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

ArcHydro Page 57

Watershed divide

Drainage direction Outlet

1:24,000 scale map of a study area in West Austin

Topography defines watersheds which are fundamentally the most basic hydrologic

landscape elements.

DEM Elevations

Contours

720

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680700720740

720 720

80 74 63

69 67 56

60 52 48

80 74 63

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45.0230

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5267

Slope:

Hydrologic Slope - Direction of Steepest Descent

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Eight Direction Pour Point Model

ESRI Direction encoding

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Flow Direction Grid32

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Flow Direction Grid

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Grid Network

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Flow Accumulation Grid. Area draining in to a grid cell

Link to Grid calculator

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Flow Accumulation > 10 Cell Threshold

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Stream Network for 10 cell Threshold

Drainage Area

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The area draining each grid cell includes the grid cell itself.

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TauDEM contributing area convention.

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

Increase elevation to the pour point elevation until the pit drains to a neighbor

Pit Filling

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

Com

municate

Initialize( D,P)Do

for all i in Pif D(i) > n P(i) ← D(i)Else P(i) ← n

endforSend( 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 elevationi denotes the cell being evaluated

1 2 3 4 5 6 7 8

050

010

0015

0020

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Processors

Sec

onds

Parallel pit fill timing for large DEMNedB (14849 x 27174)

Dual Quad Core Xeon Proc E5405, 2.00GHz

Compute

Read

ArcGIS 2087 sec

Lower elevation of neighbor along a predefined drainage path until the pit drains to the outlet point

Carving

Filling

CarvingMinimizing Alterations

+ =

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

“Burning In” the Streams

AGREE Elevation Grid Modification Methodology – DEM Reconditioning

ORIGINAL ELEVATIONMODIFIED ELEVATION

KNOWN STREAM LOCATIONAND STREAM DELINEATEDFROM MODIFIED ELEVATION

GRID CELL SIZESECTION A-A

STREAM DELINEATEDFROM ORIGINAL ELEVATION

ELEVATIONRESOLUTION

GRIDCELL SIZE

PLAN

AA

ArcHydro Page 74

172201

204

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206

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209 Each link has a unique identifying number

Stream Segments

Vectorized Streams Linked Using Grid Code to Cell Equivalents

VectorStreams

GridStreams

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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

Catchment GridID

Vector Polygons

DEM GridCode

Raster Zones

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4

5

One to one connection

Catchments, DrainageLines and DrainagePoints of the San Marcos basin

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Adjoint catchment: the remaining upstream area draining to a catchment outlet.

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Catchment, Watershed, Subwatershed.

ArcHydro Page 76

Watershed outlet points may lie within the interior of a catchment, e.g. at a USGS stream-gaging site.

Catchments

Subwatersheds

Watershed

Summary 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)

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

How to decide on stream delineation threshold ?

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Drainage Area Threshold (m2)

Dra

inag

e D

ensi

ty (

1/km

)

Mawheraiti

Gold Creek

Choconut and Tracy Creeks

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.

Dd = 760 A-0.507

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.

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.

0 1 Kilometers 0 1 KilometersDriftwood, PA Sunland, CA

Topographic Texture and Drainage DensitySame scale, 20 m contour interval

Sunland, CADriftwood, PA

Lets look at some geomorphology.• Drainage Density• Horton’s Laws• Slope – Area scaling• Stream Drops

“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.

Drainage Density• Dd = L/A

• Hillslope length 1/2Dd

L

BB

Hillslope length = B

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

Drainage Density Versus Contributing Area Threshold

Support Area km^2

Dd

km

^-1

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Hortons Laws: Strahler system for stream ordering

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Bifurcation Ratio

Order

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ber

of S

trea

ms

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1050Rb = 3.58

Area Ratio

Order

Mea

n S

trea

m A

rea

1 2 3 4 5

10^6

5*10

^65*

10^7 Ra = 4.65

Length Ratio

Order

Mea

n S

trea

m L

engt

h

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Rl = 1.91

Slope Ratio

Order

Mea

n S

trea

m S

lope

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Rs = 1.7

Constant Stream Drops Law

Order

Mea

n S

trea

m D

rop

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5010

050

0

Rd = 0.944

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 DropElevation difference between ends of stream

Note that a “Strahler stream” comprises a sequence of links (reaches or segments) of the same order

NodesLinks

Single Stream

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

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Mean Drop

T-Test for Difference in Mean Values

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Order 1 Order 2-4Mean X 72.2 Mean Y 130.3Std X 68.8 Std Y 120.8Var X 4740.0 Var Y 14594.5Nx 268 Ny 81

0

T-test checks whether difference in means is large (> 2)when compared to the spread of the data around the mean values

Constant Support Area Threshold

Strahler Stream Order

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rop

(m

)

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Support Area threshold (30 m grid cells)

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Drainage Density (km-1) 3.3 2.3 1.7 1.4 1.2

t statistic for difference between lowest order and higher order drops

-8.8 -5 -1.8 -1.1 -0.72

100 grid cell constant support area threshold stream delineation

1 0 1 KilometersConstant support area threshold100 grid cell9 x 10E4 m^2

200 grid cell constant support area based stream delineation

1 0 1 Kilometersconstant support area threshold200 grid cell18 x 10E4 m^2

Local Curvature Computation(Peuker and Douglas, 1975, Comput. Graphics Image Proc. 4:375)

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Contributing area of upwards curved grid cells only

Topsrc01 - 55-2020-5050-30000No Data

50mcont.shp 1 0 1 2 Kilometers

Upward Curved Contributing Area Threshold

Strahler Stream Order

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rop

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Upward curved support area threshold (30 m grid cells)

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Drainage Density (km-1) 2.2 1.8 1.6 1.4

t statistic for difference between lowest order and higher order drops

-4.1 -2.2 -1.3 -1.2

1 0 1 KilometersCurvature basedStream delineation

Curvature based stream delineation

Channel network delineation, other options

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Contributing Area

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Grid Order

1 0 1 Kilometers Grid networkpruned to 4thorder

Grid network pruned to order 4 stream delineation

Slope area threshold (Montgomery and Dietrich, 1992).

TauDEM - Channel Network and Watershed TauDEM - Channel Network and Watershed Delineation SoftwareDelineation 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 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 ?

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