Iowa city using inflatable dam to hold back flooding

WAVERLY - This flood-ravaged Cedar River community took an approach quite different from that of Cedar Rapids in protecting itself from future inundations.

Whereas Cedar Rapids has opted for walls and levees to hold the river at bay, Waverly, population 10,000, has installed an innovative inflatable dam that has greatly increased flood protection above the dam.

'We removed the flood threat for about 500 homes and businesses without building levees,” City Engineer Mike Cherry said Friday at the fall meeting of the Cedar River Watershed Coalition.

In addition to the inflatable dam - the third of its kind to be built in Iowa - other flood-mitigation projects were showcased during a bus tour of the city.

They include several large retention ponds that will store and slowly release future floodwaters, the buyout of about 90 flood-prone homes and a $7.1 million re-engineering of the of troublesome Dry Run Creek, set to begin in April.

Waverly Mayor Charles Infelt said the flood of 2008 helped the community realize that the river was at the forefront of the city's identity.

Cherry said flood mitigation studies conducted after a serious flood in 1999 indicated two possible sources of relief - a conventional levee and wall system and an unconventional inflatable dam.

After the flood of 2008, when the availability of funding made mitigation a realistic possibility, residents overwhelmingly opposed levees, which would obstruct views of the river and limit accessibility, he said.

Work still needed

The inflatable dam, completed in 2011 with $4.2 million in federal funds, maintains an upstream water level elevation that adjusts automatically to changing river flow rates, virtually eliminating flooding above the dam.

'It permanently removes about 500 homes and businesses from the 100-year-flood plain, greatly reducing their flood insurance premiums,” Cherry said.

The lower above-dam water levels also prevent the breakout of floodwater into the watershed of Dry Run Creek, a Cedar River tributary on the city's west side that flooded more than 200 properties in 2008.

The inflatable dam, however, does not afford any protection for property below the dam, he said.

Cherry said no funding was available for downstream levees and walls, even if the community had wanted them, 'because the cost of the levees would have greatly exceeded the value of the property protected.”

While progress has been made in mitigating damage from future Cedar River floods, much remains to be done to reduce their height through improved management within the Cedar's 7,830-square-mile watershed, according to State Sen. Rob Hogg, D-Cedar Rapids, co-chairman of the Cedar River Watershed Coalition.

Speaking at the afternoon session of the fall meeting, Hogg said just 12 of the Cedar's 224 subwatersheds have active organizations working to improve the land's ability to absorb, store and slowly release water from extreme rainfall events.

'We at the bottom end of the watershed are doing our part,” Cedar Rapids Mayor Ron Corbett said.

During the flood of 2008, Corbett noted that the city's flooded wastewater treatment plant pumped more than 1 billion gallons of raw sewage into the river during the 43 days it was offline.

'It pains us to even admit that happened, but it won't happen again,” Corbett said, noting that the city recently cut the ribbon on a project designed to protect the treatment plant from future flooding.

The City Council, he said, also recently approved development of a 73-acre greenway that will allow the river to breathe during floods while creating recreational space when it is not flooding.

'We can't control the climate, but we can work to mitigate flood risks. These are investments we can't afford not to make,” he said.

l Comments: (319) 934-3172; orlan.love@thegazette.com