Engineers Choose Redi-Rock Channel For Colorado River Diversion
Diversion project prevents erosion while allowing construction of fish ladders
This award-winning Bureau of Reclamation project required the entire Colorado River to be diverted for six months to allow construction of fish ladders.
The Price-Stubb Dam near Palisade, Colorado was constructed in 1911 to divert water into canals for irrigation. The concrete roller dam is 325 feet (99.1 meters) wide and eight feet (2.4 meters) high, spanning the width of the river. Though no longer in use, the dam had been blocking the upstream migration of several endangered species of fish. The goal of the fish ladders is to create a pool and drop effect that would allow fish to rest on their upstream migration in hopes of improving fish population in the river.
The project was designed by Charlie Larson, P.E., hydrology/hydraulics engineer with Kleinfelder Engineering's Surface Water Resources Program. An existing though unused canal acted as the framework to divert the river to allow the fish ladders to be installed. The canal had been filled in after a landslide more than 30 years ago.
"As with many construction projects, there were some surprises," Larson wrote in an article published in the August 2008 issue of U.S. Water News. "During the excavation of the diversion channel, crews discovered existing canal feature that required timely design modifications, including the discovery of an existing stacked rock wall along the right side of the diversion immediately downstream of the headworks and situated on a 2.5 feet (0.8 meters) high concrete pony wall."
Engineers performed stability analyses of the existing 19 foot (5.8 meter) high stacked rock wall and designed a shoring system to stabilize the design.
"The canal had some tight constraints. We didn't have room to put in a slope, so we needed an MSE to stabilize the canal," Larson said. At the suggestion of Kissner General Contracting, Redi-Rock was chosen for the MSE wall the canal required.
Kleinfelder engineers selected a design flow and consulted Redi-Rock design charts and did their own analysis to confirm that a Redi-Rock reinforced wall constructed using 28in (710mm) blocks could withstand the force of the water. Due to an existing feature, the length of geogrid extending behind the block had to be shortened from 13-15 feet (4-4.6 meters) to 8-10 feet (2.4 - 3 meters). To compensate, engineers designed the wall with a wedge piece under the base course of blocks so that the wall tilts back, giving it a 10 degree setback instead of the standard 4 degree setback on a 28 inch (710 millimeter) series wall.
Robby Lewis of Redi-Rock producer Grand Juntion Pipe and Supply explained that Redi-Rock was used to "armor plate" a curve in the diversion channel to prevent erosion.
The river is diverted into the canal and directed into a 21 foot (6.4 meter) high Redi-Rock retaining wall that was 200 feet (61 meters) long. The wall was a radius but turned 90 degrees.
"It worked out really well," Larson said. "We were impressed with how Redi-Rock performed and have specified it on another project since this one was completed."
The project also utilized Redi-Rock blocks in the Limestone texture to create two temporary bridge abutments for a construction access bridge. The bridge was constructed using 41in (1030mm) series blocks. Redi-Rock was also used to create a platform from which cement trucks could pour the concrete into the forms that created the fish ladders. The trucks could drive up and pour their concrete into the forms below without necessitating pump trucks, saving time and money.
When the river channel was clear, construction of the 600 foot (182.9 meter) long passage commenced. Larson explains that "190 concrete cylinders [were] placed in a chevron pattern of 38 baffle arrangements consisting of five cylinders each. The center cylinders are spaced 15 feet (4.6 meters) apart along the fish ladder. These provide a cascading effect of pool and drop that allow fish a chance at resting on their upstream migration."
This project was the recipient of the 2008 Golden Hardhat Award for Outstanding Environmental Project. The award is sponsored by Colorado Construction Magazine and honors the best construction projects in Colorado each year.
Project: Upper Colorado River Recovery Implementation Program #84 Owner: Bureau of Reclamation Block Manufacturer: Grand Junction Pipe & Supply Engineer: Charlie Larson, P.E. Location: Palisade, Colorado Year Built: 2007