Thursday, December 4, 2008

River’s Edge North Flood Wall Weakness

The US Army Corps of Engineers warned that Flood Wall 298 must be strengthened as part of the Roanoke River Flood Damage Reduction Project.

In a morning briefing Monday, Roanoke City Council listened as Col. Jefferson Ryscavage, Commander of the Wilmington District and Greg Griffith, District engineer explained what needs to be done to address wall design weaknesses.

The design for the wall, prepared in 2002, has been re-examined in light of lessons learned from Hurricane Katrina in 2005. Weaknesses in design led to the inability of the levees to withstand rapidly rising flood waters. “Overtopping“ of the levees resulted in earth erosion and levee breach.

Griffith reassured Council that the basic structure of levees like those designed for the Roanoke project have been found to function well. However, Flood Wall 298 has vulnerable locations that need improvement. The Corps’ solution includes armoring the rear of the flood wall with 4 ½” thick concrete pavers. This section would be the first to meet swift moving water. Concrete pavers or rock erosion protection will be used where there is transition from concrete walls to earthen levee. Stone erosion control will be placed at the pedestrian bridge and all earth levees will be reinforced with erosion control matting on both sides. Grass will eventually grow through the matting.

Even with the extra protection a 100 year flood would completely flood the entire Reserve Avenue area. The school maintenance building would be completely under water, said Griffith. “The area is like a bowl,” said Mayor Bowers. Griffith agreed and added that the project would provide no protection for downtown.

“We believe these design changes are absolutely required to increase the integrity of the project,” said Col. Ryscavage. The Corps is currently negotiating with the contractor, Allegheny Construction, to modify the construction. The project is expected to be completed in the Spring of 2009 except for the landscaping. Col. Ryscavage said, “we owe the citizens of Roanoke a project that is built to last … Katrina and other flood events have shown us ways to build stronger and that’s what we are determined to do.”

Posted By Valerie Garner

Categories: Roanoke City Politics



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