Streams
Geology 115
Hydrologic cycle
Surface water
• Precipitation falls and becomes overland flow
• Overland flow organizes into streams
• “Stream” is a generic term covering brooks,
creeks, rivers, really any flowing surface water
which is not the ocean
A stream’s drainage is its watershed
Continental Divide
All of the streams in a drainage are called the
stream’s network
Stream profile
Base level
Stream gradient
Water velocity is fast
Water velocity is slow
% gradient = (elevation gain) ÷ s(horizontal distance)
Streams erode and deposit to fit the
ideal profile
The base level may also be affected by rising or falling sea levels
Waterfalls alter the stream profile
The underlying rock is quite erosion-resistant
As the stream tries to achieve the ideal stream
profile, the waterfall retreats as the rock is eroded
Plunge pool develops
Niagara Falls State
Park, New York
The fall line –
A stream’s discharge is the volume of water that
flows past a given point per time for that stream
When a river floods, its discharge increases, mostly because
the stream’s width increases and not so much its depth.
Parts of a stream
Headwaters
Tributaries
More vocabulary words about streams
Braided streams are characteristic
of rivers near their headwaters
Denali NP, Alaska
Meandering streams are
characteristic near their outlet
Vicksburg NMP, Mississippi
Floodplain and levee
Levee,
enhanced
with a
revetment
Former
stream
channel
Floodplain
Levee, enhanced with a
revetment
Floodplain
Point bar
Cut bank
Meanders both erode and deposit
Cut bank
Point bar
Meanders migrate
The material deposited by a stream is called alluvium,
which tend to be rich in nutrients, especially metals,
which makes for a good soil
An alluvial fan is a feature of a stream that
emerges from a mountain gorge onto a plain
(Death Valley NP, California)
Different types of stream mouths delta
Distributaries
Mississippi River Delta NHA, Louisiana
Different types of stream mouths estuary
Oregon Dunes NRA, Reedsport, OR
Estuaries are
major coastal
wetlands that
provide not
only wildlife
habitat but
also remove
metals and
organic
toxins from
streams prior
to the ocean
Different types of stream mouths –
drowned river mouth
Chesapeake Bay
Stream evolve over time – for instance,
meander migration causes valleys to widen
Oxbow lake
Antecedent streams – the stream was there first,
and, by gum, it’s going to keep to its path whatever
uplift or erosion happens
Fold mountains
Peneplain mountains
Fault block mountains
The Potomac River at Harpers Ferry NHP (WV, VA, MD)
These ridges are made of a resistant
metamorphic rock called quartzite
Consequent streams follow the topography (they
don’t cut through)
In this example from Virginia, Beaverdam Creek was an
antecedent stream that incised through a ridge of resistant
rock; it was captured by Shenandoah River (a consequent
stream) in an act of stream piracy.
A water gap is where
the river cuts through
resistant rock
(Harpers Ferry NHP)
A wind gap is where
the river once cut
through resistant
rock but has been
captured by another
river and only a low
spot in the hills
remains
Cumberland Gap NHP (TN, KY, VA) was an important
wind gap for Native Americans and settlers through
the Appalachian Mountains
Note that fog uses it, too!