Ice-Jam Flooding Including Debris

Unique identifier / Notation

MH0608

Synonyms

Flash Flood Flooding

An ice-jam flood including debris is defined as an accumulation of shuga including ice cakes, below ice cover. It is broken ice in a river which causes a narrowing of the river channel, a rise in water level and local floods (WMO, 2012).

Shuga is defined as the accumulation of spongy white ice lumps, a few centimetres across, formed from grease ice or slush, and sometimes from anchor ice rising to the surface (WMO, 2012).

Primary reference(s)

WMO, 2012. Definition number 1352. International Glossary of Hydrology. WMO-No. 385. World Meteorological Organization (WMO). Accessed 15 May 2025.

Annotations

Additional scientific description

Ice-jam flooding is caused by an accumulation of ice in a river, stream or other flooding source that reduces the cross-sectional area available to carry the flow and forces an increase in water-surface elevation (WMO, 2012).

Metrics and numeric limits

Not applicable.

Key relevant UN convention / multilateral treaty

Sendai Framework for Disaster Risk Reduction 2015-2030.

Drivers

In rivers/streams that experience seasonal ice formation and melt, if the melting is more rapid upstream than downstream, ice floes can accumulate in rivers, forming constrictions and damming flows, causing river levels to rise upstream of the ice jam. A sudden release of the ‘ice jam’ can cause a flood wave similar to that caused by a dam break, to move downstream. Both meltwater and heavy rainfall in steep areas can cause landslips and debris flows. As the debris picked up by rivers moves downstream, major constrictions can build up. When these build-ups collapse or are breached, severe flooding can result. These phenomena are difficult to predict (WMO, 2011; FEMA, 2018).

Impacts

Floods are one of the most common hazards. In line with the general impacts defined in the chapeau, ice-jam flooding can have both a slow onset (when flooding occurs upstream to the ice jam) and an abrupt occurrence (similar to a dam break) when the ice jam collapses, leading to a flash-flood-like impact downstream.

The effects of flooding on health are extensive and significant, ranging from mortality and injuries resulting from trauma and drowning, to infectious diseases and mental health problems (acute and long- term). While some of these outcomes are relatively easy to track, ascertaining the human impact of floods is still weak. For example, it has been reported that two-thirds of deaths associated with flooding are from drowning, with the other third from physical trauma, heart attacks, electrocution, carbon monoxide poisoning and fire. Often, only immediate traumatic deaths from flooding are recorded (WHO, 2013).

Morbidity associated with floods is usually due to injuries, infections, chemical hazards and mental health effects (acute as well as delayed) (WHO, 2013). Hypothermia may also be a problem, particularly in children, if trapped in floodwaters for lengthy periods (WHO, no date). There may also be an increased risk of respiratory tract infections due to exposure (loss of shelter, exposure to flood waters and rain). Power cuts related to floods may disrupt water treatment and supply plants, thereby increasing the risk of water-borne diseases as well as affecting the proper functioning of health facilities, including cold chain (WHO, no date). Floods can potentially increase the transmission of the following communicable diseases: water-borne diseases (such as typhoid fever, cholera, leptospirosis and hepatitis A) and vector-borne diseases (such as malaria, dengue and dengue haemorrhagic fever, yellow fever, and West Nile Fever) (WHO, no date).

The longer-term health effects associated with a flood are less easily identified. They include effects due to displacement, destruction of homes, delayed recovery and water shortages (WHO, 2013).

Multi-hazard context

The figure below summarises common interactions between ice-jam flooding, including debris, and other hazards. This information should be used with caution and not be solely relied upon in Disaster Risk Management, particularly as some interactions may not have been included. Note that hazardous events occurring together or locally in space or time may not necessarily cause, amplify, or be otherwise related to each other. Specific examples of multi-hazard context can be found in the ‘Hazard drivers’ and ‘Impacts’ sections above.

Multi-hazard diagram

Risk Management

No Information Available

Monitoring

The section above and the table below offer an overview of monitoring ice-jam flooding, including debris. This information can be used for forecasting within a national early warning system (EWS). Since EWS capacities and processes differ across countries, the most current and specific information regarding EWS should be obtained from the appropriate national or regional agency/authority responsible for disaster management.

Which institution(s) produce(s) Disaster Risk Data/Information?

Meteorological services tracking temperature fluctuations, precipitation, and freeze-thaw cycles that contribute to ice jam formation.
Hydrological services monitoring river levels, ice thickness, flow velocity, and debris accumulation in water channels.
Geological and geophysical agencies studying riverbed morphology, sediment transport, and terrain conditions affecting ice jam development.
National, subnational, and local disaster management agencies responsible for monitoring ice-jam flood risks, issuing warnings, and coordinating emergency response.
Health authorities assessing public safety risks, including waterborne diseases, hypothermia exposure, and emergency medical needs.
Engineers and water resource management agencies designing ice control structures, flood defences, and debris removal strategies.
Land use and urban planners incorporating ice-jam flood risk assessments into zoning laws, infrastructure siting, and watershed management.
Energy and utility companies monitoring risks to hydropower plants, bridges, pipelines, and other infrastructure vulnerable to ice and debris blockages.
Researchers and academics, including hydrologists and climate scientists, studying ice jam formation, flood forecasting, and climate change impacts on freeze-thaw dynamics.
Environmental organiszations and conservation groups working on river ecosystem management, ice jam mitigation, and debris control strategies.

How is the Hazard Observed/Monitored/Forecast?

Ice-jam flooding, including debris, is monitored using river gauges, aerial and satellite imagery, and on-the-ground observations to track ice buildup and water levels. Hydrologists analyse temperature fluctuations, river flow rates, and freeze-thaw cycles to predict when and where ice jams may form. Models simulate ice movement and water flow, helping forecasters issue early warnings. By combining real-time data with historical patterns, experts provide alerts to protect communities, infrastructure, and ecosystems from sudden flooding and debris blockages.