Transcript WEPP Winter Routine

Winter Erosion Processes
Research at
Washington State University
Joan Wu, Shuhui Dun
Prabhakar Singh, Cory Greer
Washington State University
Don McCool
USDA-ARS-PWA
Introduction
 Water erosion is a serious and continuous
environmental problem in the US PNW and many
other areas nationwide and worldwide
 In the inland PNW, winter rain season, cyclic freezethaw of soil, steep slope, and improper management
practices act together to cause high erosion rate
 Soil freeze-thaw alters hydrological processes and
reduces soil cohesive strength
 Modelers must properly simulate winter hydrology in
order to adequately simulate surface runoff and water
erosion for cold areas
Introduction
cont’d
 WEPP: Water Erosion Prediction Project
– a process-based erosion prediction model developed
by the USDA ARS to replace the USLE
– built on fundamentals of hydrology, plant science,
hydraulics, and erosion mechanics
 WEPP’s unique advantage: it models
watershed-scale spatial and temporal
distributions of soil detachment and
deposition on event or continuous basis
 Equipped with a geospatial processing
interface, WEPP has GREAT POTENTIAL as
a reliable and efficient tool for watershed
Introduction
cont’d
 WEPP winter routines were designed to simulate
– Snow accumulation and snowmelt
– Soil frost and thaw
 The routines include
–
–
–
–
Adjustment for aspect in calculating incoming radiation
Surface temperature estimation based on energy balance
Accounting for snow drift
Snowmelt simulation based on a generalized basin snowmelt
equation
– Frost simulation considering thermal conductivity of the snowresidue-soil system as well as upward water movement in the
soil
 However, the model was unable to properly represent
the winter processes at the PNW and other colder
regions as previous studies have shown
Snow and Frost Depth
(Pullman, WA)
Snow Depth (mm)
500
(a)
Observed
Simulated
400
300
200
100
0
Frost Depth (mm)
500
(b)
400
300
200
100
0
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Snow and Frost Depth
(Morris, MN)
Snow Depth (mm)
600
(a)
Observed
Simulated
500
400
300
200
100
0
Frost Depth (mm)
1200
(b)
1000
800
600
400
200
0
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1994
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1995
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1996
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Long-term Research Efforts
 Goal
– To continuously develop and improve the WEPP model
for solving water quantity and quality problems
 Objectives for winter hydrology study
– Experimentally identify and mathematically formulate in
WEPP the mechanisms by which freezing and thawing
of soils affect runoff and erosion
– Examine WEPP’s original winter routines and an
alternative energy-budget based approach
– Test the improved WEPP model using data sets from
different localities under different hydrological
conditions
Major Funding Sources
 Wash. State Univ., USDA-ARS-PWA (in
house)
 USFS Rocky Mountain Research Station
(1998–far future???)
 Inland Northwest Research Alliance
(2005–08)
 USDA NRICGP (2001–05)
 USGS/SWWRC (2000)
Major Collaborators
 USDA-ARS-NSERL
 USFS Rocky Mountain Research Station
 USDA-ARS-PWA
 USDA-ARS-CPCRC
 Univ. Idaho, USA
 Univ. Bologna, Italy
Laboratory and Field Investigation
 Water erosion experimentation
using a tilting flume
 Field experimentation on water
balance and erosion
Experimental plots at PCFS
On-site weather station
Tilting Flume at PCFS
An Energy-balance Approach
(Lin and McCool, 2006)
 The approach was based on the principle of
a balance between the model simplicity and
rigor and adequacy in representing snow
and frost dynamics
 In the newly incorporated algorithm
– Energy is balanced cross air-earth interface
– Frost (thawing) depth is computed by dividing the net
energy influx by soil water (ice) content and latent
heat of fusion
Energy Flow into Soil
G = Rn – LE – H
Rn – net radiation
H – sensible heat
LE – latent heat of vaporization
G – energy flow into the soil
Net Energy Flux into Soil
Gn = G – Ln – S + Ju
S – heat storage change
Ln – latent heat utilized by snow melting
Ju – upward heat flux within soil
Lin, C. and D.K. McCool, 2006. Simulating snowmelt and soil frost depth by an
energy-budget approach. Trans. ASABE 49, 1383–1394.
Preliminary Results Using
Datasets in Lin and McCool (2006)
The Alternative Approach
(Pullman, WA)
Snow Depth (mm)
500
(a)
Observed
Simulated
400
300
200
100
0
Frost Depth (mm)
500
(b)
400
300
200
100
0
J
1984
A
J
O
J
A
1985
J
O
J
A
1986
J
O
J
A
1987
J
O
J
A
1988
J
O
J
A
1989
J
O
J
1990
A
J
O
J
1991
The Alternative Approach
(Morris, MN)
Snow Depth (mm)
600
(a)
Observed
Simulated
500
400
300
200
100
0
Frost Depth (mm)
2000
(b)
1500
1000
500
0
O
J
1994
A
J
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J
1995
A
J
O
J
1996
A
J
O
Preliminary Results Using New
PCFS Datasets in Greer et al.
(2006)
BF
Winter Season, 2003–04 (Simulated)
400
Depth, mm
300
200
Snow
100
Frost
0
Thaw
-100
-200
16-Oct
15-Nov
15-Dec
14-Jan
13-Feb
14-Mar
13-Apr
Winter Season, 2003–04 (Observed)
400
Depth, mm
300
200
Snow
100
Frost
0
Thaw
-100
-200
16-Oct
15-Nov
15-Dec
14-Jan
13-Feb
14-Mar
13-Apr
BF
Winter Season, 2004–05 (Simulated)
100
Depth, mm
50
0
Snow
-50
Frost
-100
Thaw
-150
-200
16-Oct
15-Nov
15-Dec
14-Jan
13-Feb
15-Mar
14-Apr
Winter Season, 2004–05 (Observed)
100
Depth, mm
50
0
Snow
-50
Frost
-100
Thaw
-150
-200
16-Oct
15-Nov
15-Dec
14-Jan
13-Feb
15-Mar
14-Apr
BF
Winter Season, 2005–06 (Simulated)
100
Depth, mm
0
Snow
-100
Frost
Thaw
-200
-300
16-Oct
15-Nov
15-Dec
14-Jan
13-Feb
15-Mar
14-Apr
Winter Season, 2005–06 (Observed)
100
Depth, mm
0
Snow
-100
Frost
Thaw
-200
-300
16-Oct
15-Nov
15-Dec
14-Jan
13-Feb
15-Mar
14-Apr
NT
Winter Season, 2003–04 (Simulated)
400
Depth, mm
300
Snow
200
Frost
100
Thaw
0
-100
16-Oct
15-Nov
15-Dec
14-Jan
13-Feb
14-Mar
13-Apr
Winter Season, 2003–04 (Observed)
400
Depth, mm
300
Snow
200
Thaw
100
Frost
0
-100
16-Oct
15-Nov
15-Dec
14-Jan
13-Feb
14-Mar
13-Apr
NT
Winter Season, 2004–05 (Simulated)
200
Depth, mm
150
100
Snow
50
Frost
0
Thaw
-50
-100
16-Oct
15-Nov
15-Dec
14-Jan
13-Feb
15-Mar
14-Apr
Winter Season, 2004–05 (Observed)
200
Depth, mm
150
100
Snow
50
Thaw
0
Frost
-50
-100
16-Oct
15-Nov
15-Dec
14-Jan
13-Feb
15-Mar
14-Apr
NT
Winter Season, 2005–06 (Simulated)
200
Depth, mm
150
100
Snow
50
Frost
0
Thaw
-50
-100
-150
16-Oct
15-Nov
15-Dec
14-Jan
13-Feb
15-Mar
14-Apr
Winter Season, 2005–06 (Observed)
200
Depth, mm
150
100
Snow
50
Thaw
0
Frost
-50
-100
-150
16-Oct
15-Nov
15-Dec
14-Jan
13-Feb
15-Mar
14-Apr
WEPP’s Original Approach
 Snowmelt estimation following Hendrick et
al. (1971) using a modified generalized
basin snowmelt equation for open areas
developed by the US ACE
 Frost formation is governed by the
temperature on the surface of the snowresidue-frozen soil system and energy is
balanced across the freezing front
Hendrick, R.L., B.D. Filgate and W.M. Adams, 1971. Application of environmental analysis
to watershed snowmelt. J. Appl. Meteor. 10, 418–429.
Surface Temperature
Thra – hourly surface temperature (°C)
Tave – hourly air temperature (°C)
Rnet – net radiation (Ly min−1)
conht – convective heat transfer coefficient (Ly s min−1 cm−1)
radco – radiation coefficient (Ly s min−1 cm−1)
vwind – wind velocity (cm s−1)
efthco – effective system thermal conductivity (Ly min−1 °C−1)
depth – system depth (m)
Frost Simulation
 Heat flux from surface
Ksrf – thermal conductivity(W m−1 °C−1)
ΔTsrf – temperature difference (°C)
Zsrf – depth from surface to frozen front (m)
 Heat flux from soil below
 Energy balance in the order of
– Conduction
– Heat of fusion
– Storage
Current Improvement
 Mixed use of energy flux and energy has
been corrected
 Coding mistakes in energy balance during
frost formation have been corrected
 Thermal conductivity of the snow under
testing
 Snow-drift routines have been activated
 Improved adjustment for aspect in
calculating incoming radiation
Current Concerns
 Standing residue currently not considered in
frost simulation
 Single value for thermal conductivity of flat
residue without considering residue type and
percent cover
 Snow-drift influence appears small
 Temperature set at 7 °C at 1 m below frozen
zone
Preliminary Results Using
Datasets in Lin and McCool (2006)
The Improved WEPP
(Pullman, WA)
Snow Depth (mm)
500
(a)
Observed
Simulated
400
300
200
100
0
Frost Depth (mm)
500
(b)
400
300
200
100
0
J
1984
A
J
O
J
A
1985
J
O
J
A
1986
J
O
J
A
1987
J
O
J
A
1988
J
O
J
A
1989
J
O
J
1990
A
J
O
J
1991
The Improved WEPP
(Morris, MN)
Snow Depth (mm)
600
(a)
Observed
Simulated
500
400
300
200
100
0
Frost Depth (mm)
2000
(b)
1500
1000
500
0
O
J
1994
A
J
O
J
1995
A
J
O
J
1996
A
J
O
Summary
 A simplified, energy-balance based
approach to modeling snow accumulation
and soil frost and thaw was incorporated into
WEPP v2004.7
 The model simulated adequate timing for
frost occurrence
 The effect of snow insulation appeared
insufficient
 Model testing using the new PCFS data
showed consistent results with those from
using the historical data
Summary
cont’d
 Improvement of the original WEPP winter
hydrology codes is ongoing
 The current improved version has potential
in improved modeling of frost depth
 Over-predicted frost duration and frequent
thawing for PCFS are being examined (frost
depth’s ceiling near 200 mm appears
problematic)
Thank You!