How Do Floods Happen?

Floods are a disaster that often builds up slowly and then comes to a cataclysmic climax with power and fury. Floods are the number 2 natural disaster after tornadoes. The cost of floods in the US is in the billions per year.

When water falls it is usually absorbed into the earth where it helps plants grow. But there are situations where the natural absorption can’t happen. Sometimes water falls on surfaces which are impervious like concrete or asphalt. Or if the ground is already soaked and can’t absorb any more, then problems can occur.

Water runs downhill

Water will always take the path of least resistance. It runs downhill in small channels. When the channels overwhelm it will break the banks and become a larger channel joining with others doing the same thing.

If there’s a lot of rain, or there’s a steep hill – or in the final perfect storm – there’s both, the collection of water can become quickly, increasingly threatening.

Flood waters don’t need to be swift moving though. When high volumes of water spread into a flat area they can become a widespread but (relatively) shallow flood. This type of flood can take days or even weeks to dissipate. This type of flood is even helpful. Rice which is grown in paddy fields needs this type of flooding to grow properly.

Flash floods

It is flash floods which are deadly. According to the National Weather Service, flash floods are the number 1 cause of weather-related deaths in the USA.

Flash floods occur in a period of intense rain over a period of time. Slow moving thunderstorms or thunderstorms that move around the same area are usually the culprits. But not the only ones, a sudden release of water held back by ice which breaks, or of course the breach of a levee or dam wall as a result of heavy rain or pressure.

The danger in a flash flood comes from the depth of the water and its power. A flash flood can be strong enough to uproot trees and destroy bridges. It only takes 18 inches of water to float the typical car and 24 inches to sweep vehicles downstream.

Flash floods can travel for miles, which is why they can take the unsuspecting by surprise, and they are not seasonal. They can happen anytime the conditions bring everything together.

Storm surge and wave damage

It’s lovely by the beach except when it isn’t. Hurricanes with low pressure at the center suck in water. While the eye is over the sea problems are minimized, but when the eye moves onto land it brings water with it. This additional water plus the waves can cause incredible damage. If this occurs at the same time as high tide water can reach a long way inland with huge destructive potential.

Don’t underestimate water’s potential for damage

Water is essential for life, but its ability to destroy it is obvious. Underestimating its power can be hazardous.