Lecture 7-River Ice Introduction Introduction River Ice Formation River Ice Formation Timing and Duration of River Ice Break- up Timing and Duration of River Ice Break- up Break-up Processes-Forecasting Break-up Processes-Forecasting Strength and Variability of River Ice Types Strength and Variability of River Ice Types Summary Summary

River Ice Notable feature of lakes and rivers in the North is that they are ice-covered for portions of the year Notable feature of lakes and rivers in the North is that they are ice-covered for portions of the year “ floating ice ” “ floating ice ” Effect on the flow and water level in a stream Effect on the flow and water level in a stream Seasonal storage-rep. by the ice itself Seasonal storage-rep. by the ice itself

River Ice (continued) *Hydrological Significance of Floating Ice can be Substantial* Extremes-floods vs. low flows Therefore, important function of stream processes Therefore, important function of stream processes Peak Q……..Snowmelt Peak Q……..Snowmelt Peak water Level…..Flooding….f’ of ice conditions on the stream Peak water Level…..Flooding….f’ of ice conditions on the stream

River Ice (continued) Impt. for North……snowmelt peak……peak Q…..occurs when the stream is still ice covered or otherwise influenced by ice in the channel Impt. for North……snowmelt peak……peak Q…..occurs when the stream is still ice covered or otherwise influenced by ice in the channel ice jams-made up 30% of floods in Canada ice jams-made up 30% of floods in Canada Floods are responsible for more flood damage than open-water floods (rain generated)

River Ice (continued) 1987: St. John’s N.B. $30 million 1987: St. John’s N.B. $30 million NWT: threat-river communities (Mackenzie River) NWT: threat-river communities (Mackenzie River) Low Flow Low Flow Affected by ice conditions Affected by ice conditions i.e. Q over Niagara Falls was halted March 29, 1848 by ice obstructing the outlet of Lake Erie i.e. Q over Niagara Falls was halted March 29, 1848 by ice obstructing the outlet of Lake Erie

Beneficial? Floods-lakes in Mackenzie Delta depend on seasonal flooding caused by ice jams to refill and refresh them Floods-lakes in Mackenzie Delta depend on seasonal flooding caused by ice jams to refill and refresh them Economic Concerns: Economic Concerns: H.E. power H.E. power Need to regulate water during winter-don’t want too much or too little Need to regulate water during winter-don’t want too much or too little Environmental concerns….pollution (i.e. Pulp and Paper Mills along the Athabasca River. Environmental concerns….pollution (i.e. Pulp and Paper Mills along the Athabasca River.

River Ice (continued) High Flows have been studied* High Flows have been studied* Low Flows-little studied Low Flows-little studied While, floating ice has little effect on long- term yield, it can be responsible for major shifts in the timing of the yield….through its influence on storage While, floating ice has little effect on long- term yield, it can be responsible for major shifts in the timing of the yield….through its influence on storage

Climate Change? Later Freeze-back Later Freeze-back Earlier Thaws Earlier Thaws

Freeze-up on a River Like lake-but 2 differences Like lake-but 2 differences 1) turbulence (generated by own flow) 1) turbulence (generated by own flow) 2 no thermal stratification, temp. similar throughout the depth (due to turbulence) 2 no thermal stratification, temp. similar throughout the depth (due to turbulence)

Freeze-up (continued) 1) sheet ice over the quiet water of the shallow edges 1) sheet ice over the quiet water of the shallow edges 2) central portion-turbulent-prevents sheet ice- instead frazil forms and is mixed throughout the depth 2) central portion-turbulent-prevents sheet ice- instead frazil forms and is mixed throughout the depth Frazil- (mm’s)-fine discs of ice. When frazil first forms, it is sticky and attaches to things-bed materials-frazil accumulates and then forms Anchor Ice Frazil- (mm’s)-fine discs of ice. When frazil first forms, it is sticky and attaches to things-bed materials-frazil accumulates and then forms Anchor Ice It blankets rapids and gravel beds and when it becomes about 1 m thick can project above water surface-known as ICE DAMS It blankets rapids and gravel beds and when it becomes about 1 m thick can project above water surface-known as ICE DAMS

Frazil Ice Shore Ice

Anchor Ice

Freeze-Up (continued) If turbulence is not too intense, frazil particles will accumulate at the surface….lead to slush…and then to frazil pans If turbulence is not too intense, frazil particles will accumulate at the surface….lead to slush…and then to frazil pans As air temperatures drop-border ice moves out from the shore, conc. of frazil ice increases on the free surface….and they start to close in…..then pans will lodge As air temperatures drop-border ice moves out from the shore, conc. of frazil ice increases on the free surface….and they start to close in…..then pans will lodge

Freeze-up (continued) Accumulation of ice pans occurs….leads to ice jam……ice cover….see increase resistance to water flow upstream and flow downstream Accumulation of ice pans occurs….leads to ice jam……ice cover….see increase resistance to water flow upstream and flow downstream

1) Formation Cooling Snowfall Tranquil Turbulent Frazil BorderIce Snow Slush growth open water frazil ice covered icing,snowslush ice thickness anchor ice ice dam

Ice Decay Thermal Thermal Energy Balance Energy Balance Mechanical Mechanical Ice Fracture Ice Fracture Flow and Jams Flow and Jams

Timing and Duration of River Ice Breakup FDI: First deterioration of ice (FDI)- this date marks the beginning of the breakup process, which may be manifested by a definite movement of the ice, or the formation of cracks, leads or open water areas in the ice-all the result of weakening of the ice due to melting FDI: First deterioration of ice (FDI)- this date marks the beginning of the breakup process, which may be manifested by a definite movement of the ice, or the formation of cracks, leads or open water areas in the ice-all the result of weakening of the ice due to melting

WCI WCI: Water clear of ice refers to the earliest date on which water was reported to be completely free of all floating ice and remained so until the following freeze-up. WCI: Water clear of ice refers to the earliest date on which water was reported to be completely free of all floating ice and remained so until the following freeze-up.

Prowse and Onlin (19**) 1) Found significant differences among the regions in regards to the northerly rate of advance of the two break-up dates. 1) Found significant differences among the regions in regards to the northerly rate of advance of the two break-up dates. B.C and Atlantic: slowest rate of advance (5.4 to 6.1 days/degree) B.C and Atlantic: slowest rate of advance (5.4 to 6.1 days/degree) Prairies and NWT, Nunavut: rapid rate of advance (3.5 – 4.1 days/degree) Prairies and NWT, Nunavut: rapid rate of advance (3.5 – 4.1 days/degree)

Continued 2) Distinct differences among regions in the timing of the breakup for comparable latitudes (i.e. B.C. and Atlantic) 2) Distinct differences among regions in the timing of the breakup for comparable latitudes (i.e. B.C. and Atlantic) Mean date for FDI at 50 o (B.C.) Feb. 25 Mean date for FDI at 50 o (B.C.) Feb. 25 “” “” (Atlantic) April 17 “” “” (Atlantic) April 17 “ WCI (B.C) Mar. 21 “ WCI (B.C) Mar. 21 “ “” Atlantic May 2 “ “” Atlantic May 2 *controlling effect of climate in the breakup processes-regional differences. *controlling effect of climate in the breakup processes-regional differences.

FDI and WCI Dates for each can be considered to bracket the beginning and end of the break-up period Dates for each can be considered to bracket the beginning and end of the break-up period Alan (1964) calculated the mean duration of the breakup to be 10.0 days for 60 Can. Rivers. Alan (1964) calculated the mean duration of the breakup to be 10.0 days for 60 Can. Rivers. Prowse and Onlin (19**)-avg. time was 50% higher… days Prowse and Onlin (19**)-avg. time was 50% higher… days

Initiation of River Ice Break-up a major consequence of ice cover formation in northern rivers is the jamming that occurs during the spring breakup of the ice and the clearance of the ice from the river a major consequence of ice cover formation in northern rivers is the jamming that occurs during the spring breakup of the ice and the clearance of the ice from the river Due to their large thickness and hydraulic resistance relative to those of sheet ice, jams tend to cause unusually high water stage. Due to their large thickness and hydraulic resistance relative to those of sheet ice, jams tend to cause unusually high water stage.

Break-up continued Repercussions in many operational and design problems of which the most pressing is spring flooding Repercussions in many operational and design problems of which the most pressing is spring flooding 1) when will breakup commence 2) how severe will it be several factors are important several factors are important Total heat input/unit ice area Total heat input/unit ice area Snow and ice thickness Snow and ice thickness Hydromorphic channel characteristics Hydromorphic channel characteristics

FDI and WCI Also found that there does not appear to be any sign. relationship in the duration of breakup with latitude on a regional or national basis. Also found that there does not appear to be any sign. relationship in the duration of breakup with latitude on a regional or national basis. Break-up duration- controlled more by physical factors such as the size and steepness of the river, the # of upstream tributaries and the length of the river contributing ice and even the frequency of ice jamming which can impede the process of ice clearance. Break-up duration- controlled more by physical factors such as the size and steepness of the river, the # of upstream tributaries and the length of the river contributing ice and even the frequency of ice jamming which can impede the process of ice clearance.

Forecast Simple Approach Simple Approach Need a general conceptual model of the break-up process Need a general conceptual model of the break-up process

Maximum Stable Freeze-Up Stage (H F ) At a certain time, which may be termed the beginning of freeze-up, the actual stage begins to rise, while the effective stage begins to drop. Eventually, the actual stage attains a peak and then declines. At a certain time, which may be termed the beginning of freeze-up, the actual stage begins to rise, while the effective stage begins to drop. Eventually, the actual stage attains a peak and then declines.

H F continued Pattern reflects the dynamic nature of ice cover formation in a river Pattern reflects the dynamic nature of ice cover formation in a river With the onset of cold weather, frazil ice forms and is initially transported freely….effect on water stage is negligible With the onset of cold weather, frazil ice forms and is initially transported freely….effect on water stage is negligible As more frazil is produced…..it begins to agglomerate into slush pancakes..ice transport is impeded somewhere downstream of the gauge….ice cover begins to propagate upstream As more frazil is produced…..it begins to agglomerate into slush pancakes..ice transport is impeded somewhere downstream of the gauge….ice cover begins to propagate upstream

H F continued The presence of the ice cover causes a local stage increase which eventually begins to be “felt” at the gauge site. The presence of the ice cover causes a local stage increase which eventually begins to be “felt” at the gauge site. The gauge ht. then increases until the time when the edge of the ice cover arrives at the gauge site….the gauge ht. Then declines, as the Q decreases The gauge ht. then increases until the time when the edge of the ice cover arrives at the gauge site….the gauge ht. Then declines, as the Q decreases

H F continued Peak stage (H F ) during this period is considered an important factor in influencing the succeeding breakup because it defines the stage at which the ice cover is formed Peak stage (H F ) during this period is considered an important factor in influencing the succeeding breakup because it defines the stage at which the ice cover is formed The width of the cover is approx. = to channel width at stage H F The width of the cover is approx. = to channel width at stage H F

Stage of Initiation of Break-up (H B ) When a thaw does lead to break-up of the ice cover When a thaw does lead to break-up of the ice cover The gauge record shows irregularities that cannot be explained by Q variations The gauge record shows irregularities that cannot be explained by Q variations Have spikes and peaks (breaking or broken ice effects) even though “effective” stage varies smoothly Have spikes and peaks (breaking or broken ice effects) even though “effective” stage varies smoothly A probable value for the stage at the initiation of breakup may be set at the first significant spike….not too objective…tend to use a range A probable value for the stage at the initiation of breakup may be set at the first significant spike….not too objective…tend to use a range

Stage of Initiation of Break-up (H B ) Lower limit of this range is the stage before the rise starts and the upper limit is the first peak that cannot be attributed to broken ice effects. Lower limit of this range is the stage before the rise starts and the upper limit is the first peak that cannot be attributed to broken ice effects. H m -maximum stage reached during breakup H m -maximum stage reached during breakup

Maximum Ice Effect on Stage: Δ H m The ice effect on stage is the difference between the actual stage and the effective stage. The ice effect on stage is the difference between the actual stage and the effective stage. The time of max. ice effect can usually be determined by simple inspection and does not necessarily coincide with the time of H m. The time of max. ice effect can usually be determined by simple inspection and does not necessarily coincide with the time of H m. Effective stage….determined by joining daily values plotted at noon of each day Effective stage….determined by joining daily values plotted at noon of each day

Total Heat Input to the Outer Ice Surface (  q) - first day when q is positive….index - first day when q is positive….index q= aΘ + b Su + c q= aΘ + b Su + c q= daily amount of heat in J/cm 2 ; Θ is mean daily air temp. in 0 C; Su is total hours of bright sunshine during the day; a, b, and c are coeff…depend on latitude and time of year. q= daily amount of heat in J/cm 2 ; Θ is mean daily air temp. in 0 C; Su is total hours of bright sunshine during the day; a, b, and c are coeff…depend on latitude and time of year.

Initiation of break-up Shulyakovsky (1963) suggested that the rise of (H B -H F ) required to initiate break-up of ice cover, depends on ice thickness (hi) and total amount of heat input to the ice cover (  q) Shulyakovsky (1963) suggested that the rise of (H B -H F ) required to initiate break-up of ice cover, depends on ice thickness (hi) and total amount of heat input to the ice cover (  q)

Initiation of Break-up For pre-mature break-up events (  q=0) a rise of about 0.9 m over H F is necessary to initiate breakup. For pre-mature break-up events (  q=0) a rise of about 0.9 m over H F is necessary to initiate breakup. “mature events” (  q> 6300 J/cm 2 ) are initiated at stage 6300 J/cm 2 ) are initiated at stage < 0.6 m below H F

Max. Stage During Break-up H m  with  H F H m  with  H F H m = H F (upper envelope) H m = H F (upper envelope) H m …..  q, hi, and Q are important…also depends on whether and where (relative to the gauge site) ice jams occur H m …..  q, hi, and Q are important…also depends on whether and where (relative to the gauge site) ice jams occur

Continued Considering the thermal effect, expect that with   q, H m will deviate from the upper envelope. Considering the thermal effect, expect that with   q, H m will deviate from the upper envelope.

Continued Water stages can be used to forecast breakup initiation and severity Water stages can be used to forecast breakup initiation and severity

Strength and Variability of Major River Ice Types See Prowse and Demuth (1993) See Prowse and Demuth (1993) Ice cover deterioration processes are also controlled by meteorological conditions Ice cover deterioration processes are also controlled by meteorological conditions Latent heat fluxes, sensible heat fluxes, conductive and radiative fluxes within the ice cover Latent heat fluxes, sensible heat fluxes, conductive and radiative fluxes within the ice cover

Continued Once all or a portion of the cover has reached the melting point…only the shortwave portion is responsible for the transformation and evolution of inter- granular voids or porosity; the structural changes that affect cover strength Once all or a portion of the cover has reached the melting point…only the shortwave portion is responsible for the transformation and evolution of inter- granular voids or porosity; the structural changes that affect cover strength

Continued Prowse et al (1990a) found that 10% melt-pore volume produces a strength- reduction equivalent to that resulting from a 5 to 10 degree C warming of the ice. Prowse et al (1990a) found that 10% melt-pore volume produces a strength- reduction equivalent to that resulting from a 5 to 10 degree C warming of the ice. Examined the strength and energy balance of two major river ice types Examined the strength and energy balance of two major river ice types White ice and black ice White ice and black ice

Continued White Ice White Ice Small dia. grains comprised of snow-ice and/or frazil ice; translucent to opague appearance Small dia. grains comprised of snow-ice and/or frazil ice; translucent to opague appearance

Black Ice Black Ice: Large columnar grains with a transparent to translucent appearance Black Ice: Large columnar grains with a transparent to translucent appearance Study site was the Liard River-confluence with the Mackenzie Study site was the Liard River-confluence with the Mackenzie

Energy Balance Energy Balance Energy Balance Black Ice: low albedo-increase -  S Black Ice: low albedo-increase -  S White Ice: high albedo-moderate  S White Ice: high albedo-moderate  SStrength -initially, black ice higher than decreased below white ice

Continued At the end, black ice was only 60% of the strength of white ice At the end, black ice was only 60% of the strength of white ice Strength of the white ice…little changed Strength of the white ice…little changed Why? Why? 1) White-small accum. of radiation within the white ice cover-has high extinction coeff. Compared to snow> black ice 1) White-small accum. of radiation within the white ice cover-has high extinction coeff. Compared to snow> black ice Absorption of radiation near surface and porosity develops near the surface…leaves lower layers undisturbed. Absorption of radiation near surface and porosity develops near the surface…leaves lower layers undisturbed.

Continued 2) Snow ↓ amt. of radiation by  reflection and high attenuation 2) Snow ↓ amt. of radiation by  reflection and high attenuation 3) rough surface….traps snow 3) rough surface….traps snow Black ice-more prone to wind swept, and had minimum snow cover at the beginning of the melt phase. Black ice-more prone to wind swept, and had minimum snow cover at the beginning of the melt phase.

Significance 1) Break-up front will proceed more rapidly thru columnar ice (black ice) than white ice 1) Break-up front will proceed more rapidly thru columnar ice (black ice) than white ice 2) Likely, that the sudden barrier created by a change in cover type (such as black to white ice) may initiate jamming….implications for regulating streams 2) Likely, that the sudden barrier created by a change in cover type (such as black to white ice) may initiate jamming….implications for regulating streams

Continued 3) Try to regulate the type of ice which forms in the rivers…desirable to promote the development of largely black ice (columnar type ice)…..offers the minimal resistance to break-up advance. 3) Try to regulate the type of ice which forms in the rivers…desirable to promote the development of largely black ice (columnar type ice)…..offers the minimal resistance to break-up advance.

Summary Introduction Introduction River Ice Formation River Ice Formation Timing and Duration of River Ice Break- up Timing and Duration of River Ice Break- up Break-up Processes-Forecasting Break-up Processes-Forecasting Strength and Variability of River Ice Types Strength and Variability of River Ice Types Summary Summary