Below are two schematic drawings of streams flowing acoss two contour lines (cha

Question

Below are two schematic drawings of streams flowing acoss two contour lines (changes in elevation) from Point A to Point 8. Calculate the gradents of each of these streams and add the answer to the attached answer worksheet Example A The contour lines are the vertical lines and the stream is the ine unning between A and B The contour lines tell you the change in elevation Every contour line crossed is one contour interval of elevation In this example, the contour interval is 25 m and two contour lines are crossed The horizontal distance is based on the map scale The map scale in this example is 1 15000, which means that every 1 cm on the map is 15.000 cm in real life In this example, the length of the line running between A and B on the map is 2 cm Answer the following questions on the attached answer worksheet a) What is the change in elevation in meters between Points A and B? b) What is the horizontal distance between Points A and B in kilometers? c) The stream gradient is the change in elevation divided by the horizontal distance What is the stream gradent in m/km Example B

Explanation / Answer

Ex. A

a). Change in elevation

Contour interval 25ft

So elevation difference between A and B = 25*2

=50 ft = 15.24 meter

b) Scale = 1: 15000

distance between A- B 2 cm

Horizontal distance = 2*15000 cm

= 30000 cm

= 0.3 km

c) Stream gradient

= change in elevation/ horizontal distance

= 15.24/0.3 ft/km

= 50.8 m

Exercise B

a) change in elevation

Contour difference= 10 m

Change in elevation between A and B = 4*10

=40 m

b) Horizontal distance

Scale = 1:5000,

distance between point A and B= 2 cm

Horizontal distance = 2*5000 cm

= 10000 cm

= 0.1 km

c) Stream gradient= change in elevation/horizontal distance

=40 meter/0.1km

= 131.23/0.1 (40 m= 131.23 km)

=1312.3 feet/km

Exercise C

a) 3.2 miles saved by cutoff

(8.25- 5.05)

b) Gradient using oxbow

Elevation difference = 119-116 ft

=3 ft

Gradient= elevation difference/ horizontal distance

=3/8.25

= .36 ft/mile

c) Gradient using pecan point cutoff

= 3/5.05 ft/ mile

= 0.59 ft/ mile

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