(Use the attached PowerPoint® presentation, All About Levees, to accompany this introduction.)

How many of you have heard of Hurricane Katrina? What can you tell me about it? Approximately 80% of New Orleans was flooded in the aftermath of Hurricane Katrina. Today we'll think about what engineers can do to prevent a similar disaster from happening again.

Some people confuse hurricanes with aornados. While they are both destructive, naturally-occurring phenomena, they occur in different types of regions, are caused by different elements and have very different characteristics. Today, we are going to learn about hurricanes. A hurricane is an enormous rotating storm — 20-30 miles wide at its "eye" up to 400-500 miles wide at its maximum — that is centered around an area of very low pressure. Hurricane winds are so strong and powerful that they usually destruct whatever gets in its way (structures, cars, trees, etc.); gale force winds (39-54 mph) get stronger and stronger, finally turning into hurricane force winds that blow at at an average speed of more than 74 miles per hour. Compare that to the speed a car travels on the highway. How fast do you think cars travel? (Answers will vary, but may be ~65 mph). Right! So these winds are even faster than that! These strong winds pull debris — both large and small — into the eye of the hurricane, violently rotate the debris around and then spit it back out again, leaving a path of destruction behind.

Hurricanes are so tall (up to 10 miles) and so wide (up to 500 miles) that one could completely cover the state of Texas with some extending into surrounding states. That is huge! These storms move forward like an immense spinning top, at speeds of about 20 miles per hour. (If students are confused, explain that the whole storm moves at 20 mph, but the winds within it are going 74 mph.)

How do hurricanes form? A few things must happen for this powerful, natural phenomenon to occur. First, you need a source of very warm, moist air. Where on the globe do you think we might find a lot of warm, wet air? That's right! Warm regions of the ocean. As these ocean waters evaporate, they form warm, moist air. Next, we need wind to blow in a very specific way in order to cause the huge tropical storm that is a hurricane: spinning slightly near the surface of the water. Next, winds at higher levels need to be blowing in slightly different directions from those below it. And finally, the storm needs a little "push" from the Coriolis force (this is the large-scale curving of wind that causes wind to turn to the right in the Northern Hemisphere and to the left in the Southern Hemisphere).

Unfortunately, some coastal areas get hit season after season by hurricanes. The people who live in these areas are well aware of the risk living in a hurricane zone. However, each city or region that is commonly hit by these large storms has an emergency plan in place to help predict and prevent large scale disasters from taking place so that its residents remain as safe as possible and informed. Though it is impossible to stop a hurricane from hitting (at least in this day, it is impossible!), it is possible to track and predict its course to enable evacuation of residents. These early warning systems help inform people of when they need to leave the city so that they do not get become hurricane casualties.

So if city planners know that their city gets hit by hurricanes quite frequently, what do they do to protect the town's residents? Well, they create infrastructure that is considered "hurricane proof," or as close to being hurricane proof as current technology can provide. So, once a storm does hit, the buildings, roads and bridges must be strong enough to survive. Therefore, civil and structural engineers working in coastal regions make sure that their designs are strong enough to withstand the full force of strong hurricane winds.

Along with predictive equipment and hurricane-resistant structures, many cities also have systems in place to prevent large-scale flooding using barriers, such as levees, pumps and floodwalls. A levee (from the French verb lever, to raise) is an embankment created to prevent the overflow of a river or other water source. Levees are used in many regions of the southeast US. In many of the regions that were affected by Hurricane Katrina in 2005, levees and floodwalls failed, resulting in widespread flooding.

The main purpose of levees is to protect people from the flooding of nearby rivers or lakes. Levees are usually built by piling up earth (and firmly packing it and adding more earth in layers over and over) on a cleared, level surface. They are wide at the bottom and level at the top, with extra room for sandbags or temporary embankments if needed for reinforcement. Some areas that see a lot of flooding may have several levees.

Engineers design and build levees and other flood-protection systems in frequently-hit places such as New Orleans. During Hurricane Katrina, New Orleans at first seemed to withstand the storm without much destruction. However, after the storm passed, breaches (breaks) in several levees occurred. Also, some of the pumps used to extract water also broke. This led to the widespread flooding that eventually devastated the city. In today's activity, you become an engineer designing a new levee system for New Orleans to prevent another hurricane from causing such total devastation to a city.

Engineers are involved in many different projects from levees, to the reconstruction of roads, offices, homes, utilities, etc. Disaster prevention is a key part of any city's plan, as to reconstruct and rebuild is both a timely and costly process. Engineers working to redesign and rebuild levees in the south must be extremely cautious in designing to the highest standard possible. People living in coastal areas that are frequently hit by hurricanes depend on these engineers for their safety.