Secure Levees Through Risk Analysis

No one is able to predict the weather with 100 percent accuracy.  There will always be disturbances, storms, and unfortunately, disasters.  For this reason—and for the safety and well being of all people—it is quite important that there is an attempt to minimize risks and thoroughly analyze variables to avoid catastrophic events.

Recently, the floods in the Midwestern United States made many people question the standard in which levees are rated and certified. 

The common standard is to determine a levee height based on the “100-year flood” rule.  A height is calculated and a three-foot freeboard is added as reinforcement.  For many areas affected by the late spring floods, however, 2008 brought the third “100-year flood” in 15 years.  And, once again, the levees were not capable of protecting the land, buildings, and people from rushing water. 

It is certainly not a secret that there are definite challenges to develop, manage, and maintain appropriate levees at the local level.  What engineers and quality professionals are examining are statistical methods that can better assess the current situation and also analyze past and (possible) future variables. 

Cliff Moser, chair of the ASQ Design and Construction Division, states that his colleagues from the U.S. Corps of Engineers and American Society of Civil Engineers mention that risk and uncertainty analysis has become more frequently used in recent years.  In this method, statistical modeling is used, “to calibrate the 1 percent flood opportunity,” Moser said, “providing a statistical estimate to the range of uncertainty of water surface calculations.”

Risk and uncertainty analysis is not new.  In fact, the U.S. Corps of Engineers has been conducting risk analyses in flood damage reduction studies since 1996.  However, there had always been concerns that risk and uncertainty analysis was too difficult to use in these situations.

In recent years, with growing concern of the nation’s infrastructure being vulnerable in many areas, more professionals became vocal in changing the traditional way of thinking.  T he traditional method assumed the three-foot freeboard was a sufficient flood deterrent.  However, r isk and uncertainty analysis is favorable to the current method because it addresses more variables and every possible result is examined closely.

“As the analysis is calculated,” Moser explains, “variables include traditional weather history, watershed behavior, and other factors such as urban build-up—or, impervious ground cover. This utilizes different parameter combinations for hydrological, hydraulic, geotechnical, and economic models.”

While risk and uncertainty analysis might not be the only answer, it does arm engineers with a more powerful tool now.  One that can give us levees, as Moser comments, “that come with a greater assurance of safety.”  And, that’s what we all want.