(Street signs are seen in floodwaters from the Mississippi River in Vidalia, La., in Concordia Parish in May 2011. (Gerald Herbert, The Associated Press))
Floods are one of the most common hazards in the United States, however not all floods are alike. Some floods develop slowly, while others such as flash floods, can develop in just a few minutes and without visible signs of rain. Additionally, floods can be local, impacting a neighborhood or community, or very large, affecting entire river basins and multiple states.
Flooding is a significant potential threat throughout Louisiana, representing the state’s most prevalent and pervasive natural hazard threat. Louisiana is located along the southernmost part of the Mississippi River Basin, which has the largest drainage of any basin in North America. The state’s sub-tropical climate has the potential for producing heavy rainfalls at any time of the year.
Most injuries and deaths related to flooding events occur when people are swept away by flood currents, and most property damage results from inundation by sediment and debris-filled water. According to the statistics compiled by the Office of Climate, Water, and Weather Services of the National Weather Service (NWS) and the NCDC, Louisiana averaged 91 flood related deaths per year from 1980 to 2009.
Flash floods can occur within a few minutes or hours of excessive rainfall, or a dam or levee failure. Overland flooding, the most common type of flooding event typically occurs when waterways such as rivers or streams overflow their banks as a result of rainwater or a possible levee breach and cause flooding in surrounding areas. It can also occur when rainfall exceeds the capacity of underground pipes, or the capacity of streets and drains designed to carry flood water away from urban areas.
(A resident expresses frustration as water rises in his yard after heavy rains in Garyville on Wednesday, May 28, 2014. (Michael DeMocker, Nola.com / The Times-Picayune))
Flooding along the Mississippi and Atchafalaya Rivers more often results from upstream runoff (from states as far away as Kentucky and Wisconsin) rather than local rainfall. Flooding along the lower Mississippi can have significant agricultural, economic and emergency response impacts. Major flooding on waterways can seriously affect river and barge traffic, especially along the Mississippi River where cargo is handled at the Port of New Orleans, Port of Baton Rouge, Plaquemines Port, and the Port of South Louisiana. It is the combination of these ports that make the lower Mississippi River in Louisiana such a powerful port complex.
(An inspector in Vidalia, La., checked a levee in May 2011 that was protecting a medical center from flood waters.)
Even if you feel you live in a community with a low risk of flooding, remember that anywhere it rains, it can flood. Just because you haven't experienced a flood in the past, doesn't mean you won't in the future. Flood risk isn't just based on historical events; it's also based on a number of factors including rainfall, topography, flood-control measures, river-flow and tidal-surge data, and changes due to new construction and development.Here are some tips to prepare for a flood:
- Purchase flood insurance for your home.
- Avoid building in a floodplain unless you elevate and reinforce your home.
- Elevate the furnace, water heater and electric panel in your home if you live in an area that has a high flood risk.
Over ten years ago, the NOAA National Weather Service developed the Turn Around, Don’t Drown (TADD) campaign. TADD was developed to educate people on the hazards of walking or driving a vehicle through flooded waters.The following are important points to remember when walking or driving in flood conditions:
- Six inches of water will reach the bottom of most passenger cars causing loss of control and possible stalling.
- Six inches of fast-moving water can knock over an adult.
- A foot of water will float many vehicles.
- Two feet of rushing water can carry away most vehicles including sport utility vehicles (SUV’s) and pick-ups.
- Do not attempt to drive through a flooded road. The depth of water is not always obvious.
- The road bed may be washed out under the water, and you could be stranded or trapped.
- Do not drive around a barricade. Barricades are there for your protection. Turn around and go the other way.
- Do not try to take short cuts. They may be blocked. Stick to designated evacuation routes.
- Be especially cautious driving at night when it is harder to recognize flood dangers.
- State of Louisiana Hazard Mitigation Strategy – Volume I
- State of Louisiana Hazard Mitigation Plan Update