Introduction to River Ice Kathleen D. White, PE Research Hydraulic Engineer Ice Engineering Research Division US Army Cold Regions Research and Engineering Laboratory NWS Hydromet 99-2 Boulder, CO Monday, June 28, 1999

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Ice Cover Crystal Structures Fine grained iceFine grained ice – Frazil or snow – “White” ice – Resists solar penetration Columnar iceColumnar ice – Thermally grown – “Black” ice – Transparent, allows solar penetration,”candle ice”

Frazil Ice Frazil is the predominant type of ice found in most river and streamsFrazil is the predominant type of ice found in most river and streams Formed only in areas of open waterFormed only in areas of open water Formed in turbulent waterFormed in turbulent water Flow velocity Wind mixing Formed in supercooled waterFormed in supercooled water -.01°C to -.02°C

FRAZIL ICE IN RIVERS

Frazil Slush Anchor Ice

Frazil Evolution: Ice Floes Frazil Slush Pancake Ice Large Floes “High Energy” “Low Energy” Mountain Streams Steep Rivers Large Waves Rivers with Mild Slopes

Ice Cover Formation Static Ice Cover FormationStatic Ice Cover Formation – Typical of ponds, small lakes, and slow flowing rivers – Dominated by thermal growth Air Water Ice Ice Growth Heat transfer

Ice Cover Formation Dynamic Ice Cover FormationDynamic Ice Cover Formation – Dominated largely by the interaction between ice floes and the flowing water – An ice cover may initially form dynamically and later thicken due to thermal growth

River Ice Cover Breakup Thermal Breakup: Ice cover melts in placeThermal Breakup: Ice cover melts in place – Direct sunlight plays a large role – Surface color influences absorption of sunlight: Dusting ice promotes melting – Water on ice decreases reflection, may promote melting promote melting – Open water areas absorb sunlight

River Ice Cover Breakup Mechanical Breakup: Hydrodynamic forces acting on cover exceed cover strengthMechanical Breakup: Hydrodynamic forces acting on cover exceed cover strength Results from an increase in flowResults from an increase in flow – Precip. event – Snowmelt event – Dam operation

Mechanical Ice Cover Breakup Increase in flow & stageIncrease in flow & stage Fractures in ice coversFractures in ice covers Ice cover freed from constraints of banks and transported downstreamIce cover freed from constraints of banks and transported downstream – Stage rise 1.5 to 3 times ice thickness Ice floes broken into smaller floesIce floes broken into smaller floes Ice jam formation downstreamIce jam formation downstream

Ice Jam Formation Jams occur at locations where the rivers transport capacity is exceededJams occur at locations where the rivers transport capacity is exceeded – Intact ice cover – Sharp bends – Decreases in channel slope – Constrictions – Confluences Abrupt flooding can occur upstream of jamAbrupt flooding can occur upstream of jam

What constitutes a Jam ?

IAHR Working Group on River Ice Hydraulics Definition IAHR Working Group on River Ice Hydraulics Definition An ice jam is a stationary accumulation of fragmented ice or frazil that restricts flow An ice jam is a stationary accumulation of fragmented ice or frazil that restricts flow

Ice Jams Cause floodingCause flooding Promote bed and bank erosionPromote bed and bank erosion Remove or damage bank vegetationRemove or damage bank vegetation Suspend navigationSuspend navigation Damage channel training worksDamage channel training works Flood upland wetlandsFlood upland wetlands May be important for maintaining near- stream habitatMay be important for maintaining near- stream habitat

Freezeup Jams Early to mid-winter formation Subfreezing air temperatures Frazil and broken border ice Unlikely to release Fairly steady water flow May exhibit cohesion Smooth to moderate surface roughness

Primary Flow Area FrazilFrazil Drained Frazil Refrozen Surface Layer Surface LayerRefrozen Border Ice Pieces Cross Section of Freezeup Jam

Breakup Jams Mid to late winter formation Mid to late winter formation Near-freezing air temperatures Near-freezing air temperatures Broken sheet and border ice Broken sheet and border ice Highly unstable, releasing suddenly Highly unstable, releasing suddenly Unsteady water flow (surges) Unsteady water flow (surges) Negligible cohesion Negligible cohesion Moderate to extreme surface roughness Moderate to extreme surface roughness

Primary Flow Area Cross Section of Breakup Jam Brash/slushBrash/slush Ice Blocks Water Level

Brash, frazil, and larger pieces

Mid-winter Jams Forms due to "mid-winter thaw" Forms due to "mid-winter thaw" Breakup jam characteristics Breakup jam characteristics Refreezes in place to form significant Refreezes in place to form significant blockage blockage Refreezes in place to form significant Refreezes in place to form significant blockage blockage May result in more jamming during May result in more jamming during subsequent spring breakup subsequent spring breakup May result in more jamming during May result in more jamming during subsequent spring breakup subsequent spring breakup

Undercover Transport and Deposition Frazil (and small blocks) transported beneath a Frazil (and small blocks) transported beneath a cover come to rest at areas of low water velocity cover come to rest at areas of low water velocity Frazil (and small blocks) transported beneath a Frazil (and small blocks) transported beneath a cover come to rest at areas of low water velocity cover come to rest at areas of low water velocity Accumulation builds up until critical velocity is Accumulation builds up until critical velocity is reached ( m/sec) reached ( m/sec) Accumulation builds up until critical velocity is Accumulation builds up until critical velocity is reached ( m/sec) reached ( m/sec) Tends to fill in deep sections so that accumulation Tends to fill in deep sections so that accumulation follows bed topography follows bed topography Tends to fill in deep sections so that accumulation Tends to fill in deep sections so that accumulation follows bed topography follows bed topography May deform ice surface due to buoyancy May deform ice surface due to buoyancy Also referred to as "hanging dam" Also referred to as "hanging dam"

Undercover Transport and Deposition Frazil Slush Solid Ice Cover

Pans or Blocks Ice Jam Submergence/Frontal Progression

Existing jam fails when downstream acting forces Existing jam fails when downstream acting forces rise above jam strength rise above jam strength Existing jam fails when downstream acting forces Existing jam fails when downstream acting forces rise above jam strength rise above jam strength Cover is transported downstream until resisting Cover is transported downstream until resisting force increases force increases Cover is transported downstream until resisting Cover is transported downstream until resisting force increases force increases Cover thickens as it comes to rest, thereby Cover thickens as it comes to rest, thereby increasing jam strength increasing jam strength Cover thickens as it comes to rest, thereby Cover thickens as it comes to rest, thereby increasing jam strength increasing jam strength Commonly occurs with breakup jams Commonly occurs with breakup jams Also referred to as "wide channel jam" Also referred to as "wide channel jam" Failure and Thickening

Failure and thickening Jam after failure and thickening and thickening Jam after failure and thickening and thickening Jam before failure Intact ice sheet

Modeling Ice-covered Rivers Steady FlowSteady Flow – HEC-2 – HEC-RAS Unsteady FlowUnsteady Flow – UNET – Discrete Element Models 2 Dimensional Flow2 Dimensional Flow – Currently in development

HEC River Analysis System (RAS) Water surface profiles for steady flowWater surface profiles for steady flow Full networksFull networks River geometry described by cross sectionsRiver geometry described by cross sections 1-D energy eq. or momentum eq.1-D energy eq. or momentum eq. Bridges, culverts,weirs, hydraulic structures,etcBridges, culverts,weirs, hydraulic structures,etc Multiple plans/profiles/bridge openingsMultiple plans/profiles/bridge openings Graphical and tabular outputGraphical and tabular output

HEC-RAS with ice: Highlights View results graphicallyView results graphically Profile Plot Profile Plot

HEC-RAS with ice: Highlights View results graphicallyView results graphically X-Y-Z Perspective Plot X-Y-Z Perspective Plot

What about climate change?