The temporary flood barrier breach that led to an emergency evacuation of Davenport’s lower downtown was likely caused by the barrier sliding out of place and tipping over, an investigation performed by the U.S. Army Corps of Engineers has found.
Under the conditions, which were re-created by engineers, the Corps says the barrier should have held the way the city built it. Water seeping underneath the barrier amid heavy rain and weeks of holding back the Mississippi River likely caused a shift — as little as a fraction of an inch — that provided enough momentum for the barrier to overturn, the Corps says.
“Based on the engineering evaluation completed, the initial calculated factors of safety for sliding and overturning were sufficient and indicated that the HESCO barrier should not fail under the load conditions experienced” on April 30, the report says.
But Corps officials also say the city should “include a means to fortify or add additional height as necessary for constantly changing river forecasts.” Other recommendations offered by the Corps included expanded flood barrier monitoring, proper installation training for public works employees who assemble the barriers and more communication with residents and businesses in the floodplain.
On April 30, the temporary flood barrier failed after holding back the Mississippi River for 46 days, sending several feet of water into the city’s business district. Costs for the city’s public works department have risen substantially since then, other infrastructure projects have been delayed and some downtown business owners say they will not recover.
City officials have previously said that the option of adding a second layer to the original barrier was not safe because additional work could have compromised the existing wall. Sandbags were added to the top of the barrier in a manner city officials say was recommended by HESCO — something the Corps says may have worsened the situation — after the river levels rose substantially amid heavy rains.
Aldermen received a hard copy of the report on Tuesday afternoon a few minutes before Corps officials were set to share and explain their findings. Alderman Mike Matson, 7th Ward, noted during the meeting that there was little time for the city’s elected officials to thoroughly review it before their opportunity to ask questions.
Reactions from city officials mostly centered around the report’s conclusion that the single line of HESCO barriers should have been sufficient to hold back the Mississippi River. Mayor Frank Klipsch said the report appeared to reaffirm the city’s already-held belief that the structure was installed properly.
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Alderman Ray Ambrose, 4th Ward, echoed those comments.
“It was an incredibly unique situation that happened this year. So even if we would’ve done ‘L’ shape … even that could fail,” he said of the heavy rain and record flooding, adding: “We’ll be prepared better next time.”
To reach its conclusions, the Corps reviewed surveillance video of the failure, evaluated methods used by the city to construct the barrier, performed a field investigation and re-engineered the scenario. Davenport City Administrator Corri Spiegel said Tuesday that the city asked for the analysis because “we wanted to learn if we did something wrong” and look for ways to provide better outcomes in a community that often experiences flooding.
“With any catastrophic event of this nature, you want to learn how you can do it better next time,” Spiegel said.
“The barrier as designed should have worked,” Spiegel added, referring comments made by Corps officials who briefed city officials Tuesday on the findings.
The Flood of 2019 has sparked a citywide conversation about flood protection, prompting local officials to re-evaluate Davenport’s flood protection plans. Klipsch, who is set to leave office early next year, has formed a task force that will recommend changes the city could make as more frequent and fiercer floods are expected to come with changing weather patterns.
Some flood-mitigation initiatives have already been put in place. In late May, Spiegel said public works employees would build bigger, heavier flood walls whenever record flooding might occur.
After the barrier broke down, former public works director Mike Clarke had criticized Davenport's efforts, saying the city should have double-stacked the barriers at the base and added another line on top for additional height.