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.

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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

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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