Watershed%20and%20Stream%20Network%20Delineation%20

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Watershed and Stream Network Delineation
Geomorphological Considerations

• David G. Tarboton
• dtarb_at_cc.usu.edu

http//www.engineering.usu.edu/dtarb
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Overview

• Review of flow direction, accumulation and
  watershed delineation
• Topographic texture and drainage density
• Channel network geomorphology and Hortons Laws
• Stream drop test to objectively oelect channel
  delineation threshold
• Curvature and slope based methods to represent
  variable drainage density
• The D? approach
• Specialized grid accumulation functions
• TauDEM software

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Elevation Surface the ground surface elevation
at each point
Digital Elevation Model A digital
representation of an elevation surface. Examples
include a (square) digital elevation grid,
triangular irregular network, set of digital line
graph contours or random points.
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Digital Elevation Grid a grid of cells (square
or rectangular) in some coordinate system having
land surface elevation as the value stored in
each cell.
Square Digital Elevation Grid a common special
case of the digital elevation grid
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Direction of Steepest Descent
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Slope
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Eight Direction Pour Point Model
ESRI Direction encoding
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Eight Direction Pour Point Model D8
Band/GRASS/TARDEM Direction encoding
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Grid Network
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Contributing Area Grid
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TauDEM convention includes the area of the grid
cell itself.
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Programming the calculation of contributing area

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Contributing Area gt 10 Cell Threshold
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Watershed Draining to This Outlet
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100 grid cell constant support area threshold
stream delineation
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200 grid cell constant support area based stream
delineation
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How to decide on support area threshold ?
Why is it important?
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Hydrologic processes are different on hillslopes
and in channels. It is important to recognize
this and account for this in models.
Drainage area can be concentrated or dispersed
(specific catchment area) representing
concentrated or dispersed flow.
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Delineation of Channel Networks and Subwatersheds
500 cell theshold
1000 cell theshold
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Examples of differently textured topography
Badlands in Death Valley.from Easterbrook, 1993,
p 140.
Coos Bay, Oregon Coast Range. from W. E. Dietrich
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Logged Pacific Redwood Forest near Humboldt,
California
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Canyon Creek, Trinity Alps, Northern California.

Photo D K Hagans
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Gently Sloping Convex Landscape
From W. E. Dietrich
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Mancos Shale badlands, Utah. From Howard, 1994.
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Topographic Texture and Drainage Density
Same scale, 20 m contour interval
Driftwood, PA
Sunland, CA
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landscape dissection into distinct valleys is
limited by a threshold of channelization that
sets a finite scale to the landscape.
(Montgomery and Dietrich, 1992, Science, vol. 255
p. 826.)
Suggestion One contributing area threshold does
not fit all watersheds.

• Lets look at some geomorphology.
• Drainage Density
• Hortons Laws
• Slope Area scaling
• Stream Drops

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Drainage Density

• Dd L/A
• Hillslope length ? 1/2Dd

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Hillslope length B A 2B L Dd L/A 1/2B ?
B 1/2Dd
L
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Drainage Density for Different Support Area
Thresholds
EPA Reach Files
100 grid cell threshold
1000 grid cell threshold
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Drainage Density Versus Contributing Area
Threshold
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Hortons Laws Strahler system for stream ordering
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Bifurcation Ratio
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Area Ratio
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Length Ratio
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Slope Ratio
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Slope-Area scaling
Data from Reynolds Creek 30 m DEM, 50 grid cell
threshold, points, individual links, big dots,
bins of size 100
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Constant Stream Drops Law
Broscoe, A. J., (1959), "Quantitative analysis of
longitudinal stream profiles of small
watersheds," Office of Naval Research, Project NR
389-042, Technical Report No. 18, Department of
Geology, Columbia University, New York.
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Stream DropElevation difference between ends of
stream
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Suggestion Map channel networks from the DEM at
the finest resolution consistent with observed
channel network geomorphology laws.

• Look for statistically significant break in
  constant stream drop property
• Break in slope versus contributing area
  relationship
• Physical basis in the form instability theory of
  Smith and Bretherton (1972), see Tarboton et al.
  1992

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Statistical Analysis of Stream Drops
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T-Test for Difference in Mean Values
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T-test checks whether difference in means is
large (gt 2) when compared to the spread of the
data around the mean values
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Constant Support Area Threshold
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200 grid cell constant support area based stream
delineation
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Local Curvature Computation(Peuker and Douglas,
1975, Comput. Graphics Image Proc. 4375)
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Contributing area of upwards curved grid cells
only
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Upward Curved Contributing Area Threshold
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Curvature based stream delineation
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Channel network delineation, other options
Contributing Area
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Grid network pruned to order 4 stream delineation
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Slope area threshold (Montgomery and Dietrich,
1992).
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Addressing the limitations imposed by 8 grid
directions
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Topographic Slope
Limitation imposed by 8 grid directions.

• Topographic Definition Drop/Distance

Flow Direction Field if the elevation surface
is differentiable (except perhaps for countable
discontinuities) the horizontal component of the
surface normal defines a flow direction field.
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The D? Algorithm
Tarboton, D. G., (1997), "A New Method for the
Determination of Flow Directions and Contributing
Areas in Grid Digital Elevation Models," Water
Resources Research, 33(2) 309-319.)
(http//www.engineering.usu.edu/cee/faculty/dtarb/
dinf.pdf)
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Specific catchment area a is the upslope area per
unit contour length m2/m ? m
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Contributing Area using D?
Contributing Area using D8
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Useful for example to track where sediment or
contaminant moves
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Useful for example to track where a contaminant
may come from
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Useful for a tracking contaminant or compound
subject to decay or attenuation
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Transport limited accumulation
Useful for modeling erosion and sediment
delivery, the spatial dependence of sediment
delivery ratio and contaminant that adheres to
sediment
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Reverse Accumulation
Useful for destabilization sensitivity in
landslide hazard assessment
with Bob Pack
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TauDEM Software Functionality

• Pit removal (standard flooding approach)
• Flow directions and slope
• D8 (standard)
• D? (Tarboton, 1997, WRR 33(2)309)
• Flat routing (Garbrecht and Martz, 1997, JOH
  193204)
• Drainage area (D8 and D?)
• Network and watershed delineation
• Support area threshold/channel maintenance
  coefficient (Standard)
• Combined area-slope threshold (Montgomery and
  Dietrich, 1992, Science, 255826)
• Local curvature based (using Peuker and Douglas,
  1975, Comput. Graphics Image Proc. 4375)
• Threshold/drainage density selection by stream
  drop analysis (Tarboton et al., 1991, Hyd. Proc.
  5(1)81)
• Wetness index and distance to streams
• Specialized grid analysis functions (Upslope
  influence, Downslope dependence, Decaying
  accumulation, Concentration limited accumulation,
  Downslope accumulation, Transport limited
  accumulation)

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TauDEM in ArcGIS
Visual Basic GUI application
Visual Basic ESRI ArcGIS 8.1 Toolbar
Standalone command line applications
C COM DLL interface
Available from
TauDEM C library
Fortran (legacy) components
http//www.engineering.usu.edu/dtarb/
USU TMDLtoolkit modules (grid, shape, image, dbf,
map, mapwin)
ESRI gridio API (Spatial analyst)
ESRI binary grid
ASCII text grid
Vector shape files
Binary direct access grid
Data formats
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Demonstration