Dams in cold regions [see figure 1] have the potential to experience ice runs, spillway clogging, gate inoperability/damage, frost heave, inlet blockage, concrete freeze/thaw damage, and hazards to operation and maintenance staff.
Cold weather effects on dams may be currently under-incorporated in dam engineering work. Efforts to understand and address these vulnerabilities will make dams in cold regions safer, more reliable, and safer for dam on-site personnel.
This article is to raise awareness of cold weather impacts on dams and to suggest the application of existing research and guidelines for dam siting, design, construction, risk analysis, and O&M. [1]
Ice runs, jams, and clogging
Seasonally freezing/thawing rivers drain over one third of the world’s land surface. Ice runs can occur at river dams when winter ice breaks up and moves downstream typically during the spring. The ice rubble varies in sizes and can weigh many tons. During an ice run, rubble can form ice jams at any place but particularly at river bends, constrictions, and bridges. During an ice jam river water impounds upstream, rises, and eventually breaks through the jam releasing a surge of water. This surge of water and ice rubble can impact dams downstream by damaging or failing a dam’s gates. Spillway clogging can also occur, leading to dam overtopping and failure.
Ice runs can be episodic with minor thicknesses of ice passing through a dam each year and major thicknesses of ice runs occurring only after many years or decades. The US has an ice jam historical database with 18,000 ice run events.
During siting of new dams or evaluating the vulnerability of existing dams to ice runs, professionals can research a river’s history of ice jams. Dams just downstream of river bends or constructions could be more susceptible to the effects of ice runs. For off-stream dams with river intakes, the use of stout (concrete) intake structures on a side of the river with deep entrances can lessen the damage if ice runs occur.
Mitigation of ice run vulnerability to dams can include the use of:
- Wide, ungated overflow structures to lessen clogging.
- Submersible roller gates within broad crested spillways to keep gates out of the path of ice runs.
- River jetties and ice booms to direct ice toward less vulnerable stations of the dam
- Upstream reinforced concrete icebreakers to break flowing river ice into smaller pieces.
- Designing gate piers and the gates themselves for not only static/hydraulic loading but also for dynamic impact ice loads.[1]
To minimise the impacts of ice jams, dam operations can include monitoring upstream river ice conditions, breaking of upstream ice jams before a large impoundment develops (explosives have been used early in jam development), and deployment of an ice breaking ship. Lowering the reservoir during periods when ice jams may occur may lesson ice jam impacts – however this may not be effective for small reservoirs.
Reservoir ice sheet loading
Dams with frozen reservoirs can be subject to loadings from reservoir ice sheet thermal expansion or sheet movement due to river flow or wind. These loadings can damage gates. Ensuring that all gates are functional can be critically important – several methods can be used to reduce freeze up and accumulation of ice on gates including bubblers, water movers (stirrers), and heating systems.
For embankment dams, vertical intake towers need to be designed for lateral ice loads and the dam upstream slope riprap should be adequately sized to minimize displacement and bedding disturbance due to ice movement.
Concrete freeze/thaw
If concrete has cracks, water can enter, freeze, and expand cyclically which can cause spalling. If not repaired, water can reach steel rebar causing corrosion, and popouts. To avoid freeze/thaw damage, the concrete mix and construction need to be high quality. Any cracks that exist should be promptly sealed and repaired.
Frost
If embankment dam construction has a winter shut down, susceptible materials such as silt may absorb water, freeze, and expand to create a loose layer in the dam which may be more susceptible to internal erosion. To address this concern, a dry sacrificial layer can be placed before winter and removed in the spring.
Expansion of freezing water around structures can cause movement cracks, gaps or gate binding. Frost impacts can be addressed by burying vulnerable areas below frost depth, battering structures away from vertical to reduce the potential for gaps at embankment-structural interfaces, including expansion joints/waterstops, and adding drainage. Internal erosion through zones affected by frost heaving likely contributed to the failure of Hadlock Pond Dam in 2005 [3].
Frazil ice
Frazil ice (frazil) is suspended ice crystals, which form when water is slightly below the freezing temperature. These crystals can deposit on intake racks of hydropower dams and reduce flow and hydropower production. Raking the rack to remove the frazil or providing heated racks are two methods to minimize the effects of frazil.
Effects of climate change on ice jams
Climate warming may shift numerous characteristics of river ice runs including breakup time of year, ice thickness, and rain-induced breakup. Changes in precipitation, snowpack, snow melt, and wind could affect how, when, and where ice runs occur.[4]
The temperature range between solid and liquid states of ice is narrow. Small increases in temperature could dramatically affect when and which rivers experience spring ice runs. [5]
Climate change uncertainty calls for consideration of conservative engineering practices for cold weather phenomena.
Operator safety in cold weather
Operator safety in cold regions is essential. Improvements in operator safety can also improve the safety of the public, improve gate operations, and make power production more reliable.
Dam operators in cold weather regions are exposed to potentially hazardous winter freezing conditions, including snow, ice, wind, and sleet for extended periods. Ice can build up on walkways, handrails, powerlines, and unprotected equipment. The following strategies can be used to improve O&M staff safety in cold regions [6]:
- Avoiding inclined walkways; provide stairs instead to ascend/descend.
- Heating stairs and walkways to minimise ice and snow accumulation.
- Pitching and draining horizontal walkways to prevent puddles from forming that could freeze and become a slip hazard to operators.
- For stairs, using metal stairs with open grate anti-slip metal treads and handrails on both sides. sides.
- Providing roofs over operator walkways and operable mechanical electrical equipment.
- Providing a heated space/office at the dam to protect operators from the elements and provide storage of personal protective equipment.
Mark Baker, P.E. is a Senior Dam Safety Programme Engineer specialising in dam safety programme audits and human factors in the investigation of dam failures and incidents. He is principal of DamCrest Consulting located in Denver, Colorado, US.
Peer review
This article was reviewed by Lee Wooten, P.E. (GEI Consultants), Ryan Schoolmeesters, P.E. (Eagle Creek Renewable Energy), and Clint Brown, P.E. (Engineering Analytics)
REFERENCES
[1] U.S. Army Corps of Engineers Manual No. 1110-2-1612 Engineering and Design – Ice Engineering. [2] Burrell, B. C., Beltaos, S., & Turcotte, B. (2022). Effects of climate change on river-ice processes and ice jams. International Journal of River Basin Management, 21(3), 421–441. https://doi.org/10.1080/15715124.2021.2007936 [3] Dam Failures and Incidents (book), Baker, Association of State Dam Safety Officials (ASDSO), 2024 [4] Spencer Dam Failure Investigation Report, ASDSO, 2020 [5] Woo, M. (2019). Cryohydrology in Canada: A brief history. Hydrological Processes, 33(26), 3407–3411. https://doi.org/10.1002/hyp.13581 [6] Baker, M. 2021 Dams in Cold Regions Should Account for Ice, Lessons Learned, DamFailures.org
