Development of a
Sediment Transport
Component for DHSVM
Colleen O. Doten, University of Washington
Laura C. Bowling, Purdue University
Edwin D. Mauer, Santa Clara University
Nathalie Voisin, University of Washington
Dennis P. Lettenmaier, University of Washington
Outline
• Motivation
• Distributed Hydrology-Soil-Vegetation
Model (DHSVM)
• Sediment Transport Component
• Testing and Evaluation
• Scenario Analyses
Motivation
Forest
Roads
www.homefirefightingsystems.com
Forest Fire
Timber Harvest
Distributed Hydrology-SoilVegetation Model (DHSVM)
1-D Vertical Water Balance
DHSVM Model Representation
• Physically based
hydrologic model that
simulates the effects
of spatially variable
– topography
– soil
– vegetation
• Solves energy and
water balance at each
grid cell (pixel), at
each time step
Surface/Subsurface Flow
Redistribution to/from
Neighboring Pixels
Sediment Transport Component
DHSVM
SURFACE EROSION
Qsed
CHANNEL EROSION
& ROUTING
Provides Inputs
for all Three
Components
MASS WASTING
Watershed Sediment Module
Q
OUTPUT
DHSVM Inputs to Sediment Model
DHSVM
Soil Moisture Content
Precipitation
Leaf Drip
Infiltration and Saturation
MASS WASTING
Excess Runoff
SURFACE EROSION
Channel Flow
CHANNEL EROSION &
ROUTING
Mass Wasting
http://www.for.gov.bc.ca/research/becweb/zone-MH/mh-photos/
• Dynamic soil
saturation predicted
by DHSVM
• Finer resolution grid
(10 m) for failure
computation
L. Bowling, C. Doten
Icicle Creek, WA
Mass Wasting Module (MWM)
• Slope stability is a function of soil moisture,
slope, and soil and vegetation characteristics.
• Failure is determined by the infinite slope
stability model, using a factor of safety (FS)
FS =
resisting forces
driving forces
• Slope instability is indicated by a FS < 1.
L. Bowling, C. Doten
MWM - Stochastic Nature
• Four soil and vegetation characteristics:
–
–
–
–
soil cohesion,
angle of internal friction,
root cohesion, and
vegetation surcharge
are input as probability distributions.
• They can be assigned to one of three
distributions:
– uniform,
– normal or
– triangular.
L. Bowling
Simulated Probability of Slope Failure
Rainy Creek, WA
November 28, 1995
Probability Storm
of failure Event
L. Bowling
MWM - Mass Redistribution
L. Bowling
•
Failure depth is equal to the failed
pixel soil depth.
•
Failed material travels down the slope
of steepest descent.
•
Failed area can increase in response
to the initial failure.
•
Landslide stops at an empirically
determined runout distance. The
failed volume is evenly distributed
among all downslope pixels.
•
Landslides entering channels system
continue as debris flows depending
on the junction angle.
Surface Erosion & Routing
http:www.geo.uni-bonn.de/cgi-bin/geodynamik_main?Rubrik=research&Punkt=geomorphology
DHSVM Runoff Generation and Routing
Runoff is produced via:
•
Saturation excess (pixels 6 and 7)
•
Infiltration excess based on a user-specified
static maximum infiltration capacity (pixel 3)
Runoff is routed to the downslope neighbors one
pixel/time step
Runoff Generation – Infiltration Excess
• Dominant form of runoff generation on
unpaved roads and post burn land surfaces
• Calculation of maximum infiltration capacity:
– The first timestep there is surface water on the
pixel, all surface water infiltrates.
– If there is surface water in the next timestep, the
maximum infiltration capacity is calculated based on
the amount previously infiltrated.
N. Voisin
Runoff Routing
• Pixel to pixel overland flow routed using an explicit
finite difference solution of the kinematic wave
approximation to the Saint-Venant equations
• Manning’s equation is used to solve for flow area in
terms of discharge
• Per DHSVM timestep, a new solution sub-timestep is
calculated satisfying the Courant condition, which is
necessary for solution stability.
L. Bowling
Surface Erosion
raindrop
impact
leaf drip
impact
• Transportable
sediment is the sum
of particles detached
by three
mechanisms
• Erosion is limited by
overland flow
transport capacity
shearing by overland flow
Mechanisms of Soil Particle Detachment
L. Bowling, N. Voisin
Hillslope Sediment Routing
• Sediment is routed using a four-point finite
difference solution of the two-dimensional
conservation of mass equation.
• If the pixel contains a
channel (including road side
ditches), all sediment and
water enters the channel
segment.
L. Bowling
sediment
and water
Forest Road Erosion
raindrop
impact
shearing by
overland flow
surface
erosion
• Transportable
sediment consists of
particles detached by
two mechanisms
• Overland flow will be
infiltration excess
generated.
• Routing to include
road crown type
– insloped
– outsloped
– crowned
C. Doten
Channel Erosion & Routing
www.eas.purdue.edu/geomorph/ envben.html
Channel Erosion & Routing
• Sediment Supply
– channel sediment storage from the MWM
– lateral inflow from hillslope and roads
– upstream channel segment
• Sediment particles
– have a constant lognormally distributed grain size
which is a function of the user-specified median grain
size diameter (d50) and d90
– are binned into a user-specified number of grain size
classes
E. Maurer
Channel Erosion & Routing
• Sediment is routed using a four-point finite
difference solution of the two-dimensional
conservation of mass equation.
• Instantaneous upstream and downstream
flow rates are used in the routing.
• Transport depends on
– available sediment in each grain size class, and
– capacity of flow for each grain size calculated using
Bagnold’s approach for total sediment load.
E. Maurer
Testing and
Evaluation
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Testing and Evaluation
• Mass wasting
– Land slide mapping derived from aerial photography
• Surface erosion
– Observed local and regional land and road surface
erosion rates
– Run model in location where road data are available
• Channel routing
– Observed stream sediment concentrations
C. Doten
Scenarios Analyses I: Forest Roads
Road Proximity to Streams
Road Location in the Hillslope
& Hillslope Curvature
C. Doten
Coffee Creek, British Columbia
Scenarios Analyses II: Timber Harvest
and Forest Fire
Enhanced Transport Capacity
• Decrease in annual evaporation
• Increased snow accumulation
• Enhanced snow melt
– Greater radiation exposure
– Increased turbulent energy
transfer
Enhanced Sediment Supply
• Mass wasting (landslides)
– Decreased root strength
– Enhanced soil moisture
• Surface erosion
http://www.for.gov.bc.ca/research/becweb/zone-MH/12_Res_Man.htm
C. Doten
Questions/Comments
Data Input Needed for
Sediment Model
• Smaller resolution (10m) DEM
• Debris Flow Material d50 and d90
• Soils: Bulk Density, Saturated Density, Manning
n, K index, d50, distributions (mean, stand
deviation, minimum value, maximum value) of
Cohesion and Angle of Internal Friction
• Vegetation: Vegetation Surcharge distribution
(minimum value and maximum value) and Root
Cohesion distribution (mode, minimum value
and maximum value)
DHSVM Channel Routing
• Flow is routed using a cascade of linear reservoirs.
• Each channel segment is treated as reservoir of
constant width. Discharge is linearly related to
storage. This implies a constant flow velocity.
• Storage at the next timestep can be calculated
knowing the inflow and velocity (determined using
Manning’s equation.)
• The average outflow from a reach is obtained through
a mass balance.
References
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Bagnold, R.A., 1966, An approach of sediment transport model from general physics. US Geol. Survey
Prof. Paper 422-J.
Benda, L. and T. Dunne, 1997, Stochastic forcing of sediment supply to channel networks from
landsliding and debris flow, Wat. Resour. Res, 33 (12), 2849-2863.
Beven, K.J. and M.J. Kirkby, 1979, A physically based, variable contributing area model of basin
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Chow V.T., D.R. Maidment, L.W.Mays 1988: Applied Hydrology. McGraw-Hill Book Company pp572.
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References (con’t)
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Komura, W., 1961, Bulk properties of river sediments and its application to sediment hydraulics, Proc.
Jap. Nat. Cong. For Appl. Mech.
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Rubey, W.W., 1933, Settling velocities of gravels, sands, and silt particles, Am. Journal of Science, 5th
Series, 25 (148), 325-338.
Shields, A., 1936, Application of similarity principles and turbulence research to bedload movement.
Hydrodynamic Lab. Rep. 167, California Institute of Technology, Pasadena, Calif.
Smith R.E. and J.Y. Parlange 1978: A parameter-efficient hydrologic infiltration model. Wat. Resour. Res.
14(3), 533-538.
Smith R.E., D.C. Goodrich, D.A. Woolhiser, and C.L. Unkrich 1995: KINEROS – a kinematic runoff and
erosion model. Chapter 20 in: Computer Models of Watershed Hydrology, Water Resources Publication,
Highland Ranch, Colorado. p697-732.
Sturm, T., 2001, Open Channel Hydraulics, McGraw-Hill, NY, NY, pp. 378-380.
Wicks, J.M. and J.C. Bathurst, 1996, SHESED: a physically based, distributed erosion and sediment yield
component for the SHE hydrological modeling system, Journal of Hydrology, 175, 213-238.
Wigmosta, M.S., and D.P. Lettenmaier, 1999, A Comparison of Simplified Methods for Routing
Topographically-Driven Subsurface Flow, Wat. Resour. Res., 35, 255-264.
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documentation and user manual, USDA-Agricultural Research Service, ARS-77, 130 pp.