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How to calculate stream order
Another way to look at a drainage systemis to treat it as a hierarchical network
Stream order
Stream order increases by 1 each time two streams of the same order join
No change in stream order occurs when two streams of different order joinEg a 3rd order stream receiving a 1st order stream remains a 3rd order stream.
1 km
x
Outline the Watershed of thissmall tributary to Threepoint Cr. at
the point x
First study the altitudinal contours
Locate the 5000’5500’& the 6000’Contours
What are the highest points in the area
How to map a watershed
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Now ask yourself which way would water flow from various points around the creek?
The flow path is perpendicular to the contours.
The area that delivers water to the point x includes all of the points that flow toward x, and none of the points that flow away from x
x
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Start at x , and extend a line up to the east ridge, and follow the ridgetop up to the top of Mt. Barwell, and then extend the line through the saddle and onto the small peak west of the mountain, and along the west ridge back to
the point x
All points that drain into the creek, and down
to point x will be contained within this area, and all points that drain away, should be outside the area
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The area of this watershed is 4.5 km2.
What is the avg annual discharge at
the point x?
From the runoff map we assign a value of 0.6 m/year
0.6m/yr x 4.5 x 106m2= 2.7 x 10 6 m3/yr
=0.1 m3/s
What are the units of flow measurement?Discharge (R or Q)—L3/timeVelocity (v)—L/time
Discharge can be measured by X-sectional area (L2) of the stream at a point times mean velocity (L/s)
Mean depth (L) x width (L) x mean velocity (L/s)
If the mean discharge of the creek is 0.1 m3/sec, and the mean width at the point “x” is 4 m, and the mean depth is 0.2 m, what is the mean water velocity?
V (L/t)=Q (L3/t) /(depth (L) * width (L))V= 0.1 m3/sec/(0.2m * 4m) = 0.125 m/sec
Q=r*DA
As you move down a watershed, the drainage area and discharge both increase
x4
x3
x2
x1
x1x3x4
x2
Stream cross-section
At x1 the stream is 1st order
So does the stream order
At x2 the stream is 2nd order
At x3 the stream is 3rd order
At x4the stream is ?
1st order streams –around 0.01-0.1 m3/sAround a 1-2 m wide
Drainage area 0.2-1 km2
2nd order stream in Quebec and NYAround 0.1 m3/sec, 3-4 m wideDrainage area 2-5 km2
Storm Creek, a tributary of the Highwood, 2nd order, around 0.2 m3/sec—3-5 m wideDrainage area around 8 km2
Johnston Creak above the canyon –3rd order, around 0.6 m3/s—6-9 m wideDrainage area around 25 km2
Highwood River –4th order, 8 m3/s—10-20 m wide DA around 400 km2
Waterton River –5th order, around 15 m3/s—15-25 m wide DA around 600 km2
Oldman River –7th order, around 40 m3/s—50-100 m wide, DA = 17,000 km2
Athabasca R. at Fort McMurray– 8th order, 2-300 m3/s –2-300 m wide, DA 30,000 km2
The Slave River is the largest Alberta River—9th order, discharge is 1500 m3/s, width is over 1km and Drainage Area is 600,000 km2
St.Lawrence River
10th order
Discharge around104 m3/s
Width 2-3 kmDA = 1.2 x 106 km2