ST. LOUIS -- Floodwaters driven by a swift current have torn through and spilled over levees at countless locations across the Midwest, swamping hundreds of homes and businesses. The levees are meant to protect people and property from rising water in rivers, creeks, lakes and even drainage ditches. But none of them is flood-proof. Here are some answers to common questions about levees:
Q: What are levees?
A: Levees are earthen flood barriers typically covered in grass. They generally don't have bushes or trees because the roots can create structural weakness and provide crevices where water can get in. Sometimes rocks are added to help prevent erosion.
Levees are different than floodwalls, which are typically concrete, but floodwalls are sometimes part of levee systems. In Hannibal, Missouri, for example, a levee protects Mark Twain historic sites from the Mississippi River, but the levee has openings allowing street traffic to the riverfront. When floodwaters threaten, concrete floodwalls slide into place to fill the gaps.
Q: How many levees exist in the U.S?
A: The Army Corps of Engineers oversees 2,148 levee systems totaling 14,150 miles. But there are many other small levees too, some privately owned, as well as a few operated by other federal agencies. The National Committee on Levee Safety estimates there are more than 100,000 miles of levees nationwide.
California has the most, with 9,144 miles of levees in 3,291 systems. The Mississippi and Missouri river basins in the Midwest and South are dotted with thousands of miles of levees. Missouri alone has 318 levee systems stretching a combined 2,038 miles, according to the Corps.
Q: Who operates levees?
A: The Corps of Engineers operates and maintains only a small percentage of levees, just some of the big ones. About 85 percent of the 14,150 miles of levees under the agency's oversight are actually operated by counties, cities or designated levee districts. The vast majority of the other 86,000 miles of levees have no federal oversight.
For non-federal levees, it's up to the operator to take care of maintenance, keeping drains and wells in working order and making sure the turf (and sometimes rock) isn't compromised. In times of flooding, it's also up to the local operator to patrol the levee, shore up any trouble spots with sandbags and to inform the community of any dangers.
Q: How susceptible are levees to flooding?
A: It ranges broadly. Some small agricultural levees are meant to hold back only minor flooding and, in fact, are expected to succumb to higher water. Other levees are built high and wide with the goal of protecting against even catastrophic floods.
But there are no guarantees. Extreme weather has increased in recent decades, and so has serious flooding. Consider Clarksville, Missouri, a scenic Mississippi River town, where seven of the 10 worst floods on record have happened since 1993.
Then there's Chesterfield, Missouri, a well-to-do St. Louis suburb along the Missouri River. The massive 1993 flood swamped a 7-mile long valley in Chesterfield, destroying most everything in its path.
After the levee was rebuilt bigger and stronger, hundreds of millions of dollars of development emerged in the Chesterfield valley, including shopping centers, big box stores and restaurants.
Levees like Chesterfield's shouldn't create a false sense of security, said Scott Vollink, a levee safety program manager for the Army Corps of Engineers.
"The public needs to understand that no levee system is flood-proof," Vollink said. "Levees reduce that risk of flooding, but no levee system is going to eliminate all that flood risk."
Q: How bad is levee damage from the current flood?
A: It's bad, particularly in Nebraska and Iowa and northwestern Missouri. Corps of Engineers officials say around two dozen levee systems have sustained either breaches (holes in the levee) or overtoppings (water flowing over the levee) since the flood began. The Corps said virtually every Missouri River levee along a 100-mile stretch south of Omaha was breached or overtopped.
There is no estimate of the cost of the repairs, nor is it clear how much the federal government will help fund.
Q: What is the repair plan?
A: Vollink said the agency hopes to have all of the damaged levees fully repaired by the spring of 2020. But with more flooding certain this spring, Vollink said the Corps will work with levee operators to expedite interim repairs.
"If there's a levee breach, if we could get some intermediate level of levee back into place very, very quickly while we develop the final detailed design to restore back into the original condition, that would be considered," Vollink said. "But it's very situational. It's hypothetical until we see what's out there."
Q: Does the Corps of Engineers keep tabs on levee conditions?
A: The Corps maintains the National Levee Database, and it is working with states and levee operators on a new national review of the levee system. The database includes information on inspections, levee conditions and flood risks. It isn't clear when the review will be complete since Congress has not authorized funding.