Tomhannock Reservoir, located in the state of New York, is more than 5 miles long and holds 12.3 billion gallons when full. Parts of the reservoir’s earth-filled dam date back to 1900, which means that repairs often are needed. Because the reservoir is the only water source for the nearby city of Troy, repairs are complicated—draining the reservoir is impractical for many reasons.
This was especially true in early 2013, when the dam’s bottom outlet began to fail. The 310- foot long, 60-inch diameter riveted steel pipe surrounded by earth was leaking at all seams, and threatening to give way entirely. On the reservoir side, the inlet is about 40 feet below the reservoir surface, and closed off by a gate that can be opened to release water. On the downstream side, to prevent erosion, the pipe opens into a diffusion chamber that diverts water to four short 30-inch pipes.