LA CROSSE, Wis. (AP) — The volume of sand that needs to be removed from the Mississippi River following massive floods this spring is so great that the dredging operation couldn't wait until after the water recedes, the U.S. Army Corps of Engineers said.

Of the 13 dredge sites in the Corps' St. Paul district, which runs from St. Paul, Minnesota, to Guttenberg, Iowa, 12 needed emergency attention. That means there was so much sediment that if the water level fell that day, the channel would be closed, said Dan Cottrell, the Corps' dredging manager for the district.

Cottrell told the La Crosse Tribune that the Corps starting dredging April 29.

"It's a tremendous amount of sand," Cottrell said. "On a crazy year like this, it's likely to be above average."

The Corps has already dredged 160,000 cubic yards (122,000 cubic meters) of the 1.1 million cubic yards (841,000 cubic meters) of sediment that must be removed from the St. Paul district, Cottrell said. The Corps usually dredges about 980,000 cubic yards (750,000 cubic meters) of sediment along that stretch of the Mississippi from April to November.

The Corps usually runs four dredges in the district, but this year it's using six, said Paul Machajewski, the district's dredge material manager.

He said it's too early to predict how much the operation will cost, but that $29 million has been allocated to keep that section of the river clear for navigation, which is up from $26 million in 2018.

"We've got $3 million dollars more this year, but we're going at an accelerated pace and we're not sure where we're going to end up," Machajewski said.

Machajewski said he also needs to work out where to take the sand, which can be used in concrete production, road maintenance and cow bedding, among other uses. It can be stored at nearby sites, about half of which are islands, or inland in gravel pits.

The gravel pit in Wabasha, Minnesota, has less than two years of capacity left, and the Corps is working out a plan with Wabasha on how to store dredged materials in the future, Machajewski said.