Rivers
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As rivers carve across the land they not only provide water and habitats for special
ecosystems, they change the land itself. As water flow they
ERODE the land. In Winnipeg, the erosion of riverbank property is a huge concern.
What are some ways in which riverbank erosion can be reduced?
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Control river levels
line river banks with concrete/rocks
Divert water (floodway)
Slowing boats – no wake zones
Plant trees/shrubs on banks
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Create unique landforms such as “peninsulas” (land surrounded by water on three
sides) as the river MEANDERS or wanders. The water eroding softer land causes
this.
Oxbow Lakes
• Create an OXBOW LAKE which is a
“U-shaped” lake or pond formed
when a river’s meander is cut off
from the river.
Oxbow Step 1
Deposition occurs on the
inside edge where water
flows slower
Outside edge erodes
as water hits it hard
Oxbow Step 2
More sediments are
deposited in old channel
New channel begins
to form
Oxbow Step 3
Old meander is left as an
“Oxbow Lake”
Old channel is
completely cut off
River Deltas
• Creates ALLUVIAL DEPOSITS and DELTAS
as the water deposits the minerals it
eroded on its journey. Deltas are fanshaped land forms found at the mouth
of rivers (where the river meets a lake,
sea, or ocean). The NILE River Delta may
be one of the most famous river deltas
in the world and was and is important to
Egyptian life.
• Draw a triangle around the green delta
area formed when the Nile deposits the
rich, fertile sediments eroded from the
African continent.
River Deltas
• This land is FERTILE and productive agriculturally!
• Delta () is the Greek letter D and is in the shape of a triangle!
• In Manitoba the rivers flowing into Lake Winnipeg and Lake
Manitoba form marshy deltas, areas that are important for:
– Wildlife habitat (both land and aquatic)
– Cleaning/purifying water entering the lakes
Old vs. Young Rivers
Old vs. Young Rivers
• Use the table below to compare and contrast young and old
rivers.
YOUNG
OLD
Fast
Slow
Straighter
Windy (meandering)
Energetic
Less energy
Can move large boulders
Move small sediments
Narrower
Wider
Cleaner water
More sediment/ muddier
The RED River
• As the Red River began only after Lake Agassiz
drained some 10000 years ago, it is considered to be
a young river. But it behaves like an older river
because it has a low flow rate with little energy!
• The areas on the sides of the river create a river
valley or a flood plain. The Red River’s flood plain is
wide and shallow, much like a gentle plate.
• This creates many problems with flooding.
The RED River Flooding
• Other factors leading to flooding in southern
Manitoba include:
Flat, wide flood plain
Slow flow
Flows north – mouth is still frozen
when south begins to melt
Ice jams
Heavy snow pack
Frozen land (no absorption)
Quick thaw
Heavy spring rains
Human influence – dams, dikes,
levees – keep water from moving
naturally
Global warming/climate change
Flood Protection
• People in southern Manitoba, and especially in
Winnipeg, are always concerned about flooding.
Small Scale
In use
Future Ideas
Flood insurance
Sand bags
Raise buildings
Pumps
More/bigger ditches
Flood walls/levees
Large Scale
Floodways
Dams
Clearing out the river bed
Building large holes into the
river bed
Super ice/water heaters