City to map floodplain

Wednesday, January 18, 2017

$185K study to allow for more management of Flat Creek

After massive flooding hit Cassville twice in 2015, in July and again in December, city officials have been searching for ways to better-manage Flat Creek to prevent future damages.

In a first step to allow for more accurate creek and floodplain management, the city of Cassville has entered into an agreement with HDR Engineering and Anderson Engineering to map the floodplain from Sale Barn Road, through downtown Cassville and up 11th Street.

The agreement was reached at $185,790, with the majority, $146,215, going to HDR for surveying, hydrology, hydrologic modeling, floodplain mapping and a letter of map revision (LOMR) package to be sent to the Federal Emergency Management Administration. The other $39,575 will go to Anderson for working in conjunction with HDR to complete drone mapping of the floodplain.

The city paid $135,790 for the study out of its Community Development Fund, as Cassville's Industrial Development Corporation (IDC) offered $50,000 for the project.

Steve Walensky, Cassville city administrator, said the study will allow the city to use the Hydrologic Engineering Center's River Analysis System (HEC-RAS), a U.S. Army Corps of Engineers flood mapping program that allows users to predict potential impacts of new construction or future floods.

"It's a computer model that detects water flow through our rivers and channels," Walensky said. "The end result is we intend to use the HEC-RAS to help manage development in the floodplain and to get approval from the Corps and [Department of Natural Resources] to do channel improvements, because with the HEC-RAS, we will know the effects."

The agreement was a few months in the making, as Alderman Jon Horner expressed concerns about spending so much money for only a study.

"My initial reservation was this being termed as a study," he said. "I've had concerns in the past with here, and governments in general, studying problems. I'm more interested in finding solutions and doing action more useful."

Horner said it was Walensky who helped him change his mind about the project.

"We know we flood, we have a pretty good idea why we flood and we know where we flood," he said. "It wasn't until Steve clarified more that this wasn't just a study, but an interactive tool that would be beneficial and useful to us for future growth in and out of the floodplain and those impacts.

"Another component is if we are actively trying to solicit for government funding for projects, this will help. The IDC highly recommended this project as well, and the third part that helped me change my mind was their willingness to help with funding."

The city in 2016 spent time cleaning out the gravel from Flat Creek, a project that will improve flow through the creek bed. But, to obtain the needed permits to make any changes to the banks or channels, the Corps and DNR require a recent study and precise knowledge of effects. The last floodplain mapping in Cassville was done in 2006 and is outdated, mostly due to development in the floodplain.

"There has been no maintenance on the creek for, some people say, 30 years, and construction has encroached, so the problem is getting worse," Walensky said. "One of the problems is if that silt, rock and mud settle, they can create bars on the creek bed and trees grow. Once trees get to a certain height, you can't cut them out. We hurt ourselves by allowing development, but no maintenance of the creek."

Horner said he hopes to see the study contribute to a possible lengthening of the bridge over Flat Creek on Highway 112.

"The Highway 112 bridge is the biggest bottleneck, and if we can open it at the base, water could flow through faster," he said. "The 13th Street bridge is a prime example of how that helps. When I was a kid, that bridge was tiny. When the new bridge was built in 1988, it had an amazing impact."

The creek mapping began last week, with mapping scheduled to be completed in early July and the LOMR submitted to FEMA sometime from August to October. Troublesome, Kenney, Lee and Brock branches will be included, as well as Flat Creek itself.

In total, four companies answered the city's request for qualifications for the project, and Walensky asked HDR to work with Anderson to get the best of both worlds with the mapping by combining HDR's broader package and adding Anderson's drone capabilities. The drone will cover approximately 500 acres of land along the floodplain and Flat Creek's tributaries, as well as provide high-resolution, color images of the land. Drone work is expected to be sometime from May to July.

"We had the cream of the crop to pick from," Walensky said. "And, I'm beyond pleased HDR and Anderson agreed to work together."

Cassville officials had some help from a concerned and qualified resident in putting its plan together. Lynn Hilburn, a retired floodplain manager, worked with Walensky and the city on a volunteer basis, playing a large role in crafting the city's request and identifying the city's needs.

"Lynn has a tremendous amount of skill and talent in this area," Walensky said. "He has done this for multiple cities and volunteered his time to help the city. He deserves an enormous amount of respect and credit for coming in to do this, and all because he loves Cassville."

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