Sunday, August 12, 2001
The big drain for flash floods
Giant tunnel under Mill Creek proposed
By Dan Klepal
The Cincinnati Enquirer
Solving Mill Creek flooding may take a subterranean turn: a man-made river through limestone more than 300 feet underground.
Engineers would use a drill about the size of the Apollo spacecraft to bore a 16-mile tunnel more than 30 feet in diameter under the stream wide enough to allow subway trains to cruse through.
But instead of trains, the rock tunnel would carry up to 6.2 trillion gallons of rainwater per day equivalent to a once-a-century flood to a treatment plant near Barrier Dam where the creek meets the Ohio River.
This massive drill is capable of drilling a tunnel 30 feet wide.|
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It's an elaborate and complicated plumbing job that, at an astounding $800 million, would rival in cost the two new stadiums along Cincinnati's riverfront.
But proponents say the money is worth it to accomplish three important goals:
Protect lives and property on the 1,500 parcels of land within the creek's floodplain.
Improve water quality by allowing the Metropolitan Sewer District (MSD) to eliminate 100 combined sewer overflows, outfalls for sewer lines that carry both rainwater and raw sewage and often spill into the creek during heavy rains.
Eliminate the need for the Army Corps of Engineers to pave and straighten the creek bed or build 20-foot flood walls along the channel flood prevention methods scorned by environmentalists.
Mill Creek flooding has been a serious issue for years. There have been three significant floods since 1996, including the flash floods of July 17-18, which caused millions in damage to Sharonville alone. Even minor flooding can cause sewer lines to back up into basements.
Christine Thompson, a flood plain manager who works for the city of Sharonville, said the July flood destroyed vehicles and wiped out inventory of dozens of businesses along the creek.
So-called deep tunnels have been used in about two dozen cities around the country and many more worldwide to solve those problems. The tunnel under the Mill Creek would be one of the largest such projects attempted in the U.S.
Pat Karney, director of the MSD, said the tunnel would help his organization much more quickly stop sewage from leaking into the creek. MSD is under pressure from the federal government to eliminate its combined sewers.
The tunnel will allow us to be more cost efficient and do a better job for the environment, he said.
The Corps of Engineers started considering the deep tunnel earlier this year. Linda Murphy, the Corps' project manager, said she expects to hear from Washington this month on whether the Corps can proceed with a feasibility study.
If the study is approved, at a cost between $4 million and $10 million, the Corps will recommend whether to move forward with the project by 2003.
I can't say whether the benefits will support the cost, Ms. Murphy said. But it's viable because we'd be solving two problems with one project. And it's more environmentally friendly than any of our alternatives. It seems to be publicly acceptable.
Environmentalists agree, but some are wary of the Corps' involvement.
Robin Corathers, executive director of the Mill Creek Restoration Project, said previous Corps plans to control flooding on the Mill Creek would have been environmental disasters.
Efforts at surgery
The federal government has been trying to deal with Mill Creek flooding since the early 1970s, when Congress first authorized the Corps to turn the meandering creek into a straight, concrete trough.
That plan was abandoned in the early 1990s, after about one-third of the creek was paved at a cost of $117 million. The Corps then began studying the idea of building levees and a 20-foot flood wall along the creek. That plan was ditched after intense public criticism.
A national Deep Tunnel Symposium will be held at the Cincinnati Crowne Plaza Hotel, Aug. 17-18. |
Topics include feasibility studies, tunnel design, construction, operations and maintenance.
The session will bring together professionals, educators and community leaders from around the country to share their experiences.
Attendance cost is $150, but the morning session on Aug. 18, which starts at 9 a.m. and will include discussion of the proposed Mill Creek tunnel along with similar tunnels in Cleveland, Toledo and Columbus, is free and open to the public.
The channelization of the creek really amounted to environmental surgery it removed the natural bottom of the river, the trees and other vegetation, and replaced them with concrete, Ms. Corathers said. So I'm cautiously optimistic. Concrete underground would be a lot less disruptive than concrete above ground.
Mike Fremont, president of the environmental group Rivers Unlimited, has been working with the Corps for 30 years on Mill Creek flooding. He wishes they weren't involved in the tunnel project.
I have no trust in them, Mr. Fremont said. The Corps just wants to increase its budget. In order to do so they have to keep coming up with these (huge) projects.
Whatever they say the cost will be, multiply that by two or three and you'll have the final cost.
But the project would be impossible without federal involvement specifically, federal dollars.
If approved, the Corps would pick up 65 percent of the tab. Local and state funds would be needed to pay the rest.
The $800 million price tag is an estimate of what it would cost today and is provided by the engineering firm of Parsons Brinckerhoff, which was hired to study the proposed project by the MSD. Parsons has been involved with many of the deep tunnel projects around the nation.
We're in a new era where the federal government no longer pays 100 percent of the construction on these projects, the MSD's Mr. Karney said.
"The tunnels work'
In other cities, the tunnels have been used to eliminate combined sewers.
Cleveland has more than 80 miles of deep tunnels, and is ready to spend $1 billion more over the next 20 years.
Rick Switalski, manager of sewer design for Northeastern Ohio Regional Sewer District, said the tunnel program there started in the early 1970s when the federal government passed the Clean Water Act.
We've tunnelled through every condition known to man, Mr. Switalski said. The tunnels work. They do their job in bringing (sewage) flow to our plants rather than having it dumped into the environment.
Milwaukee has dug 17 miles of deep tunnels, at a cost of $2.3 billion. Its program started in the 1980s, after the city was sued by Chicago because of its sewage discharges into Lake Michigan.
Those tunnels have reduced the sewage overflows from about 60 per year to three, said Mark Kass, spokesman for the Milwaukee Sewage District.
The Mill Creek tunnel would feature 25 drop shafts, strategically placed along the 16-mile tunnel and just outside the creek bank. Each drop shaft would be about 20 feet in diameter and would be placed in the vicinity of a combined sewer overflow or by a Mill Creek tributary.
When water begins to exceed the banks, it will flow into the tunnel rather than into homes and businesses in the flood plain.
The tunnel also will allow the MSD to store water if its treatment plant is operating at capacity.
Borer is a thriller
Digging the tunnel takes one large drill bit a custom-made boring machine that itself will cost millions. The Robbins Company, based in Solon, Ohio, has built more than 250 of the machines.
Robert Moffat, an engineer for the company, said they are complex and use space-age technology.
They're kind of like rocket ships, only short rockets, he said.
The head of the machine cuts through rock with a 120-ton spinning head armed with steel discs arranged in a sort of bulls-eye pattern. Hydraulic jacks set behind the head steer the boring machine by varying the pressure exerted in the head. Water-cooled electric motors keep the machine in motion.
A laser beam is shot through the center of the machine to keep it on track.
As the machine moves through the rock, a conveyer belt coming from the rear of the machine removes fist-sized pieces of rock. The belt can be thousands of feet long.
It would take about 15 years before the tunnel is operational, if the project is approved by the Corps.
Project Manager Ms. Murphy said the deep tunnel may be the communities' last chance to get federal help in solving the Mill Creek flooding problem, since paving the creek and building flood walls have been ruled out.
We're not under a mandate to proceed with anything, if we can't find a project where the benefits exceed the cost, she said.
Decision to be made
Bruce Koehler knows the twists and turns of the Mill Creek better than most. He is vice chairman of the Ohio-Kentucky-Indiana Regional Council of Governments (OKI), which is the creek's regional water quality manager planning agency.
Mr. Koehler said the tunnel is a viable long-term solution, but it alone won't solve the creek's problems. Short-term fixes for the creek include planting trees on the banks and more surveillance for illegal dumping.
It's going to take a lot of political will to spend this kind of money on the Mill Creek, Mr. Koehler said. Ultimately we have to decide whether we want to save it as a natural resource, or mistreat it as nothing more than a system to prevent flooding.
To me it's still a valuable natural resource. There's no other place on Earth like it.
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