STREAMS
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 Earth’s surface
• running water is a powerful agent of erosion
and principal sculpture of Earth’s landscape.
• perennial streams flow year round and
intermittent (ephemeral) streams do not.
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 subsurface—groundwater) +
evaporation + transpiration ( used by plants)
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
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
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
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
• base level STREAMS
• 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
STREAMS
Stream piracy and changing channel
direction can cause large problems at
local, state--national and international
levels
STREAMS
capture or piracy of water from stream A by stream B
can cause a problem.
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
Channel shape and stream velocity
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
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 Wentworth’s scale) a stream
can transport
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--
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
STREAMS
• braided channel
• stream channel which intertwines
• caused if slope or discharge of stream
decreases
STREAMS
braided
channel
straight
channel
meandering
channel
STREAMS
Photos of meandering and braided channels
meandering
channel
braided channels
STREAMS
• 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
STREAMS
• radial
• streams diverge from a central area like
spokes from the hub of a wheel
• develops on volcanic cones or domal
uplifts
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
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
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
STREAMS
Drainage basins and divides
STREAMS
Mississippi River Basin and Divides
STREAMS
• 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 bars—meandering
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
STREAMS
Cut-bank, point bar and water velocities
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
STREAMS
Formation of an oxbow
Development
of meander
STREAMS
Meanders can
show a curved
pattern of
development
forming an
oxbow
Oxbow Lakes
STREAMS
Meander scars
An older stage of stream meander development
STREAMS
--an Entrenched (Encised) meander is a
deepened meander channel caused by
subsequent rejuvenation (uplift) of the channel--
STREAMS
Entrenched (Encised) Meander in
Colorado River in the Grand
Canyon
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
Alluvial fan at the
base of a mountain
STREAMS
Deltas formed at mouth of streams discharging
materials entering the ocean
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
STREAMS
formation of a levee
during flooding water
velocity is slower and
material accumulates in
long mounds
as flooding recedes, mounds
are exposed.
STREAMS
Floodplain and natural levees
STREAMS
Floodplain
STREAMS
Natural levee with stream water breakthrough
STREAMS
• 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
STREAMS
STREAMS
Stream Channelization
STREAMS
Stream Channelization
Stream Discharge: Measure of the Stream volume/second
at It’s 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