Snow Hydrology Flashcards

1
Q

Why is snow hydrology important?

A
  • Flood events
  • Rain-on-snow
  • Storage of winter precipitation and eventual melt
  • Safety (cold temps associated with snow dangerous when power goes out, snow can trap people)
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2
Q

Red River Manitoba

A
  • 1997 river flooded
  • Up to 20km beyond banks
  • Caused major fires downtown
  • Built diversion channels and spill way to save city but causes problems downstream
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3
Q

What are three factors for snow hydrology physical processes?

A
  • Snow Accumulation
  • Ablation
  • Meltwater Runoff
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4
Q

What is the snow to rainfall ratio?

A

10cm of snow = 1cm of rainfall in dry and arctic environments, coast will have higher water content

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5
Q

Four simultaneous estimation problems

A
  • The quantity of water held in snow packs
  • The magnitude and rate of water lost to the atmosphere by sublimation
  • The timing, rate, and magnitude of snow melt
  • The fate of melt water
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6
Q

Why is the fate of meltwater of concern?

A
  • will it all melt and run off, or infiltrate and become part of GW
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7
Q

Which hemisphere has the largest snow extent?

A

Northern has higher max and lower minimums

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8
Q

CCIN

A

Canadian Cryospheric Information Network

  • Collects public info (Govt, universities)
  • Enhance public awareness and access to cryospheric information and related data
  • Facilitate exchange of information
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9
Q

What are the snow depth departure trends in North America?

A
  • Most spots show large negative departure from normal

- Some in Northern parts are slightly above

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10
Q

Optimal Interpolation

A
  • Statistics based grid
  • Minimal variance, similar to kriging
  • Creates interpolation
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11
Q

Why do we expect to see fluctuations in snow extent in North America?

A
  • Because it is precip driven
  • Sublimation may occur
  • Wind transffering snow to lower/warmer elevation
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12
Q

How do we see if fluctuations in snow extent in North America are within normal ranges?

A
  • Use +/- 1 standard deviations to see if fluctuations are within normal range
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13
Q

Why was snow extent elevated in North America in 2015-2016?

A
  • Polar Vortex
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14
Q

What are the 3 spatial scales for snow cover distribution?

A
  • Macroscale
  • Mesoscale
  • Microscale
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15
Q

Fractals

A

Same pattern at a multitude of scales

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16
Q

Macroscale snow cover

A
  • Up to 10^6 km^2
  • Characteristic of Distances 10-1000km
  • Larger scale meteorological effects are important
  • Air mass characteristics
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17
Q

Mesoscale snow cover

A
  • Characteristic of distances of 100m - 10km
  • Redistribution of snow along relief features due to wind
  • Deposition and accumulation of snow may be related to terrain variables and vegetation cover
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18
Q

Microscale snow cover

A
  • Characteristic of distances of 10-100m
  • Differences in accumulation result from variations in air flow patterns and transport
  • Local flow patterns and turbulence
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19
Q

Snow cover in vegetated areas

A
  • Influenced by vegetation density and type and its influence on winds
  • More accumulation in cleared areas (20-45%)
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20
Q

How does vegetation (tree) type influence snow cover?

A
  • More deep snow on ground with deciduous
  • Less deep snow with coniferous trees due to more snow landing on branches
  • More interception on coniferous than bare branched deciduous
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21
Q

Why does more snow accumulate in clearings?

A
  • Turbulent flow over vegetation causes deposition of snow in clearings where it is less turbulent (lee side)
22
Q

Why does more sublimation occur on vegetation/trees?

A
  • Increases surface area of snow exposed to atmosphere sun and wind
23
Q

Wind redistribution of snow

A
  • Alpine areas are more exposed and vulnerable to redistribution an d rain
  • Wind moves accumulation over watershed barriers and can change where snow melts and where it will contribute to flow
  • Will differ from the precipitation estimation where it was expected to fall
24
Q

Sublimation losses of snow due to wind

A
  • Wind changes shape of snow
  • Exposes more surface area of particle and increases sublimation
  • mass loss
25
Q

What are the methods for measuring snowfall?

A
  • Snow pillows
  • Heated tipping bucket
  • Meter stick
26
Q

What is an issue with measuring snowfall with a meter stick?

A
  • Doesn’t take into account sublimation loss and redistribution that will change value of what actually occurs
27
Q

What is a downfall of a heated tipping bucket to record snow fall?

A
  • requires more power
28
Q

What are 3 characteristics of snow pack?

A
  • Porous medium (ice + air + liquid)
  • Composed of layers of different types of snow (basically homogeneous within one layer)
  • Ice is in crystals and grains that are usually bonded together (forms a texture with a degree of strength)
29
Q

Snow pits

A
  • Dig and build platforms so you can get back out
  • an instrument takes samples of known volume through snow pack to get density
  • up elevation from glacier nose to tip
  • Deeper at higher elevation unless an avalanche redistributes from high to low (nose)
30
Q

Snow Water Equivalent (SWE)

A
  • How much water does the snow represent
  • = (depth of snow x density of snow)/density of water
  • settled snow has higher density as snow transitions to firn to glacial ice
31
Q

Liquid water content of snow

A
  • 0% in dry snow (snowballs difficult

- 15% in slush (small amount of air in pores)

32
Q

What are the two Temperature characteristics of Snowpack?

A
  • Temperature gradient between top of pack and ground (usually near 0) determined by thickness of snow pack and mean surface snow temp. Can be diurnal (warm during day, cold at night at surface)
  • No temperature gradient, isothermal
33
Q

What does the flow velocity (wide range between 2-60cm/min) of water through snow depend on?

A
  • Internal snow pack structure
  • Condition of snow pack prior to introduction of water
  • Amount of water available at the snow surface
34
Q

How does water flow through homogeneous snow?

A
  • Thin film of water surrounds snow grains at melting temperature (similar to capillary in soil, but more flow)
  • Water flows through this film
  • Once pores are filled, laminar flow occurs and can efficiently drain snow pack (similar to gravity flow of soil at field capacity)
35
Q

What are they 4 liquid water regimes of water flow through snow?

A
  • Capillary
  • Unsaturated
  • Saturated
  • Melt/Freeze
36
Q

Capillary water flow through snow

A

-

37
Q

Unsaturated water flow through snow

A
  • 1-14% free water
  • Water drains by gravity but air spaces are continuous
  • Pendular regime
38
Q

Saturated water flow through snow

A
  • > 14% free water
  • Water drains by gravity but air spaces are discontinuous
  • Funicular regime
39
Q

Melt/Freeze water flow through snow

A
  • Water melts and refreezes
  • Possibly several times before it drains from the snow pack
  • Complicates path of water for drainage
  • Day melt, night freeze (diurnal temperature regime)
40
Q

How does water flow through heterogeneous snow?

A
  • Preferential flow paths revealed through dye tracing. Vertical channels or macropores are natural.
  • Ice Layers that develop from surface melt and refreezing can be relatively impermeable and force ponding of water and lateral/horizontal flow
41
Q

How is meltwater percolation through snow measured?

A
  • Dye tracing

- Snow Guillotine

42
Q

How does dye tracing through snow work?

A
  • Water paths (both vertical and lateral) can be seen by allowing a coloured liquid to percolate through a slab of snow naturally
  • Problem: Digging to see path only gives a cross-section that can disturb flow and doesn’t give volume
43
Q

How does a snow guillotine work?

A
  • Takes slices of a snow slab that has been injected with dye tracing
  • Combine images of slices to reconstruct a 3D image of water flow through snow to see flow variability and connectivity
44
Q

Connectivity row statistics for a snow guillotine 3D data cube

A
  • 0 is no connectivity in a layer
  • 1 is perfect connectivity in a layer
  • More connectivity deeper in snow pack likely
45
Q

What are 3 things that the fate of snow melt depends on?

A
  • Slope
  • Snow
  • Soil Conditions
46
Q

What happens when snow melt encounters thawed, permeable, soil at the base of a snow pack?

A
  • Snow behaves much like rainfall

- Will infiltrate at a rate less than the infiltration rate and enter soil

47
Q

What happens when snow melt encounters frozen soil at the base of a snow pack?

A
  • Water will pond at the snow/soil interface
48
Q

Basal ice development

A
  • On shallow slopes ponded meltwater may refreeze at the base of snow pack
  • Ice layers formed may impede further meltwater infiltration
49
Q

Subnivean flow on a slope

A
  • Lateral flow of basal ponded water, depends on slope
  • Lateral flow is through porous medium if snow is still present
  • Water flow rapidly destructs small snow grains, leaving larger one and allows for more rapid flow
  • Erodes bottom of snow pack along the way
50
Q

Unit Hydrograph for snow

A
  • When will melt happen and how much discharge does this equate to
  • Snowfall strongly modifies the hydrograph, flood waves, and water resource management in snowmelt dominated catchments