Clearwater's cost

Saturday, November 13, 2004

PIEDMONT, Mo. -- At first glance, the photo is a bit bizarre. Curious.

A man in tan overalls and a khaki hat is holding up an orange stick, presumably to gauge depth.

In front of him is a huge hole, a moon crater on Earth, big enough to swallow a car.

And the more information that one learns about the photo, the more serious the picture becomes.

The man standing in front of the hole works for the U.S. Army Corps of Engineers. And the crater he is standing next to is two-thirds of the way up the Clearwater Dam in Piedmont.

The hole, discovered in 2003, kicked off the beginning stages of an estimated $90.3 million repair job.

By comparison, the Bill Emerson Memorial Bridge, the most expensive construction job ever done in the Cape Girardeau area, cost $100 million. Ninety million dollars would build roughly 18 interstate interchanges like the one proposed in Jackson; or three high school campuses like the one Jackson's school district asked for in the Nov. 2 election; it could buy two federal courthouses like the one being built in Cape Girardeau.

It seems like a lot of money to fix a hole.

But it's much more complicated than just a hole.

The Clearwater Dam was built in 1948 for a tenth of what repairs will cost. The dam catches 900 square miles of water drainage and was built to control flooding on the Black River, to protect towns like Poplar Bluff, Mo., and Pocahontas, Ark. Over the decades, the dam has done its job. Engineers estimate that dam has saved $202 million in flood damage.

The flood control structure is an earthen dam, a mammoth levee that stretches 4,225 feet across -- eight-tenths of a mile -- and rises 154 feet -- half a football field -- above the river bottom.

Beyond the flood protection, the lake is the economic centerpiece of the region. It draws campers, fishermen and hunters to the region. Karl Thielemann, spending time at a campground near the dam Wednesday, has been coming here for 30 years. Despite countless entertainment opportunities at his disposal near his home in St. Louis, he chooses to spend many of his weekends at the water near Piedmont. He says many of his St. Louis friends do, too.

"My son and grandson are coming down and we're going to go hunting for a while," he said. "We might put a couple rods in the lake."

Aside from an onion ring factory and a school district, there are limited job opportunities in Piedmont.

Like all earthen dams, a certain amount of seepage was expected from the beginning. Water will trickle through cracks and crevices under the earth.

It's unclear what exactly happened beneath the dam in May 2002. But it is plain what happened above ground. The areas both north and south of Clearwater were inundated by spectacular rainfalls.

The Black River south of the dam spilled out of its banks, so the Corps of Engineers had to shut down the spillway. On the north side of the dam, the water crept up the lake shore, drowning park pavilions, playground equipment and thousands of trees.

The dam had never seen such pressure, and engineers believe the "flood of '02" is what eventually led to the formation of the sinkhole, discovered Jan. 15, 2003, during a routine inspection.

The hole was 10 feet across and 8 to 10 feet deep.

Engineers immediately began testing the hole. Later they filled the hole, and some of the cracks below, with compacted clay. And they lowered the lake level.

Before the sinkhole was discovered, the corps would allow higher lake stages during the recreation season. Now, the corps is not allowing such deviations.

"It's having little if any effect on the lake," said James Beard, the local day-to-day operations project manager based in Piedmont.

Early on, readings showed no changes in the normal water tables. Initial testing did not reveal any structural damage to the core of the dam. More tests were ordered.

The corps insists the dam is safe for now.

"If left alone and allowed to continue to deteriorate the way that we think is taking place, we risk something going wrong with the dam and the chances of that happening would increase over time," said Mark Brightwell, the Clearwater Dam project manager stationed in Little Rock, Ark.

A drill rig has been set up on the side of the dam, not far from where the sinkhole formed. Drillers are taking samples of the soil, which will be turned over to geologists who are trying to figure out what is happening underground. Some of the bore holes have shown that cavities exist in the bedrock beneath the dam. More than 20 truckloads of grout have been used to fill the cavities.

In the meantime, the corps is making plans to fix the seepage problem. The solution is building a concrete wall inside the dam. The concrete will lock into the bedrock, cutting off the seepage and stabilizing the dam once and for all.

Not only is the corps planning to build a wall that is almost a mile long and the height of a half a football field. It also have to pour the concrete inside a dam that is already holding back water from a 900-square-mile watershed.

Brightwell hopes the renovation will be done some time in 2009.


Respond to this story

Posting a comment requires free registration: