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River Ice Breakup

Introductory lectures in River Ice Engineering. River Ice Breakup. photo by S. Beltaos. Thermal versus Dynamic Breakup. Breakup is influenced by both thermal (meteorological) and dynamic (hydraulic) processes.

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River Ice Breakup

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  1. Introductory lectures in River Ice Engineering River Ice Breakup photo by S. Beltaos

  2. Thermal versus Dynamic Breakup • Breakup is influenced by both thermal (meteorological) and dynamic (hydraulic) processes. • It is the relative importance of these interacting influences which dictate the nature and severity of river ice breakup.

  3. Thermal Breakup • Ice deterioration occurs much as it does in a lake – ice simply “rots” in place • Meteorological factors are most important – energy budget calculation • Hydraulic influences are negligible

  4. Important Meterological Factors • Solar insolation and warm overlying air • Reflectance (“albedo”) of the surface • fresh snow: albedo ~ 0.90 to 0.95 • open water: albedo ~ 0.05 to 0.15

  5. Thermal Breakup Processes 1. snowmelt – reduces surface albedo photo by F. Hicks

  6. Thermal Breakup Processes 2. development of open water leads – allow considerable heat to enter the flow, melting the ice from the underside photo by F. Hicks

  7. photo by S. Beltaos Thermal Breakup Processes 3. thermal deterioration of the ice cover – occurs at an accelerating rate, as surface albedo decreases

  8. Dynamic Breakup • Breakup is strongly influenced by dynamic (hydraulic) factors – usually associated with a large snowmelt runoff event. • Before any significant thermal deterioration has occurred, the ice cover is lifted by rapidly increasing water levels and it breaks into discrete pieces. • Ice sheets and ice floes will be carried downstream with the flood flow. • An ice jam will form if the ice run is arrested.

  9. Dynamic Breakup Processes 1. overflow from open leads – indication of rapid water level rise photos by F. Hicks

  10. 2. Formation of Hinge Cracks (Beltaos, 1995) • As streamflow increases due to spring runoff, the ice cover in the centre portion of the channel will lift. • Hinge cracks form parallel to the banks. • Border ice becomes inundated.

  11. Hinge Crack in a Narrow Stream Typically, hinge cracks form along both banks, but in narrow channels, like this one, a single crack may form down the middle of the channel. Notice the water on top of the ice on either side of the crack. photo by S. Beltaos

  12. photo by S. Beltaos 3. Transverse cracking As the ice cover lifts with the rising water level, transverse cracks form.

  13. Transverse cracking Border ice inundation photo by S. Beltaos

  14. Dynamic Breakup Processes (Beltaos, 1995) 4. Ice Clearing When the discharge gets high enough for the lifting ice sheets to be able to overcome geometric constraints, these sheets are then free to pass downstream.

  15. 4. Ice Clearing photo by S. Beltaos

  16. Dynamic Breakup Processes 5. ice run photo by F. Hicks 6. ice jamming photo by R. Gerard

  17. Ice Jams form when dynamic processes dominate photo by L. Garner

  18. Flooding usually results… photo by S. Beltaos

  19. ice jam near Fredericton, NB… photo by D. Bray

  20. Profile of a Long Ice Jam Backwater Head of Jam Toe of Jam (adapted from Ashton, 1986)

  21. Ice jams can be a big problem for bridges… photo source: R. Gerard

  22. Ice jams are often too big to remove … Blasting is usually ineffective in such cases. CRREL photo

  23. Large trees on this island were “mowed down” by an ice jam… jam toe was here photo by R. Gerard

  24. Mean ice free data on rivers (Allen, 1977)

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