Early Winter Update: Understanding Ice Safety Risks at Dunham Reservoir During Ongoing Drawdown
With the coldest weather of the season now here, it is important to understand what is happening beneath the surface at Dunham Reservoir.
As we are experiencing some of the coldest temperatures we have seen in quite some time, it is important to understand the conditions now developing at Dunham Reservoir. The reservoir is continuing to drain through its single operational valve. That valve is being left open because there is concern that a mechanical failure could prevent it from reopening if it is closed again. This has created an extended winter drawdown, which changes how the reservoir freezes and increases the likelihood of dangerous ice conditions.
A reservoir that continues releasing water during freeze-up does not form ice in a predictable pattern. New York State’s dam safety guidance explains that fluctuating water levels and active outflow cause irregular freeze layers and hidden weak points. The Hudson River–Black River Regulating District notes in its public advisories that under-ice flow creates gaps and voids that collapse without warning. These conditions appear across the Northeast whenever reservoirs enter winter with gates or valves left open for operational reasons.
Federal research offers the same warning. The U.S. Army Corps of Engineers describes how moving water beneath ice leads to “undermining,” a process where the underside of the ice sheet thins as water erodes it from below. Even in extremely cold air temperatures, this hidden erosion can produce deceptively fragile ice. The surface may look strong, yet the structure beneath it continues to weaken as water flows toward the outlet.
Dunham’s physical makeup heightens this risk. The reservoir covers roughly one hundred acres with a maximum depth just over twenty feet, which means most of the basin is relatively shallow. Shallow reservoirs freeze early along the edges, develop wide areas of perched or hollow ice when water levels drop, and expose mud and saturated sediment beneath the sheet as the shoreline retreats. As the water continues to drain, the remaining flow concentrates into narrow channels that stay active beneath the ice, resisting freeze even in prolonged cold. These conditions align with patterns documented by New York DEC rangers and U.S. Army Corps ice engineering research in similar winter drawdown scenarios.
As the water level lowers through the open valve, the ice above it can become unevenly supported. New York DEC rangers use the term hollow ice to describe ice that forms above gaps or soft sediment rather than water, a condition known to occur on shallow, actively drawn-down reservoirs. When hollow ice fails, people often encounter mud or pockets of air instead of buoyant water, creating a far more challenging situation for anyone attempting self-rescue. First responders in New York have noted that incidents involving hollow ice or sediment entrapment are substantially more complex due to the unstable footing and lack of flotation beneath the surface.
The reservoir’s shape magnifies the risk. Dunham is broad with narrow channels feeding the dam. As the valve continues releasing water, these channels remain active under the forming ice and resist freezing even during prolonged cold. Snow can conceal the weak areas, and the surface takes on an appearance of uniformity despite underlying instability. The National Weather Service and Minnesota Department of Natural Resources both identify under-ice currents as a leading cause of early-winter ice failures and emphasize that ice forming above moving water should never be considered reliable.
These conditions develop quietly. From the shoreline, the reservoir looks familiar, and the early ice cover gives the impression of stability. The ongoing drawdown changes that reality. A frozen surface forming over an active release behaves like a landscape still in motion, shaped by water movement that the public cannot see. As temperatures continue to fall, this gap between appearance and actual stability becomes sharper. Understanding these risks is essential for community safety, especially during a winter in which the reservoir’s valve configuration has forced an extended, uncontrolled drawdown period.
This update is provided to ensure residents have accurate information about the changing conditions at Dunham Reservoir. The risks described here are well documented in state and federal hydrologic guidance, and they reflect the known winter behavior of reservoirs experiencing continuous outflow.
As winter settles in and the reservoir enters a difficult season, it is important to remember that Dunham’s long-term future remains unresolved. Cold weather can slow public attention, yet this is the moment when community momentum matters most. Nearly 4,000 people have already added their names in support of protecting Dunham, and you can help keep that effort moving. You are invited to sign and share the petition, so that our collective voice remains strong through the winter months.
Sources
- New York State Department of Environmental Conservation (NYS DEC)
Dam Safety Program Guidance on Reservoir Operations and Winter Conditions. - Hudson River–Black River Regulating District
Seasonal Public Safety Advisories on Reservoir Ice. - U.S. Army Corps of Engineers, Cold Regions Research and Engineering Laboratory (CRREL)
Ice Engineering Manual, ERDC/CRREL. - U.S. Army Corps of Engineers
Operation and Maintenance of Dams and Reservoirs, Outlet Works and Valve Reliability. - U.S. Bureau of Reclamation
Dam Safety: Operation and Maintenance Considerations for Outlet Works. - National Weather Service (NWS)
Ice Safety Guidance and Hazard Bulletins. - Minnesota Department of Natural Resources (DNR)
Ice Safety Program Publications.
Disclaimer
This update is provided for general informational purposes only and reflects publicly available research, state and federal guidance, and observed reservoir conditions as of the date of publication. It is not a substitute for official safety directives, emergency instructions, or site-specific assessments issued by the New York State Department of Environmental Conservation, the Town of Grafton, dam safety authorities, or first responders. Conditions at Dunham Reservoir can change rapidly due to weather, mechanical factors, and active drawdown, and no ice should ever be assumed safe.
The authors and affiliated organizations make no guarantees regarding current or future ice conditions and assume no liability for actions taken or not taken based on this information. For all safety concerns or emergency situations, contact local authorities or dial 911 immediately.