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Home / Articles / News / Local NEWS /  It’s just water behind the bridge
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Thursday, February 3,2011

It’s just water behind the bridge

Does highway overpass create more flooding?

By Jim Phillips
State-St-Jan-Flood3

Photo Caption: In this Athens NEWS file photo, Athens Police help block off a waterlogged section of East State Street during the flood of January 2005.
When Ohio University graduate student David Koppel started his master’s thesis in geology, he wasn’t planning to rewrite the book on Hocking River flooding.

But now he, and some OU faculty members, think his research may have uncovered a previously unsuspected cause for the floods that seem to be getting more frequent at the far east end of Athens.

They finger the culprit as the U.S. Rt. 50 highway overpass, completed around 1979 near the current Holzer Clinic and Highway Patrol post.

Without that bridge, claimed an OU professor Tuesday, some of the rainfalls that now create flooding in the East State Street shopping district and industrial park wouldn’t be causing the river to overflow.

“You’re five times more likely to have the banks overtopped now than you were before, without Rt. 50,” estimated Greg Springer, an associate professor of geological sciences.

An official of the Hocking Conservancy District, a water management agency that oversees the river, said that though the overpass was built some eight years after a federal flood-control project that re-channeled the Hocking through Athens, he believes the bridge’s expected impact on flooding was already taken into account in the re-channelization design.

Springer and Koppel, however, said they believe the data gathered by the grad student make a strong case for the overpass as a cause of increased flooding.

“It’s backwater effects from the bridge,” Springer declared. “Basically, it’s a dam.”

IN A PROJECT COMPLETED in 1971, the U.S. Army Corps of Engineers re-routed a winding stretch of river through Athens, replacing it with a shorter, straighter, wider channel to help reduce flooding. It worked, but some research since then has suggested that the buildup of silt in the channel from runoff might be increasing the frequency of floods. Koppel and his adviser, professor Springer, expected that Koppel’s work might add some more detail to that broad picture, and maybe point to more practical ways to mitigate flooding.

For his research, Koppel used both existing data on the river – much of which he found with the help of geology department chair Gregory Nadon – and his own measurements. It’s when he tried to fit the numbers together that the results started coming in wacky.

Koppel, a 24-year-old from Gahanna, Ohio, was using photographs of a January 2005 flood to figure out how high the river got at various points along its length during that event. The elevations seemed too high, given the channel’s known capacity.

“The depths should have been much lower,” Springer said. According to the channel’s specifications, he explained, a flow of 930 cubic meters per second is supposed to “just fill it, and not overtop it.”

The 2005 flood, however, was produced by a water flow much lower than that – only about 520 cubic meters per second. Koppel knew this number, because a gauge installed near the Stimson Avenue bridge measured it.

By taking his own extensive cross-section measurements of the dimensions of the new river channel, Koppel was able to estimate values for the “roughness” of the channel – basically a measure of how much resistance it offers to the passage of water flowing through it.

And those values just didn’t fit the other data, he and Springer recalled. If the roughness numbers the channel should have had, based on its shape and the texture of its walls, were correct, the river shouldn’t have gotten as high as it did in 2005, based on the amount of added rainwater rushing through it.

Conversely, if the water flow and river elevation numbers were correct – and presumably they were – this meant the roughness of the channel was considerably higher than Koppel thought it should be.

The grad student plugged the measured flow and elevation figures into his equations, and came up with a value for how rough the channel would have to be to push water levels as high as they got in 2005.

Those roughness numbers were “absurdly high,” Springer recalled – something like 70 percent higher than what would be predicted for “a nice grassy channel like that.” Obviously, something was retarding the water’s passage through the channel. But what?

The researchers had started out thinking sediment might be to blame, partly because that had been the previous operating assumption. “We went in naively assuming it was the sediment,” Springer admitted. So Koppel duly measured the sizes of sediment bars all along the channel, then sat down at his computer. In a mathematical model, he removed the sediment bars entirely, to see what this would do to water levels.

“The amount of change was negligible,” Koppel said.

So again – what was creating the increased drag on the channel water?

According to Springer and Koppel, the answer to that question was hiding in plain sight, just as big as… a highway overpass.

“About two weeks ago, (Springer) says, ‘You know, you should look at the old photographs, and see if anything’s changed (since 1971),” Koppel recalled.

One big change that jumped out was the U.S. Rt. 50 highway bridge at Athens’ east end, built around 1979. It doesn’t encroach into the channel itself, Springer noted, but its earthen embankments eliminated what had been a wide flood plain for the channel.

That flood plain, he said, played an important role in the channel’s function as a flood-reducer. Without the highway project, he said, the area under the embankment “would be flat, like the soccer fields behind Wal-Mart,” and would provide a place for water to overflow and continue downstream.

With the embankment, he said, that water is “basically pooling behind Rt. 50.”

They said it’s not unlike what happens when you squeeze down on a garden hose.

MARK HOLDCROFT, SECRETARY/TREASURER of the Hocking Conservancy District, noted that on the original plans for the re-channeling project, there’s a notation indicating that the Corps knew a highway overpass might be coming, in just the place where it was eventually built.

“It shows State Rt. 50 being a proposed project, actually drawn in there,” Holdcroft pointed out. Given that the agency knew the highway was proposed when it rechanneled the river, he said, he believes that “obviously the Corps took all those things into consideration when the project was built.”

A Corps hydrologist contacted by The Athens NEWS did not return a phone call by the paper’s press time Wednesday.

Koppel and Springer acknowledged that for the eight-year period between the rechanneling and the highway project, there’s not enough data available to convincingly quantify the claim that floods got worse after 1979. But they said they’re confident in Koppel’s findings, and believe that one thing they show is that there’s not a lot anyone can do to mitigate flooding in Athens.

“Excavation, dredging (to remove sediment), serves no real purpose,” Springer said. “Rt. 50 cancels it all out.”

But even though his research didn’t come up with the cure for East State Street floods, Koppel said, he hopes it proves useful somehow to local residents.

“I knew that whatever we were going to find would be important to the people of Athens, and that’s what interested me in the project in the first place,” he said.

 

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