Geog 380 Watershed Analysis Digital Terrain Analysis and Geomorphology

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

The Drainage Basin Fundamental unit of geomorphology and the focus of much research. DTA and Geomorphology

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). DTA and Geomorphology

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 DTA and Geomorphology

Drainage Basin Morphometry Goal: To identify drainage basin characteristics that correlate with the basin outputs (i.e., discharge of water and sediment). DTA and Geomorphology

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

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

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 DTA and Geomorphology

Shreve Magnitude Improved accounting of low order tributaries 2 3 1 5 6 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 DTA and Geomorphology

Strahler Stream Order Shreve Magnitude Order 4 Magnitude 55 DTA and Geomorphology

Law of Stream Numbers DTA and Geomorphology

Law of Stream Lengths DTA and Geomorphology

Law of Drainage Areas DTA and Geomorphology

Law of Stream Slopes DTA and Geomorphology

Digital Terrain Analysis of Drainage Basin Size and Shape (areal morphometry) DTA and Geomorphology

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) DTA and Geomorphology

How are D & Q related? Low D High D Flashy hydrograph Sluggish Time Qw Time Qw DTA and Geomorphology

Basin II: circular Basin I: long & narrow Flashy Hydrograph Sluggish hydrograph Time Qw Time Qw DTA and Geomorphology

How can basin size be quantified? Area Perimeter Length Width What are some of the difficulties with measuring these variables in a GIS? DTA and Geomorphology

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 DTA and Geomorphology

Digital Terrain Analysis of Drainage Basin Relief (relief morphometry) DTA and Geomorphology

Relief What is relief (H)? Range in elevation DTA and Geomorphology

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 DTA and Geomorphology

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 DTA and Geomorphology

How would the curve look if the basin were more eroded? Less eroded? DTA and Geomorphology

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 DTA and Geomorphology

Digital Terrain Analysis Applications of Digital Terrain Analysis And Geomorphology DTA and Geomorphology