The Unpredictability Of Flash Floods
On the surface, flash floods seem pretty self-explanatory. If where you live is prone to rainfall, the water can accumulate and lead to flooding. But on closer examination, it’s actually a much more difficult process to understand what areas are more at risk and how to predict the impact of flash flooding. Flash Floods are extremely dangerous and must be treated with extreme caution.
Flash floods result from relatively short, intense bursts of rainfall, often from severe thunderstorms. It can occur in almost all parts of the world and poses the greatest threat of loss of life due to flooding. People have often been swept away after entering floodwaters on foot or in vehicles. These floods can also result in significant property damage and major social disruption. They are a serious problem in urban areas where drainage systems are often unable to cope.
It can also occur in rural areas where the nature of the terrain and steepness of the streams can lead to the very rapid development of flooding.
A flash flood is a flood that begins within six hours of heavy rainfall. The danger associated with flash floods is due to their sudden onset, which leaves little time for people to prepare or evacuate. Flash flooding is the second leading cause of natural disaster-related deaths in the U.S., with approximately 100 deaths occurring each year. While they can be particularly problematic in the backcountry, flash floods are not restricted to wilderness areas and can happen anytime and anywhere.
Weather conditions, as well as topography and soil conditions, influence the formation of flash floods and should be considered when planning a wilderness activity. Arid deserts are particularly susceptible to flash flood conditions due to the often-impermeable clay-like soil, the funnelling effects of slot canyons, and the infrequency of storms. A storm occurring many miles away can quickly flood a desert area. This is a major problem because when adventurers go into the backcountry, they see blue skies above them and may have no idea that it is raining heavily 30 miles away. A flash flood can present four to five hours after rainfall and after the storm has passed.
The head of a flash food is often choked with debris, dirt, and rock, giving it a dark brown color and slowing down its speed, causing water to back up behind it. It is a ‘moving dam’, and it has incredible momentum. Even a small flood could knock a person over. A surprising fact to most is that more than half of the flood-related fatalities in the U.S. occur in vehicles such as cars or trailers.
Being inside a vehicle during a flood can offer a false sense of security, when in fact, most vehicles lose complete control in less than six inches of water and begin to float in a foot of water. Vehicles often flip once floated, trapping their passengers. Never attempt to drive through a flooded area. You need to abandon your vehicle if it does become surrounded by water and seek higher ground. It is not uncommon for trees or even boulders to be carried by floodwaters. This debris has the potential to harm or kill anyone or any animal in its path. It is difficult to gauge the speed, depth, and contents of floodwater, and for that reason, one should never attempt to cross-flowing flood water. If you are caught in a flood, seek higher ground immediately.
The best way to prevent flood-related injuries is prevention through planning and exercising caution when conditions are variable. When planning a trip, it is important to be aware of the flooding potential for the immediate backcountry area you will be in. As well, you should be aware of the drainage potential and slope of the land. Remember, flash floods usually occur hours after a rainstorm has ended.
If the conditions are wrong, “turn around, don’t drown” (TADD).
Flash floods can occur with little or no warning, which is why they can be dangerous. Flash flooding in urban areas can pose health and safety risks, including disease, infection and injury. Avoid walking in all floodwaters if possible, and take safety precautions if you have no choice.
