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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.
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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 –4th order, around 3-4 m3/sec—10-20 m wide DA around 400 km2
Annual mean discharge of the Crowsnest River at Frank
Exceedance probability (percentiles)
99.9 99 90 70 50 30 20 10 1 0.1
Non-exceedence probability (percentiles)
Recurrence interval is the reciprocal of the probability
Based on this plot we can estimate that 1 year in 100 there will be a year wetter than 20m3/s and a year drier than 0.8 m3/s, if there is no-longterm climate change
Annual average 6.0 m3/s
2 yr out of 4 discharge above this line
Annual average 4.1 m3/s
3 yr out of 4 discharge above this line
Annual average 2.7 m3/s
After Ottawa R dams
River Management can significantly alter the seasonal hydrograph
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?
Short-term response to a precipitation event
How would you expect deforestation to influence this response?
---Consider the terms of the hydrological balance equation
How does deforestation affect the hydrological balance
[P-E]DA – DS/Dt
Fig 5-2 in your text
We can explain the effects of deforestation on the hydrograph in terms of the hydrological balance, mainly in terms of changes in Evaporation and storage.
Biological Impacts that generally occur when watersheds are hydrologically disturbed by deforestation
Patterns in stream flow and how they generate habitat diversity in streams
Oxbow lake and the Chippewa River. Eau Claire, Wisconsin.
Meander pattern of the Sacramento River, CA, note old abandoned channels and oxbows, and the encroachment of agriculture on the river channel.
Such restoration can involve breaching of levees and removal of dams with the aim of.re-establishing natural floodplain vegetation and habitat
In streams and rivers of different sizes
Rivers meander when they are traveling on top of a relatively flat surface.
Streams flow down hill and take the path of least resistance, however the path is usually a meandering instead of straight
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
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,
Geol. Soc. America, Bull., v. 71,
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
Showing old river channels
When rivers cut deeply into the landscape the meander pattern becomes entrenched and from then on shifts downward only.
If you want to learn more about the landforms and deposits created by running water, with particular reference to western Canadian watersheds, take
Fluvial Geomorphology—Hester Jiskoot
Other courses of relevence are
Integrated Watershed Management—Jim Byrne
Correlations between seasonal river discharge and landings of American Lobster and Atlantic halibat in the Gulf of St. Lawrence.
J.Fish. Res. Bd. Can. 30:856-859.