Posted on 08/30/2005 9:59:07 AM PDT by yankeedame
Storm Surge
Storm surge is simply water that is pushed toward the shore by the force of the winds swirling around the storm. This advancing surge combines with the normal tides to create the hurricane storm tide, which can increase the mean water level 15 feet or more. In addition, wind driven waves are superimposed on the storm tide.
This rise in water level can cause severe flooding in coastal areas, particularly when the storm tide coincides with the normal high tides. Because much of the United States' densely populated Atlantic and Gulf Coast coastlines lie less than 10 feet above mean sea level, the danger from storm tides is tremendous.
"The greatest potential for loss of life related to a hurricane is from the storm surge." - Brian Jarvinen, National Hurricane Center.
The level of surge in a particular area is also determined by the slope of the continental shelf. A shallow slope off the coast (right, top picture) will allow a greater surge to inundate coastal communities. Communities with a steeper continental shelf (right, bottom picture) will not see as much surge inundation, although large breaking waves can still present major problems. Storm tides, waves, and currents in confined harbors severely damage ships, marinas, and pleasure boats.
One tool used to evaluate the threat from storm surge is the SLOSH model. Emergency managers use this data from SLOSH to determine which areas must be evacuated for storm surge. The links below provide some altered photos that show how the intensity of the storm (as given by the Saffir-Simpson Hurricane Scale) affects the possibility of flooding from storm surge at two locations. Storm surge also affects rivers and inland lakes, potentially increasing the area that must be evacuated.
Slosh Model
Example
The point of a hurricane's landfall is crucial to determining which areas will be inundated by the storm surge. Where the hurricane forecast track is inaccurate, SLOSH model results will be inaccurate. The SLOSH model, therefore, is best used for defining the potential maximum surge for a location.
If you have a Hurricane Evacuation Study (which combines SLOSH model results with traffic flow information), you do not need information about storm surge heights in a real hurricane situation. You will only need to know the forecast of the storm's intensity at landfall and the tide at that time to be able to make an appropriate evacuation decision.
See an example of a SLOSH "run" from the NOAA SLOSH Display Program that animates surge:
Example
Inland Flooding From Hurricanes
The next time you hear hurricane -- think inland flooding!
Inland Flooding Backgrounder
Freshwater Flooding 59%;
Wind 12%;
Surf 11%;
Offshore 11%;
Tornado 4%;
Other 2%;
Surge 1%
While storm surge has been the number one cause of hurricane related deaths in the past, more people have died from inland flooding associated with tropical systems in the last 30 years. Since the 1970's, inland flooding has been responsible for more than half of all deaths associated with tropical cyclones in the United States. Flooding from hurricanes can occur hundreds of miles from the coast placing communities, which would not normally be affected by the strongest hurricane winds, in great danger.
Some of the greatest rainfall amounts associated with tropical systems occur from weaker Tropical Storms that have a slow forward speed (1 to 10mph) or stall over an area. Due to the amount of rainfall a Tropical Storm can produce, they are capable of causing as much damage as a category 2 hurricane.
FACTS ABOUT INLAND FLOODING FROM HURRICANES
--Freshwater floods accounted for more than half (59%) of U.S. tropical cyclone deaths over the past 30 years. These floods are why 63% of U.S. tropical cyclone deaths during that period occurred in inland counties.
--Over the past 30 years, 78% of children killed by tropical cyclones drowned in freshwater floods.
--One cubic yard of water weighs 1700lbs. The average automobile weighs 3400lbs. Many automobiles will float in just 2 feet of water.
--The average person can be swept off their feet in 6 inches of moving water.
--The average automobile can be swept off the road in 12 inches of moving water.
--The average automobile can be swept off the road in 12 inches of moving water. At least 23% of U.S. tropical cyclone deaths occur to people who drown in, or attempting to abandon, their cars.
--Rainfall is typically heavier with slower moving storms.
--Rainfall Rule of Thumb: to estimate the total amount of rainfall that can be expected from a tropical system, divide 100 by the forward speed of the storm in miles per hour. Example (100/Forward Speed = estimated inches of rain). Your local NWS forecast office will have a more accurate estimation method to predict rainfall.
Lesson, don't build on the coast or in a flood plain.
My half-wit idea: spread oil on the water ahead of the storm, to lessen the wind-friction which pushes the water and thus reduce the storm surge. Killing some seabirds seems far preferable to what we're seeing now.
Ben Franklin beat you to it about 340 years ago.
I don't think it works that well for winds over 100MPH.
Good info, Thanks.
isn't that what's happening with the oil rigs and such busting up anyway?
The entire city of Fairbanks is built on a flood plain. It was flooded in 1967, flooded real good. The city was rebuilt and greatly expanded right there.
Another great place to build a city is on a glacial outwash plain. Anchorage is built on such a plain, and was sunk in the '64 earthquake. Anchorage has been completely rebuilt right there and greatly expanded.
There aren't a lot of sites for cities that are both good from a commercial point and ideal for geological stability. Commercial wins every time.
I find this very hard to believe. Would a full bathtub hold a cubic yard?
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