Activity 9.5 Relief and Gradient (Slope) Analysis Date: Name: some friends find

Question

Activity 9.5 Relief and Gradient (Slope) Analysis Date: Name: some friends find a nice place along the Merced River for a picnic. You have a topographic con- the decide to gain a bett map (Fig. A5. tour map (Fig. A9.5.1) better t) in which the index contours are labeled in feet From your resting place at point A. you vantage point by walking up to point B. 6200 8 North 6Merced River C1000 feet Figure A9.5. A Using the labeled elevations of the index contours as your guide, what is the contour interval (the elevation difference B You have a bar scale on the map that indicates a distance of 1000 ft. on the ground in your picnic area. How long is that C What is the horizontal distance from A to B measured along a straight line in f? (Hint: Measure the distance from A to B -ft. between two adjacent contours) in Fig. A95.1? bar scale on the map in mm?mm using a metric ruler on the map, and then use your measurement of how many mm on the map equal 1000 ft. in the field to find the answer using proportions.) ft. D What is the average gradint elevation change divided by horizontal distance, both expressed in ft.) along a straight line from A to B? -

Explanation / Answer

a)

In the map it is clearly visible that between the Two marked contours there are 5 contour intervals so contour interval = diffrence between two marked contours / 5 = 6400-6200/5 = 200/5 = 40

so the contour interval is 40 feet

b)

In any topographic map the least measuring distance is its contour interval that is here 40 feet, so the bar scale should be such that it can read least count so 1000feet is divided by 40feet will give the bar scale divisions

no of divisions = 1000/40 = 25

each division = 1 mm

so lenth of the scale in terms of mm = 1mm x 25 divisions = 25 mm

c)

Measured by the bar scale the distance between the points A to B = 51 mm

1 mm = 40 feet

the distance between the points A to B in feet = 51 x 40 = 2040 feet

d)

Elevation change between point A to B = contour value of point B - Contour value of point A

contour value of Point A = 6100 feet ( 6000 + 40 + 40+ 20)

contour value of Point B = 6560 feet ( 6400 + 40 + 40+ 40+40)

Elvation change = 6560 - 6100 = 460 feet

the distance between the points A to B in feet = 2040 feet (above)

Gradient between A to B = 460 / 2040 = 0.2255

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