The U.S. Army Corps of Engineers will begin opening a historic flood control structure near New Orleans this week to divert water from a rain-swollen Mississippi River.

Col. Michael Clancy, the Corps’ district engineer in New Orleans, says heavy rains in the Mississippi Valley led to the decision to open the Bonnet Carre Spillway, upriver from New Orleans.

The spillway will be opened in anticipation of the river reaching a rate of 1.25 million cubic feet per second at New Orleans.

The spillway diverts some of the flow from the river into Lake Pontchartrain, easing pressure on the levees that protect New Orleans. This will mark the 13th opening of the spillway since it was completed in 1931 — and the first time it’s been opened in consecutive years.