Below you’ll be able to explore the five most common types of flooding events. Please bear in mind that one or more of these events can occur at the same time:
Did you know?
Large bodies of water moving at just 16kph (10mph / 8.69 knots) carry the same amount of energy as gusts of wind exceeding 434kph (270mph / 234.62 knots)!
What most people tend to think of when imagining a “flood.” In Australia the most common cause for this flood is heavy rainfall, but in other parts of the world these types of floods can occur after the Summer sun melts snow. The water within a river’s banks swell and overflow, pouring out and over onto the surrounding land. When the flood plain in question is wide and flat, the water spreading over it tends to be slow moving, in comparison to areas where the river banks are higher (a valley for example), where the surging waters simply gather momentum, picking up hundred-ton boulders as they move. Generally speaking, water that travels faster over a given area of land takes less time to dissipate compared to water that seeps out over a large expanse of land.
For a flood to qualify as a “flash flood,” the waters creating it need to rise to flood level within six hours of the events that created it, in other words; floods that occur too quickly for any nearby populations to react appropriately. Waters moving at 2.7metres (9ft) per second, the average speed of waters in a “flash flood,” carry enough inertia to transport 45kg (100lbs) boulders. Moreover, their ability to transport such heavy debris leads to major structural damage wherever those objects smash into walls and supports.
Ice Jam Flooding
“Ice Jam Flooding” occurs in much cooler parts of the world, namely places such as the far North Americas, Russia and Scandinavia. Rivers that are exposed to extremely cold temperatures (-30C and less) can become almost entirely frozen in a matter of hours. Later on in the year, when rain begins to fall, those huge pieces of ice get broken down into smaller chunks before being carried along by the mixture of rain and melted ice. As the volume of water increases, so too does the size of the ice being transported. Larger pieces are lifted down steam, where they then get trapped in narrower stretches of the river. Incoming chunks of ice join them and, within a matter of days, enough ice becomes trapped in the river bed that a natural dam is formed. As the river’s height increases and exceeds the limits of it’s banks, the surrounding area becomes flooded. Not long thereafter, the constant movement of water behind it and its continual exposure to the warming sun results in the ice dam breaking open. This, in turn, causes flash floods in the areas further downstream.
“Coastal Flooding” is usually as a direct result of a hurricane, tsunami or tropical storm out at sea – in some cases, explosions underwater can also result in major coastal floods! Australia is lucky enough to be relatively free of the phenomena, but in other parts of the world, coastal floods are responsible for 90% of all deaths during hurricanes and tornadoes.
While human beings are notoriously very good at building things, we do make mistakes. In cases where man-made dams, in some cases holding several-hundred-million gallons of water, have collapsed or ruptured, all of that pent-up water is released, resulting in major flash floods further downstream.