Gravity walls help city revitalize flood-prone riverfront
In late 2010, the city of Sunbury, Penn., began a major revitalization project to repair its damaged riverfront. Flooding and erosion are major issues for Sunbury because it is located on the banks of the Susquehanna River, which was frequently in the news in 2011 because of the floods caused by Hurricane Irene.
According to the Sunbury Riverfront Master Site Plan, approximately 18 in. of riverfront was being lost each year. If this instability and erosion continued, the loss of riverfront would persist, further damaging the existing retaining walls and floodwalls. To stop erosion and begin construction on the riverfront project, the city first needed a structural solution to stabilize the banks of the river.
Originally, plans for the project included poured-in-place walls and restacking the WPA stone in some areas. The first phase of construction had already begun when Jason Metzger, the project manager for the contractor, HRI Inc., suggested Redi-Rock as a more efficient alternative.
Redi-Rock has built tall gravity walls for shoreline protection projects across North America. The gravity walls minimize excavation and offer easy installation and three natural stone textures: Ledgestone, Cobblestone and Limestone. HRI believed that the wall system could save on installation time and match the look of the stone better than the poured-in-place walls.
Jim California, P.E. and lead structural engineer on this project with Buchart Horn Inc., and Scott Russell, P.E. and regional manager of Buchart Horn Inc., agreed: “Redi Rock provided a robust retaining wall capable of sustaining periodic impacts by floating debris during periods of high river levels. In addition, the walls had the ability to maintain a more vertical profile, limiting the impact on the cross-sectional floodway.”
“In one location, there was an existing concrete wall in place that had experienced some apparent shifting. We wanted to leave the old wall in place and build a new structural wall in front of it. In this situation, geogrid tie-backs could not be used. The Redi-Rock system, with its massive blocks and gravity wall capabilities, worked well in this application without requiring geogrid,” added the engineers.
To construct these walls, engineers designed one course of 60-in. base blocks in the base of the walls, with 41-in. blocks above and a 28-in. block in the top course—all manufactured by local Redi-Rock producer Paxton Precast.
“We’re prone to flooding here on the Susquehanna River,” said Sunbury City Councilman Jim Eister. “The walls were installed last summer [in 2011], and then we had a flood from Hurricane Irene in the fall. The walls were completely underwater, but we had no damage at all.”
In total, the project required 17,000 sq ft of Redi-Rock gravity walls, freestanding walls and caps. City officials and the residents of Sunbury are happy with the way the project has turned out.
“There’s no maintenance, it’s very durable and when it goes through a flood like it did, it sets the standard for being a great solution,” Eister said.
Kevin Loe is business development manager for Redi-Rock Intl. Loe can be reached at [email protected].