Officials worry drainpipe limit under road will hinder flood relief

Sunday Times Newspapers

ALLEN PARK – City officials are concerned that the 24-inch diameter drain pipe size limit imposed by the Michigan Department of Transportation for the line that would run under the Southfield Freeway would not do enough to prevent basement flooding during periods of heavy runoff.

City Engineer Rick Lang said at the Oct. 13 City Council meeting that the original drain size was proposed to have a 72-inch diameter, a dimension that later was increased to 96 inches. The wide pipe tunnel is used for rainwater conveyance and as a holding tank during heavy downpours and allow water to move constantly.

Lang an 18-inch pipe currently crosses under the freeway now to the north. He said city officials must be careful how much they push for a larger drain, because MDOT could pull the 24-inch drain and even the stimulus money.

Larger drainage holding pipes could be installed on the side of the freeway, Lang said.

Engineering experts say pipes larger than 24-inch diameter can’t be steel and must be concrete. Pipes running under a freeway have to withstand intense vibration and load. Concrete pipes, with a wider diameter, react and withstand the constant vibration and loading stress from freeway traffic differently than 24-inch diameter steel pipes.

Michigan state law allows trucks weighing 80 tons (164,000 pounds) to travel many of its freeways when their weigh is supported over multiple axles. That transmits a constant vibration and load stress through the roadway and down through the ground.

Even a 24-inch diameter steel drain pipe with a relatively small footprint (compared to a 72- or 96-inch diameter pipe) would have to be installed at least 12 feet deep to absorb the tremendous vibration and load it would be subject to under a busy freeway, experts say. The ability of a pipe to withstand vibration and load stress when buried under a heavily used, freight-carrying freeway subject to constant load forces directly impact a pipe’s structural integrity.

The ability of an underground pipe absorbing constant vibration and load-bearing forces also would be affected by the type of surrounding soil. Different underground material, like sand or clay, transmit, baffle and absorb vibration and other wave-transmitted forces differently to structural objects – like drain pipes — resting within its layer.

Engineering experts say that some metropolitan Detroit cities, like Sterling Heights, effectively have prevented basement flooding by using fenced-in, above-ground grassy depressions that act as surge ponds. That strategy, however, depends on a city having available open park land that can be fenced off in order to install the surge ponds. Since the surge ponds can fill up rapidly during a rainstorm, they must be cordoned off to prevent children from entering them.

Pamar Enterprises, an underground utilities contractor specializing in sanitary, storm and water mains, has been selected to carry out the U.S. District Court-mandated sewer upgrade.

According to its company Web site, Pamar Enterprises Inc. is a family owned company, and is affiliated with the Michigan Infrastructure & Transportation Association, Associated Builders & Contractors and the Michigan Chamber of Commerce. Pamar is also prequalified by the MDOT and metropolitan-area municipalities.

The $17.2 million contract initially will be paid by the city. If Allen Park pays for 60 percent of the project cost, American Recovery and Reinvestment Act money will pay the remaining 40 percent.

City Administrator Eric Waidelich said the original project cost has increased from $17.2 million to $21.5 million, mostly due to material costs. With the stimulus money reimbursement, Waidelich says the city will realize over $8 million in savings.

The city will take out $17.2 million in bonds, but will be left with $12.9 million to repay after receiving the stimulus money.

Last year voters approved adding 0.24 mills to their property taxes so the city could borrow money to pay for the cost of the sewer project.