Scouring

1
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 illuminationdue to? forest cover
  ?light penetration
• warming ? changed species composition
  (?cold-water species ?warm-water species)
• ?illumination ? ? algal growth on rocks

2
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 streams 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.

3
meanders In streams and rivers of different sizes
4
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/River20Artic
les/meander.htm
5
(No Transcript)
6
It takes more velocity to suspend and move larger
particles
7
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
8
Oxbow lakes and braided channels on the Upper
Amazon River
http//muller.lbl.gov/travel_photos/AmazonWebPages
/AmazonWebPages-Thumbnails/1.jpg
9
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
10
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
11
Oldman R Below Summerview Showing old river
channels
12
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
13
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
GeomorphologyBob Rogerson Other courses of
relevence are Geography 4015 Integrated
Watershed ManagementJim Byrne And Geography
4012 HydrologyStefan Kienzle