Rivers
Rivers
1. Energy
2. Stages of River Development
3. Drainage Basins
4. Drainage Patterns
5. Geomorphological Features
A river is all about energy.
If a river is moving fast (due to gravity) and has
a lot of water – it has great energy. With great
energy comes erosion and the transport of the
eroded material. With a loss of energy comes
deposition.
Energy
• Features due to erosion or deposition
depending on speed.
• Low energy/low speed = deposition
• High energy/high speed = erosion
Stages of River Development
A: Youthful/Upper Stage
B: Mature/Middle Stage
C: Old/Low Stage
Physical Geography, Strahler and Strahler
Stages of River Development
A: Youthful Stage
• Steep, fast, straight, vertical erosion
B: Mature Stage
• Less steep, slower, meanders, horizontal
erosion
C: Old Age Stage
• Flat, slow, meandering, depositional
Drainage Basins
• Area in which all raindrops eventually
drain into the same river system, ocean, or
lake (catchment, watershed)
The Amazon Drainage Basin
Drainage Basins
Drainage Basins
• Tributaries: smaller rivers that drain into
larger rivers.
• Interfluves: pieces of higher land between
tributaries.
• Divide: higher ground
between drainage basins.
Drainage Patterns
• There are 5 Drainage Patterns:
– Dendritic
– Trellis
– Radial
– Rectangular
– Deranged
Drainage Patterns
Dendric Drainage Pattern
• Flow across level land, merging with other
rivers
• Resemble branching tree
Trellis and Rectangular
• Ground is made of folded bedrock, rivers may
follow a straighter course along the softer
bedrock, with hard rock on either side.
• Often in mountainous areas.
• Trellis: one main trunk
• Rectangular: square pattern
Rectangular
Trellis
Radial Pattern
• Landforms influenced by volcanoes and
cone-shaped hills.
• Streams radiate outward in all directions
from central zone
Deranged Pattern
• No distinct pattern noted
• Often lakes are found
throughout
• Glaciation has torn
the landscape leaving
this deranged pattern
Geomorphological Features!
LEVEES
Form on floodplains when rivers flood.
Water quickly loses its velocity as it spreads out from the
channel and deposition occurs
Heavier sediments tend to settle out immediately close to the
channel and an area of slightly higher ground is built up on
both sides of the river
Because of levees, the river channel is often built up higher
than the floodplains, which is then very susceptible to flooding
Below is a picture of Wilket Creek in Toronto. It flooded
during a violent storm in 2005. What you see is the sediment
that the river was carrying when it flooded. Note that the
sides have heavy material and the interior is very sandy.
The River could not carry the heavier rocks.
Natural levees
have been built
up by man for
flood control.
http://www.spk.usace.army.mil/what/envir/fldpln/fldpln.html
Meanders and levees, Red River flood, Manitoba, 1997
http://sts.gsc.nrcan.gc.ca/page1/landf/smanitoba/levees.htm
FLOODPLAINS
Valley area through which a river flows in the mature (old age)
stage
Built by river depositing material on the insides of the bends as it
meanders and when finer materials are deposited on the valley
floor when the river floods.
Finer materials traditionally added nutrient value to the soil and
thus helped to make floodplains very fertile areas, supporting
large populations
Unfortunately, large floods also usually meant a loss of life as
well.
A few floodplains support a large portion of the world’s
population: Hwang Ho, Yangtze, Indus, Ganges and the Nile.
A Landsat 5 image taken Sept.
1992 shows a section of the
Missouri River. The oblique
perspective of this image is
looking upstream. This image
has been color enhanced and
modified to show an
exaggerated topographic relief.
Bare soil and plowed land
appears red, vegetation
appears green, and water is
dark blue. A flat river flood
plain can be seen in the center
of the image. Because of the
season, most of the farmland
located on the rich and fertile
soils of the floodplain is plowed
and devoid of vegetation.
http://www.geog.ouc.bc.ca/physgeog/contents/11j.html
• Meander: back and forth sweep of a river
in old age. As a river reaches its mature
stage its ability to erode diminishes and
whenever it does erode material it will
quickly deposit that material. As it erodes
material from one bank (on the outside Pool) it deposits material on the other
bank (the inside - Riffle) and river begins
to bend or meander.
•
Example of a Pool and Riffle from the Don River
• Oxbow lakes: an area of poor drainage
that occurs when a meander is cut off from
the main river channel, forming a lake.
• Delta: depositional feature found at the
mouth of a river.
• River’s water reaches mouth of river and
the sediment is carried settles.
This is the mouth of the Humber River (flowing into
Lake Ontario). Notice the width of the river and the
flow is very slow.
This is near the mouth of the Humber river. Notice under the
bridge the ‘Bulrushes’. This area is also called the Humber
Marsh. The river has slowed down and has deposited some
silt or dirt, allowing the vegetation to grow.
• Estuary: the flooded mouth of a river
valley. If there is an ocean involved we get
a mixture of fresh and salt water.