It started with a tiny hole on that July day in 1993, expanding quickly to a 12-inch gash.

Within 30 minutes, a portion of the Monarch Levee was gone, blown out by water pressure, and the Chesterfield Valley began to fill with Missouri River water.

Since then, the levee has been repaired, improved and is being raised to the 500-year-flood protection level.

The new levee, when it reaches its full height, would have certainly kept the Chesterfield Valley dry in July 1993, said David Human, a lawyer with Husch & Eppenberger, who represents the Monarch-Chesterfield Levee District.

"Bring it on," Human said. "We'd be fine because of our sand berms. I just wouldn't want (another big flood) for everyone else."

Human said the Monarch Levee was breached in 1993 when water seeped underneath and was blown upward by hydrostatic pressure. That water punched a hole in the wall, then washed away an entire segment of the levee.

Human says the Missouri River would have flooded the Chesterfield Valley even if that hadn't happened. That's because the rising river eventually would have topped the levee.

In response to the '93 flood, the levee district has addressed both possible flooding scenarios, Human said.

First, sand berms were added to prevent water pressure from breaking a hole in the levee wall, he said.

A sand berm is a layer that sits under the clay and earthen levels of the levee and extends on both sides of the levee, he said. The sand berms allow water that seeps under the levee to pass through without damaging the earthen and clay portions, he said.

"The sand berms hold the earthen material in place and act as a filtration device," Human said. "They relieve the hydrostatic pressure."

The Federal Emergency Management Agency requires sand berms for levees to be certified at the 100-year- flood protection level.

The levee district also is raising the Monarch Levee to the 500-year level to minimize the risk of water coming over the top, Human said. That will increase the height of the levee by about three feet, Human said. Flood experts believe the '93 flood was between a 250-year and 400-year flood, Human said.

If the conditions of 1993 were replicated, Human said, the Monarch Levee would need its new sand berms and extra height to hold back floodwaters.

Monarch Levee officials said the entire length will be tall enough to protect against a 500-year flood by year's end, if construction moves at its current pace.



Reporter Eric Heisler:
E-mail: eheisler@post-dispatch.com
Phone: 314-340-8183