Concrete pumps are playing a key role in enhancing 2.5 miles of the Chattahoochee River in Columbus, GA by creating rapids that will challenge whitewater rafters and kayakers. The $23 million Ready2Raft! Whitewater Columbus, GA project includes pumping concrete into fabric bags that alter the river’s flow characteristics and building support structures for a mechanical wave shaper. StahlCo Pumping with locations in nearby Phenix, AL and Atlanta, GA is working within narrow time limits to fill the bags before an upstream power plant releases daily torrents of water that make pumping impossible. Upon completion in summer 2013, the flow from the river will create the longest urban whitewater course in the world and add an expected $42 million in economic development to the surrounding area.
Batson-Cook, headquartered 40 miles north in West Point, GA is the general contractor for the project. Scott Bridge Company, 30 miles away in Opelika, AL, is overseeing the work performed by StahlCo. Brothers Matt and Walter Stahl, co-owners of the company, and ages 34 and 29 respectively, bring youthful enthusiasm to the difficult project, “It’s certainly different than anything we have done before, “ explains Matt, “Working downstream from an active hydroelectric plant means we were subject to the release of water from the Georgia Power dam two and half miles upstream.” Normal flow of the river is 800 cubic feet per second. When water is released to power the three turbines, flow increases to 13,500 cubic feet per second and floods the job site with up to 15-feet of water.
One channel of the river had a deep hole that created a vortex. This section required five months of concrete pumping under constantly changing water conditions to contour the bottom of the river. A Schwing SP 500 trailer-mounted concrete pump was towed by a bulldozer over the rocky river bottom to a point 300-feet from the placing area. Another 75-feet of hose was used to reach the deep hole below the water’s surface. In order to shorten the clean-up time, the flexible 2.5-inch placing hose was anchored to the river bottom with bolts and chains. After blowing out the line at the end of the day, the hose stayed in place to speed placement the next day. “The pump did a great job,” according to Matt, “The engineers tested several mixes before they settled on one and the pump handled them all.”
Divers filled fabric bags with a special concrete mix in order to fill the void and create three 20-foot steps to provide the turbulence kayakers and rafters enjoy. The bags are a nylon fabric sewn together as needed to shape the river bed. They were placed in the water, filled with concrete and sealed.. “A typical day would allow us to get on-site by nine in the morning, tow the trailer pump in place and start pumping by ten,” according to Walter Stahl, “If there was heavy rain the night before, we might have to clear debris or there could be too much flow and we would lose a day.”
Each bag could hold two to sixty cubic yards depending on the design of the bag. Divers fit the bags into the areas that need to be filled, inserted a two-foot tremmie pipe and communicated with underwater radios to the pump operator. After a bag was filled, divers would insert #4 rebar into the top with one-foot of rebar exposed to retain the next bag placed on top. Approximately 30 bags were placed, filled and anchored in this way. “We could place and fill two to three bags a day,” according to Walter, “We had to allow time for the concrete to set and for the crew to clear the area before the water flow increased and the site was flooded.” The force of the released water at certain times was powerful. “Twice, the current dislodged a bag and bent the rebar ninety degrees,” Walter said. The fabric-formed concrete is economical to install because it eliminates heavy-lifting equipment, steel reinforcement and forming and stripping of conventional concrete forms or dewatering of the job site prior to installation.
The SP 500 is one of 13 pumps owned by the company. It combines the Long Rock sequencing valve with standard hopper agitator. The filling efficiency of the material cylinders is enhanced due to a deeper valve housing and positioning of the agitator lower in the hopper. A 72 hp diesel powers the pump allowing up to 45 yards per hour output with horizontal pumping distances as far as 1,160-feet depending on the mix. “This has been a very versatile pump for us on residential and commercial projects, “ according to Matt Stahl.
The SP 500 is being used to pump a “grouted boulder mix” that utilizes an anti- washout agent and fine #7 granite to create a high strength concrete with impermeability and absorption resistance. This mix is being used to anchor existing boulders above and below the water level as well as fill the fabric bags. “The concrete is going into the pump at two to three-inch slump and reaching a one-inch slump at the point of placement, “ Matt explains, “The anti-washout agent is added at the mixer truck on-site and we have 45-minutes to get it emptied and through the line before the mix is stiff.”
The ¾-mile section that is completed to date is “just the tip of the iceberg,” according to the Stahl brothers. Their Schwing KVM 39 X and Schwing KVM 32 XG four-four section boom pumps shared pumping duties in a dewatered section of the project. The area will house a hydraulically operated wave shaper that will raise and lower metal plates to affect the rapids depending on water level. With up to 114-feet of horizontal reach the booms can reach all areas of the pour area from a service road next to the river. The six-foot thick, 27’ x 66’ slab also includes walls to protect the hydraulic equipment from the force of the river.
According to the architects for the project, McLaughlin Whitewater Design Group, Denver, CO there are over 500,000 low head dams (2 to 20-feet high) on rivers in the U.S. These dams often block fish passage and increase river temperatures, killing fish and invertebrates. Dam modifications and channels built around them like the Ready2Raft! Whitewater Columbus, GA project can remedy the environmental problems and create recreational and economic opportunities for surrounding communities. The company currently has developed or is in the process of creating 14 whitewater projects.
StahlCo Pumping is perfectly situated to take advantage of the continuing work related to the project located approximately five-minutes from their offices. Their corporate philosophy of “providing the most sought-after customer service in the concrete pumping industry,” combined with a fleet of 28 to 61-meter boom pumps has created rapid growth for the company since starting in 2008. Now they have to work on their whitewater skills, according to Matt, “The owners invited us to test the rapids in kayaks and we all got tossed out.”