Click here for a printable version of this article.

December 2012: Storm Surge

The major hazards associated with hurricanes are:

For coastal areas, storm surge and large waves produced by hurricanes pose the greatest threat to life and property.

Storm Surge is an abnormal rise of water generated by a storm's winds. Storm surge can reach heights well over 20 ft. and can span hundreds of miles of coastline.

Storm Tide is the water level rise during a storm due to the combination of storm surge and the astronomical tide.

As shown throughout history, the destructive power of storm surge and large battering waves can result in loss of life, destruction of buildings, beach and dune erosion and road and bridge damage in coastal areas. Storm surge can travel several miles inland as shown during Hurricane Ike in 2008, when the surge moved inland nearly 30 miles in some locations in southeastern Texas and southwestern Louisiana. All locations along the U.S. East and Gulf coasts may be vulnerable to storm surge.

There have been many exceptions to the projected storm surge of the Saffir-Simpson Hurricane Wind Scale noted below:

Category

Wind Speed

Projected Storm Surge

1

74 to 95 mph

(120 to 153 km/h)

Possible storm surge 4 to 5 ft (1.2 to 1.5 m) above normal

2

96 to 110 mph

(154 to 177 km/h)

Storm surge of 6 to 8 ft (1.8 to 2.4 m) above normal

3

111 to 130 mph

(179 to 209 km/h)

Possible storm surge 9 to 12 ft (2.7 to 3.6 m) above normal

4

131 to 155 mph

(211 to 249 km/h)

Storm surge 13 to 18 ft (4 to 5.5 m) above normal

5

> 155 mph

(249 km/h)

Storm surge greater than 18 ft (5.5 m) above normal

Some notable exceptions include:

Why are there so many exceptions? Because there are many factors that that can impact surge.

Storm surge is caused primarily by the strong winds in a hurricane or tropical storm. The maximum potential storm surge for a particular region/location also depends on a number of different factors including storm intensity, forward speed, size (radius of maximum winds-RMW), angle of approach to the coast, central pressure (minimal contribution in comparison to the wind), and the shape and characteristics of coastal features such as bays and estuaries.

Let's examine the above factors for Superstorm Sandy:

The Total Water Level = Storm Surge + Tides + Waves + Freshwater Input

Tidal ranges can reach approximately 5 ft. in the New York area as opposed to the much lower tide ranges down south. This was also a factor in the local flooding throughout coastal New York and New Jersey.

Freshwater Input takes into account heavy rainfall ahead of a hurricane, which can cause river levels to rise well inland from the coast. When this water flows downriver and reaches the coast, local water levels will rise, especially near deltas and in bays. Luckily, there were no sustained heavy rains just prior to Sandy in the northeast region.

In addition to the destructive power of storm surge, battering waves may increase damage to properties directly along the coast. Water weighs approximately 1,700 pounds per cubic yard. Repeated and extended pounding by frequent waves can destroy any building or structure not specifically designed to withstand such forces. The two work together to increase the impact inland because the surge makes it possible for waves to extend on land.

If your facility is built along the U.S. East or Gulf coasts, then it may be vulnerable to storm surge. If you would like an analysis of the level of preparedness and protection at your site, you may contact Risk Logic Inc. for a professional consultation. Risk Logic can also review plans and drawings for new construction and roofing systems to ensure they are properly designed with regard to windstorm resistance. These are services offered to all locations under contract in Risk Logic's property loss control program.