Canadian Prairie
Hydrology and Runoff
Generation
John Pomeroy
Centre for Hydrology,
University of Saskatchewan, Saskatoon
www.usask.ca/hydrology
Prairie Hydrology
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
Major river flow is primarily from mountain runoff, but
prairie runoff supplies smaller rivers, streams, wetlands,
and lakes
Prairie Runoff
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forms in internally drained (closed) basins that are locally
important but non-contributing to river systems that drain the
prairies, OR
drains directly to small prairie rivers (Battle, Souris, Assiniboine)
>80% of runoff during snowmelt period
Redistribution of snow to wetlands and stream channels in
winter is critical to formation of runoff contributing area
Drainage of small streams and wetlands ceases
completely in summer when actual evaporation*
consumes most available water.
Baseflow from groundwater often nonexistent.
Prairie streams are almost completely ungauged and
often altered by dams, drainage, water transfers, etc
*evaporation used here as transpiration + evaporation + sublimation
Prairie Hydrological Cycle
Prairie Runoff Generation
Snow Redistribution to Channels
Spring melt and runoff
Dry non-contributing areas to runoff
Water Storage in Wetlands
Non-Contributing Areas to Streamflow a
Prairie Characteristic
Prairie Hydrology – don’t blink
Smith Creek, Saskatchewan
Drainage area ~ 450 km2
20
Average 1975-2006
15
Streamflow m
3
per second
25
1995 High Year
10
2000 Low Year
5
No baseflow from groundwater
0
27-Dec
27-Nov
28-Oct
28-Sep
29-Aug
30-Jul
30-Jun
31-May
01-May
01-Apr
02-Mar
31-Jan
01-Jan
Information Needed to Estimate
Runoff
Snow accumulation and redistribution
 Melt rate
 Infiltration to frozen soils
 Infiltration excess forms runoff
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>80% of all runoff is snowmelt runoff
Blowing Snow: Transport, Sublimation
and Redistribution of Snow
Pomeroy and Gray, Wat Resour. Res. (1990)
Pomeroy and Male, J Hydrol. (1992)
Pomeroy, Gray and Male, J Hydrol. (1993)
Pomeroy and Gray, NHRI Science Report No. 7 (1995)
Effect of Blowing Snow Sublimation
on Prairie Snow Supply (losses, mm SWE)
Location
Calgary
Peace River
Swift Current
Prince Albert
Regina
Yorkton
Portage
Winnipeg
Stubble-field
19.7
6.6
28.2
24.9
39.4
18.6
23.5
27.4
Pomeroy and Gray, NHRI Science Report No. 7 (1995)
Fallow-field
37.5
7.6
37.8
29.6
48.1
28.6
33.8
36.5
1970-1976 hourly simulations
Distribution of Blowing Snow over Landscapes
Blowing snow transport, and
sublimation relocate
snow across the
landscape from sources
to sinks depending on
fetch, orientation and
area.
Source
Sink
Fallow
Field
Stubble
Field
Grassland
Brush
Trees
Shelterbelts on Prairies
Winkler,
Manitoba
Transport to shelterbelts
depends on upwind fetch
and vegetation roughness
Conquest, Saskatchewan
Spatially Distributed Snow Redistribution
Snow mass balance equation
St Denis, Saskatchewan
Results – Spatially distributed SWE
Fang and Pomeroy, Hydrol Proc, in preparation
Spatially distributed SWE cont’
Spatially distributed SWE cont’
Spatially distributed SWE cont’
Spatially distributed SWE cont’
Spatially distributed SWE cont’
Spatially distributed SWE cont’
Spatially distributed SWE cont’
Spatially distributed SWE cont’
Spatial Pattern of Blowing Snow Sublimation
Simulations vs. Snow Surveys
Snowmelt
Degree Day Method
has problems in open
environments with late melt, & in forests.
 Energy Balance snow CAN be estimated
using reliable and readily applicable
methods

Coupled Mass and Energy
Equations for Snowmelt

MELT of SWE = QM/(w Lf Bi)

Melt Energy QM = Q* - QE – QH – QG – dU/dt
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Q* Net radiation (+ to snow surface)
QE Evaporative energy (+ away from snow surface)
QH Sensible energy (+ away from snow surface)
QG Ground heat flux (+ downward from snow)
dU/dt Internal energy change (+ loss from melt)
Diurnal Variation in Radiative Fluxes clear day near Saskatoon
700
600
500
400
Incoming SW
Net SW
Net Rad
Net LW
Radiation 300
(W/m²) 200
100
0
-100
-200
0:00
4:00
8:00
12:00
Time
16:00
20:00
24:00
Empirical atmospheric
transmittance equations
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Qsi can be calculated directly if the
atmospheric transmittence is known
Many similar relationships, all give similar
results:
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Bristow and Campbell and Walter et al.
Annandale
All use a simple relationship between daily
atmospheric transmittance and the range
of daily air temperatures
Edmonton 1979-2000
Snowpack Albedo Decay
CRHM Snowmelt Simulation
Infiltration to
Frozen Soils
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Frozen soils can be
permeable, but show
reduced infiltration
compared to unfrozen conditions
‘Frozen’ means a frost depth of at least 0.5 m
Simple grouping of soil types
Three classes of
infiltrability:
unlimited
restricted
limited
Inf=SWE
Inf=0
Inf = f(SWE, Saturation)
Gray’s Model of Infiltration into Frozen
Soils - Prairie Environment
120
Unlimited
Restricted
100
1:1
80
Saturation
0.3
0.4
0.5
0.6
0.7
Infiltration
60
(mm)
40
20
0.9
0
0
30
60
90
120
150
Snow Water Equivalent (mm)
180
Effect of Thawed Soils on
Prairie Spring Runoff
Daily Flow, m 3/s
1.4
Observed
Frozen Soil
Unfrozen Soil
1.2
1
0.8
0.6
0.4
0.2
0
95
100
105
110
Julian Date
115
120
125
Local Scale Prairie Runoff
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Because of frozen soils and rapidly melting
snowcovers in the spring, 80% - 90% of prairie
runoff is produced from snowmelt
Snowmelt runoff is strongly controlled by snow
drift location and size, soil moisture and mid
winter thaws.
In wet years, there is often excess water to
dryland cereal grain growing needs.
Hydrological computer simulations may tell us
something about the reliability and behaviour of
local prairie water supplies
Cold Regions Hydrological Model
Prairie hydrological modelling requires consideration of the
following:
1. Transport of water in liquid, vapour and frozen states (runoff,
percolation, evaporation,
sublimation, blowing snow);
2. Coupled mass and energy balances;
3. Phase change in snow & soils (snowmelt, infiltration in frozen
soils, soil freezing and thawing);
4. Snow and rain interception in forest canopies;
5. Episodic flow between soil moisture, groundwater, ponds and
streams.
6. Variable storage, drainage and contributing area
7. Land use change
CRHM Module Development
DATA
ASSIMILATION
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Data from multiple sites
Interpolation to the HRUs
PROCESSES
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SPATIAL
PARAMETERS
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Basin and HRU parameters
are set. (area, latitude,
elevation, ground slope,
aspect)
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Infiltration into soils (frozen
and unfrozen)
Snowmelt (prairie & forest)
Radiation – level, slopes
Evapotranspiration
Snow transport
Interception (snow & rain)
Sublimation (dynamic & static)
Soil moisture balance
Sub-surface runoff
Routing (hillslope & channel)
Advection
Creighton Tributary, Bad Lake as a
typical Prairie Basin
Moderately well drained plateau of grains and fallow drains into a coulee
Semi-arid to sub-humid climate
Typical drainage and landcover for much of southern prairies
Snowmelt Runoff over Frozen Soils
Bad Lake:
Semi-arid
SW Saskatchewan
Soil moisture is
FALL soil moisture
Snowmelt runoff is
Spring
Physically based
Infiltration equations
(Zhao & Gray, 1999)
Cold Regions
Hydrological Model
Bad Lake – Creighton Tributary Water Balance
With 30% Summer Fallow
Fallow
Stubble
Coulee
Basin
500
mm water equivalent
400
300
200
Snowfall
100
Rainfall
Runoff
0
Sublimation
-100
Drifting Snow
-200
Evaporation
-300
-400
-500
Pomeroy, De Boer, Martz (2007)
Stubble
Coulee
Basin
500
Changed to
Continuous
Grain Cropping
mm water equivalent
400
300
Snowfall
200
Rainfall
100
Runoff
Sublimation
0
Drifting Snow
-100
Evaporation
-200
-300
-400
runoff
infiltration
snowmelt
sublimation
drift
evaporation
snowfall
rainfall
-40
-20
0
20
% Change
40
60
Prairie Streamflow & Climate Change
“first more, then less”

Three most “reliable” climate change
scenarios for hydrology suggest increases in
annual prairie winter temperature and
precipitation from the 1961-1990 average:
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2050
2080
+2.6 ºC and +11%
+4.7 ºC and +15.5%
Using these scenarios in the virtual upland
basin results in a 24% rise in 2050 spring
runoff, but a 37% drop by 2080, compared to
conditions in the mid 1970s.
29/04/1975
15/04/1975
01/04/1975
18/03/1975
04/03/1975
18/02/1975
04/02/1975
21/01/1975
07/01/1975
24/12/1974
10/12/1974
26/11/1974
70
12/11/1974
60
29/10/1974
15/10/1974
01/10/1974
SWE (mm)
Prairie Climate Change –
Winter Snow
Winter Snow Accumulation at Bad Lake, SK
Normal SWE (Winter of 1974/75)
50
SWE (Winter of 2049/50)
40
SWE (Winter of 2079/80)
30
20
10
0
Prairie Climate Change –
Spring Runoff
70
Spring Runoff from Creighton Tributary at Bad Lake, SK
Normal Spring Runoff (Spring of 1975)
50
Spring Runoff (Spring of 2050)
40
Spring Runoff (Spring of 2080)
30
20
10
29/04/1975
15/04/1975
01/04/1975
18/03/1975
04/03/1975
18/02/1975
04/02/1975
21/01/1975
07/01/1975
24/12/1974
10/12/1974
26/11/1974
12/11/1974
29/10/1974
15/10/1974
0
01/10/1974
Runoff (mm)
60
Conclusions
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Prairie hydrological processes that control water
balance and runoff generation have been largely
quantified and described and model
requirements are known, but have not been
widely implemented in models.

Major unknowns are the changing contributing
area and its interaction with surface storage
terms in poorly defined drainages.