The Shandaken Tunnel, which carries water from the Schoharie Reservoir in Greene County and pours into the Esopus Creek, will be closed for March and April, the New York City Department of Environmental Protection (DEP) has announced. The temporary shutdown is the first of several that will enable DEP to make upgrades to the reservoir, including installation of a system to draw water into the tunnel from multiple levels, addressing concerns about water temperature for the Esopus cold-water fishery.
“Overall, it will be good for the fish,” said Ed Ostapczuk of Trout Unlimited (TU), pointing out that warmer water from upper layers can be diverted to the Esopus in the off-season, saving the coldest water of lower layers for summer, when the trout can be impaired by heat. DEP is also installing a high-level outlet system for the Gilboa Dam, at the northern end of the reservoir, enabling diversion of warmer water into the north-flowing Schoharie Creek, instead of taking out cold water that benefits the Esopus trout.
DEP is investing $400 million in repairs and upgrades to the Schoharie Reservoir, which has the least operational flexibility of all the 21 reservoirs that collect drinking water for the residents of New York City. “When it was built,” said DEP spokesperson Adam Bosch, “it was designed only for one purpose — to take the Schoharie Creek and have it make a U-turn into the Esopus Creek, to increase the natural flow of the upper portion of Esopus, so the Ashokan Reservoir would stay more reasonably full.” (The Esopus flows into the Ashokan Reservoir in the town of Olive.) In the past, water temperature was not an issue, nor was turbidity, since chemicals were effective at forcing silt suspended in the water to settle. Lately, possible toxicity of the chemicals used has prompted DEP to find other ways to address turbidity, which impairs the quality of drinking water.
“Over the years,” said Bosch, “one of consequences of reservoir storage is that it created cold water, and that created cold-water fisheries, which didn’t exist on this scale before.” The Esopus attracts anglers from around the world, boosting the local economy.
DEP is now making infrastructure changes to go along with changing requirements. There is presently no way to divert water through the dam into the Schoharie Creek. Modern dam safety regulations demand a way to draw down the water in case an emergency inspection or repairs are needed. The originally proposed outlet at the reservoir bottom would have taken only cold water, prompting TU to raise objections to the plans. The Schoharie Creek has never been a cold-water fishery, nor is there a prospect of creating one there. Now a high-level outlet is planned, with a completion date of approximately 2023.
Meanwhile, work is about to begin on the system that sends water into the Shandaken Tunnel. The rehabilitation project includes replacing eight sluice gates that control the flow of water into the tunnel by way of an intake chamber. The gates were installed in the 1920s when Schoharie Reservoir was built. Three of the gates broke off their lifting mechanisms and became wedged in place.
Before the gates can be removed and replaced, skilled divers must descend 130 feet into the chamber’s shaft, using sonar equipment to take precise measurements of the gates and the grooves that guide them. These measurements will be used to fabricate new gates, lifting mechanisms, and other infrastructure to restore the full function of the intake chamber. The initial shutdown, this March and April, will allow the divers to make their descent without being sucked down the tunnel.
The timing and duration of the shutdown was planned in close coordination with the New York State Department of Environmental Conservation (DEC). Because the tunnel contributes additional water to the Esopus Creek, the shutdown was planned to coincide with the period of spring rains and melting snow that have historically provided the greatest quantity of natural flow within the creek. The temperature of water in the creek will also not be a concern during early spring.
The tunnel will again be closed for two months in 2019, as workers install a plug and a smaller bypass tunnel within the intake structure. The bypass system will allow DEP to safely move water into the Shandaken Tunnel while the gates are replaced, a process that will take approximately two years, from 2019 to 2021. At some points, other tunnel closings may occur, on a schedule subject to change due to extreme weather or other unforeseen circumstances. DEP expects to consult with state regulators as each shutdown period approaches, and it will keep local residents and elected officials informed of the project as its plans proceed.
After the intake chamber is finished, a portion of the bypass system will be left in place. The pipe will be connected to an articulating arm, which can pivot up and down, giving DEP the ability to draw water from multiple depths within Schoharie Reservoir, allowing water to be selected for passage into the Esopus based on temperature and turbidity of specific layers. Ongoing water testing identifies the characteristics of the different layers at different times.
When asked which layers contain the most turbid water, Bosch said the answer is complex, depending on the time of year and the weather, since runoff from spring melt and from storms elevates turbidity in the upper layers, followed by settling of silt into lower levels. A further complication comes from the “seiche” (pronounced “saysh”), a standing wave that forms in the summer, affecting reservoirs, lakes, and other contained bodies of water.
“On the surface,” explained Bosch, “the waters look calm, but below the surface, there’s a wave rocking back and forth like a seesaw, in 12-hour intervals. The top layer will rock down to the intake and bring along crystal-clear water. Twelve hours later, the bottom layer will reach the intake, bringing intensely murky water.” The seiche seems to be initiated by prevailing winds piling up water against the dam. When the wind calms down, the water sloshes back in the other direction, setting up the wave. Sometimes the seiche goes on for months, while other years the wave is gentle and has almost no effect. Bosch added, “Articulating the intake will help us manage the effects of the seiche.”