Transcript Digital Elevation Model Based Watershed and Stream Network Delineation  Conceptual Basis  Eight direction pour point model (D8)  Flow accumulation  Pit removal and DEM reconditioning  Stream delineation  Catchment.

Digital Elevation Model Based Watershed
and Stream Network Delineation

Conceptual Basis

Eight direction pour point model (D8)

Flow accumulation

Pit removal and DEM reconditioning

Stream delineation

Catchment and watershed delineation



Geomorphology, topographic texture
and drainage density
Generalized and objective stream
network delineation
Reading – Arc Hydro Chapter 4
Conceptual Basis


Based on an information model for
the topographic representation of
downslope flow derived from a
DEM
Enriches the information content of
digital elevation data.
 Sink
removal
 Flow field derivation
 Calculating of flow based
derivative surfaces
Duality between Terrain and
Drainage Network
• Flowing water erodes
landscape and carries
away sediment sculpting
the topography
• Topography defines
drainage direction on the
landscape and resultant
runoff and streamflow
accumulation processes
Topography defines watersheds which are
fundamentally the most basic hydrologic
landscape elements.
Watershed
divide
Drainage
direction
ArcHydro Page 57
Outlet
1:24,000 scale map of a study area in West Austin
DEM Elevations
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Contours
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Hydrologic Slope
- Direction of Steepest Descent
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Slope:
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ArcHydro Page 70
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Eight Direction Pour Point Model
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ESRI Direction encoding
ArcHydro Page 69
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Flow Direction Grid
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ArcHydro Page 71
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Flow Direction Grid
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Grid Network
ArcHydro Page 71
Flow Accumulation Grid.
Area draining in to a grid cell
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Link to Grid calculator
ArcHydro Page 72
Flow Accumulation
> 10 Cell Threshold
Stream Network for
10 cell Threshold
Drainage Area
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TauDEM contributing area convention.
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The area draining each grid cell includes the
grid cell itself.
2
Streams with 200 cell Threshold
(>18 hectares or 13.5 acres drainage area)
Watershed Draining to Outlet
Watershed and Drainage Paths
Delineated from 30m DEM
Automated method is more consistent than hand delineation
The Pit Removal Problem
• DEM creation results in artificial pits in the
landscape
• A pit is a set of one or more cells which has
no downstream cells around it
• Unless these pits are removed they become
sinks and isolate portions of the watershed
• Pit removal is first thing done with a DEM
Pit Filling
Increase elevation to the pour
point elevation until the pit
drains to a neighbor
Parallel Approach
• Improved runtime
efficiency
• Capability to run larger
problems
• Row oriented slices
• Each process includes
one buffer row on either
side
• Each process does not
change buffer row
Pit Removal: Planchon Fill
Algorithm
Initialization
1st Pass
2nd Pass
Planchon, O., and F. Darboux (2001), A fast, simple and versatile algorithm to fill the
depressions of digital elevation models, Catena(46), 159-176.
Parallel Scheme
Communicate
Initialize( D,P)
Do
for all i in P
if D(i) > n P(i) ←
D(i)
Else P(i) ← n
endfor
Send( topRow, rank-1 )
Send( bottomRow, rank+1 )
Recv( rowBelow, rank+1 )
Recv( rowAbove, rank-1 )
Until P is not modified
D denotes the original elevation.
P denotes the pit filled elevation.
n denotes lowest neighboring elevation
i denotes the cell being evaluated
Parallel pit fill timing for large DEM
2500
NedB (14849 x 27174)
1500
1000
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Read
0
Seconds
2000
ArcGIS 2087 sec
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Processors
Dual Quad Core Xeon Proc E5405, 2.00GHz
8
Carving
Lower elevation of neighbor along a
predefined drainage path until the pit
drains to the outlet point
Filling
Carving
Minimizing
Alterations
“Burning In” the Streams
 Take a mapped stream network and a DEM
 Make a grid of the streams
 Raise the off-stream DEM cells by an arbitrary elevation
increment
 Produces "burned in" DEM streams = mapped streams
+
=
AGREE Elevation Grid Modification
Methodology – DEM Reconditioning
PLAN
GRID
CELL SIZE
A
A
SECTION A-A
GRID CELL SIZE
ELEVATION
RESOLUTION
MODIFIED ELEVATION
ORIGINAL ELEVATION
KNOWN STREAM LOCATION
AND STREAM DELINEATED
FROM MODIFIED ELEVATION
STREAM DELINEATED
FROM ORIGINAL ELEVATION
Stream Segments
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ArcHydro Page 74
209
Each link has a unique
identifying number
Vectorized Streams Linked Using
Grid Code to Cell Equivalents
Vector
Streams
Grid
Streams
ArcHydro Page 75
DrainageLines are drawn through the centers of cells on
the stream links. DrainagePoints are located at the
centers of the outlet cells of the catchments
ArcHydro Page 75
Catchments
• For every stream
segment, there is a
corresponding
catchment
• Catchments are a
tessellation of the
landscape through a
set of physical rules
Raster Zones and Vector Polygons
One to one connection
DEM GridCode
Catchment GridID
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3
5
Raster Zones
Vector Polygons
Catchments, DrainageLines and DrainagePoints of the
San Marcos basin
ArcHydro Page 75
Adjoint catchment: the remaining upstream area draining
to a catchment outlet.
ArcHydro Page 77
Catchment, Watershed, Subwatershed.
Subwatersheds
Catchments
Watershed
Watershed outlet points may lie within the interior of a
catchment, e.g. at a USGS stream-gaging site.
ArcHydro Page 76
Summary of Key Processing Steps
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[DEM Reconditioning]
Pit Removal (Fill Sinks)
Flow Direction
Flow Accumulation
Stream Definition
Stream Segmentation
Catchment Grid Delineation
Raster to Vector Conversion (Catchment Polygon,
Drainage Line, Catchment Outlet Points)
Arc Hydro Tools
• Distributed free of charge from ESRI Water
Resources Applications
• Version 1.3 Latest release
http://support.esri.com/index.cfm?fa=downloads.
dataModels.filteredGateway&dmid=15
• Start with a DEM
• Produce a set of DEM-derived raster products
• Convert these to vector (point, line, area)
features
• Add and link Arc Hydro attributes
• Compute catchment characteristics
Delineation of Channel Networks and Catchments
500 cell
theshold
1000 cell
theshold
3
AREA 1
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10
1
Dd = 760 A-0.507
Mawheraiti
Gold Creek
0.1
AREA 2
Drainage Density (1/km)
How to decide on stream
delineation threshold ?
10000
Choconut and Tracy Creeks
100000
1000000
2
Drainage Area Threshold (m )
Drainage density (total channel length divided by drainage
area) as a function of drainage area support threshold used
to define channels for the three study watersheds.
Why is it important?
Hydrologic processes are different on hillslopes and in
channels. It is important to recognize this and account
for this in models.
Area defining
concentrated contributing
area at P
Contour width b
P
Specific catchment
area is A/b
Flow path originating
at divide with dispersed
contributing area A
Drainage area can be
concentrated or dispersed
(specific catchment area)
representing concentrated
or dispersed flow.
Examples of differently textured topography
Badlands in Death Valley.
from Easterbrook, 1993, p 140.
Coos Bay, Oregon Coast Range.
from W. E. Dietrich
Logged Pacific Redwood Forest near Humboldt, California
Canyon Creek, Trinity Alps, Northern California.
Photo D K Hagans
Gently Sloping Convex Landscape
From W. E. Dietrich
Mancos Shale badlands, Utah. From Howard, 1994.
Topographic Texture and Drainage Density
Driftwood, PA
0
Driftwood, PA
1 Kilometers
Same scale, 20 m
contour interval
0
Sunland, CA
Sunland, CA
1 Kilometers
“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
• Horton’s Laws
• Slope – Area scaling
• Stream Drops
Drainage Density
• Dd = L/A
• Hillslope length  1/2Dd
B
B
Hillslope length = B
L
A = 2B L
Dd = L/A = 1/2B
 B= 1/2Dd
Drainage Density for Different Support Area Thresholds
EPA Reach Files
100 grid cell threshold
1000 grid cell threshold
D
d
k
m
^
1
0.8 2.0 3.0
Drainage Density Versus
Contributing Area Threshold
D d=0.
0.
0.
05
10
0.
1.
50
0
Suppo
Hortons Laws: Strahler system
for stream ordering
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3
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Bifurcation Ratio
=
N1 umberofStams5 10 50
Rb
12345
Order
M
e
a
n
S
t
r
m
A
e
a
10^6 5*10^6 5*10^7
Area Ratio
Ra
=
4. 6
12345
Order
M
e90 anStrmLengh 20 40
Length Ratio
Rl
=
12345
Order
MeanStrmlope 0.5 0.1
Slope Ratio
Rs
=
1.
1.
2.
0
2.
5
3.
0
3.
5
4.
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Order
MeanStrmD5o0p 10 50
Constant Stream Drops Law
Rd
=
0.
1.
1.
2.
0
2.
5
3.
0
3.
5
4.
0
5
0
Order
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.
Stream Drop
Elevation difference between ends of stream
Nodes
Links
Single Stream
Note that a “Strahler stream” comprises a sequence of
links (reaches or segments) of the same order
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 as
stream delineation threshold is reduced
• Break in slope versus contributing area
relationship
• Physical basis in the form instability
theory of Smith and Bretherton (1972),
see Tarboton et al. 1992
Statistical Analysis of Stream Drops
Elevation Drop for Streams
600
Drop (meters)
500
400
Drop
Mean Drop
300
200
100
0
0
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2
3
Strahler Order
4
5
6
T-Test for Difference in Mean Values
Mean X
Std X
Var X
Nx
0
Order 1
72.2
68.8
4740.0
268
72
Mean Y
Std Y
Var Y
Ny
Order 2-4
130.3
120.8
14594.5
81
130
T-test checks whether difference in means is large (> 2)
when compared to the spread of the data around the mean values
S
t
r
a
h
l
e
m
D
r
o
p
(
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0 50 10 150 20 250
Constant Support Area Threshold
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1
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Str a h le r
Support Area threshold (30
m grid cells)
50
100
200
300
500
Drainage Density (km-1)
3.3
2.3
1.7
1.4
1.2
-8.8
-5
-1.8
-1.1
-0.72
t statistic for difference
between lowest order and
higher order drops
S
100 grid cell constant support area threshold stream delineation
1
0
1 Kilometers
Constant support
area threshold
100 grid cell
9 x 10E4 m^2
200 grid cell constant support area based stream delineation
1
0
1 Kilometers
constant support
area threshold
200 grid cell
18 x 10E4 m^2
Local Curvature Computation
(Peuker and Douglas, 1975, Comput. Graphics Image Proc. 4:375)
43
48
48
51
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56
41
47
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58
Contributing area of upwards curved grid cells only
50mcont.shp
Topsrc
0
1-5
5-20
20-50
50-30000
No Data
1
0
1
2 Kilometers
S
t
r
a
h
l
e
m
D
r
o
p
(
)
0 50 10 150 20 250
Upward Curved Contributing Area Threshold
1
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5
1
3
5
1
3
5
1
3
5
Str a h le r
Upward curved support area
threshold (30 m grid cells)
10
15
20
30
Drainage Density (km-1)
2.2
1.8
1.6
1.4
-4.1
-2.2
-1.3
-1.2
t statistic for difference
between lowest order and
higher order drops
S
Curvature based stream delineation
1
0
1 Kilometers
Curvature based
Stream delineation
Channel network delineation, other options
4
2
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5
6
1
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8
Contributing Area
Grid Order
1
1
1
1
1
1
1
1
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1
1
4
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1
2
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1
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12 1
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16 1
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25
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1
Grid network pruned to order 4 stream delineation
1
0
1 Kilometers
Grid network
pruned to 4th
order
Slope area threshold (Montgomery and Dietrich, 1992).
Channels mapped using a S2 > 200 m. a is specific catchment
area and S is slope.
downslope
Proportion flowing to
neighboring grid cell 3
is 2/(1+2)
flowing to
neighboring
grid cell 4 is
1/(1+2)
TauDEM - Channel Network and Watershed
Delineation
Software
• Pit removal (standard flooding approach)
3
4
5
6
2
1
2
1
8
7
Flow direction measured as
counter-clockwise angle
from east.
• Flow directions and slope
– D8 (standard)
– D (Tarboton, 1997, WRR 33(2):309)
– Flat routing (Garbrecht and Martz,
1997, JOH 193:204)
• 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, 255:826)
– Local curvature based (using Peuker
and Douglas, 1975, Comput.
Graphics Image Proc. 4:375)
• Threshold/drainage density selection by
stream drop analysis (Tarboton et al.,
1991, Hyd. Proc. 5(1):81)
• Other Functions: Downslope Influence,
Upslope Dependence, Wetness index,
distance to streams, Transport limited
accumulation
Available from http://www.engineering.usu.edu/dtarb/
Summary Concepts
• The eight direction pour point model approximates
the surface flow using eight discrete grid
directions
• The elevation surface represented by a grid digital
elevation model is used to derive surfaces
representing other hydrologic variables of interest
such as
–
–
–
–
Slope
Flow direction
Drainage area
Catchments, watersheds and channel networks
Summary Concepts (2)
• Hydrologic processes are different between
hillslopes and channels
• Drainage density defines the average spacing
between streams and the representative length of
hillslopes
• The constant drop property provides a basis for
selecting channel delineation criteria to preserve
the natural drainage density of the topography
• Generalized channel delineation criteria can
represent spatial variability in the topographic
texture and drainage density
Are there any questions ?
AREA 2
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AREA 1
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