Presentation on theme: "Fish and other aquatic biota that live in rivers and streams have to contend with the variability of the flow regime. How variable is runoff/discharge?"— Presentation transcript:
Fish and other aquatic biota that live in rivers and streams have to contend with the variability of the flow regime. How variable is runoff/discharge? From year to year? From month to month From day to day
Crowsnest River –4 th order, around 3-4 m 3 /sec—10-20 m wide DA around 400 km2
Annual mean discharge of the Crowsnest River at Frank m 3 /s 20
Annual mean discharge of the Crowsnest River at Frank m 3 /s Exceedence probability 0.90 0.50 0.25 0.10 0.75 90 percentile 75 percentile 50 percentile 25 percentile 10 percentile 199512 19919.8 20058.7 19936.3 20026.2 19965.9 19925.5 20044.6 19994.4 19944.2 19864.1 19903.8 19883.7 19893.5 19983.1 19872.5 19971.7 20031.5 20001.4 20011.2
10.0 1.0 100 o o o We can now plot these data on cumulative probability paper Non-exceedence probability (percentiles) Based on this plot we can estimate that 1 year in 100 there will be a year wetter than 20m 3 /s and a year drier than 0.8 m 3 /s, if there is no-longterm climate change Discharge m 3 /sec Exceedance probability (percentiles) 99.9 99 90 70 50 30 20 10 1 0.1 o o Recurrence interval is the reciprocal of the probability
1 yr out of 4 discharge is above this line 3 yr out of 4 discharge above this line Annual average 2.7 m3/s 2 yr out of 4 discharge above this line Annual average 4.1 m3/s Annual average 6.0 m3/s
River Management can significantly alter the seasonal hydrograph Before Ottawa R dams After Ottawa R dams
St.Lawrence River Flood Plain at Lac St. Pierre—has rarely been flooded since the late fifties—What effect might this have on the river?
The hydrograph Short-term response to a precipitation event How would you expect deforestation to influence this response? ---Consider the terms of the hydrological balance equation
Human activities can markedly influence the shape of the hydrograph Deforestation reduces the lag time raises the peak reduces the base flow Fig 5-2 in your text How does deforestation affect the hydrological balance [P-E]DA – S/ t
The hysteresis curve can be used to estimate the storage capacity Discharge m3/sec Precipation For a system with no storage capacity like a storm sewer, the hydrograph will tend to stick close to the center line
Patterns in stream flow and how they generate habitat diversity in streams Annual discharge patterns—floodplain habitats Stream meander—pool/riffle alternations Stream channel changes over time—oxbow lakes, braided streams
Flood plain habitats greatly increase biodiversity in river systems. They contribute mostly temporary wetlands, but some remain as permanent because of groundwater inputs. Important for Waterfowl, mammals, amphibians, fish, aquatic insects, molluscs etc. Most of the species found in flood plain wetlands would be lost from the river if the floodplain were not allowed to be flooded regularly. Flood plains depend on seasonal variability in river discharge
Oxbow lake and the Chippewa River. Eau Claire, Wisconsin. http://www.uoregon.edu/~millerm/meander.html River flood plains often undergo extensive urban development
Meander pattern of the Sacramento River, CA, note old abandoned channels and oxbows, and the encroachment of agriculture on the river channel. http://www.uoregon.edu/~millerm/meander.html
http://vernalfishandwildlife.fws.gov/vernalfloodplain.jpg Such restoration can involve breaching of levees and removal of dams with the aim of.re-establishing natural floodplain vegetation and habitat Green River, Wyoming
meanders In streams and rivers of different sizes
Rivers meander when they are traveling on top of a relatively flat surface. a straight line is not the most efficient path for water to flow. A meandering river will dissipate more energy through friction with the riverbed than one that flows straight 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.
http://www.kented.org.uk/ngfl/rivers/River%20Articles/meander.htm Streams flow down hill and take the path of least resistance, however the path is usually a meandering instead of straight
Oxbow lake forming from a river meander 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 lakes and braided channels on the Upper Amazon River http://muller.lbl.gov/travel_photos/AmazonWebPages/AmazonWebPages-Thumbnails/1.jpg
http://waterknowledge.colostate.edu/meander.htm 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. 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
A good example of braiding in the river channel Rivers often simultaneously occupy several of their historical channels at once. We call this type of river channel braided
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
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