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A computer model has taken the guesswork out of how to avoid flooding that chased primates to higher ground and caused minor damage to a MidAmerican Energy Co. substation in June 2008.

Since that time, the Iowa Department of Transportation (DOT) has compiled data and plugged it into a computer model that lets the eye see what an engineer’s mind can only guess at when trying to determine how various landforms affect water flow.

State and federal officials began to ponder hydraulics in 2008 when Des Moines River floodwater exceeded projections in an area of southeast Des Moines that is hemmed in by the U.S. Highway 65 bypass. The river swamped the highway and encroached on Great Ape Trust of Iowa as well as the substation.

Less water created higher floodwater than during the Floods of 1993.

Those waters also generated a fair number of rumors about what caused the flooding.

Rumors aside, an apparent answer was that the bypass, with its levee-like embankment, didn’t exist in 1993.

DOT and Corps work together

Using data supplied by the U.S. Army Corps of Engineers, which oversees the Des Moines River floodplain in the area as part of its supervision of Red Rock Reservoir, and information about the river channel that was compiled by students at the University of Iowa, the DOT created a two-dimensional computer model. This would show river volumes and velocities and how they are affected by various landforms.

Dave Claman, an engineer who leads the DOT’s office of bridges and structures, said the model has confirmed, at least at first blush, that the highway led to an excessively high flood pool, more than could be diverted under a Highway 65 bridge near Vandalia Road.

“Basically, the two-dimensional model took the engineer’s guesswork out of determining river flow,” Claman said.

When the bypass was designed in the early 1990s, engineers would have looked at a relatively flat model, then used their expertise to project what would occur in the area during times of high water, Claman said.

“You have to model where water that has velocity is going through the bridge. There is some engineering analysis that is done with the one-dimensional model, whereas you can make the two-dimensional model do the analysis,” he said.

DOT to propose two more bridges

The DOT has determined that two new 466-foot-long bridges – one for the northbound lanes of the highway and one for the southbound lanes – would eliminate future flooding problems, Claman said.

He noted that if the highway had not been constructed, the flood waters of 2008 would have flowed along an unrestricted flood plain.

However, the DOT analysis is being scrutinized by an engineering firm in Omaha, so the department is not ready to commit to the bridge project.

Claman said it would cost an estimated $6.7 million to punch a hole in the highway embankment and build the bridges.

If the engineering company confirms the DOT’s suspicions, the department would hope to start construction in 2012.

Building the bridges also would alleviate some headaches for the Army Corps of Engineers, which considered shoring up its levee system.

“It somewhat addresses our concerns,” said Roger Less, chief of the Army Corps of Engineers Rock Island District design branch.

The Corps of Engineers plans to make minor modifications to the levee system, primarily by adding berms behind one existing flood wall and installing a panel closure for a railroad spur north of Vandalia Road. The closure would be set in place during times of high water and removed at all other times.

“We would be doing this work regardless,” Less said. “Obviously, if the DOT was not proceeding ahead with some mitigating efforts, we would be going ahead with some additional levee-raising work.”

Much of the work planned by the Army Corps of Engineers also is in response to a Federal Emergency Management Administration (FEMA) decision in April 2009 to decertify the area for federal flood insurance protection as part of a remapping project for federal levees.

FEMA is waiting to accredit levees

At the time, the Army Corps of Engineers Rock Island District was waiting for the DOT to release its study of the 2008 flooding. However, because the program was not complete, the Army Corps of Engineers could not submit its remapping plan.When the levee work is completed, the remapping information will be submitted to FEMA for certification, Less said. Construction bids should go out this summer.

Regarding the potential for floods this spring, the Army Corps of Engineers is not deviating from its normal operation guidelines, pending release of information from the National Weather Service on the potential for floods as a result of near-record snowfall this winter, Less said.

“If we head into spring and we have the National Weather Service putting out projections for a spring snow melt of significant levels, then we would begin looking at advanced measures,” he said.