Download How do discharge, width, depth, and velocity change along a river

How do discharge, width, depth, and velocity change
along a river course, as watershed area increases and
more and more runoff enters the river?
Discharge increases linearly with watershed area as you move down a
river if it remains more or less the same runoff zone.
Discharge is the product of stream width, mean depth and mean
velocity: therefore each of these also tends to increase with watershed
area.
Width tends to increase the most rapidly, then mean depth, and velocity
the least rapidly along the stream course
If we plot these relationships on a log-log plot the slopes tend to add up to 1
Because the total discharge is the product of all three factors.
o
1000
1.0
oo
o
o
100
Discharge
m3/sec
o
Slope velocity line =0.2
Velocity m/sec
xo
o
o
Slope of depth line=0.25 o
oo
oo
x
x
xx
o
o
10
100
o
Slope ofowidth line =0.55
o
1.0
Depth
m
10
0.1
o
Slope of discharge line=1
1.0
x
x
x
0.1
x
Watershed Area (km2)
0.1
1,0
Width
m
The pattern of flow in rivers and streams creates a diversity of habitats
both within the stream and on the floodplain.
Much of this pattern results from the tendency for rivers and streams to
meander instead of following a straight path
Meander is a result of friction between the stream bed and the stream and is
the pattern of flow that dissipates the energy in the stream most rapidly.
This meandering pattern moves downstream because each year erosion
occurs on the outer (deep) edge of the loop and deposition occurs on the
inner (shallow) edge.
The erosion that occurs during a flood even may cause the river to take a
shortcut from one loop to the next--thus leaving the loop below this
shortcut as an oxbow lake.
If the land rises, the river cuts deeper and no longer meanders,
technically. Instead, it exhibits an entrenched meander. In other words, it
is fixed into its previously meandering pattern. The Grand Canyon is a
dramatic example.
Streams flow down hill and take the path of least resistance, however the path is
usually a meandering instead of straight
http://www.kented.org.uk/ngfl/rivers/River%20Articles/meander.htm
http://waterknowledge.colostate.edu/meander.htm
Meander pattern of the Sacramento River, CA, not old abandoned channels
and oxbows, and the encroachment of agriculture on the river channel.
http://www.uoregon.edu/~millerm/meander.html
Oldman R
Below
Summerview
Showing old
river
channels
An important reference on River Meanders
Leopold, L.B., and M.G. Wolman, 1960,
River Meanders:
Geol. Soc. America, Bull., v. 71,
pp. 769-794.
http://waterknowledge.colostate.edu/meander.htm
Rivers often simultaneously occupy several of their historical channels at once.
We call this type of river channel braided
A good example of braiding in the river channel
http://www.sciencelives.com/braid.html
Oxbow lake and the Chippewa River. Eau Claire, Wisconsin.
http://www.uoregon.edu/~millerm/meander.html
Agricultural development often encroaches on the river channel
If you want to learn more about the landforms and deposits created by running
water, with particular reference to western Canadian watersheds, take
Geography 3035
Fluvial Geomorphology—Bob Rogerson
Other courses of relevence are
Geography 4015
Integrated Watershed Management—Jim Byrne
And
Geography 4012
Hydrology—Stefan Kienzle
Standing Water – lakes and ponds
Large storage pools within drainage systems
Lakes result from either from barriers to drainage or
when depressions (or excavations) form along a
drainage system
Majority of lakes are found in glaciated areas and are
formed by glacial action
Others are formed by geological faulting, volcanic
action, or sea level changes
Beavers form ponds by impeding drainage and then excavate the basins and
seal the dam with the mud they dig up—Humans do much the same thing.
The vast majority of lakes in the world occur in glaciated areas—74%
Glaciers can form lakes in the following ways:
Ice can impound the flow in a drainage system
The flow can be blocked by glacial till or
moraines
Ice flow can scour or deepen a basin
Ice blocks in till can melt out to form a “kettle” or
“pothole” which then fills up with seepage or
surface flow
Proglacial lakes
•Following the retreat of the last
glaciation most of the Canadian landscape
was covered by proglacial lakes
•Species tolerant of coldwater (salmonid
and coregonids) became very widespread.
•Opportunities for dispersal of
cool and warmwater species were much more limited
because these water bodies disappeared with the ice.
Lake Memphremagog-Quebec. A glacial moraine blocked the outflow, and
glacial scour deepened the basin to over 100 m
Waterton Lakes have a similar origin—Both Waterton and Memphremagog
have contain glacial relict animal species in their deep waters.
Cirque lakes in the rockies
•Glaciers in headwater valleys tend to
scour out a bowl shaped basin and the
excavated material helps impede the
drainage and deepens the lake that forms
when the glacier recedes
•Drainage in Moraine lake was further
impeded by a large landslide across the
outflow
•Most cirque lakes are fishless unless
stocked
Pothole or kettle lake formed in glacial --usually small < 30 ha, but can be
quite deep--10-40 m. Watersheds are very small.
•Large blocks of ice left behind in moraines and till mounds as glaciers melt
and grow “stagnant”.
•As they gradually melt, they leave behind a depression in the till that fills by
seepage
•Many of the small pothole lakes in Alberta are kettle lakes.
Another type of basin associated with ice melting.
Polygonal ponds
near the Lena
River, Russia
Polygon ponds form along the Arctic coastal lowlands.
Form in the summer as wedges of ice melt within the permafrost to form small
polygonal basins (around 50 m across) that fill up with surface water.
See Fig. 6.2 in your text
Riverine lakes—develop on wide flood plains
Oxbow lakes are examples—abandoned meanders
Most of the large lakes in the world are Tectonic lakes
Many occupy ancient basins called grabens—formed by large geological faults
Rocks before faulting
Lake in a symmetrical graben
Lake in a tilted graben
Lake Baikal