Mar 23, 2022
Catskill Aqueduct Rehab Reaches the Finish Line
At the end of 2021, we completed the final shutdown that was required for the $158 million project to clean, repair and upgrade the Catskill Aqueduct. The complex project, which comprised more than a dozen work locations stretched across 74 linear miles of the aqueduct, was the first major rehabilitation of the critical conduit since it began delivering water from Ashokan Reservoir to New York City in 1915.
The work aimed to prepare the Catskill Aqueduct for its most important mission in decades — supplying a maximum amount of water to the five boroughs while the Delaware Aqueduct is shut down to connect its new bypass tunnel under the Hudson River. While the Delaware Aqueduct is out of service, the Catskill Aqueduct will convey upwards of 600 million gallons of water each day, nonstop, to meet the needs of our customers. Known as the Catskill Aqueduct Repair and Rehabilitation (CATRR), the project sought to improve the flow of water through the aqueduct by cleaning its concrete lining, repairing several known leaks from the aqueduct, and reinforcing some of its structural components to guarantee its reliable delivery of water for decades into the future.
The project specifically focused on the 74 miles of aqueduct between Ashokan Reservoir and Kensico Reservoir, not including the pressure tunnel sections that plunge deep below some of the major river and creek valleys. Those pressure tunnels, and portions of the 92-mile-long aqueduct south of Kensico, will be rehabilitated during capital projects that are planned to begin within the next 10 years.
- Work crews cleaned about 310,000 feet (59 miles) of the aqueduct’s concrete lining. A naturally occurring and harmless film had built up over the decades and created friction which slowed the travel speed of the water, thereby constricting the capacity of the aqueduct. Historic records indicate the Catskill Aqueduct could carry well over 600 million gallons each day when it was first constructed. More recently, it only carried a maximum of about 590 million gallons. Engineers expect to regain some of that lost capacity because of the cleaning.
- Skilled workers also removed and replaced 35 blow-off valves connected to the steel-pipe siphon portions of the Catskill Aqueduct. These valves are designed to help drain the aqueduct by discharging its water into local streams, creeks or rivers. The valves connected to the aqueduct were from its original construction, and they were rarely used. They were replaced with new valves and mechanical components to ensure their operability into the future. This part of the project required more than just mechanical skill. The belly of each siphon needed to be pumped dry, and each siphon had to be carefully refilled to prevent air from becoming trapped and harming the structure. The steel pipe siphons, which allow the Catskill Aqueduct to travel under smaller streams along its route, were also repaired during the project.
- The third core mission of the project was to repair structural defects and leaks at several locations along the aqueduct. The cut-and-cover portions of the aqueduct were known to be leaking at several locations. These leaks were sealed by grouting or by the installation of a special carbon-fiber lining within the aqueduct.
CATRR included other tasks, too. Three of them were large or technical enough that they required special teams or efforts within the larger project. Special plugs were installed inside the Wallkill Drainage Chamber and the Rondout Drainage Chamber to seal leaks inside these structures. The plugs were installed during special dive operations that required contractors to live inside pressurized conditions and plunge more than 100 feet into the chambers to complete their work.
Special attention was also paid to a bridge in Ulster County that carries the Catskill Aqueduct over a small creek. To improve its structural integrity in this location, workers used steel, concrete and a special spray liner to tighten the arch of the aqueduct and its bridge.
Lastly, the shutdown of the Catskill Aqueduct included a special effort to reconstruct much of the Catskill Influent Weir — the structure that discharges water from the aqueduct into Kensico Reservoir. The inside of the weir was cleaned and the piers that hold the weir together were completely reconstructed with new concrete.
The Catskill Aqueduct was shut down for approximately 10 consecutive weeks each autumn and winter, for four consecutive years, to accomplish the work. Even before the work started, we had to collaborate with several communities north of the city who purchase water from the Catskill Aqueduct and did not have an adequate backup supply to sustain themselves during the shutdown. For example, we purchased a water truck for the hamlet of High Falls in Ulster County so that it could get water from neighboring Rosendale and pump it into its water tower during the shutdowns. Miles of pipe were also run from Gardiner to New Paltz so that we could pump water from another portion of its system to keep New Paltz from going dry. New Paltz’s own reservoir system only has enough storage to sustain the village and parts of the town for approximately two weeks, making it dependent on the Catskill Aqueduct.
With much of the structural and mechanical work finished, contractors will return to several of the work sites in the spring to plant grass and finish other site-restoration tasks. Many thanks to our staff and contractors that have worked so diligently to make this project a success.
