What Are Storm Surges and How Does One Form?
Storm surges are strong ocean movements that result from wind action and low pressure at the ocean’s surface.
These events can cause flooding in low-lying areas and sometimes extend several kilometres inland.
Cyclones and deep low-pressure systems can create these severe weather events as a consequence of their movements on coastal communities.
As previously stated because the air pressure inside or near the centre of cyclones and strong low-pressure systems is so low, this can cause a bulge in the ocean surface, welling the water upwards.
In conjunction with the cyclonic winds and currents, this can cause abnormally high tides and swells to form.
What Is The Difference Between a Storm Surge and Storm Tide
Storm surge: Refers to an abnormal rise of sea level that is not normal or astronomical.
This is the result of an increase in water level caused by a storm. Strong winds push water up against the coast when a cyclone approaches, causing these powerful ocean movements.
Storm tide: The combination of the storm surge with the normal (astronomical), tide is what creates a storm tide.
Storm tide is 5 metres higher than the mean sea level when a 3-metre storm surge is added to a 2 m high tide.
Low-lying areas can be flooded by storm tides, sometimes for several kilometres. Large waves can be created by strong winds off the coast, which can worsen the impact.
Although large surges are common with tropical cyclones or hurricanes, storm surges can be caused by large low-pressure systems and can cause storm tides that cause damage to coastal communities around Australia.
Storm Tide Dangers
Storm surges can be dangerous at high tide when the sea is already at its highest point. Inland areas can be flooded by the storm tide.
This is what happened in New Orleans when Hurricane Katrina struck in August 2005. It caused the worst flooding and deaths in the city for over 100 years.
The predicted tide was also 1.4 metres. The resultant storm surge was 4.9 metres. The storm surge would have occurred at high tide.
This is 2.6 metres higher than the highest astronomical tide. (The highest possible tide as shown by the straight line)
This example shows that because of the high tidal ranges along Australia’s tropical coast, the storm surge will only have the greatest impact at high tide.
Effects Of Storm Surges on Land Masses
Storm surges and tidal impacts can cause several dangerous and destructive effects. They are as follows:
- Coastal inundation
- Flooding inland
- Damage to the ecosystem
Storm Surge Warning
Storm surges can be very sensitive to the characteristics of a low-pressure system of a tropical cyclone and are difficult to predict.
Cyclones can often travel in unpredictable ways, making it difficult to predict when and where they will land.
Storm surge risk is also affected by the speed and intensity of the cyclone, its angle to cross the coast and the shape and topography of the local area.
All these factors make it difficult to predict storm surges’ arrival and severity.
We have already seen that very large storm surges are uncommon because they require a strong tropical cyclone to cross at high tide. But, if this happens, it can have a devastating impact.
Tsunamis and Storm Surges
Tsunamis and storm surges are caused by very different phenomena. Both can cause significant flooding in coastal areas and damage, but they have very different characteristics.
Storm surges are caused by weather systems pushing water onto a stretch of coastline. As a cyclone approaches, it will usually build up over several hours.
Tsunamis are caused by earthquakes, undersea landslides, volcanic eruptions and explosions. These waves can travel long distances and sometimes affect entire oceans.
What Is The Highest Recorded Storm Surge and Tide?
Severe Tropical Cyclone Mahina, which struck Bathurst Bay in Australia on March 1899, saw the highest combined storm surge-wave action to strike Australia.
It claimed more than 400 lives. The world’s highest high-water mark was 14.6 metres (48ft). It is still claimed by some quarters to be the world record.
Things You Can Do To Prepare For a Cyclone In Australia
- Identify where to take shelter
Identify which room is the strongest part of the house, in case you need to shelter in your home during a severe storm or cyclone. Usually, this would be the smallest room in the house, with the least windows e.g. bathroom or laundry.
- Location of utilities
Identify where and how to turn off the mains supply for water, power and gas.
- Emergency and evacuation kits
Pack your emergency and evacuation kits – ensure the location is included on your household emergency and evacuation plan.
- Spare fuel
Store safely a spare supply of fuel for use in your vehicle.
- Indoor drains
Have readily available hessian bags and sand for sandbagging indoor drains to prevent sewerage backwash from flooding.
- Secure outdoor items
Identify loose items that would need to be secured that could cause damage if blown around in high winds (such as garden furniture and toys).
- Secure poisons
Store all poisons well above ground level.
- Secure indoor items
Identify which indoor items you will need to raise or empty if flooding threatens your home.