Transcript Forest Hydrology - Center for Science in the Earth System

Forest Hydrology
Issue: Interaction of forests, fish, and climate
• One of the dominant pathways by which land cover change
affects freshwater fish habitat is via sediment loading
associated with forest disturbance
• Vegetation management, forest fires, and forest roads affect
both the amount of sediment available for transport and the
amount of surface water available to transport it.
• The interaction of climate with these processes has not
previously been explored but is likely to have implications for
integrated management and conservation efforts, especially
recovery of PNW salmon (for which expenditures in the region
are several hundred $million annually).
• An enhanced ability to project the likely effects of climatic
change, fire, and vegetation management on sediment
transport would improve our understanding of forest-aquatic
interactions and the scientific basis for forest management.
Research questions
• What are the relative contributions of sediment
generation from landslides, road and road cut erosion,
and surface erosion over the general landscape, and
how do these relative contributions vary over the climate
regimes represented by forested areas of the PNW?
• How do the amounts and proportions of sediment
generated from the above sources compare to sediment
generated by extreme storms, droughts, and fire
regimes, and to sedimentation amounts under forest
different management scenarios?
• How will sediment generation from PNW watersheds
respond to the interaction of land cover change with
climatic variability and change at decadal to century time
scales?
Approach
• Modify existing Distributed Hydrology-SoilVegetation Model (DHSVM) to include the
capability to represent sediment generation by
slope failures, and hillslope and road erosion, as
well as sediment routing through channel
systems (partially completed, see Doten et al,
2004, in review, WRR)
• For both “generic” watersheds and specific
demonstration applications, conduct evaluations
of impacts of alternative forest policy and
management scenarios with respect to harvest,
thinning, prescribed burning, and road
construction or obliteration, and evaluate (via
“shuffled deck” experiments), climate risk (and
effects of changing climate) associated with
these scenarios.
Distributed hydrology-soilvegetation model (DHSVM)
1-D Vertical Water Balance
DHSVM Model Representation
• Physically based
hydrologic model that
represents the effects
of
– Topography
– Soil
– Vegetation
Surface/Subsurface Flow
Redistribution to/from
Neighboring Pixels
• Solves the energy
and water balance at
each grid cell at each
timestep
Erosion and Sediment Transport Module
MASS WASTING
Soil Moisture
Content
Q
Sediment
Qsed
Channel Flow
Sediment
DHSVM
CHANNEL ROUTING
Precipitation
Leaf Drip
Infiltration and Saturation
Excess Runoff
Erosion
Deposition
HILLSLOPE
EROSION
ROAD
EROSION
Failure Prediction
• Mass wasting algorithm
performed at a finer
resolution
• TOPMODEL topographic
wetness index used to
redistribute soil saturation
(Beven and Kirkby, 1979;
Burton and Bathurst,
1998)
• Run for critical times
Overroad Flow Routing
• Routing takes into account crown
hillslope
road crown
road- side
ditch
fillslope
Erosion
raindrop
impact
leaf drip
impact
shearing by overland flow
Mechanisms of Soil Particle Detachment
• Sediment becomes
available for
transport by:
– three
mechanisms
(hillslopes)
– two mechanisms
(roads)
Sediment Routing
Hillslope:
• If a pixel contains a
channel (including roadside ditches), all sediment
enters the channel.
Hillslope Sediment Routing
Road surface sediment:
• Routed according to the crown type.
• Added to the road-side
Particle Size,
ditch is routed through
mm
the network to a culvert.
0.5-2
• Delivery from culvert
0.63-0.5
to stream based on proximity
≤0.63
and particle size:
Percent
Delivered
10
30
100