how do you calculate the gradient of a slope as indicated in topographical map reading?

Question

please indicate formula and examples.

Answer 1

1. Draw a line on the topo map over the place where you want to calculate slope.
2. Read the elevation at each end of the line (example - one end is on a 1220ft elev'n contour and the other may be on a 1480ft elev'n contour. If the ends are between contour lines, you have to estimate the elev'n.
3. The difference in elevation is the RISE (1480ft - 1220ft = 260ft).
4. Measure the length of the line and get its length in map units. For example if the line is 3 inches, and the map is 1:25,000 scale, the RUN distance is (3in)x25,000 = 6250ft.
5. Be sure your RISE and RUN are in the same units (feet is usually best).
6. SLOPE = RISE / RUN so in this example Slope = 260ft / 6250 ft or .0416 (no units on slope)...this can also be stated as 4.16% slope.

Hope this helps.

Answer 2

The formula would be your contour scaling and the scale of the topo map. If each contour line represents 100 feet, say, and two contour lines are 1/8 inch apart, then whatever scale the map is (1 inch per mile, or whatever) will give you the slope of the terrain for 1/8 of an inch. It means that the ground is 1/8 x 5,280 feet higher at the next contour line.

Answer 3

Scale off the distance between contour lines in the direction in which you want the gradient. Divide the contour interval by the distance.
g = ∆c/d

Answer 4

With the help of countour lines, by ccounting there numberes in one cm or inch u can calculate the gradient. Moreover there are different methods of calclating the above. i.e. Robinson Method.

Answer 5

Use the isohyets on the map, figure out the vertical exaggeration and there ya have it.