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Overton Garage Detention Basin (designed by Powers Hill Design, LLC) benefits the community

August 10th, 2014

Stormwater projects already paying off in Midtown

As printed in the Commercial Appeal

By Tom Charlier

As the rain came down so heavily and incessantly that late June weekend — setting records and causing trouble all across Memphis — Tommy “Tee” Cloar and Mary Wilder noticed something really strange:

Their neighborhoods weren’t flooding.

To understand how unusual that was, it helps to know that Cloar considers it “a good spring” if his backyard doesn’t get covered in 3 feet of floodwater, and that Wilder is used to finding her apartment building basement flooded after downpours less severe than the June 28-29 event that dumped 7.09 inches of rain.

Cloar, who lives in the Belleair neighborhood, and Wilder, a resident of Vollintine-Evergreen, are among the residents in the Lick Creek basin of Midtown who have benefited from nearly $18 million in City of Memphis projects to detain floodwaters. The city in recent years has completed detention basins in the Overton Square parking garage, Christian Brothers University and Snowden School, and is getting ready to build another at Catholic High.

Now, with the Lick Creek problems largely under control, officials are undertaking a citywide master plan to attack flooding issues in neighborhoods from Southwest Memphis to Cordova. They’re initially focusing on seven particularly floodprone basins, which have been the focus of a series of public meetings in recent weeks.

Although the city uses computer models to identify areas subject to flooding, the meetings will further define the problems, said City Engineer John Cameron.

“What we’re looking at is information where people have seen and experienced flooding,” he said. “The models are not perfect, and we like to calibrate them with real-world experience.”

Once the problems are clearly defined, Cameron said, officials will try to design a project to fix them. They then will have to develop a priority list to identify which projects can be built with available funding.

For all its general budget problems, Memphis has a healthy stormwater fund. Generated by monthly fees on property owners — the standard rate for most residences is $4.02 — the fund brings in $24 million a year. Like the sewer fund, it is a dedicated revenue source that can’t be used for non-drainage capital projects or operating costs in the city’s general fund.

The city has been spending about $22 million annually from the fund, said Robert Knecht, deputy director of public works.

Memphis officials say it’ll take five to seven years to complete the citywide master plan. The initial drainage basins they’re studying include South Cypress in Southwest Memphis, Cane Creek in Orange Mound and South Memphis, Cypress Creek in the Binghamton area, Todd Creek in Frayser and larger watersheds in Raleigh, Whitehaven and along Walnut Grove.

Eventually, the city plans studies of 30 drainage basins.

“You need to have a broad understanding of how these basins interact,” Knecht said.

City officials have said drainage improvements not only protect lives and homes, but enhance property values, thereby strengthening the tax base.

As is the case in many cities, Memphis essentially outgrew a drainage system that in most areas is more than 75 years old. The development of commercial areas with great expanses of paved, impervious surfaces sends runoff into storm sewers and drainage ditches faster and in greater volumes than their designed capacities allow.

Much of the Lick Creek basin has been served by a drainage system dating back to the 1930s.

“It was big enough in 1936, but it’s not big enough in 2014 because we’ve added so much impervious surface,” said Wilder, a neighborhood volunteer in Vollintine-Evergreen.

To accommodate the extra flow, the city began work on a network of detention basins, which are dry depressions or reservoirs that briefly store floodwater, then release it gradually as storm sewers have space.

The basin beneath the Overton Square garage, part of a project that cost $14.8 million to design and build, can hold 7.5 million gallons of runoff — the amount expected from a 100-year flood. During the June 28-29 deluge, which city officials describe as between a 25- and 100-year flood, it was “about half-full,” Knecht said.

The city also constructed a $2.24 million basin at CBU that can hold more than 5.5 million gallons and a nearly $900,000 facility at Snowden that can detain 3.4 million gallons. Early next year, work will begin on a basin at Catholic High that will have a capacity of nearly 1.5 million gallons.

Cloar, the Belleair resident, said he was pleasantly surprised that this past spring and early summer didn’t bring the kind of yard flooding as past ones. “It’s been almost up to the house before,” he said.

Wilder said the June 28-29 rainfall brought minor street flooding, but nothing compared to the problems experienced before the detention basins were built.

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