1. Geog 380 Watershed Analysis Digital Terrain Analysis and Geomorphology

2. Geomorphology is…
The study of land-forms and the processes that have fashioned them.
The two main themes in geomorphology are form and process.
How are they related?
DTA and Geomorphology

3. The Drainage Basin
Fundamental unit of geomorphology and the focus of much research.
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4. The Drainage Basin
Since the late 1980s and early 1990s, researchers have used GIS to automate the process of watershed extraction (e.g. lab 2).
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5. Drainage Basin Morphometry
Is the quantitative measure of the:
Arrangement and organization of the enclosed river network (network analysis).
Surface form of a drainage basin
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6. Drainage Basin Morphometry
Goal:
To identify drainage basin characteristics that correlate with the basin outputs (i.e., discharge of water and sediment).
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7. Drainage Network (linear morphometry)
Refers to the internal structure of networks, specifically the topologic and geometric properties.
- each stream within a basin is assigned to a particular order indicating its relative importance in the network, with the lowest order streams being the most minor tributaries and the highest order, the main trunk river
DTA and Geomorphology

8. Digital Terrain Analysis of Drainage Networks
Must use DEM with both depressions and flats removed.
Must use ‘digital’ stream (i.e., derived) and not streams digitized off of maps.
Analysis done with the D8 flow algorithm. Why do you think?
DTA and Geomorphology

9. Strahler Stream Order 1 4 2
Each reach is assigned an order to indicate its relative importance in the network.
Any problems?
a segment with no tributaries is designated as a first-order stream
Where two first-order segments join they form a second-order segment; two second-order segments a third-order segment, and so forth
Any segment may be joined by a channel of a lower order without an increase in its order; I.e., third-order segments may have an infinite number of second- or first-order tributaries
Only where two segments of equal magnitude join is an increase in order required
PROBLEM: does not account for all tributaries
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10. Shreve Magnitude Improved accounting of low order tributaries 2 3 1 56 5 3 2 9
Improved accounting of low order tributaries
- shreve’s system gives a number that at any point within the basin is equal to the number of first-order streams upstream from that point
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11. Strahler Stream Order Shreve Magnitude Order 4 Magnitude 55
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12. Law of Stream Numbers
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13. Law of Stream Lengths
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14. Law of Drainage Areas
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15. Law of Stream Slopes
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16. Digital Terrain Analysis of Drainage Basin Size and Shape (areal morphometry)
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17. Drainage Density (D)
D = total stream length / basin area (units: km/km2)
A measure of the dissection of the landscape by the stream network
Ranges from 0.5 to 30 (as high as 100)
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18. How are D & Q related? Low D High D Flashy hydrograph Sluggish
Time Qw
Time Qw
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19. Basin II: circular Basin I: long & narrow Flashy Hydrograph
Sluggish hydrograph
Time Qw
Time Qw
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20. How can basin size be quantified?
Area
Perimeter
Length
Width
What are some of the difficulties with measuring these variables in a GIS?
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21. How can basin shape be quantified?
A number of ratios have been developed to compare the basin area with either a circle or with basin length.
Form Factor = basin area / basin length2
Circularity Ratio = area / area of circle with same perimeter
Basin Elongation = diameter of circle with same area / basin length
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22. Digital Terrain Analysis of Drainage Basin Relief (relief morphometry)
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23. Relief
What is relief (H)?
Range in elevation
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24. Hypsometric Analysis Relates basin relief and area
Indicates the distribution of mass above the base plane
mouth
summit
base plane
summit plane H h
total basin area = A
area above contour = a
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25. Hypsometric Curve y x = relative area = a / A
0.5 1
Proportion of total basin area
Proportion of total basin relief x y
(x, y)
x = relative area = a / A
y = relative height = h / H
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26. How would the curve look if the basin were more eroded? Less eroded?
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27. Hypsometric Integral y Hypsometric Integral = 46.7%
0.5 1
Proportion of total basin area
Proportion of total basin relief
Hypsometric Integral = 46.7%
Expresses the volume of
the original basin that remains
Area under the Hypsometric Curve x
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28. Digital Terrain Analysis
Applications of
Digital Terrain Analysis
And Geomorphology
DTA and Geomorphology