WHAT IS COASTAL FLOODING?
COASTAL FLOODING
Coastal flooding, often referred to as coastal inundation, is the natural process by which land is inundated by water from the ocean. Coastal flooding (inundation) is distinct from riverine flooding (when there is too much water, the flow capacity of water ways become overwhelmed and burst their banks) however they are not independent. Riverine flooding and coastal flooding can occur simultaneously resulting in higher flood depths.
COASTAL FLOODING MECHANISMS:
There can be a number of different causes of coastal flooding (inundation), these include:
STORM SURGE
Increased water levels associated with storm activity due to waves, wind and changes in atmospheric pressure. Larger waves associated with storm events lead to more water being moved shoreward than under typical conditions this increase in water volume near the shoreline results in an increased water level along the coastline. Winds can increase water levels at the shoreline if the wind direction is blowing onshore as the force of the wind causes water to pile up against the shoreline. Changes in barometric pressure can influence the water level with periods of low barometric pressure associated with higher sea levels as there is not as much atmospheric pressure pushing down on the ocean.
TIDES
Natural fluctuations in water levels due to gravitational pull of the sun and the moon. Significant coastal flooding can occur when higher tidal water levels associated with spring tides coincide with a storm surge event.
SEA LEVEL RISE
The increase in the global mean sea level predominantly due to global warming as well as local sea level rise factors such as land subsidence and ocean circulation.
TSUNAMIS
Large waves caused by significant volcanic eruptions or earthquakes under the sea. Tsunamis have extremely long wave lengths anywhere from 10km to 500km, these wave lengths are magnitudes higher than those of typical waves on the open coastline where an uncharacteristically large wave length would be anything over 200m.
COASTAL FLOODING AND SEA LEVEL RISE
Sea level rise will see the landward migration of the shoreline as the oceans increase in volume due to the melting of ice sheets, glaciers and from thermal expansion (see our sea level rise information page for more info). As the water level increases extreme coastal flooding (inundation) events will increase in frequency and severity. Areas with low tidal ranges are particularly at risk as even small rises in sea level can result in a substantial increase in the frequency of coastal flooding. An simplified example of how sea level rise will impact coastal flooding levels over an arbitrary time period is presented below. The first graph shows the likelihood of an extreme coastal flooding event at the current sea level, the second chart shows the relative likelihood of an extreme coastal flooding event after a significant amount of sea level rise.
AFTER SEA LEVEL RISE:
Sea Level Rise
=
Increased Coastal Flooding Severity and Frequency
IS YOUR PROPERTY AT RISK OF COASTAL FLOODING?
If you are unsure of your property’s vulnerability to coastal flooding as a result of sea level rise the team at OMCN can help, our team has extensive experience assessing non tsunami coastal flood risk across australia. To determine whether your property is at risk of coastal flooding the team at OMCN will investigate the local coastal conditions and use the most up to date sea level rise science to predict future flooding levels. Typically a 1 in 100 year flood event is used to convey the flood risk and is the event by which many planning schemes take into consideration when developing planing controls. Flood mapping is integral for future planning and is included in all OMCN coastal risk assessments, an example detailing the 1 in 100 year flooding levels under various sea level rise scenes in the years 2040, 2070 and 2100 can be found below.
Stay ahead of the market with an OMCN Coastal Risk Assessment.
“Rising sea levels over the 21st Century will put many of Australia's coastal cities and economic centres at risk of inundation (temporary or permanent flooding)”
— Infrastructure Australia (2020)