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City seeks to map flood problem

By Burk Krohe

City commissioners favored moving ahead Tuesday with two projects to better understand flooding risks.

“I think it’s a great step in assisting this commission and future commissions in a whole bunch of areas,” Commissioner Rich Jankovich said at a work session on the subject. Jankovich co-chairs the Wildcat Creek Watershed Area Working Group. “

Commissioner Wynn Butler agreed. Butler said the projects will be important in “getting ahead” of flooding by mapping the city in detail thus identifying problem areas.

Wildcat Creek has flooded several times in the past few years, causing millions of dollars in damage to residential and commercial properties along its banks this past June alone. The flooding prompted the city to review “best management practices” to protect against the damage. Chad Bunger, city planner and floodplains administrator, said the city is working toward that goal in two areas.

Bunger said the first project is enhancing the city’s flood insurance rate maps (FIRMs) via “future conditions mapping.” He added the technique has been utilized by other cities with flooding problems.

The mapping will calculate the stormwater runoff generated from a full development build-out of the Wildcat Creek Watershed and Marlatt Ditch drainage basin based on the future land use map included in the Manhattan Urban Area Comprehensive Plan. Bunger said it will identify future conditions for the 100-year floodplain, otherwise known as the 1 percent annual chance floodplain.

The second project involves the creation of a mapping tool called depth grids, which Bunger said will show boundaries of floods and graphically represent the depth of stormwater.

Bunger said the future conditions mapping and depth grids provide several benefits including: informing current and future property owners of flooding risks, using the models and maps to design developments that are better protected from flooding, using the information to potentially identify future policy for the city, using the information to design infrastructure to protect against future flooding, planning emergency evacuations more efficiently and potentially adopting stricter local floodplain regulations.

Currently, the Kansas Department of Agriculture, Division of Water Resources, city and county are starting to update the local flood insurance study and subsequently FIRMs. The FIRMs are used by the Federal Emergency Management Agency (FEMA) to regulate development in floodplains and to determine requirements for flood insurance under the National Flood Insurance Program.

“We do need to get a decent map on there,” Butler said. “Then future growth can be controlled.”

AMEC Earth and Environment, an engineering firm from Topeka, has contracted with the Department of Agriculture to produce the updated flood study and maps for the city and county. Rob Ott, city engineer, advocated contracting with AMEC for future conditions flood models and depth grids.

“AMEC is very familiar with our floodplain,” Ott said. “It’s important that we do this.”

Ott and Ron Fehr, city manager, said there would be some efficiencies and advantages in undertaking the projects now, especially considering the benefits and that funds are currently available. 

The cost of both projects would total $40,890 with an anticipated completion date of March. The future conditions mapping would also be included in the update of the Riley County flood insurance study and FIRMs. The projects would be funded entirely from the Stormwater Management Fund under the 2012 capital improvements program watershed analysis project.

“I think it works to everybody’s best interests,” Fehr said.

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