(Posted March 12, 2012, at 10:52 a.m.) March 12 to 16 has been declared National Flood Safety Awareness Week. Although spring is normally a dry season in the Desert Southwest, Arizona’s monsoon season will soon return, and with it will come thunderstorms, heavy rainfall and the potential for flooding.
Flooding is a serious problem throughout the United States. Nationwide, flooding causes more fatalities than any other type of severe weather. Factors that contribute to flooding include the intensity and duration of rainfall, the steepness of the terrain, soil type, existing soil moisture, type of land cover and the amount of urbanization. In metro areas, flooding often occurs more frequently due to the inability to channel heavy rainfall, resulting in ponding of water on roadways.
Flash flooding is the primary threat in Arizona and occurs when there is a rapid and extreme flow of high water into a normally dry area, or a rapid water level rise in a creek or stream. Flash flooding occurs within a few hours of a heavy precipitation event. Flash flooding can also occur from the failure or overtopping of a dam or flood retarding structure.
Many roadways in the Desert Southwest cross into the channels of normally dry washes or streams. These low water crossings are especially susceptible to flooding during and following heavy rainfall. Water rushing across the roadway can quickly become deadly. Just a few inches of fast moving water will force most cars off the road. Most of the time it is also difficult to determine the depth of water flowing over the road surface, and the pavement may have been eroded away by the water.
Most flood death occur in automobiles. When approaching a flooded roadway turn around and go the other direction. Turn Around … Don’t Drown.
Always be alert for the presence of flooding during and following heavy rainfall events. Know the areas that are flood prone where you normally travel. When heavy rain and flooding threaten your area, stay informed by tuning to NOAA weather radio, local television and radio.
For additional information on Flood Safety Awareness Week visit www.floodsafety.noaa.gov
(source: National Weather Service Forecast Office, Phoenix)