Title: Digital Elevation Model Based Watershed and Stream Network Delineation
1Digital 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
2Duality 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
3Topography defines watersheds which are
fundamentally the most basic hydrologic landscape
elements.
124,000 scale map of a study area in West Austin
ArcHydro Page 57
4DEM Elevations
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Contours
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5Hydrologic Terrain Analysis
- 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
6Hydrologic Slope - Direction of Steepest Descent
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Slope
ArcHydro Page 70
7Eight Direction Pour Point Model
ESRI Direction encoding
ArcHydro Page 69
8Flow Direction Grid
ArcHydro Page 71
9Flow Direction Grid
10Grid Network
ArcHydro Page 71
11Flow Accumulation Grid. Area draining in to a
grid cell
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Link to Grid calculator
ArcHydro Page 72
12Contributing Area Grid
TauDEM convention. The area draining each grid
cell including the grid cell itself.
13Flow Accumulation gt 5 Cell Threshold
14Stream Network for 5 cell Threshold Drainage Area
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15Streams with 200 cell Threshold(gt18 hectares or
13.5 acres drainage area)
16Watershed Draining to Outlet
17Watershed and Drainage Paths Delineated from 30m
DEM
Automated method is more consistent than hand
delineation
18The 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
19Pit Filling
- Increase elevation to the pour point elevation
until the pit drains to a neighbor
20(No Transcript)
21Carving
Lower elevation of neighbor along a predefined
drainage path until the pit drains to the outlet
point
22Filling
Minimizing Alterations
Carving
23Burning 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
24AGREE Elevation Grid Modification Methodology
DEM Reconditioning
25Stream Segments
26Stream links grid for the San Marcos subbasin
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Each link has a unique identifying number
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ArcHydro Page 74
27Vectorized Streams Linked Using Grid Code to Cell
Equivalents
Vector Streams
Grid Streams
ArcHydro Page 75
28DrainageLines 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
29Catchments
- For every stream segment, there is a
corresponding catchment - Catchments are a tessellation of the landscape
through a set of physical rules
30Raster Zones and Vector Polygons
One to one connection
31Catchments, DrainageLines and DrainagePoints of
the San Marcos basin
ArcHydro Page 75
32Adjoint catchment the remaining upstream area
draining to a catchment outlet.
ArcHydro Page 77
33Catchment, 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
34Summary of Key Processing Steps
- 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)
35Arc Hydro Tools
- Distributed free of charge from ESRI Water
Resources Applications - Version 1.2 Latest release http//support.esri.com
/index.cfm?fadownloads.dataModels.filteredGateway
dmid15 - Version 1.3 Beta ftp//RiverHydraulicsriver.1114
_at_ftp.esri.com - 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
36Delineation of Channel Networks and Catchments
500 cell theshold
1000 cell theshold
37How to decide on stream delineation threshold ?
Why is it important?
38Hydrologic 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.
39Examples of differently textured topography
Badlands in Death Valley.from Easterbrook, 1993,
p 140.
Coos Bay, Oregon Coast Range. from W. E. Dietrich
40Logged Pacific Redwood Forest near Humboldt,
California
41Canyon Creek, Trinity Alps, Northern California.
Photo D K Hagans
42Gently Sloping Convex Landscape
From W. E. Dietrich
43Mancos Shale badlands, Utah. From Howard, 1994.
44Topographic Texture and Drainage Density
Same scale, 20 m contour interval
Driftwood, PA
Sunland, CA
45landscape 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
46Drainage 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
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47Drainage Density for Different Support Area
Thresholds
EPA Reach Files
100 grid cell threshold
1000 grid cell threshold
48Drainage Density Versus Contributing Area
Threshold
49Hortons Laws Strahler system for stream ordering
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50Bifurcation Ratio
51Area Ratio
52Length Ratio
53Slope Ratio
54Constant 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.
55Stream DropElevation difference between ends of
stream
56Suggestion 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
57Statistical Analysis of Stream Drops
58T-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
59Constant Support Area Threshold
60100 grid cell constant support area threshold
stream delineation
61200 grid cell constant support area based stream
delineation
62Local Curvature Computation(Peuker and Douglas,
1975, Comput. Graphics Image Proc. 4375)
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63Contributing area of upwards curved grid cells
only
64Upward Curved Contributing Area Threshold
65Curvature based stream delineation
66Channel network delineation, other options
Contributing Area
67Grid network pruned to order 4 stream delineation
68Slope area threshold (Montgomery and Dietrich,
1992).
69TauDEM - Channel Network and Watershed
Delineation Software
- 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) - Other Functions Downslope Influence, Upslope
Dependence, Wetness index, distance to streams,
Transport limited accumulation
Available from http//www.engineering.usu.edu/dtar
b/
70Summary 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
71Summary 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
72Are there any questions ?