A controlled underwater explosion took place in the Mississippi River on 15 October 2023 as part of a US$23 million bridge demolition project being carried out by Helm Group for the Iowa Department of Transportation.
The old crossing between the cities of Bettendorf, Iowa, and Moline, Illinois is undergoing gradual demolition after a replacement bridge carrying four lanes in each direction and a shared pedestrian-bicycle path opened upstream in 2020.
The old Iowa-Illinois Memorial Bridge was a basket-handle, through arch twin bridge with one span built in 1935, after which a second span was added in 1959. The crossing operated toll booths up to 1970, five years before merging with interstate route I-74. Each span carried two narrow lanes without a shoulder and had an 80 km/h speed limit. A study commissioned by the Illinois DOT in 1994 deemed the old crossing was functionally obsolete and not built to modern standards.
A combination of jackhammering, drilling and underwater blasting is being used to remove the piers; concrete is to be recycled and used for other projects. A fourth and final explosion is scheduled for the upcoming winter.
One pier built into the riverbed will remain to avoid disturbing a colony of endangered mussels.
