A. Definition, origin and course of stream
1. Definition and explanation
·
a stream is a flowing body of water mostly contained in a
channel at the Earth's surface--running water is a powerful agent of
erosion--the water in steam channels may flow year-round (perennial streams) or
may flow at intermittent times (intermittent streams) of the year based on
water supply
·
the prime source of stream water is from runoff--to
understand this better we should look at the Earth's water balance called the "hydrologic
cycle"---the cycle explains the fate of or paths taken by
precipitation---precipitation amounts can evaporate (evaporation), be used by
plants (transpiration), migrate into the subsurface (infiltration) or empty
(runoff) into the lakes, ponds or streams
·
click here to see the hydrologic
cycle or see page 217 in text
3. Stream course
·
the path of a stream can depend on slope of the land,
geologic structures as fractures and faults and rock hardness
·
the retention of water in the stream channel depends largely
on the coating of channel with silt, clay or other impermeable substances
B. Stream profile and related terms
1. Stream profile
·
includes the point of origin of the stream called the head,
the point of termination called the mouth, and a decreasing gradient of the
stream channel towards the mouth---examples of the mouth of the stream are the
juncture of the stream and: another stream; a pond or lake; the ocean
·
the slope of the land and stream channel is greatest at the
head and smallest at the mouth— stream
water flows faster if gradient or slope is higher and erodes in its channel
primarily in a downward direction, while water moves slower if slope is more
gentle and water may erode less downward and more sideways—if
land and channel uplifts, water moves faster and erodes downward
·
click here to see the stream
profile
2. Base level
·
is the lowest level to which a stream can erode---the
ultimate base level is sea level--local or temporary base levels include lakes,
resistant rock formations and main streams which act as base levels for their
tributaries
3. Head-ward erosion and stream
piracy
·
head-ward erosion is the extension of a stream channel
head-ward up the slope of erosion
·
stream piracy is the diversion of the waters of one stream
by another and is caused by the extension of the channel of the pirating stream
by head-ward erosion—stream piracy and changing channel direction can
cause large problems at local, state-national and international levels---Rio Grand River
C. Stream system
1. Tributaries
·
are the smaller streams which collect materials and supply
it and water to the main stream in the area
2. Main trunk
·
is the main stream which receives materials from the
tributaries and is the prime transporter of materials in this system
D. Stream water velocity
E. Stream loads
1. Suspended load
·
particles suspended in steam waters--usually includes clay
and silt sizes--most streams carry the largest part of their load in suspension
2. Bed load
·
particles bounced or skipped (saltation) along the bottom of
the stream bed--usually consists of sand size particles
3. Dissolved or solution load
·
the velocity of the stream has essentially no affect on a
stream's ability to carry its dissolved load--precipitation occurs only when
the chemistry of the water changes
II. Stream and drainage patterns, drainage
basins and divides
A. Stream patterns
1. Straight
·
a stream channel is often straight near the headwaters where
much of the erosion is in a downward direction
2. Meander
·
is a stream channel which meanders or is snakelike in
shape--this pattern usually is more abundant farther downstream nearer the
mouth of the stream--we will discuss this type of pattern in more detail later
under "Stream features"--see
page 225 in text
·
is a stream with numerous inter-twinning channels--often
results when the slope along the stream decreases or if the discharge of the
stream decreases
·
click here to see a braided
stream ---- see bottom
of page 226 in text
B. Drainage patterns are in reference to a stream and its
tributaries
·
is the most common type of pattern which resembles the
branching of a deciduous tree or veinlet pattern on an oak leaf
·
this type of pattern forms where the rock over which the
stream flows is uniform in hardness or uniform in resistance to erosion
·
click here to see a photo of a
dendritic drainage pattern
2. Radial
·
is a pattern which forms where streams diverge from a
central area like spokes from the hub of a wheel
·
this type develops on volcanic cones or domal
uplifts
3. Rectangular
·
is a pattern which is comprised of many right-angle bends
·
this pattern develops in bedrock crisscrossed by a series of
joints and/or faults--the cracked surface represents precut channels in which
water can flow
4. Trellis
·
is a rectangular type of pattern in which tributary streams
are nearly parallel to each other and have an appearance of a garden trellis
·
this pattern forms in areas underlain by folded rocks
resulting in alternating parallel bands of resistant and less resistant
rock--best example is in the folded Appalachian Mountains
click here to see
and review the drainage patterns discussed above --- see
page 233 of text for drainage patterns
C. Drainage basin and divide
III. Stream features and channelization
C. Floodplain and natural levee
click here for more on streams