STREAMS

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STREAMS
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STREAMS

• hydrology or geo-hydrology is the study of
  streams or groundwater
• Basic nature of steams
• Definition, origin and course of stream
• definition and explanation
• a flowing body of water mostly contained in a
  channel at Earths surface
• running water is a powerful agent of erosion and
  principal sculpture of Earths landscape.
• perennial streams flow year round and
  intermittent (ephemeral) streams do not.

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STREAMS

• origin
• prime source of stream water is from runoff from
  the hydrologic cycle

fate of precipitation runoff (into streams,
ponds and lakes) infiltration ( into
subsurfacegroundwater) evaporation
transpiration ( used by plants)
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STREAMS

• stream course and retention of water in channel
• path of stream can depend on
• slope of land
• geologic structures as folds, fractures and
  faults
• rock hardness
• retention of water in channel depends largely on
  the presence and degree of channel coating by
  clay, silt or other impermeable substances

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STREAMS

• Stream system
• tributaries
• smaller streams which collect and supply
  materials and water to the main stream
• main stream or main trunk
• the main stream which receives materials and
  water from the tributaries and is the prime
  transporter of materials in the stream system

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STREAMS

• Stream profile and related terms
• stream profile
• head
• mouth
• examples of mouth are juncture of stream with
  another stream a pond or lake the ocean
• decreasing gradient of channel downstream
• slope of stream channel is greatest at head and
  smallest at mouth

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STREAMS
Stream profile
many tributaries
trunk
Stream water flows faster if the gradient is
higher and erodes mostly downward, while slower
with lesser gradient, and water can start eroding
sideways resulting in channel meander
Land uplift results in faster flow and higher
downward erosion
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STREAMS

• base level
• lowest level to which a stream can erode its
  channel
• local or temporary base levels include lakes,
  resistant rock formation(s) and streams which act
  as base level for their tributaries-- ultimate
  base level is sea level
• head-ward erosion and stream piracy
• head ward erosion is the extension of a channel
  head ward up the slope of erosion
• stream piracy is the diversion of waters of one
  stream by another stream and head ward erosion
  of pirating stream

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STREAMS
Stream piracy and changing channel direction can
cause large problems at local, state--national
and international levels
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STREAMS
capture or piracy of water from stream A by
stream B can cause a problem.
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STREAMS

• Stream water velocity
• governs both erosion and deposition
  rates--magnitude of erosion is proportionate to
  stream velocity and that for deposition is
  inversely proportionate to velocity
• some factors affecting stream velocity
• shape of stream channel
• a deep narrow or wide shallow channel retard
  total water velocity
• a semicircular channel allows faster moving water
  based on area of friction

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Channel shape and stream velocity
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STREAMS

• roughness of channel
• rough channel with boulders and large rocks
  causes a decrease of water velocity
• stream gradient
• is a measure of the slope of the channel
  expressed as the number of feet dropped per mile
  as measured between 2 points along the path of
  the stream

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STREAMS

• change in channel area along the stream
• if channel area increases downstream, water
  velocity decreases
• alluvial fans or deltas form when depositional
  rates of materials increase as velocity of water
  decreases--these features will be discussed in
  detail later
• Stream loads
• materials carried by stream waters
• stream competency refers to the maximum size
  particle(see Wentworths scale) a stream can
  transport

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STREAMS

• suspended load
• suspended particles in stream waters
• usually includes clay and silt sizes
• most streams carry largest part of their load in
  suspension
• bed load
• particles which bounce or skip (saltation) while
  being transported by the stream
• for most streams sand size particles
• dissolved or solution load
• stream velocity has no influence on
  this--precipitation occurs based on water chem.

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STREAMS

• Stream and drainage patterns, drainage basins and
  divides
• Stream patterns
• are in reference to shape of individual stream
  channel
• straight channel
• often present near headwaters where erosion is
  downward into the channel
• meander channel
• snakelike in shape and present downstream from
  the head--these are significant near the mouth

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STREAMS

• braided channel
• stream channel which intertwines
• caused if slope or discharge of stream decreases

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STREAMS
braided channel
straight channel
meandering channel
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STREAMS
Photos of meandering and braided channels
meandering channel
braided channels
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• Drainage patterns
• are in reference to a stream and its tributaries
• dendritic or arborescent
• resembles veins of a tree leaf and is the most
  abundant type of drainage pattern

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STREAMS

• radial
• streams diverge from a central area like spokes
  from the hub of a wheel
• develops on volcanic cones or domal uplifts

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STREAMS

• rectangular
• comprised of many right angle bends
• develops in bedrock crisscrossed by a series of
  joints and/or faults which represent precut
  channels in which water can flow

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STREAMS

• trellis
• a rectangular type of pattern in which tributary
  streams are nearly parallel to each other and
  look like a garden trellis
• forms on folded rocks resulting in alternating
  parallel bands of resistant and less resistant
  rock like in the Appalachian Mountains

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STREAMS

• Drainage basin and divide
• a drainage basin is the total land area that
  contributes water and material to a stream
• a divide is an elevated area which separates
  drainage basins and range in size from a ridge
  separating small gullies to continental divides
  which split continents into large drainage basins

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STREAMS
Drainage basins and divides
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STREAMS
Mississippi River Basin and Divides
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• Stream features and channelization
• Meander and oxbow
• stream velocity is greatest on outside of meander
  causing a cut bank and slowest on inside
  resulting in point barsmeandering starts to form
  when a slight difference in roughness on channel
  bottom occurs
• the water molecules in a stream moving around a
  bend align like a line of ice skaters in which
  the outside skaters are moving much faster then
  those in the inside

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STREAMS
Cut-bank, point bar and water velocities
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STREAMS

• as the outside portion of the meander continues
  to erode the neck of land between, the outer
  portions become narrowed to the extent which
  isolates or cuts off the loop called an oxbow
• typically this horseshoe shaped feature is a lake
  initially but with time will become a oxbow scar
  as the lake fills with sediment
• typically oxbow scars are located a longer
  distance from the river than oxbow lakes

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STREAMS
Formation of an oxbow
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STREAMS
Development of meander
Meanders can show a curved pattern of
development forming an oxbow
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Oxbow Lakes
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STREAMS
Meander scars
An older stage of stream meander development
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STREAMS
--an Entrenched (Encised) meander is a deepened
meander channel caused by subsequent rejuvenation
(uplift) of the channel--
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STREAMS
Entrenched (Encised) Meander in Colorado River
in the Grand Canyon
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STREAMS

• Alluvial fan and delta
• as the water leaves it's channel and spreads, the
  water moves slower and material is deposited
• this is apparent at the base of mountains as
  water enters valleys and at the mouth of large
  streams as they enter the oceans
• the results of this deposition forms alluvial
  fans and deltas

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Alluvial fan at the base of a mountain
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STREAMS
Deltas formed at mouth of streams discharging
materials entering the ocean
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STREAMS

• Floodplain and natural levee
• a floodplain is a relatively flat region flanking
  large streams and formed by deposition of finer
  sediments during periodic flooding
• a natural levee is a ridge or platform built on
  the floodplain adjacent to and trending along the
  course of the stream and represents the highest
  area or point on a floodplain
• levees are caused during flooding and can inhibit
  subsequent flooding

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STREAMS
formation of a levee
during flooding water velocity is slower and
material accumulates in long mounds
as flooding recedes, mounds are exposed.
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STREAMS
Floodplain and natural levees
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Floodplain
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Natural levee with stream water breakthrough
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• Channelization
• structural alteration made to the channel of a
  stream in order to speed flow of water and thus
  prevent flooding
• usually involves cutting off a meander to
  straighten the course of a stream
• the resultant shorter straight channel is made to
  have a steeper gradient and the increased steam
  water velocity will transport more water possibly
  enough to prevent flooding in an area

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STREAMS
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Stream Channelization
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Stream Channelization
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Stream Discharge Measure of the Stream
volume/second at Its Mouth (7.5 gallons/cubic
foot)
WORLD'S TEN LARGEST RIVERS BY DISCHARGE
River Country Average Discharge at Mouth (Thousands of cubic feet per second)
Amazon Brazil 7,500
Congo Congo 1,400
Yangtze China 770
Brahmaputra Bangladesh 700
Ganges India 660
Yenisey Russia 614
Mississippi USA 611
Orinoco Venezuela 600
Lena Russia 547
Parana Argentina 526