GEOG2016: Drainage Basin Geomorphology€¦ · Drainage Basin Components zHillslopes – area of...
Transcript of GEOG2016: Drainage Basin Geomorphology€¦ · Drainage Basin Components zHillslopes – area of...
Drainage Basin GeomorphologyFundamentals & Basin Morphometry
Source: http://www.ucmp.berkeley.edu/tectonics/globe1.gif
Dr Steve Darby
The Fluvial System: Components
Sources, transfers, sinks– (Schumm, 1977)
Independent variables– Climate, geology, land
cover/use, tectonics, etc
Dependent variables– See this lecture…
Source: Schumm, S.A. 1977. The Fluvial System, Wiley, New York
The Fluvial System: Functions
© Steve Darby
Mont Mine Glacier, SwitzerlandTerrestrial and aquatic ecosystemsTransports matter from sources to sinks
– Water– Solids (sediment,
organic matter, carbon)– Solutes (mineral and
carbon solutes)– Nutrients (N, P, etc)
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S-45-05 (~8S, 143E)
LANDSAT 7 2000
Global Sediment Yield
70% of the total (15 000 Mt a-1) load comes from 10% of the land– 3 rivers (Ganges, Brahmaputra & Huang He) carry 20% of the load
Source: Skinner, B. J., and Porter, S. C. (1995). The Dynamic Earth, An Introduction to Physical Geology (3rd Edition), New York, John Wiley and Sons.
Global Denudation Rates
Calculated by estimating total sediment/solute load and dividing by basin area to give average ‘lowering rate’ in mm ka-1
– Global mean is ~ 8 mm ka-1
Masks huge variations amongst the world’s large drainage basins
– Chari Basin, interior Africa (3 mm ka-1)– Brahmaputra Basin, eastern Himalayas (677 mm ka-1)
Scale dependent– Haast River, Southern Alps, NZ (4,717 mm ka-1)– Huangfuchan, China (19,814 mm ka-1)
The Scientific Method
Observation Formulate ‘Theory’(Hypothesis/Model)
Make Prediction
Test ‘Theory’ (Hypothesis/Model)
Robust Theory/Model/Hypothesis
Observation
New Observations
INDUCE
DEDUCE
PASS
REVISETHEORY
?
Drainage Basins
Area of land that contributes water to a stream/river– Also known as “catchments” (UK) or “watersheds” (US)
Drainage Basin Components
Boundaries– Watersheds or divides
Landscape elements– Hillslopes– Channels– Channel heads– Valleys– Interfluves
Materials– Bedrock– Regolith– Colluvium vs. alluvium
HyMap airborne imaging spectrometer data (19 June 2000) draped overDEM based on digitised OS 1:25 000 map contours for portion of Highland
Water Research Catchment, New Forest, UK
Drainage Basin Components
Drainage divide/watershed– Topographical– Hydrological– Military
Interfluve– A region of higher land
separating two rivers in the same drainage basin
Source: Figure 14.4 from Christopherson, R.W. 2005. Geosystems: An Introduction to Physical Geography(5th Edition), Prentice Hall, New Jersey.
Drainage Basin Components
Hillslopes– area of land between
drainage divide and a channel or valley
Channel– a passage for water to flow
throughValley
– elongated lowland between mountains, hills, or other uplands, usually with a well developed drainage network
Photo courtesy of USGS photo library
Rocky Mountain NP, Colorado
Where do channels begin?
© Frans Kwaad 2002
Valley side gullies, Rif Mountains (N Morocco)
Channel Heads
Diffuse channel headRambla Mofar, near Turre, Almeria
© Professor Mike Kirkby© Professor Mike Kirkby
Abrupt channel headSouth of Lake Balaton, Hungary
Hillslope Morphology
Hillslope morphology is complex and multi-dimensional, so many parameters can be used as descriptors
– steepness, length, shape (i.e. rounded), degree of linearity, concavity or convexity (in plan and/or in profile), etc.
Hillslopes are usually mantled in sediment (colluvium)– Sediment synonyms: Soil, regolith
The significance of all these metrics is that water and gravity mediated sediment transfer is strongly controlled by slope
– and the way in which slope varies across the landscape
Slope Profiles
Linear Hillslope Profile
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Basic hillslope profile shapes– linear, convex, concave– all have average slope of 0.1
Convex Hillslope Profile
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Concave Hillslope Profile
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3D Slope Morphology
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Hillslopes are 3-dimensionalSlope curvature controls the flow of surface and sub-surface water across a landscape
– areas with concave plan curvatures have focusedflows, whereas convex plan curvatures have dispersed flows
– areas with convex profile curvature have accelerated flows, concave profile curvature have decelerating flows
L = linear, V = convex, C = concave
Hillslope Morphology: Examples
HIGH RELIEF, STEEP GRADIENT,LINEAR IN PROFILE
NOTE CONVEX PLAN CURVATURE
© Philip Owens
LOW RELIEF, LOW GRADIENT,CONCAVE PLAN CURVATURE
River Severn Catchment, UK
NOTE RUNOFF CONCENTRATIONIN CONCAVE CURVATURE
© Deborah Tappan
Badlands NM, South Dakota
Drainage Basin Morphometry
Morphometry– The quantitative measurement of form– Provides a systematic basis for description and comparison
(e.g. between basins, model predictions vs. observations)Topology versus topography
– Topological variables represent network structure– Implies that two basins may look utterly different but be
functionally similar if their topology is similarDimensional versus non-dimensional variables
– All things can be measured with 3 scales: M, L, T– Dimensional: area (L2), velocity (L/T), density (M/L3)– Non-dimensional: slope (L/L)– Non-dimensional variables can be compared across basins
of different scale
Morphometric Variables
Basic descriptions of basin shape & network structure– Drainage patterns and network characteristics– Basin size and shape (e.g. elongation ratio)– Drainage density
Topographic characteristics– Analysis of slopes and curvature– Basic mapping and DEM cartography– Basin elevation– Hypsometry– Relief (local and total)– Ruggedness
Drainage Patterns
Redrawn from Summerfield (1991, Fig. 161.1, p406); itself modified from Morisawa (1985, Fig. 10.3)
Drainage Patterns
Used to infer underlying geological/other controlsTYPE STRUCTURAL CONTROL
Dendritic Lack of structural control; rock/sediment of uniform resistance
Parallel Closely spaced faults; steep topography; non-cohesive sediments
Radial Volcanic cones, domes
Trellis Tilted or folded alternately resistant/weak sedimentary units
Rectangular Joints or faults
Annular Eroded dome in alternate resistant/weak sediments
Centripetal Calderas, craters, tectonic basins
Deranged Glaciated terrainSource: M. Summerfield (1991, Table 16.2, p406)
Drainage Patterns: Examples
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N-51-15 (~ 15N, 120E)
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Mount Pinatubo, PhillipinesRADIAL DRAINAGE
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tml Allegheny Plateau, E West Virginia
DENDRITIC DRAINAGE
Valley & Ridge province, NW VirginiaTRELLIS DRAINAGE
~ 38N, 80W
Drainage Patterns: Examples
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N-18-40 (~ 44N, 74W)
LANDSAT 7 2000
N New York State, USADERANGED DRAINAGE
Val D’Herens, SwitzerlandPARALLEL DRAINAGE
Network Structure: Stream Order
Scale-independent system for comparing streams– A stream with no tributaries is 1st order– Strahler (1952): A stream of order N forms at the
confluence of two streams of order (N -1)– Shreve: N is the sum of the stream order of the tributaries
Source: Summerfield (1991, Figure 9.1, p208)
Some Data…
Wheeling Creek, Ohio (2nd Vs. 3rd Order Basins)
Sulphur Creek, CA (2nd Order)
© Steve Darby
© Wheeling Jesuit University
The largest river is the 12th order Amazon
– Assuming 1st order streams are identified correctly!
Over 80% of the total length of Earth’s rivers are 1st or 2nd orderBasin area increases non-linearly with increasing stream orderBifurcation Ratio (Rb)
– Rb = Nx/Nx+1– Strahler says R is typically ~ 3– Hence N1 > 175 000 for the
Amazon (N1 = 3x-1)Source areas make up in numbers what they lack in size
Drainage Basin Shape
Basin shape influences the fluxes and delivery of runoff and sediment from headwater reachesCan be represented using the Elongation Ratio (E)E = (2/L)×(A/π)0.5
E is dimensionless
Source: Redrawn from Benda, L. et al. 2004. Water Resources Research, 40, W05402, doi:10.1029/2003WR002583.
Significance…
Runoff delivery to streams– Elongated basins have
flatter hydrographs
Influences confluence geomorphology (Benda et al., 2004)
– Tributaries of elongated basins have less impact on main stem geomorphology
Source: Redrawn from Benda et al. 2004.
Drainage Density
Extent to which a landscape is channelled reflects the balance between erosive and resisting forces
– So, likely influenced by climatic and geologic factors
Ratio of total stream length to drainage area (ΣSL/A)DD (has dimensions L-1) varies across a wide range
– e.g. 5 km-1 on permeable rocks, to 500 km-1 on badlands
Can be problematic to define where channels are indistinct or ephemeral
– Locating channel heads is critical to accurate estimation
Examples…
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N-14-40 (~ 40N, 100W)
LANDSAT 7 2000
N-19-05 (~ 5N, 70W)
LANDSAT 7 2000LANDSAT 7 2000
N-19-05 (~ 5N, 70W)
LANDSAT 7 2000
Middle Loup River, NebraskaSEMI-ARID - Low Drainage Density
Upper Orinoco Basin, VenezuelaHUMID - High Drainage Density
Physical Significance (?)
Drainage density values can sometimes surprisePerhaps best interpreted as a long-term measure of the relative difference between rainfall and infiltration
Nazca, Peru (~15S, 75W)
© Steve Darby
Drainage Basin Topography
Elevation is the vertical height above a datum Relief (R) refers to differences in elevation at local (e.g. for a hill) or total basin (difference in elevation between the drainage divide and the basin outlet) scales
© Martin Geertsema
HIGH RELIEFLOW RELIEF
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Drainage Basin Ruggedness
Measured with the ruggedness number
– RN = R × DD
Measures the extent to which basin topography is dissected
DEM of the headwaters of the Smith River in Oregon – an example of a rugged
basin with high relief
Drainage Basin Topography
Elevation is spatially distributed so representing the topography of a drainage basin with a single parameter is hard
Smith River, Oregon
DEM visualisation and analysis
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© USGSDEMs can be used for visualisation and to extract variablesAs accurately as the base data allow…
Image Source: http://geology.wlu.edu/plate2.html
Terrain Analysis with GIS
Source: Mitasova, H. and Mitas, L. 1998. Terrain Analysis and Erosion Modelling.Accessed online at http://skagit.meas.ncsu.edu/~helena/gmslab/viz/erosion.html on 12/5/05
ELEVATION SLOPE ASPECT
FLOWLINESTANGENTIAL (PLAN)CURVATURE
PROFILE CURVATURE
Drainage Basin Hypsometry
Provides a means of summarising the distribution of elevations in a landscape
Source: Redrawn from Summerfield (1991, Fig. 9.5, p211), which is itself based on Strahler (1952) Bull. Geol. Soc. Amer. 63, Figs 1 & 2.
Examples & Significance
Provides a basis for comparing basin formDistinct hypsometries are associated with different processes
– Fluvial (concave)– Tectonic (linear/convex)– Glaciated (shoulder)
Stage of evolution?– ↓HI implies ↑age (Strahler,
1952)
Source: Montgomery et al. 2001. Geology, 29(7), 579-582.
Why does Basin Form Matter?
© Hans Andren
Rapaälven River, Sweden
Sebaskachu River, Labrador
© Norm Catto
Relief influences steepness, which controls the energy available for driving forces (runoff, gravity)Basin form influences the connectivity between landscape units and hence the potential to store sediment
– Implies form-process interaction
Conclusion
Morphometric analysis is needed to provide a systematic basis for describing & comparing drainage basin geomorphology & to test hypothesesMorphometry can highlight links between basin forms and environmental variables, but it provides no direct insight into formative processesCare is required: Underlying data are derived from maps, DEMs, etc.
– Relationships depend on the basic quality of acquired data– Relationships can be scale dependent
Urumchi, NW China
© Matthias Jakob