rise to compute the water level results. It provides an estimate of water level that includes, sea level rise and storm surge on top of highest astronomical tides but not processes like wave run-up. Follow the steps below to determine the extreme water levels for a range of scenarios at Palm Beach.