A flood-control project in the works for more than 20 years should be completed next year, removing 1,500 properties from Sioux Falls, S.D.’s flood plain, a city official said.
Once the flood-control measures are in place, probably by the end of 2011, the Federal Emergency Management Agency will redo its flood-plain maps.
“Wal-Mart, Sam’s Club, The Empire Mall, Target are some of the businesses” that will be taken out of the flood plain, said Project Manager Tom Berkland.
Businesses and residents learned three years ago that FEMA was “modernizing” its flood-plain map, which required updates in the levee system and resulted in an expansion that included a number of properties in western Sioux Falls.
“The reason we’re making improvements is, when they built them, there was only about 10 years of data on flooding on Skunk Creek and the Big Sioux River,” Berkland said. “As statistics go, that isn’t much. They did not make an accurate projection out to a 100-year event.”
The U.S. Army Corps of Engineers determined that the city’s flood-control system was inadequate to protect the city during a 100-year flood, which is estimated to have a 1 percent chance of occurring in a given year. After a number of area floods, controls were re-examined by the Corps beginning in the 1980s, Berkland said.
When it was found that the levees did not provide protection to the newly calculated 1 percent chance of major floods each year, the levees could not be certified. The Corps determined they needed to be raised another 5 feet.
Property owners who moved into the newly identified flood plain with federally regulated mortgages were required to buy flood insurance, costing hundreds of dollars a year – at least.
The Corps, which constructed the levees in the late 1950s, notified the city in the 1980s that it would need to strengthen and raise its levees. But insufficient money restrained the work. Congress authorized the project in 1996 but initially put only $2 million a year into it. That made progress difficult, Berkland said.
“We were getting little pieces done at a time, but it’s not very efficient, not getting very far very fast,” he said. “That’s when the city passed the bond issue to pay for the 41st Street bridge and all of the work on the levee system to get it done.”
Levee improvements will cost $55 million, not including rebuilding the 41st Street bridge.
Sioux Falls has 27 miles of levees and three major structures, including a spillway and a dam. Another dam is being built near the confluence of the Big Sioux River and Skunk Creek. It should be completed this year at a cost of $4 million.
“We’re raising all the levees in the southwest part of town by about 5 feet,” Berkland said. “The spillway has already been completed.”
Earlier this year, the city agreed to pay more than $1.3 million to Minnehaha County Club for land needed to raise the levee along the course. As part of that agreement, the city decided it needed less of the golf course’s property by building a concrete wall atop the existing levee.
The number of properties in the flood plain was not immediately available from FEMA. A new flood-plain map takes about a year to complete, and flood insurance rates aren’t affected until the map becomes final.