Transcript Hydrological cycle- the hydrosphere Rivers and Fluvial landforms Streams redistribute more material from the landscape than any other process.   A frequently tapped resource.

Hydrological cycle- the hydrosphere
Rivers and Fluvial landforms
Streams redistribute more material from
the landscape than any other process.


A frequently tapped resource for
domestic, commercial, and agricultural
needs
Floods have played important roles in
human history.
Devistating loss of life, but needed to
replenish the land
Introduction
• The Earth is unique in having abundant liquid water.
3
Location
Volume (km )
Oceans
Icecaps and glaciers
Groundwater
Freshwater and saline lakes
Atmosphere at sea level
Average in stream channels
1,327,500,000
29,315,000
8,442,580
230,325
12,982
1,255
Percentage of Total
97.20
2.15
0.625
0.017
0.001
0.0001
Rivers and their landforms compose what are
known as fluvial systems
Fluvial deposits (sediment transported and
deposited by streams) is called alluvium
Flowing Water
very low velocity = no erosion, low ability to
transport sediment
Turbulent flow occurs
when streamlines are
not parallel, but flow into
one another.
• The cause of erosion and
transport.
low to very high velocity = variable ability to
transport sediment
Stream Gradient
• is the slope over which a stream flows and is calculated by dividing the
vertical drop by the horizontal distance.
• steeper gradient streams have higher flow velocity
> more energy for moving things
Stream gradient
generally decreases
as one moves
downstream
However,
local exceptions to
this do occur
Velocity & Discharge
• Velocity (V) a measure of distance
travelled over time.
ft
for example
sec
> affected by gradient, discharge and channel
charcteristics
Discharge (Q) is a volume of water
flowing by a particular point in a given
3
unit of time.
ft
for example
sec
> affected by gradient, velocity, channel dimensions
Discharge (Q)
• Discharge = Cross-section Area x
Velocity
60 seconds to go 30 ft
>
Q=AxV
V= 0.5 ft
sec
10 ft = width (w)
cross
sectional
area
2 ft = depth (d)
Area (A)= 20 ft 2
What is the discharge here?
A1 = w1 x d1
A3 = w3 x d3
A2 = w2 x d2
V1
V2
A5 = w5 x d5
A4 = w4 x d4
V3
Q1 = A1 x V1
V4
V5
Q5 = A5 x V5
Q4 = A4 x V4
Q2 = A2 x V2
Q3 = A3 x V3
Qtotal = Q1+Q2+Q3+Q4+Q5
• Velocity within a stream varies due to friction of water with
the stream banks and bed.
depth within the channel is known as the
-Area of maximum velocity
Thalweg
Thalwegplan or map view
Thalweg
crosssection
view
• Meandering Streams have different velocities on the inside and outside of
curves.
Thalweg
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Transport of Sediment
• Sediment is transported as
> dissolved load
- Dissolved load is the ions taken into suspension
by chemical weathering.
> suspended load
- Suspended load is silt to clay sized particles
carried in suspension.
> bed load
- Bed load is the sand to gravel sized particles
carried along the bed of the stream.
- Bed load moves by saltation.
¥ Competence is the maximum sized particles a
stream can transport.
¥ Capacity is a measure of the total load a
stream can carry.
Stream "Work"
• Streams do most of their work
(erosion and deposition) when they
flood.
• Stream deposits represent a
combination of both continuous
gradual deposition and erosion,
punctuated by periodic large-scale
events.
Channel Types
• Straight
• Meandering
> single flow channel
that has many bends
- bends = meanders
• Braided
> multiple channels
at high discharges
> many gravel islands
during low flow
• A braided stream near Santa Fe, New Mexico. The deposits in this
stream are composed entirely of sand
Point Bars and Cut Banks
• Oxbow Lakes are actually cutoff meanders.
Oxbow and Meander scrolls
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Meander with scrolls along the Ohio River
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Floodplains
floodplain width
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• Natural Levees buildup from vertical accretion of fine
grained sediments along the banks of a stream.
• Levees separate the channel from most of the
floodplain, which is mostly swampy and poorly
drained.
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sometimes the levees wor
sometimes they don't
breeched levees
Deltas
• form when one body of water flows
into another and begins depositing
some of its load.
• Deltas occur in lakes but are larger
and more complex in the ocean.
• Sediment begins to build out or
prograde
The Mississippi River DeltaclassicRiver,
"birds
foot"
• Stream-dominated deltas, like the a
Mississippi
exhibit
long or
fingerlike progradations.
fluvial dominated delta
Alluvial Fans (1:2)
• are "deltas" deposited on land when a
stream flows from the narrow mountain
valleys onto the broad flat lowlands.
• Sediment accumulates at the mouth of
the canyon/valley, forming a broad ramp
often dissected by braided streams.
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Terraces
Former floodplains of the river
•abandoned as the river downcuts,
creating a new floodplain as it erodes
back and forth across the valley
Older abandoned
floodplain - a.k.a. a
stream “terrace”
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Modern floodplain
Terrace
Modern
floodplain