Hydrologic analysis
This presentation is the property of its rightful owner.
Sponsored Links
1 / 26

Hydrologic Analysis PowerPoint PPT Presentation


  • 165 Views
  • Uploaded on
  • Presentation posted in: General

Hydrologic Analysis. Francisco Olivera, Ph.D., P.E. Srikanth Koka Department of Civil Engineering Texas A&M University. Watershed Delineation. Watershed delineation is the process of identifying the drainage area of a point.

Download Presentation

Hydrologic Analysis

An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -

Presentation Transcript


Hydrologic Analysis

Francisco Olivera, Ph.D., P.E.

Srikanth Koka

Department of Civil Engineering

Texas A&M University


Watershed Delineation

  • Watershed delineation is the process of identifying the drainage area of a point.

  • For many years, Civil Engineers have been using USGS paper maps for watershed delineation.

  • The maps are in Universal Transverse Mercator (UTM) coordinates and in 1:24,000 scale.


Watershed Delineation

  • Water flows in the direction of the terrain steepest downhill slope. Streamlines (blue arrows) are orthogonal to the contour lines.

  • Drainage divides (red line) are found along the highest points of the terrain.

  • Streamlines do not flow towards drainage divides, and do not intersect them.


DEMs

  • Digital Elevation Models (DEMs) are grids of elevation.

  • DEMs store the same type of information contour lines do, but with a different data structure.

  • Watershed delineation can be based on DEMs rather than contour lines.


30-Meter DEMs

  • For the United States, 30-meter DEMs have been developed by USGS.

  • 30-meter DEMs are consistent with 1:24,000 paper maps.


720

720

740

720

700

680

720

700

740

680

30-Meter DEMs


700

680

30-Meter DEMs


30-Meter and 3" DEMs

~ 90m

30m


Hydrologic Functions

  • The eight-direction pour point algorithm (D-8) assigns a flow direction code to each cell, based on the steepest downhill slope as defined by the DEM.

  • The flow direction code indicates the cell – out of the eight neighbor cells – towards which the water flows.

  • Flow direction cannot be defined for cells within a terrain depression. DEMs have to be filled before determining flow directions.

Flow direction codes


1

67

56

49

53

44

37

58

55

22

Hydrologic Functions

1

67

56

49

53

44

37

58

55

22

Slope:


Hydrologic Functions

Function:Flow direction

Argument:DEM

2

2

2

4

4

78

72

69

71

58

2

2

2

4

4

74

67

56

49

46

1

1

2

4

8

69

53

44

37

38

128

128

1

2

4

64

58

55

22

31

128

128

1

1

4

68

61

47

21

16

Flow network

(not a grid)

Flow direction grid

DEM


DEM


Flow Direction


Hydrologic Functions

Function:Flow accumulation

Argument:Flow direction

0

0

0

0

0

78

72

69

71

58

0

1

1

2

1

74

67

56

49

46

0

3

8

5

2

69

53

44

37

38

0

1

1

20

0

64

58

55

22

31

0

0

0

1

24

68

61

47

21

16

Flow network

(not a grid)

Flow accumulation grid

DEM


Flow Accumulation

  • Flow accumulation is a measure of the drainage area in units of grid cells.

  • The cell itself is not included.


0

0

0

0

0

0

1

1

2

1

0

3

8

5

2

0

1

1

20

0

0

0

0

1

24

Hydrologic Functions

Process:Stream delineation

Argument:Flow accumulation

78

72

69

71

58

74

67

56

49

46

69

53

44

37

38

64

58

55

22

31

68

61

47

21

16

Flow accumulation

(> 2 cells)

DEM


Stream Network

  • All grid cells draining more than a user-defined threshold value are part of the stream network.

  • Red streams correspond to a lower threshold than the blue streams.


Hydrologic Functions

Function:Stream links

Argument:Delineated streams

78

72

69

71

58

74

67

56

49

46

69

53

44

37

38

64

58

55

22

31

68

61

47

21

16

Streams links

DEM

Delineated streams

  • Stream links are assigned an identification number randomly.


Stream links

  • Stream links are the segments of a stream channel connecting two successive junctions, a junction and an outlet, or a headwater and a junction.


Hydrologic Functions

Process:Outlets

Argument:Stream links

78

72

69

71

58

74

67

56

49

46

69

53

44

37

38

64

58

55

22

31

68

61

47

21

16

Streams links

DEM

Outlets

  • Outlets are assigned the identification number of their link.


Watershed Outlets

  • The most downstream cells of the stream segments (yellow/brown cells) are watershed outlets.

  • User-defined points (red dots) are also watershed outlets.


Modified Stream Links

  • User-defined outlets modify the stream links by subdividing the segment in which they are located into two segments.


Hydrologic Functions

Function:Watershed

Argument:Flow direction and Outlets

78

72

69

71

58

74

67

56

49

46

69

53

44

37

38

64

58

55

22

31

68

61

47

21

16

DEM

Outlets

Watersheds

  • Watersheds are assigned the identification number of their outlet.


Watershed Delineation

  • The drainage area of each watershed outlet is delineated.


Raster to Vector Conversion

  • The grids of stream links and watersheds are vectorized to obtain stream line and watershed polygon feature classes.

  • Both feature classes include a field Grid-Code in their attribute tables, which stores the stream link and watershed identification number.

  • Since the identification number of the streams and their corresponding watershed is the same, the attribute tables can be related.


Merging Watersheds

  • Adjacent watershed polygons can be merged into a single polygon, if they share their outlet or one flows into the other.


  • Login