August 1, 2006 A group of U.S. civil engineers and city officials went on a recent trip to the Netherlands -- a country much of which is below sea level -- to study the country's storm surge barrier system. The system has multiple lines of defense, with floating barriers that can be deployed and sunk to the seafloor by filling them with water.
DELFT, Netherlands -- We are just heading into what is traditionally the worst part of hurricane season. But is New Orleans ready? When Hurricane Katrina hit New Orleans, levees broke; homes crumbled. Now the levees need to be replaced by stronger ones.
Eighty million dollars have been spent so far to repair the levees, but some say it's not enough. That's why civil engineers and city officials went the Netherlands -- a country where water invades on three sides -- to find out how they can continue to improve the levees.
The Netherlands got their own wake-up call in 1953. Five hundred dikes collapsed, and 2,000 people were killed. Now the country is better prepared.
"Barriers have been built all over the place," Jurjen Battjes, a civil engineer at Delta University of Technology in Delft, Netherlands, tells DBIS.
Levees were replaced with storm surge barriers. As the water rises, computers close the walls and fill the tanks along the barrier. This causes the walls to sink to the bottom, keeping most of the water from passing through.
Battjes says, "This whole structure is supposed to be enclosing this waterway in cases of extreme storm surges."
This barrier near Rotterdam is one of many built as part of the delta project.
"One of the primary philosophies behind it all is to shorten the line of defense," Battjes says. In New Orleans, only a few levees had to be breached for the water to flood the city. In the Netherlands, there is a series of barriers that would need to fail before the storm surge would hit land.
The total cost? $5 billion, but it's worth it for the people living in the Netherlands. The entire country pays taxes for the construction and upkeep of the dams throughout the country.
"It's a matter of survival," Battjes says. It's as simple as that."
BACKGROUND: To avoid disasters when water levels rise near major cities, exposing citizens to dangerous floodwaters, civil engineers are taking a closer look at new ways to build dams. This could help protect coastal cities from tragedies like that of the broken levees due to Hurricane Katrina's strong winds and rising water. Taking inspiration from the Netherlands, a country that's mostly below sea level, civil engineers are studying computer models of a series of dams and levees between water and city -- rather than just one layer.
THE DUTCH BARRIERS: The Dutch barriers are several layers of dams and levees that protect the country from rising waters during storms. The most complex one, the Oosterschelde Barrier, was the one studied. This barrier's several layers include:
- A beam under which water flows when gates are open
- A steel gate that is lowered when sea level reaches "danger" height
- A 5-million-ton stone block beam steadies giant piers, which have holes that fill with sand
- A synthetic "mattress" filled with sand and gravel to strengthen the nearby sea floor
STORM SURGE: During a storm, high winds cause a wall of water to build up in front of the storm. Strong winds push on the oceans surface, and the pressure pushes the water upward, above sea level. Storm surges are particularly dangerous when they arrive near land at the same time as high tide, when the water is naturally at its highest. If the sea floor in the path of the storm surge is deep and sloping, the wall of water can be dispersed more easily. But in areas where the sea floor slopes up gradually and is very shallow for a long distance from the shore, winds push the wall of water directly up the slope.
DAMS VS. LEVEES: A dam is a wall built across a waterway, such as a river, that controls the flow of water along its natural path. Sometimes dams can be used to create lakes or to propel water-generated electric plants. A levee is a wall or embankment built along the side of a body of water to divide the water from the land, and prevent the water from overflowing its natural boundaries.
The American Society of Civil Engineers contributed to the information contained in the TV portion of this report.