Flood thy neighbor: Who stays dry and who decides?

Southern Illinois professor, said it’s hard to prove the levee was built too high because the Corps gives itself a lot of leeway on this front. When the agency designed the levee, it modeled the size of the 100-year flood at Valley Park and found the baseline levee height needed to hold back that flood. Then the Corps added an extra 3 feet to the levee design for safety and up to 4 feet more to account for how the levee might settle over time. That meant the levee was built up to 7 feet higher than the elevation of the 100-year flood.

For Valley Park, the added height makes it virtually certain that the city will be protected from a major flood, even if its flow rate is larger than what the Corps calculated in 1993.

On the flip side, every extra inch of the levee above the baseline height increases the possibility of passing more damage on to Valley Park’s neighbors.

Chad Berginnis, executive director of the Association of State Floodplain Managers, said Valley Park should shoulder more of the responsibility for making sure its levee doesn’t harm its neighbors. Most federal levees are maintained by local levee districts, and it’s up to them to ensure the structure stays up to date with changing flood patterns and regulations. But few local governments have the expertise or funding to check the Corps’ calculations. And just like the Army Corps, they have little incentive to do anything that might indicate their levees are piling extra harm onto surrounding communities.

Tim Engelmeyer, the Valley Park city attorney, said it’s unrealistic to expect a “little town of 7,000” to handle a complex modeling update.

U.S. Geological Survey scientists also have proposed a sophisticated computer model that would do what the Corps says it cannot: conclusively demonstrate the levee’s impact on the region. The model, said Geological Survey hydrologist Paul Rydlund Jr., would consider the Meramec Valley as it looked in the 1930s, then slowly add in the development over time: bridges, neighborhoods, the levee. Rydlund said he hopes such a study could help people on the river understand its changing behavior.

So far, the Geological