Since 1802, the tradition at the US Military Academy, West Point, has been to graduate highly trained military officers.
More than 900 cadets are commissioned annually. For just as long, the US Army Corps of Engineers has had roots at West Point and has worked with the academy ensuring the Army’s officers are prepared for their important missions by providing optimum training and living facilities.
This past winter, the corps’ New York District began restoring a historic dam and reservoir near the shore of the Hudson River on the grounds of the sprawling campus to ensure a continuous freshwater supply and to prevent a potential flooding hazard.
The US Military Academy was established primarily to train engineers. The academy sits on the western shore of the Hudson River, approximately 50 miles north of New York City in lower Orange County. Since its establishment, the academy has shared a close relationship with the corps.
In the late 1800s, the academy needed an additional source of drinking water. The corps augmented the academy’s drinking water system by constructing the Lusk Dam and Reservoir in 1895; both now are considered significant elements within the academy’s National Historic Landmark property.
The Lusk Reservoir Dam provides the academy with fresh water. The reservoir dam is a large, arched masonry block structure–225 feet long and 35 feet high. A few years ago it was observed during a corps inspection that leaks were present behind a buildup of efflorescence, a crystallization that had accumulated on the structure’s surface. The discovery raised concerns that there could be a more serious future problem if the dam was left unmonitored.
The dam was constructed under the direction of Captain James L. Lusk, a West Point graduate. The dam created the reservoir. To date, water has been piped into the reservoir from area ponds, creeks, and brooks and is purified by the academy’s water treatment plant. Because the dam is located upstream of and adjacent to several high-occupancy academy facilities, such as the Association of Graduates building, any potential structural problems in the dam are unacceptable.
During the winter of 2005, the corps’ New York District performed the dam’s first cleaning in its 100 years of service. The joints on the downstream face of the dam were cleaned of efflorescence, and leaks that had been covered by this crystallization crust were located, cleaned, and sealed. The cleaning revealed a “fresh face” for the corps to observe and categorize leaks currently present at the dam and determine any further repairs that may be needed.
“Efflorescence is caused by the dissolving calcium carbonate in the dam’s mortar with the reservoir water,” explains Marty Goff, a project engineer with the corps’ New York District. “The water up there is slightly acidic, so it reacts chemically with the mortar between the dam’s stones. When efflorescence builds up over the stones, it becomes difficult to determine the location of leaks because the water from the leak is diverted. The water from the leak is moving under the efflorescence crust and away from the leak source. By cleaning away the efflorescence we will be able to see the actual location of the leak.”
Goff says it took a month to clean the dam; the cleaning process was similar to cleaning a shower stall of lime buildup. The dam’s stones were sandblasted with small, coarse-grained silica, or glasslike particles, under water pressure to remove the calcite buildup along the seams of the dam’s masonry stones. Workers performed the cleaning by standing on a platform, similar to those used by high-rise-building window washers, which was lowered over the side of the dam’s stone balustrade and 8-foot-wide brick walkway.
With the cleaning completed, leaks that were found are being monitored. Plans for the near future include inspections of the structural condition of the dam’s upstream face by a dive team, because this portion of the structure needs to be visually examined. Goff hopes to correlate the leak locations on the downstream face with the upstream face cracks, which will allow the corps to determine future work.
Corps’ suggestions for engineers who plan on performing similar dam restoration work include working closely with environmental and cultural resources staff on the project, who can be invaluable in the selection of the proper cleaning method. Even though the main focus of a dam restoration project is dam safety, it’s important to be aware of the cultural and environmental resource impacts of the work being performed. In addition, it’s important to ensure that enough time is available to perform the work. For example, if the dam is located in a cold climate, avoid beginning work in the fall, which may cut restoration time short.
“If we didn’t clean the dam, we would not be aware of the severity of the seepage problem, which could be the result of a more significant problem,” notes Goff. “The location and hazard classification of this dam make it essential that we monitor and maintain it on a regular basis. If the dam were to ever experience a breach, the potential for loss of life would be high.”
