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

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

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

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

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

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

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

Dynamic Breakup Breakup is strongly influenced by dynamic (hydraulic) factors – usually associated with a large snowmelt runoff event. 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.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.Ice sheets and ice floes will be carried downstream with the flood flow. An ice jam will form if the ice run is arrested.An ice jam will form if the ice run is arrested.

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

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

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

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

Transverse cracking Border ice inundation photo by S. Beltaos

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. (Beltaos, 1995) Dynamic Breakup Processes

4. Ice Clearing photo by S. Beltaos

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

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

Flooding usually results… photo by S. Beltaos

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

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

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

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

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

(Allen, 1977) Mean ice free data on rivers