Unit 7 - Snow Hydrology

What are the different techniques you can use to manipulate water runoff?

Change Interception

Change Runoff

Change Infiltration

all of this discussion was based on rainfall, but what about snow?

Snow has

unique properties:

• frozen

• stays in place

• freezes the soil below

Hydrology impacts:

• has no immediate runoff

• once ground freezes, reduced infiltration

• when snow melt occurs

  • pulse of runoff can be quite large

Rule of thumb for snow water content - average of

10%

10 inches of snow yields 1 inch of liquid water

wet snow typically yields about

20% water content

not all of a snowflake is

frozen

water content of dry snow is about

3% water

dry snow structure contains more

air pockets

you cannot make snowballs or snowmen out of

dry snow

water content of snow varies by

Temperature

Packing and settling while on the ground

Melting and recrystallization

Illegal to have snowball fights in some areas

Houghton, MI - $50 fine

In cold months precipitation falls 

as snow

In many areas, during the cold months is when

most precipitation falls

during the cold months, snow accumulates as 

snow pack or snow fields

In the cold months, snow serves as a natural reservoir for water because it

Stores precipitation

Water supplies

Up to 75% in some western states

In spring, snow

melts

in spring, snow Contributes to

river flow

In some rivers, source of majority of water

South Platte River in Colorado and Nebraska

Historically, virtually dry in summer

snow melt magnitude depends on

Depth of snow pack

Onset of warm temperatures

• Rapid onset -> rapid melt

• Slower onset -> extended period of melt

Rainfall on melting snow

• Accelerates melt

Humidity

humidity impacts on snow melt: at higher humidity, there is

More condensation on snow

Releases latent heat

Warming snow and increasing melt

historically, humidity is changing - it is increasing in 

coastal ranges

California, Oregon, Washington, British Columbia, and Alaska

Decreasing in inland areas

Consequences?

results of rapid snow melt include major 

Flooding downstream

Result of rapid melt with rainfall

• Called a “rain-on-snow event” or ROS

• Flooding downstream

• Mass wasting of hill sides

• Debris flows

• Damage to riparian zones

• Ice blocks

  • Damage to structures

  • Fatalities

causes of the 2019 midwestern floods

January through early March

• Average temperatures – remained low (20-30oF)

• Record snowfall in many areas

  • Up to 3 ft. on the ground in some places

11-13 March

• Temperatures rose 60 degrees F

• Combined with 1.5” of rain

result of the 2019 midwestern floods

Rapid snow melt

Ground still frozen

• So, little infiltration and Massive Flooding

Many of the rivers were still frozen over

• Broken up into chunks

• Described as “plows” as they damaged structures

Over $3 billion in damages and 3 deaths

Management of Runoff is important

Infrastructure design

• Culverts, bridges, ...

Resource planning

• Reservoirs

• Flood sensitivity (i.e., return period)

Traditionally based largely on rainfall events... not snow

Studies show that peak flow volumes in northern climates derive from

both rainfall and snow melt

studies show from climate change, there is

Less snow in the fall

• because of Higher temperatures

Greater snow pack at highest elevations

Slower snow melt

• Shift to earlier in the season

• Period with lower solar radiation

• Models show as much as 2 months earlier

management needs to reflect 

climate changes in snowmelt

impacts of these changes

More moisture in the soil for vegetation

Potential for less flooding due to snow melt but greater potential for it to be catastrophic

• Greater variability in temperature

• More soil moisture -> more runoff

Warmer stream temperatures

• May adversely impact trout and other aquatic species

Management of Snow for Water Yield

Ability to alter

• When snow melt occurs

• Snow melt rates

• Where snow fall accumulates

How to alter snow melt rate or when melt occurs

• Change albedo

• Provide insulation

To increase melt rate

Spread “Lamp Black” on the surface

• Ground up carbon

• Absorbs solar radiation, heating the snow

• Increase rate up to 2.7 times

problems of spreading “Lamp Black” on surface

Adds carbon – alters C:N ratio in the soil

Could apply, then it snows

• Cover up the Lamp Black

to decrease snow melt rate

Spread 2” of sawdust on the surface

Acts as an insulator

Purpose of decreasing melt rate

Hold the snow to melt at a later time

problem of adding sawdust to decrease melt rate

Adds carbon – alters C:N ratio in the soil

Currently – 20 million tons of salt each year to melt

snow and ice on pavement

with impacts on vegetation along roadsides

Recent Research - Concrete that melts snow on its own

Use of “phase change materials”

for example:

Paraffin oil, for example

Tests

1. Paraffin-filled pipes

2. Concrete mixed with paraffin

3. Control – normal concrete

Both tests with paraffin – melted 5” of snow in 25 hours

Control – no melt in 25 hours

Purpose of snow fence

Alter where snow fall accumulates

Provide shelter for livestock

Keep snow off roads and railroads

Avalanche control

Increase depths in specified areas

types of snow fences

Fence

Trees and shrubs

Combination of both

Solid fence vs. fence with openings

Both slow the wind and produce drifts

Difference

Solid fence – drifts upwind of fence

• Shelter for livestock

Fence with openings – drifts downwind of fence

• Creates pressure differential – higher in front, lower behind

• Causes air to drop snow behind the fence

tips on building snow fences

Know prevailing wind direction

Standard placement away from a road

• 35 times the height of the fence

• Adjust as needed

Place gap under the fence

• If none, fence can get buried and lose effectiveness

Reduce risk of avalanche

Can direct snow to accumulate in desired place

Combine with a trench

• Direct snowmelt to swale or pond

• Use for irrigation or livestock

• Common practice in some regions