Stream and WatershedDelineation from DEM’s

David Maidment, Ph.D. and Francisco Olivera, Ph.D.Center for Research in Water Resources

University of Texas at Austin

Texas Department of Transportation (TxDOT)Water Resources Modeling Using GIS2000 - Austin, Texas

Overview

Study area in West Austin with a USGS 30-meter DEM from a 1:24,000 scale map

Eight direction pour point model (flow direction and flow accumulation grids)

Stream network definition

Watershed delineation

DEM data sources

Study Region in West Austin

Hog Pen Creek

4 km

4 km

Topographic Map

20 ft contour

100 ft contour

Stream Center Line

Austin West, 1:24,000 Scale http://www.tnrcc.state.tx.us/gis/raster.html

Direction of Steepest Descent

Watershed Delineation by Hand

Watershed divide

Drainage directionOutlet

200-Meter Mesh

1km

1km

Universal Transverse Mercator (UTM) Coordinates

100-Meter Mesh

100m

100m

1km

1km

30-Meter Mesh

Standard for 1:24,000 Scale Maps

Austin West 30-Meter DEM

Elevations in meters.ftp://ftp.tnris.state.tx.us/tnris/demA.html

USGS 30-Meter DEM

30 Meter DEM Cell Boundaries

DEM Lattice Points

DEM Lattice Points

DEM Cells Store Elevation at Lattice Point

DEM Elevations

720

700

680

740

680700720740

720 720

DEM Elevations

700

680

Overview

Study area in West Austin with a USGS 30-meter DEM from a 1:24,000 scale map

Eight direction pour point model (flow direction and flow accumulation grids)

Stream network definition

Watershed delineation

DEM data sources

67 56 49 46 50

12 11 12

53 44 37 38 48

58 55 22 31 24

61 47 21 16 19

3453

Digital Elevation Model

67 56 49 46 50

12 11 12

53 44 37 38 48

58 55 22 31 24

61 47 21 16 19

3453

50

cell size

cell

(cell value)

Cell Definition

32

16

8

64

4

128

1

2

Eight-Direction Pour-Point Model

67 56 49

53 44 37

58 55 22

1

67 56 49

53 44 37

58 55 22

1

26.162

4467

14

1

5367

Slope:

Direction of Steepest Descent

2 2 4 4 8

1 2 16

1 2 4 8 4

128 1 2 4 8

2 1 4 4 4

11

Flow Direction Grid

Austin West 30-Meter DEM

Elevations in meters.ftp://ftp.tnris.state.tx.us/tnris/demA.html

Flow Direction Grid

32

16

8

64

4

128

1

2

Grid Network

0 0 000

0

0

0

0

0

0

0

0

032 2

111

115

2 524 1

0 0 00 0

0

0

0

0

0

0

0

0

0

3 2 2

11 1

1

12

15

245

Flow Accumulation Grid

Overview

Study area in West Austin with a USGS 30-meter DEM from a 1:24,000 scale map

Eight direction pour point model (flow direction and flow accumulation grids)

Stream network definition

Watershed delineation

DEM data sources

0 0 00 0

0

0

0

0

0

0

0

0

0

3 2 2

11 1

1

12

15

245

Flow Accumulation Threshold

Flow Accumulation > 5 cells

Stream Network

0 0 000

0

0

0

0

0

0

0

0

032

2

111

115

2 5

241

Stream network for a 5-cell threshold drainage area.

Stream Network

Stream network for a 13.5-acres threshold drainage area (200 cells).

+ =

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 Burned-in DEM streams = Mapped streams

Burning-in the Streams

Filling in the Pits

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 filled they become sinks and isolate portions of the watershed

Pit filling is first thing done with a DEM

Overview

Study area in West Austin with a USGS 30-meter DEM from a 1:24,000 scale map

Eight direction pour point model (flow direction and flow accumulation grids)

Stream network definition

Watershed delineation

DEM data sources

Watershed Outlet

Watershed Draining to an Outlet

DEM-Based Delineation

Found error hand delineation!!!

Watershed and flow paths

0 0 000

0

0

0

0

0

0

0

0

03 2 2

111

115

2 5

241

Stream Segments (Links)

55

11

3

22

334 4 4

4 45

5

666

Stream Segments Grid

3

6

9895101504 (>1000)

Threshold at Stream Junction

1000 cell threshold exceeded at stream junction.

Same Cell Value

Sub-Watersheds

Stream Vectorization

VectorStreams

GridStreams

Stream and Sub-Watersheds

Overview

Study area in West Austin with a USGS 30-meter DEM from a 1:24,000 scale map

Eight direction pour point model (flow direction and flow accumulation grids)

Stream network definition

Watershed delineation

DEM data sources

DEM Data Sources

30-m DEM’s from 1:24,000 scale maps

3" (100-m) DEM’s from 1:250,000 scale maps

15" (500-m) DEM for the US resampled from 3” DEM

30" (1-Km) DEM of the earth (GTOPO30)

30-m DEM’s

Best resolution standardized data source available for the US

Coverage of the country is incomplete

Data by 7.5’ map sheets in UTM projection

Link for US: http://edcwww.cr.usgs.gov/Webglis/glisbin/guide.pl/glis/hyper/guide/usgs_dem

Link for Texas:ftp://www.tnris.state.tx.us/tnris/demA.html

3” DEM’s

Derived by US Defence Mapping Agency, available from USGS for the whole US.

Data in geographic coordinates by 1:250,000 map sheet names (1°x 1°) cells in (1°x 2°) maps

Needs to be projected to planar coordinates

Link:http://edcwww.cr.usgs.gov/doc/edchome/ndcdb/ndcdb.html

7.5´

7.5´

1º

1º

3" (100m) DEM

30m DEM

Coverage of 30-m and 3" DEM’s

Cell Size30m 100m

30-m and 3" DEM’s

15" DEM

Derived by USGS from 3" DEMs by resampling each fifth point

Best resolution for seamless coverage of the US in a single grid

Projected cell size is 500m

Link:http://nsdi.usgs.gov/nsdi/wais/water/gcip.HTML

30" DEM GTOPO30

Produced by USGS from 3" grids and Digital Chart of the World topography

Coverage complete for the earth

Projected cell size is 1km approximately

Data must be projected before use

Link:http://edcwww.cr.usgs.gov/landdaac/gtopo30/gtopo30.html

30" DEM GTOPO30

Drainage in North America

Source: http://edcwww.cr.usgs.gov/landdaac/gtopo30/hydro/namerica.html

Summary Concepts (1)

Topographic maps are the traditional way of representing land surface terrain and streams.

Watersheds can be hand-delineated from these maps.

DEM’s of equivalent accuracy are now available for most map series in the US.

DEM cell elevation is at the cell center.

Eight direction pour point model leads to flow direction and flow accumulation grids.

Summary Concepts (2)

Stream network is defined as cells whose flow accumulation exceeds a threshold.

Streams can be divided into links and sub-watersheds defined for them.

Watershed outlet is the cell with highest flow accumulation.

Resulting grids can be vectorized.

Standardized DEM data sources: 30m, 3”, 15”, 30”, which cover from local scale to the whole earth