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Gilboa Dam reconstruction includes major facelift
Written by: Troy Johnson, Two Rivers Marketing

Delivering drinking water to New York City taps is a critical and complex process. More than 9 million New Yorkers depend on one of the world’s most extensive municipal water supply systems to provide 1 billion gallons of clean water each day.

Big Apple water comes from a watershed that extends more than 125 miles from the city, including 19 reservoirs and three controlled lakes. Approximately 7,000 miles of water mains, tunnels and aqueducts bring the water to homes and businesses throughout the city and four nearby counties.

Gilboa Dam is one of the upstate dams that form the backbone of the city’s water-supply infrastructure. Nestled in the Catskill Mountains 125 miles northwest of Lower Manhattan, Gilboa Dam impounds Schoharie Reservoir, a 17.6-billion-gallon basin that accounts an average of 15 percent of the city’s daily supply. 
 
Ensuring the stability of this 87-year-old dam is critical for delivering plentiful water to America’s most populous city. The New York City Department of Environmental Protection (DEP) is nearing completion on a $400 million, full-scale reconstruction that will enable Gilboa Dam to serve the city for another 50 to 100 years. 
 
The Gilboa Dam reconstruction project is a joint venture between D.A. Collins Construction Co. Inc., based in Wilton, New York, and Barnard Construction Company Inc., of Bozeman, Montana. After a series of productive construction seasons, the dam rehabilitation is nearly complete — two years ahead of schedule.

Among the finishing touches is a facelift for the weathered training walls. This component of the project presented the Barnard-D.A. Collins Joint Venture (BDJV) with a special challenge that called for an unusual equipment solution.

Dam overhaul overdue

Built from 1919 to 1927 and placed into operation in 1927, Gilboa Dam forms Schoharie Reservoir, the northernmost reservoir in the Catskill water supply system. The 160-foot-high by 1,326-foot-long dam features a stair-stepped gravity cyclopean concrete design with a stone masonry spillway and rolled earthfill embankment with a concrete core wall. 
 
After nearly 80 years of service, Gilboa Dam was showing significant signs of age-related deterioration. The dam needed reconstruction to extend its service life and comply with the latest state and federal dam safety standards, including an enhanced capacity to safely release water in the event of a dam safety emergency. 
 
DEP started the reconstruction in 2005 with a series of emergency stabilization efforts. Following the subsequent installation of crest gates to control the level of the reservoir and site preparation to facilitate reconstruction, the major construction phase began in 2011. When complete, the dam will feature approximately 234 million pounds of concrete reinforcement, a reconstructed spillway and a newly installed release tunnel around the dam from Schoharie Reservoir into Schoharie Creek. 
 
The rehabilitation has stayed ahead of schedule despite damage and disruptions caused by hurricanes Irene (2011) and Sandy (2012). BDJV is currently finishing reconstruction of the spillway to address deterioration, improve hydraulic flow and enhance structural stability. 
 
“We’re updating the dam and giving it a facelift,” says Craig Valente, P.E., assistant project manager for BDJV. “We’re adding mass concrete to strengthen it, and we’re improving the hydraulics. But there’s also a large masonry aspect to this project. The dam had masonry facing on it, and we’re working to make the training walls look like the original.” 
 
Restoring the stone face of those walls posed a significant logistical challenge for Barnard and D.A. Collins, a full-service construction firm and trusted name in dam construction, alteration, repair and removal. 
 
Challenge set in stone 

Decades of weather, water and erosion caused some of the original stones to weaken and dislodge. The DEP contract called for the replacement of the existing deteriorated stone with a new stone façade that would replicate the original look. 
 
BDJV was faced with maneuvering 600 new stones up and down a 160-foot wall. Valente says BDJV first considered using one of its massive crawler cranes to set the stones from either below or behind the wall. Each option was deemed infeasible because the approximately 30-by-30-foot footprint of the equipment would interfere with other critical rehabilitation work. Besides, with stones weighing from about 300 to 3,000 pounds, a crawler crane represented “too much crane” for the job. 
 
“We wanted something that was more optimized and economical for the operation,” Valente says. “We determined we didn’t want to use a big crane or a footprint that would hurt our logistics. We started thinking, ‘Can we come up with anything else that can do this work from above?’” 
 
Unusual solution emerges 
 
Looking to efficiently maneuver stone and save space on the construction site, BDJV turned to Reading Equipment, a truck equipment distributor based in Bowmansville, Pennsylvania.
 
“We had to get out of the heavy highway contractor mentality and try to think on a smaller scale instead of ‘big job, big equipment,’” Valente says. “We had to think about what we truly needed.” 
 
Reading helped BDJV devise an unconventional solution: telescopic cranes mounted on engineered pedestals anchored atop the spillway and driven by a 49-hp diesel power pack. 
 
The cranes Reading specified were IMT 8600 hydraulic telescopic models from Iowa Mold Tooling Co. Inc. (IMT), a leading manufacturer of mechanics trucks, truck-mounted cranes, air compressors and other equipment. IMT 8600 cranes are typically found on IMT mechanics trucks serving multiple industries including construction. 
 
Elevated cranes lift efficiency 
 
With 8,600 pounds of lift capacity, 30 feet of hydraulic reach and radio-remote-control operation, the IMT 8600 cranes have met the demands of the non-traditional application. 
 
Stones are staged on the back side of the training wall, where one by one they are loaded into a nylon lifting device and easily lowered by the crane operator to masons working in a man lift or on scaffolding. Masons guide and anchor the stone, fill the cavity, and continue moving up the wall. 
 
The radio remote control enables the crane operator to move around and maintain optimized visibility of the load. It also allows the operator to precisely “feather” each stone into place, a valuable capability when handling such a heavy object. 
 
Once one section of the wall is topped off with a capstone, the other IMT 8600 crane is used to begin work on the adjacent section. All the while, other work continues unimpeded below and behind the wall. 
 
“We’ve been happy with the size, performance and production of the cranes,” Valente says. “The equipment has done the job efficiently, and there have been a lot fewer logistical issues than there would have been with a larger crane solution that caused the mason work to overlap with other operations. In a few short months, we’ve been able to restore and improve the aesthetic appearance of the training walls.” 
 
With that touch of style, the efficient Gilboa Dam reconstruction project led by D.A. Collins and Barnard is helping secure the reliability of the New York City drinking water supply for decades to come.