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Flood mitigation in Davenport to cost $165 million, take 10-20 years
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Flood mitigation in Davenport to cost $165 million, take 10-20 years

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Mitigating the effects of more frequent river flooding along Davenport's nine miles of riverfront will likely begin underground and require a more than $165 million investment in public and private funds over the next 10 to 20 years.

That's according to a recent report from a city-hired consulting firm on recommended flood mitigation measures.

"It attempts to strike this balance of living with the river, but making living with the river a little bit easier," said Teresa Stadelmann, project manager for Cedar Rapids consulting firm HR Green, Inc. "And, by doing so, we're trying to adopt an equitable approach along the riverfront."

The report is a culmination of a years-long effort by city officials to respond to increasing calls for a permanent solution to flooding in the wake of historic flooding in 2019 when a temporary flood wall made of HESCO barriers failed, sending floodwaters rushing into several blocks of downtown and causing an estimated $30 million in lost revenue and damages.

Flat-bottom boats were dispatched to rescue the stranded. Vehicles were left behind in the gushing floodwaters; some floated down the street.

Davenport had for many years depended on its levee of sand-filled HESCO barriers to protect the downtown from the river.

The "road map" provided by HR Green and architecture and engineering design firms Sasaki and Shive-Hattery include dozens of projects for the downtown and the city's nine miles of riverfront. Earthen berms, partially buried flood walls, permanent pumping stations and major storm-sewer repairs are among the tools recommended to reduce the severity of damage wrought by increasingly frequent Mississippi River floods.

Some private property owners may qualify for buyouts.

What's in the plan

The proposed projects include: upgrading storm sewers and installing floodgates; elevating River Drive east and west of Mound Street; elevating parts of LeClaire Street north of the railroad past Third Street; building a mix of raised berms and partially buried flood walls north of the railroad tracks from areas around the Arsenal Bridge west past Veterans Memorial Park; and replacing temporary city pumps with automated permanent pump stations.

In west Davenport, recommendations include consolidating and reducing a large number of storm sewer outfalls and constructing standardized backflow prevention gates; repairing existing berms around the Garden Addition and adding an eastern closure; building a new detention basin to collect storm water runoff; and replacing the Credit Island causeway with a bridge.

"The recommended projects in this really repair the infrastructure that's already around the Garden Addition, shoring up those existing flood mitigation elements that area already in place," Stadelmann said.

Other recommendations include:

  • The targeted purchase of properties located in the floodway that have experienced repeated property losses from flooding and were identified during the U.S Army Corps of Engineer's Silver Jackets Project and assessed for their flood risk and mitigation alternatives. 

    "(A)cquiring targeted properties would include removing owners from that ongoing risk that they face, and also reducing City effort to furnish services in flood-prone areas," Stadelmann said.

  • Establishing a cost-share program between the city and building owners to flood-proof properties and address the residual risk that remains after other infrastructure improvements are made. 

    "So it's vital private property owners in the flood plain take responsibility for their flood risk, and the city can support this and their efforts through that public-private partnership," Stadelmann said. "Yes, the city is going to be putting in public infrastructure. It's going to try to keep transportation routes open and improve commerce across the city during flood events, but there is always residual risk."

    Individual building mitigation would also apply to public facilities along the riverfront to reduce city flood-fighting efforts.
  • Updating the city's storm water plan to improve storm water drainage and reduce pumping requirements, including opportunities for green space and improved water quality, as well as updating city building and zoning codes to address flood risk and encourage flood mitigation.
  • Performing further studies of flooding risk from inland creeks and streams, including a watershed study of Blackhawk Creek to look at both the risk of flash flooding and identify solutions to ongoing erosion and sedimentation in the creek.

Projects would be phased over time and rely on annual capital-improvement funding by the city and on state and federal grants. The price tag is likely to exceed $165 million in total, according to estimates from HR Green.

"It offers both incremental and transformational recommendations," Stadelmann said. "(A)nd it works with prior planning studies along the riverfront. Many of the recommendations can be scaled, which allows the city flexibility to adjust to constraints or opportunities as they arise in the future. Finally, there's a balance of structural and non-structural mitigation recommendations that combine policies and programs that address individual flood risk with public investment in flood resilient infrastructure."

Davenport aldermen will meet Wednesday to discuss and listen to comments from the public about the flood plan, followed by a vote the following week on whether to accept the flood resiliency plan.

Prevention vs. mitigation

Davenport Public Works Director Nicole Gleason and Stadelmann reiterated the plan is not one of flood prevention but mitigation. The city cannot prevent floods, but rather make specific plans to lessen the severity, disruption and damage caused by river flooding to city assets, while helping citizens and businesses protect their property.

The proposed measures would provide protection up to a flood stage of 22 feet, below the record 22.7-foot crest reached in 2019.

Previous major flooding in Davenport has ranged from about 18 to 22 feet, per city data.

However, the intensity, duration and frequency of major flooding has increased over the last two decades. More than half of the major floods Davenport has witnessed in the last 143 years have occurred within the last 20 years.

"There's an old adage that there's always a bigger flood," Stadelmann said. "But Davenport's three-pronged approach of retreat, flood-proof (and) flood fight cost-effectively prepares the city to deal with the inevitable future."

Protecting to a 22-foot flood stage would significantly improve access across the city and reduce flood risk and disruption to public infrastructure, businesses and residents, according to the consultants.

"Structural mitigation to stage 22 offers the city of Davenport a balanced, equitable and cost-effective solution that's rooted in the city's rich history of co-existing with the river," according to the report.

While the risk of higher floods always remains, major flood impacts would be deferred to the very largest flood events, according to HR Green. And the city retains the ability to deploy temporary flood fighting measures if needed, such as the use of HESCO barriers, to protect to a higher elevation in the future for anticipated floods, Stadelmann said.

The city's current flood response plan includes provisions for actions up to a flood stage of 26 feet.

"Completion of storm sewer and roadway improvements … would quickly provide improved access to the Arsenal and Centennial bridges and allow the city to delay the start of flood fighting in many areas until higher river stages," according to HR Green. "This would reduce both disruption to the public and labor costs, and provide a permanent flood detour route across Davenport up to flood stage 22’."

Implementation

Moving forward, Gleason said city staff plan to set aside recurring funding as part of the city's annual budgeting process, as well as "aggressively looking at grants," to begin tackling some of the recommended projects, beginning with storm sewer repairs and upgrades.

Both Stadelmann and city officials noted much of what needs to happen to reduce flood damage in Davenport must first occur under ground to fix damaged and dated storm sewers that allow floodwaters to rise from below.

Alderman have set aside $4 million in federal COVID-19 rescue funds for improvements to the storm sewer system on River Drive from Federal to Third streets and from Iowa to Main streets to keep the area accessible during flood events up to a river stage of 22 feet. The sections of roadway flood and become impassible at a river stage of 17.5 to 18 feet, depending on conditions.

Initial investments will also likely focus on establishing a flood buyout and floodproofing cost-share programs, along with raising River Drive and the rehabilitation of existing pump stations and flood berms around the Garden Addition.

Subsequent projects would likely focus on building a mix of berms and flood walls and raising roads along the riverfront, beginning at the Arsenal Bridge and working downstream, and constructing permanent pump stations.

Reaction

Overall, alderman praised the work of the consultant and the flood plan.

"After a flood that really shook this city and sort of reset the deck for us, we committed to funding this plan and here we are," Ald. JJ Condon, at-large, said. "And I'm grateful that this is plan that seems to understand and reflect the relationship the city has with the river — both good and bad — and understands the financial commitment that is being put before us.

"It's a holistic effort and it's going to take time," Condon said. "Our identity and our soul is aligned with the Mississippi River."

He and Aldermen Matt Dohrmann, Ward 5, and Kyle Gripp, at-large, urged their colleagues and future councils to be deliberate and stay the course in putting the flood plan into action.

Gripp stressed the plan will require support of community partners and state and federal officials.

"We've got to work together to figure out how to fund this," Gripp said.

Mayor Mike Matson, who campaigned on the future of flood-fighting in Davenport, heralded the recommendations as a "historic, balanced plan for the city of Davenport."

"Folks since 1965, both citizens and others have asked to do something," Matson said. "Here, this council, working with this staff and the public input are doing it. They brought you a plan that has a road map to get this flood mitigation system going … with a purposeful plan in each area (of the riverfront) specific to that area. … This plan will help significantly reduce our city and flood-fighting efforts in personnel and equipment."

Kyle Carter, executive director of the Downtown Davenport Partnership, an affiliate of the Quad Cities Chamber of Commerce, lauded the recommendations.

"I think we've actually, finally, produced a document that we can all agree on," Carter said. "It does a good job of being balanced in that it address the entire nine miles (of riverfront). … That is historic. We've never had anything that comprehensive, let alone one that had such a specific game plan. And I think we finally have something we can go and do."

Carter, too, noted the $165 million estimated price tag is "a drop in the bucket" compared to Cedar Rapids' $750 million permanent flood control system.

"It is actually an incredibly small number when the federal government is spending trillions of dollars in infrastructure," Carter said. "We can figure out a way to find $150 million, especially over time. I don't think that number is as scary as it might seem."

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