Storm surge, a killer side effect
A good sized hurricane can push a dome of water 40 to 60 miles across and ten to twenty feet high onto the shoreline as the hurricane makes landfall. This dome is primarily wind driven water, though the low pressure of the storm system plays a part in the domes creation. It is only when this dome of water comes ashore that it becomes deadly. While ships at sea have their own problems with wind driven water, their issue is with the waves which get whipped to such towering heights they can't sustain themselves, and they break. It is the breaking action that packs the real punch. A cubic yard of seawater weighs around 1,700 pound and breaking waves on the shoreline will quickly shatter most structures they come in contact with.
As the surge of water moves inland in advancing rows of breaking waves, it becomes filled with the debris of broken houses, trees, and cars which further help to break up other structures in its way. Most articles on storm surge will note that the bulk of the deaths resulting from a hurricane tend to be from the surge, it being hard to swim when you are being swept along and pummeled with debris.
If you build along the coast line you will find that there are a set of construction codes put forth by Federal and State agencies working on Coastal Zone Management which detail projected surge heights and generall require new houses and older ones undergoing more than 50% reconstruction which require the house be elevated enough so that rising storm water will pass underneath. You may lose your stairs and plumbing connections, but in most cases the house should be there, at least in theory.
The ultimate height of a storm surge is determined by a number of variables such as the strength of the storm, the forward speed of the storm,where the eye makes landfall and when the local high tide is. This last can make a big difference.
In the Blizzard of 1978, the town I am writing from lost over two hundred houses, one of them was ours, and we lost the front third of a second one. The Blizzard landed on a high course of tides. My understanding was that the surge was about 4 feet, landing as it did, on top of an astronomically high tide (in this case astronomically is not just hyperbol, the height of tides is related to the lunar cycles. In my area "High Tide" can be 9.5 feet above "Mean Sea Level" or in this case 11.2 feet above Mean Sea Level) Coupled with the surge, the tide topped out at somewhere around 15.2 feet. One of the things that made the Blizzard such a killer was that the storm stalled and the water did not go to a real low tide for two days.
In October of 1991 another storm battered New Englad, gaining national fame as The Perfect Storm", chronicled by Sebastian Junger. Although this was not quite as strong in wind as the'78 Blizzard,78 mph vs 92, it stalled for three days and built up a 5 foot storm surge. Fortunately for us, the storm arrived on a low course of tides and the 5 foot surge only gave us a total storm height of 14.3 feet.
What did this mean in practical terms? The replacement cottage built to the new codes lost only the stairs. The older cottage, which an incompetent builder had told my family could not be raised, was heavily damaged again, because it was still at 15 feet above sea level, and the broken waves still had some serious punch when they hit the house.
Pictures of our cottages after the water has pummelled them
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