Flood Risks

Life/Recreation - Outdoors

By: sparkybates 24-Apr-2011

Introduction:

Floods are the most common disaster in the United States. They've caused nearly $24 billion in losses over the last ten years.

Storm Surge

Along the coast, storm surge is often the greatest threat to life and property from storms like a hurricane, tropical storm, or Nor'easter. Storm surge is an abnormal rise of water generated by a storm, over and above the predicted astronomical tides. Storm surge is produced by water being pushed toward the shore by the force of the winds associated with a storm. Storm surge is a very complex phenomenon and its flooding effect can be heavily affected by related factors such as its timing relative to astronomical tides, the the width and slope of the continental shelf, the the shape and characteristics of coastal features, etc. For example, a Category 4 storm hitting the Louisiana coastline, which has a very wide and shallow continental shelf, may produce a 20-foot storm surge, while the same hurricane in a place like Miami Beach, Florida, where the continental shelf drops off very quickly, might result in only an 8 or 9-foot surge. As water weighs approximately 1,700 pounds per cubic yard, battering waves associated with storm surge can inflict a lot of damage on the structures, and other obstacles, that they reach.

Flash Floods

Flash floods can develop quickly, sometimes in just a few minutes and without any visible signs of rain (some of the most dangerous floods originate many miles away). A flash flood is typically caused by sudden, excessive rainfall that sends a river, stream or other body of water rapidly out of its banks. Often this occurs in a short amount of time, only several hours or even less. Sometimes, flash floods can result from sources such as dam or levee breaks and floating debris or ice that accumulates at a natural or man-made obstruction and restricts the flow of water. Water held back by the ice jam or debris dam can cause flooding upstream. Subsequent flash flooding can occur downstream if the obstruction should suddenly release.

Most flood deaths are due to flash floods, making them the #1 weather related killer in the United States. Flash floods often have a dangerous wall of roaring water that carries rocks, mud, and other debris and can sweep away most things in its path. 95% of those killed in a flash flood try to outrun the waters along their path rather than climbing rocks or going uphill to higher grounds. 80% of flood deaths occur in vehicles, and most happen when drivers make a single, fatal mistake trying to navigate through flood waters.

Spring Thaw / Snowmelt

During the spring, frozen land prevents melting snow or rainfall from seeping into the ground. Each cubic foot of compacted snow contains gallons of water and once the snow melts, it can result in the overflow of streams, rivers and lakes. Add spring storms to that and the result is often seriously dangerous and/or damaging water levels. Snowmelt can produce large amounts of runoff in a short period of time. This runoff flowing into lakes, streams and rivers can cause them to rise to levels causing excess water to spill over their banks. River basins well downstream are often the most severely affected.

Overburdened or Clogged Drainage Systems

Drainage and flood problems may be caused when debris or overgrown vegetation accumulates and clogs waterways, or when the capabilities of existing drainage systems are exceeded during heavy rains. If drainage easements, floodways, stream beds and banks, channels become obstructed or clogged-whether natural or artificial and whether on private or public land-they will be unable to adequately provide the drainage that they are expected or designed to provide. Instead, water will back up and cause flooding.

Construction / New Development / Forest Fires

After a wildfire, the charred ground where the vegetation has burned away cannot easily absorb rainwater, increasing the risk of flooding and mudflows. Similarly, construction and new development can change natural drainage and create new flood risks. New buildings, parking lots, and roads also mean less land to absorb precipitation and runoff.

Final Thoughts

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. As with any other emergency situation, preparedness is key.

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goodselfme 3/1/2012
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Floods are definitely terrible. You have detailed the risks well here.
pamperedpen 1/8/2012
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Thanks for these tips. H5
litetender 12/17/2011
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Nice list!
snowfence 4/26/2011
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Thanks for the list on flood risks. H5
jseven 4/26/2011
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My friend's house flooded years ago and one of her little dachshund dogs died because he could not get up high enough in the house when the waters rose, so sad. I feel for anyone going through this mess.