New retaining walls save a dangerously deteriorating spillway in Kansas
By Lindsey Manthe
The spillway of historic Lake Shawnee Dam near Topeka, Kan., recently received a much needed facelift with retaining walls. The original spillway was built in the 1930s as a Work Project Administration project to create Lake Shawnee. The lake’s outlet channel and dam needed major repair; the rebar of the poured-in place concrete primary and secondary spillways was beginning to show.
Along the north end of Lake Shawnee lies 2,200 ft of earthen dam. Th ree drop structures control discharge before going under an arched
The outlet channel was lined with hand-placed stone that still exists along most of the banks. Only one major repair project had been completed since the lake opened, and years of channel erosion had exposed the main spillway footing. The soil surrounding the dam had a slope of 30 degrees and consisted of sandstone and shale.
“If not repaired, the large spillway retaining wall could be undermined and complete failure of the spillway wall could occur, leading to an emergency unsafe situation,” Kansas Water Structures Engineer Joe D. File told the Topeka Capital-Journal in 2004.
The county chose Redi-Rock due to the product’s ability to build walls that minimize the need for geogrid reinforcement while withstanding
Engineers decided to utilize a concrete backfi ll design that minimized excavation while creating a reinforced wall that provided adequate sliding and overturning resistance. A rebar cage was constructed and tied into the blocks’ lifting eye. Concrete was then poured, creating a solid unit
“The most notable change [in the spillway design] was the construction of observation areas on the downstream side of the main spillway. During large rainfall events, the resulting waterfall over the spillway attracted many spectators. Steep banks and slippery conditions created a safety risk
When the 8,000-sq-ft wing walls were completed, they were capped with a concrete platform. Columns and freestanding wall blocks were used to create matching fencing atop the 18-ft-high wing walls for both aesthetics and safety. Visitors are now able to get closer to the spillway.
In March 2007, the dam repairs were tested when a storm event approaching the 100-year level occurred. The renovations prevented what could have been a catastrophic failure and turned it into a spectacular show.