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)

LANDSAT 7 2000

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