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Chapter 14

Chapter 14- Textbook

6 pages62 viewsWinter 2011

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Joseph Leydon

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Chapter 14- River Systems and Landforms 01:55
Fluvial Processes and Landscapes
Stream- related processes are fluvial
Fluvial systems like all natural systems have characteristic process and produce recognizable
The term river is applied to a trunk or main stream or an entire river system
Stream is a more general term not necessarily related to size
Isolation and gravity power the hydrologic cycle and are the driving forces of fluvial systems
Water dislodges , dissolves or removes surface material in the erosion process
Streams produce fluvial erosion in which weather sediment is picked up for transport to new
A stream is a mixture of water and solids are carried in suspension by mechanical transport and
in dissolved solutions
Materials are laid down by another process, deposition
Alluvium is the general term for the clay, silt , sand, gravel and mineral fragments deposited by
running water as sorted or semi-sorted sediment on a floodplain, delta or streambed
Base Level of Streams
Base level is a level below which a stream cannot erode its valley
The ultimate base level is seal level, the avg level btw high and low tides
A local base level or temporary one, may control the lower limit of local streams for a region
The local base level may be a river, a lake , hard and resistant rock
Landforms are produced by 2 basic processes: 1. Erosive action of flowing water and 2.
Depostion of stream- transported materials
Drainage Basins
Every stream has a drainage basin, ranging in size from tin to vast
Every drainage basin is defined by ridges that form drainage divides that is the ridges are the
dividing limes that control into which basin precipitation drains
Drainage divides define a watershed the catchment area of the drainage basin
In any drainage basin, water initially moves downslope in a thin film called sheetflow or overland
Drainage Divides and Basins
Several high drainage divides called continental divides in Canada and USA
A major drainage basin system is made up of many smaller drainage basins
Each drainage basin gathers and delivers its precipitation and sediment to a larger basin
Drainage Basins as Open Systems
Drainage basins are open systems
Inputs include precipitation and the minerals and rocks of the regional geology
System outputs of water and sediment disperse through the mouth of the river into a lake another
Change that occurs in any portion of a drainage basin can affect the entire system
A stream drainage system constantly struggles toward equilibrium among the interacting
variables of discharge, transported load channel shape and channel steepness
Internal Drainage
Most streams find their way to progressively larger rivers and eventually into the ocean
In some regions however stream drainage does not reach the ocean
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The water leaves the drainage basin by means of evaporation or subsurface gravitational flow,
such streams terminate in areas of internal drainage
Drainage Density and Patterns
A primary feature of any drainage basin is its drainage density
Drainage density is determined by dividing the total length of all stream channels in the basin by
the area of the basin
The drainage pattern is the arrangement of channels in an area, patterns are quite distctive for
they are determined by the combination of regional steepness, variable rock resistance, variable
climate, variable hydrology, relief of the land and structural controls imposed by the underlying
Streamflow Characteristics
A mass of water positioned above base level in a stream has potential energy
As the water flows downslope or downstream under the influence of gravity this energy becomes
kinetic energy
Streams vary in width and depth, the stream that flow in them vary in velocity and in the
sediment load they carry. All of these factors increase with increasing discharge or the streams
volume of flow per unit of time
Discharge is calculated by multiplying the velocity of the stream by its width and depth for a
specific cross section Q= wdv
Q= discharge, w= channel width, d= channel depth and v= stream velocity
As Q increases some combination of channel width, depth and stream velocity increases,
discharge is expressed either in cubic meters per second (m^3/s)
Exotic Streams
Most streamflows increase discharge downstream because the area being drained increases
Stream can originate in a humid region and subsequently flow through an arid region
In that case high potential evapotranspiration rates in the arid area
Such stream is an exotic stream ex. Nile
Stream Erosion
Hydraulic action is the work of flowing water alone, running water causes hydraulic squeeze and
release action that loosens and lifts rocks
As debris moves along it mechanically erodes the streambed further through the process of
abrasion with rock particles grinding and carving the streambed like liquid sandpaper
Stream velocity determines rates of erosion and deposition
Sediment particles are deposited onto the streambed at slower velocities whereas they are eroded
at higher velocities
Stream Transport
the amount of material available to a stream depends on topographic relief, the nature of rock and
soil through which the stream flows, climate vegetation and human activity in a drainage basin
competence which is a streams ability to move particles of specific size is a function of stream
velocity and the available energy to suspend materials
capacity is the total possible load that a stream can transport
four processes transport eroded materials: solution, suspension, salutation and tractions
solution refers to the dissolved load of stream the chemical solution is derived from minerals
such as limestone or dolomite or from soluble salts
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