Stream biology can be greatly
impacted when watersheds are
hydrologically disturbed by
deforestation
Scouring—↑flashiness of the hydrograph → scour and gravel shift.
Siltation—↑ overland flow vs percolation→ ↑fine particle transport to
streams.
•plug up interstitial spaces in gravels and ↓ water percolation and oxygen
supply to interstitial benthic organisms and fish eggs.
•↑particle transport → ↑abrasion (algae and invertebrates)
•↑suspended particles + ↑dissolved organic matter→↓light penetration
Nutrient enrichment—↑ loading of N & P to the stream ↑ algal growth
on the substrate.
Warming & illumination—due to↓ forest cover ↑light penetration
•warming → changed species composition (↓cold-water species ↑warmwater species)
•↑illumination → ↑ algal growth on rocks
The pattern of flow in rivers and streams creates a diversity of habitats
both within the stream and on the floodplain.
Rivers meander when they are traveling on top of a
relatively flat surface.
•Meander is a result of friction between the stream
and its bed. The pattern of flow that dissipates the
stream’s energy most rapidly is a meandering helical
pattern.
•The meander pattern shifts constantly since the river
is cutting the bank on the outside of meander loops
and depositing alluvial sediment on the inside.
meanders
In streams and rivers of
different sizes
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
It takes more
velocity to suspend
and move larger
particles
The erosion that occurs during a flood even may cause the river to take a shortcut from
one loop to the next--thus cutoff loop will remain as an oxbow lake.
Oxbow lake
forming from a
river meander
Oxbow lakes and braided channels on the Upper Amazon River
http://muller.lbl.gov/travel_photos/AmazonWebPages/AmazonWebPages-Thumbnails/1.jpg
The physical stresses on the river bed during
floods often cause a river to change course.
The river valley contains many old channels
superimposed on each other
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
Oldman R
Below
Summerview
Showing old
river
channels
When rivers cut deeply into the landscape the meander pattern becomes entrenched
and from then on shifts downward only.
http://courses.missouristate.edu/EMantei/creative/WeathStrem/entrenched.jpg
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