Recommended Sites to Explore

• The drainage basin concept, Stream Morphometry, Dr. Michael Pidwirny, University of British Columbia Okanagan, Fundamentals of Physical Geography
• NASA Geomorphology From Space: Chapter 4- Fluvial Landforms , site URL: http://disc.gsfc.nasa.gov/geomorphology/GEO_COMPLETE_TOC.shtml

Terms: fluvial, tributary, drainage basin, watershed, delta, alluvial fan, distributary, hydrologic divide, topographic divide, discharge divide, incised meander, misfit stream, floodplain, oxbow, natural levee, stream terrace, yazoo tributary, drainage basin patterns  (dendritic, trellis, rectangular, radial, annular, multibasinal, barbed, contorted), stream capture, drainage density, badlands topography.  Test you knowlege: interactive web crossword / PDF

Introduction to fluvial systems and their drainage basins

The three components defining a fluvial system are the tributary system, the main trunk, and the mouth. Each component differs in a relative sense by the dominance of one process over another.   Although sediment erosion, transportation and deposition occur in all three zones erosion dominates the tributary system, transportation the main trunk, and deposition the mouth. Water is also collected by tributaries, moved through the main trunk, and dispersed at the mouth.

Summary of Features

• Tributaries are streams that collect water and deliver it to the main trunk. (Dominant processes: erosion and input of mass). They form the primary zone of sediment production and mobilization.
• The main trunk or principle stream transports water and sediment to the mouth. (Dominant processes: transportation of sediment and throughput of mass)  Example: Mississippi River (NASA GFS)
• The mouth lies at base level, where the stream terminates (dominant processes: deposition and dispersal, output of mass). Base level can be another stream, a lake, an alluvial basin, or the ocean.  The depositional regime at the mouth is dominated by a distributary system, which disperses water and sediment forming a delta in a lake or sea or an alluvial fan in basin or valley. The morphology of deltas and fans are strongly influenced by fluvial input and processes dominating the receiving basin. For example, the size and principal morphology of a delta is a function of sediment supply, river discharge and processes , energy within the receiving basin (wave and tidal energy), and climate, which controls vegetation and evaporative processes.  (Visit my Coastal delta page for details.)  A stream discharging into another river may create a small delta or series of bars and rapids.
  • Examples of Deltaic Landforms (NASA GFS): Body of sediment deposited as a stream flows into a standing body of water.

    • Colorado River delta (NASA GFS)
    • Chang Jiang (Yangtze) River delta (NASA GFS)
    • Mississippi River (NASA GFS)
    • Yukon River Delta (NASA GFS)

  • Examples of alluvial fans: Fans of Asia, southeast Iran (NASA GFS)
    
• Drainage basin or watershed is the entire area drained by a stream section and its tributaries.   Most fluvial systems and their drainage basins are part of a hierarchical system, which means they are nested subsets of a larger system, for example the Platte River is a tributary of the Missouri, which is a tributary of the Mississippi.  The perimeter of a basin is defined by topographic divides.
• Hydrologic divides: Divides are boundaries across which water can't flow. Water from rain falling on a hill flows away from the crest, the crest is therefore a topographic divide, a divide defined by topography.   Water does not flow across streams either, rather it's captured by a stream and discharged.  Streams therefore are another type of hydrologic divide called a discharge divide and form the axes of basins. 

Figure 1. Mancos River and its tributaries cutting into Mesa Verde, Southwestern Colorado.  The Mancos drainage basins is defined by the topographic high around its perimeter. The watershed is also composed of smaller tributary basins, each separated from neighboring watersheds by interfluve ridges.  A stream delineates the axis each watershed.  The Mancos River is a tributary of the San Juan River which flows into the Colorado River.

Components of an individual river or stream trunk

Stream valleys

A valley is the trough through which the stream channel meanders. It can be carved entirely by the stream, excavated along a weak lithologic zone, or structural in origin (e.g. rift valley).  The width and depth of an alluvial valley is a function of the rate of down-cutting relative to lateral and  vertical accretion, which are controlled by relief and base level fluctuations. For example, rapid uplift over the last 5 ma is responsible for creating the incised Goosenecks (meanders) of the San Juan River shown below.  Most large valleys have complex histories. Some may be relict features of earlier events, for example broad valleys in alpine regions with misfit streams are common in glaciated regions.

Features associated with alluvial valleys: (See Chapter 11 and lecture 2 on streams) alluvium, valley flat, floodplain, valley walls, oxbow lakes, natural levees, yazoo tributary, backswamp, terraces

The stream channel (Streams Part 1: Introduction)

Descriptions and Classifications of Drainage Basins

1. Stream order and magnitude

Horton(1945) devised a system for classifying tributaries based on their order in the of drainage hierarchy.  A finger-tip tributary is a first order streams. A second order stream lies below the confluence of two first order streams, and third order below the confluence of two second order streams.  Therefore a nth order stream is always located immediately below the confluence of two (n-1)th order streams.  Stream magnitude (Strahler, 1952) labels stream segment to reflect the total number of first order streams in its watershed.  For example the magnitude for the fourth order stream below would be 26.

Figure 4.  Ordering streams in a drainage basin.  What is the order stream segment"?"

2. Drainage basin pattern refers the the pattern made by the tributaries.  It is primarily a function of basin geology (structure, lithology, and overburden), climate, developmental history, and slope. Basin patterns commonly reveal the first clues to understanding the geology of an area.  (See Chapter 12 in Bloom. See also Thornbury pp. 119-128 and Howard, 1967 who first defined drainage basin patterns) 

Pattern	Description	Controlling influences
dendritic	random, tree-like branching pattern	flat-lying sedimentary rock, thick sediment, or homogeneous rock uninterupted by fractures
trellis	long (subsequent) streams follow strike valleys fed by short tributaries decending from adjacent obsequent and dip slopes	developed in differentially eroded fold belts containing lithologies of varying strengths
multibasinal	stream flow towards an interior basin	Region of interior drainage such as the Basin and Range. Characteristic of an arid climate.
centripetal	streams flow into a central location and disappear underground	Karst region formed by the solution of soluble rock (typically limestone) and subterranian drainage
deranged	interrupted by numerous lakes and wetlands	Common in glaciated regions where bedrock was differentially scoured and glacial sediments were dumpled in pre-existing drainage networks
annular	accurate subsequent stream with short tributaries	eroded dome or basin containing rocks of varying resistances
radial	tributaries radiate away from a central region	central highland such as a volcano or eroding pluton surrounded by sedimentary rock
rectangular	tributaries make right angle bends	jointed or faulted bedrock
barbed	one or more tributaries enter at an angle >90%	captured drainage

3. Drainage density is a measure of runoff potential and degree of landscape dissection. It is quantitatively defined as the total of all stream lengths in a basin divided by the area of the basin. Drainage density is influenced by geology (permeability, erodibility of surface materials), climate (precipitation and vegetation), slope, and time. The interpretation of DD varies with map scale. Typically its measured on a scale of 1:24,000.

Badlands topography is highly dissected, rugged landscape characterized by extremely high drainage densities. Such regions are underlain by impermeable and easily eroded rock or sediment, and are poorly vegetated. DD may be greater than 100 km/km² (>60 miles/sq. mile)

4. Drainage frequency: total number of streams/area (inverse of DD)

References Cited

Bloom, Arthur. 2004, Geomorphology, A systematic analysis of Late Cenozoic Landforms, (4th edition): Waveland Press Inc., Longe Grove , IL 482 p.

Horton, R. E., 1935, Erosional development of streams and their drainage basins: hydrophysical approach to quantitative morphology: Bulletin of the Geological Society of America, v. 56, pp. 273-370.

Howard, A.D., 1967, Drainage analysis in geologic interpretation: a summation: The Amer. Assoc. of Petr. Geol., v. 51, n. 11, p. 2246-2259.

Morisawa, Marie, 1985, Rivers: Longman Inc., New York, 222 p.

Strahler, A. N.,1952, Dynamic basis of geomorphology: Geological Society of America Bulletin, 63, pp. 923-938.

Thornbury, William D., 1969, Principles of Geomorphology (2nd edition): Wiley and Sons, New York 594 p.

Streams Part 1: Introduction / Streams Part 2: Classifications /Streams Part 3: Drainage Basins

Lindley Hanson/Department of Geological Sciences/Salem State College/Geomorphology/GeoIndex/QkRef