Transcript Drainage System Maintenance

CHAPTER 19:
SURFACE WATER
Water covers
71% of Earth’s
surface and is
the dominant
agent governing
environmental
processes.
Bassano Dam – part of major irrigation
system in central Alberta
?
Which country has the most abundant
resources of renewable fresh water?
We have much less water than
we think, and a majority of
surface water in Canada drains
to the Arctic, so is not actually
available to most Canadians.
Data from www.woldwater.org 2011, drawing by Steven Earle
Water Use
• In Canada most of our water use is
for energy generation and industrial
purposes.
The Hydrologic Cycle
• The Hydrologic Cycle is the transfer of water between the atmosphere, the
ocean, lakes and streams and the crust (as groundwater)
Runoff enters channels that join other channels
to form a drainage system
Drainage Systems
•
•
•
•
A Stream is any flowing body of water following a channel
A river is a large stream, although there is no specific size cutoff for a “river”
A Drainage System is a network of channels
The total area feeding water
to a stream is the watershed
Stream ordering within a drainage system
Drainage Patterns
What situation will lead to a radial pattern? What about a trellis?
Stream discharge
• Stream discharge is the volume of water passing a point in a specific amount of
time
• (e.g., m3/s)
• Q is stream discharge (volume/time)
• A is the cross-sectional area of the stream channel (shown here in blue)
• V is flow velocity (the average of the velocities indicated by the arrows)
Q = AV
Flow can be laminar or turbulent
Which type of flow is likely to be
most effective at transporting
sediment? Why?
The amount of water in a river’s watershed
increases downstream, with the addition of
tributaries
Thalweg
• The thalweg is the
part of the stream
that has the highest
flow velocity.
What is the relationship
between the water
velocity and depth
shown by these
diagrams?
Materials are carried in different ways within a
stream
Suspended load - Bed
load - Dissolved load
What is meant by “dissolved load”?
Hjulstrom Diagram
•
•
•
The Hjulstrom Diagram
shows the relationship
between sediment size
and the water’s ability to
erode and transport
sediments
For sand and larger sizes
there is a positive
relationship between
erodability and velocity.
For silt and smaller sizes
this same relationship
applies to deposition, but
not to erosion. It takes
much high water
velocities to erode clay
once it has been
deposited.
Why is clay so hard to erode?
There are three types of stream channels:
straight, meandering, and braided
Straight
Meandering
Cut-off meander bends form Oxbow Lakes
Braided
Cedar Rapids,
Iowa - 2008
Red River in
Manitoba - 1997
Flooding is a natural
process in healthy
streams
Flood Animation
Normal
discharge
“Bank-full”
“Flood-stage”
Why is there a delay between the
rain event and the flood peak?
Normal versus flood-stage
Streams may develop a graded profile
What is meant by “graded profile”?
Stream Piracy
Fluvial landscape evolution
Fluvial systems adjust to changes in Base
Level
Dams can cause problems
What other types of problems – upstream and downstream – can be
caused by the construction of dams?
Incised Channels and Terraces
Fluvial sediment builds Alluvial Fans and
Deltas
Death Valley, California
Mississippi Delta, Louisiana
Delta Terminology
Mississippi Delta avulsion
What does avulsion mean?
Water problems exist on a global scale
Which factors lead to the likelihood
that a country will face water stress?
Drainage System Maintenance
• We need to look after drainage systems to avoid:
– polluted runoff
Drainage System Maintenance
– … and anoxic dead zones
Label the fluvial processes and landforms
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