Representatives from the U.S. Army Corps of Engineers presented an $18 million proposal for raising the height of the levee that protects the downtown area of the city Wednesday, saying it would raise flood protection here to the 300-year level.
John Grothaus, chief of planning section for the Corps, made the presentation during a lightly attended public meeting. He said the current 5.4 mile levee protects about $1 billion in property to a level of 100 years.
Grothaus said the existing levee “is still performing well for what it was authorized and intended to do,” but the area behind the levee is growing, raising the consequences of a topping event.
The meeting was intended to gauge public interest and desire to raise the levee from the current standard of a 100-year flood protection level to a 300-year or 500-year flood protection level. Grothaus said any upgrade would be a 65/35 cost split between the Corps and the city. He said some of that cost by the city included the cost of purchasing the land needed to raise the levee, although it’s possible that land may already be owned by the city.
Grothaus also said that the proposal would have to be approved by the Corps head offices, approved for federal funding, possible state funding, and finally city funding before it could move forward. He said if it was deemed too costly at any of those levels, the proposal would be put on a shelf until a time when it was financially viable.
Grothaus also said building up the levee is not a federal requirement. He said the Federal Emergency Management Agency approved the levee recently in an independent study as maintaining the “minimum requirements” of the 100-year flood protection. He said while the levee was certified, it was not optimal, and he thought it could always be bigger.
“Generally, higher—if affordable, if desirable—more robust protection is what is best,” Grothaus said.
He said if the proposal to build up the levee to a 300-year flood protection level is deemed not affordable, the Corps may ask the city to consider replacing gatewells, and moving or replacing utility lines that may be displaced during a flood such as the one in ‘93. He said the Corps would also see whether it could provide funding for those improvements, but if not, the city would have to fund those projects independently. They are estimated to cost $9 million.
The study was initiated after the 1993 flood, the first major flood since 1951, when the Corps determined that Manhattan needed a levee. Construction was completed in 1963. Since then, no flood had tested the integrity of the levee until ‘93.
He said the recent study, funded partially by the Corps and partially by the city of Manhattan, concluded the levee “may need to be improved.”
Grothaus said even though the levee held during the ‘93 flood and “functioned as intended,” there were some areas of concern.
He said the Corps wants to build up portions of the levee, extend the levee an additional 440 feet along Casement Road, improve the slope and stability of parts of the levee, replace five gatewells that control water seepage under the levee during a flood, and replace or move utility and water lines that could be displaced during a major flood.