Witold Krajewski worries about that last 10 percent.
The Turkey River Watershed Management Authority has released its comprehensive plan to reduce flooding in the 1.1 million-acre Turkey River watershed. The 20-year, $32.8 million plan — the first of its kind for a watershed of such scale — has a goal of knocking the top 10 percent off flood crests, substantially reducing the cost of major floods.
“Absolutely, the last 10 percent is the most destructive. That’s where the money is,” said Krajewski, director of the Iowa Flood Center, which performed the much of the computer modeling upon which the plan is based.
Krajewski said the two main ways to reduce the flooding effects of heavy rains are to increase infiltration of water into the soil and to construct a system of ponds and detention basins to store water for a more controlled release.
The plan’s water storage component calls for building 300 water and sediment control basins, creating or restoring 50 wetlands and establishing 10 linear miles of riparian buffers.
Methods to increase rainfall infiltration include many of the same conservation practices recommended in the state’s nutrient-reduction strategy — reduced tillage or no-till, cover crops, contour buffer strips, grassed waterways, strip cropping, tree and shrub planting, prairie strips, rotational grazing and the Conservation Reserve Program.
“It’s the same flowing water that causes floods and nutrient pollution,” Krajewski said.
The watershed group hopes the many benefits will make the plan “more sellable” to the Legislature and other potential funding sources, said Rod Marlatt, chairman of the group’s board of directors.
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Citing statistics from the Federal Emergency Management Agency, Lora Friest said every dollar invested in flood prevention saves the government $5.10 in recovery expenses. She is executive director of Northeast Iowa Resource Conservation and Development (RC&D), the agency that spearheaded development of the plan.
Ross Evelsizer, watershed planner for the RC&D, said plan developers have not yet established a complete accounting of Turkey River flood losses.
Responding to a recent survey, six communities and one county — out of 23 communities and five counties represented on the watershed management authority’s board — reported flood losses since 1995 totaling $20.7 million. They reported 105 homes lost, 79 businesses damaged or lost and 1,518 road segments, bridges or culverts damaged or destroyed.
That figure, Evelsizer said, does not include losses suffered in other cities and counties within the watershed, extensive agricultural losses or the millions of dollars in federal FEMA funds spent on property buyouts or recovery.
The Turkey River plan stands in marked contrast both in terms of cost and approach to Cedar Rapids’s $600 million flood defense system, which will consist primarily of walls and levees designed to channel floodwaters downstream.
Friest said the board members wanted to treat the underlying issue rather than its symptoms.
“They realized that protecting one or two communities with levees wouldn’t protect any of the other public and private infrastructure, urban or rural, that is damaged during large rainfall events. It also would not address the true social and personal impact of flooding that occurs throughout the watershed outside of those communities,” she said.
Friest said the board members also valued the plan’s multiple benefits that include, in addition to flood prevention, water quality improvement, wildlife habitat creation, reductions in nutrients and sediment, beautification of communities and helping communities and farms function more efficiently and effectively.
Board members, Friest said, are confident that implementing the proposed practices — based on the Iowa Flood Center’s modeling — will decrease rainfall runoff to a degree that protects them just as effectively as a multimillion-dollar levee system.
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Friest said the partners already have begun implementing as many of the practices as possible and are working with producers and producer groups, communities, counties and other private and public entities to implement or identify funding to implement other parts of the plan.
Krajewski said the flood center’s modeling focused on a hypothetical storm that dumps 5.67 inches of rain in 24 hours across the entire watershed, which includes parts of Howard, Chickasaw, Winneshiek, Fayette, Clayton, Allamakee, Delaware and Dubuque counties.
Implementing the plan would reduce by 10 percent the discharge of such a 50-year flood at Garber, where the Turkey and its major tributary, the Volga River, flow together, according to the plan’s authors.
In the wake of massive statewide flooding in 2008, the Legislature two years later authorized creation of Watershed Management Authorities, a mechanism for cities, counties, Soil and Water Conservation Districts and stakeholders to cooperatively engage in watershed planning and management.
The state’s 11 WMAs, including one on Linn County’s Indian Creek, are authorized, among other activities, to assess and reduce flood risk and to assess and improve water quality.
They can allocate funds for purposes of water quality and flood mitigation. But they cannot levy taxes or acquire property through eminent domain.
Four large floods have been recorded at the Turkey River gaging station at Garber since 1991. Those four flood peaks — 49,900 cubic feet per second in June 1991, 53,900 cfs in May 1999, 66,700 cfs in May 2004 and 45,500 cfs in June 2008 — are the four largest discharges observed during the continuous operation of this gage since 1932.