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 ↑warm-water 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