Flash floods can damage property, threaten lives
Editor’s note: This is the second in a three-part series being published in conjunction with Tennessee Severe Weather Awareness Week.
With the ability to sweep away automobiles, houses and people in a blink of an eye, flash floods are generally regarded as one of the most dangerous weapons in Mother Nature’s arsenal.
Flash floods can occur as soon as a few minutes, or as long as several hours, after an excessive rainfall, exacting a toll on anything in the water’s path. Flash floods can also be caused by the failure of a dam or levee or a sudden increase of water held by an ice jam or mud slide.
The danger presented by flash floods comes because they occur in such a short amount of time, leaving little time for extended warning.
Warren County saw first-hand the dangers of flooding in January 2002 when torrential rains dumped over 7 inches of precipitation in two days, causing rivers to overflow their banks, forcing several people from their homes. In addition to threatening homes, the floods left hundreds of thousands of dollars worth of damage to local roads and utilities. More recently, this past May, Warren County set a modern-day record for precipitation when 11.14 inches of rain fell between May 5-10. The flood left around $100,000 in damage to roads and private property.
Areas most susceptible to flash flooding are mountainous streams and urban areas, low-lying areas, storm drains and culverts. The mountain regions of Middle and East Tennessee, which include Warren County, normally have more flash flood problems than do the western parts of the state.
In this region, flash floods are normally caused by slow-moving thunderstorms that move repeatedly over the same area. The massive amounts of excess water generated by these storms can unleash enough force to rip trees from the ground, destroy buildings and rip bridges from their foundations.
The National Weather Service issues flash flood warnings when flooding has been reported or is imminent. The warnings normally focus on specific communities, streams or areas where flooding is in progress. Persons in the warning areas should take proper precautions immediately. The warnings are normally broadcast on radio and local TV. In addition, the local Emergency Management Agency may interrupt programming on the local cable system to announce such warnings.
When a warning is given, persons in the effected area should seek higher ground, especially if you live in an area prone to flooding.
When traveling in an automobile or on foot, avoid flooded, high-velocity flow areas. A rapidly flowing stream or flooded drainage ditch can sweep a person or automobile downstream.
Motorists should use an extra degree of caution when traveling at night due to the fact it is harder to recognize flooded areas in the darkness. Most flood deaths occur at night when people become trapped in automobiles that stall in flooded areas.
Experts say motorists should never try to drive through a flooded area because the road bed could be washed away below the water. If your vehicle does stall in a flooded area, abandon it immediately and seek higher ground. Rapidly rising water could engulf the vehicle in a short time, trapping its occupants inside.
Unlike flash floods, river floods normally take more time to develop. However, they can be just as damaging as flash floods. River flooding is caused by an increased water level in an established watercourse, such as a river, creek or drainage ditch.
While normally a slow-developing problem, smaller rivers may be prone to a faster rate of flooding because they are not able to offset the sudden onset of excessive water generated by heavy rains.