The U.S. Army Corps of Engineers on Wednesday notched a first in its efforts to repair badly damaged levees along the Missouri River.
A 1,200-foot hole in the levee south of Council Bluffs was closed.
The breach is one of four priority repairs along the Missouri River between Omaha and Rulo, Nebraska, and it is the first of the four to be completed, said Matthew Krajewski, readiness branch chief for the Omaha district of the corps. There are 40-some breaches in levees between Omaha and Rulo. Initial repairs to all of those won’t be completed until next year, Krajewski, said.
“We got it closed,” he said of the $6 million effort. The funding comes from federal coffers.
The levee protects parts of the Bluffs, Highway 34, the MidAmerican Energy coal plant, Southwest Renewable Energy — the plant that President Trump visited Tuesday — a Google data center and the town of Pacific Junction. It is known as L611-614 — the L refers to the left bank of the Missouri as one looks downstream; the numbers refer to river mile markers.
The patch isn’t final, Krajewski said. The hole has been filled to a minimum level of protection — roughly the equivalent of a 25-year flood — but not to the levee height or condition prior to this spring’s flooding. Additional work will be needed to do that, he said.
The breach was patched with river sand. Now that the breach has been closed, the corps will focus on shoring up the patch against the river’s corrosive power, Krajewski said. Crews will do that by placing rock or clay over the sand to give the patch more resilience. As money and time permits, the corps will return and restore the levee to preflood conditions, he said.
The work was done by Western Contracting of Sioux City, Iowa.
Closure of another significant breach — the one that allowed the river to flow into Percival, Iowa — also should be completed yet this week, Krajewski said. It is known as the L575-A breach.
Another is scheduled for completion later this month, but the last of the four may not be completed until early July.
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Omaha's levee system: Omaha is protected by a 13-mile system made up mostly of levees. The system starts near the Omaha Public Power District’s North Omaha power plant and runs south to the Missouri River Wastewater Treatment Plant. The entire system is designed to provide protection from a 500-year flood, which has a 0.2 percent chance of occurring in any given year.
What is a levee? A levee is a berm of compacted earth that’s designed to hold water in a river channel. The top of Omaha’s levees stands at about 40 feet. Levees are only as good as their maintenance, which must include protecting faces from erosion with rock or grass and other vegetation and keeping them free from trees and animal burrows that can serve as an entry point for water.
Levees protecting Council Bluffs: Council Bluffs has 28 miles of levees, which start near Big Lake on the north side of town, travel west to the Missouri River and then south to the MidAmerican Energy plant. The levees along the Missouri are designed to provide protection from a river level of about 36 feet, with 2 to 5 feet of extra space above that.
Omaha's 1-mile flood wall: Omaha is also protected by a 1-mile stretch of flood wall in the downtown area. Flood walls are used where there’s not enough room for the slopes of a levee. Omaha’s flood wall, built in 1949, is a concrete barrier that starts near the National Park Service's Midwest headquarters building and continues to near the Interstate 480 bridge.
How the flood wall works: At three points along the wall are huge steel gates that can be lowered into gaps in the flood wall to keep water out when the river rises. When the river is lower, the gates are left open so storm water can drain from the land side into the river by gravity. Each gate is made of three-quarter-inch steel and is about 21 feet wide, 6 feet tall and 6,000 pounds.
What role do interior pumps play? With the flood wall gates in place, getting water out of the city becomes an issue. The city can bring in temporary pumps to pump out water in low-lying areas. They're used to bolster the city's permanent pumps when water's high.
The Papillion Creek system is made up of three creeks — the Little Papillion Creek in the north and east, the Big Papillion Creek through the city center and the West Papillion Creek in Papillion and Bellevue. They join in Bellevue to form the Papillion Creek, which flows into the Missouri River. The system aims to hold back and slow the movement of water in the upper portion of the watershed — that's the area drained by a river or stream — and keep it in the channels in the lower portion.
There are 11 reservoirs on creek branches and tributaries in the Papillion Creek Watershed and 52 miles of levees (out of the 90 total in the NRD’s territory), as of spring 2019. Three of the reservoirs are on tributaries of the Big Papillion. Cunningham Lake helps control the Little Papillion. More reservoirs have been constructed on the West Papillion and its tributaries, because the area developed later.
Maintenance programs also help maintain the channels, including making sure they’re clear of debris and large enough to carry needed volumes of water. John Winkler, the Papio-Missouri River NRD’s general manager, stressed that these elements — plus proper floodplain management to keep homes, office buildings and shopping centers from encroaching on waterways and out of harm’s way — have to come together to provide effective flood control.