Name:_____________________________
Lab3: Contour Mapping and Topographic Profile
MATERIALS NEEDED: Ruler, pencil, eraser, calculator
QUESTION 1: CONTOUR LINES DRAWING
1. Using an interval of 50 ft draw contour lines on the map below. You are constructing a topographic map for an island. The spot heights are feet above sea level. The coastline, sea level, is 0 ft. Initially you may want to draw the contours lightly in pencil in case you need to erase them. Think about what you know about the pattern of the elevation of an island in order to guide you once you get started. Once all contour lines are drawn, mark the index contours using a heavier (thicker) line or ink. Give careful consideration to the elevations at which you should draw them. Make sure you label the contour lines.
2. On graph paper draw a topographic profile along the river shown on the island from its source to the point it drains into the ocean. This type of profile is commonly referred to as a long-profile.
NOTE: Usually, the long-profile starts with the source of the river at distance=0.
3. Calculate the vertical exaggeration and write it next to the profile. Show your calculations here.
4. What is the average gradient of the river? To do this, calculate the gradient from the source of the river to the point it enters into the ocean (see Labs 1 and 2 for how to calculate a gradient).
Record your answer in feet per mile.
Make sure you measure the true distance of the river, i.e., it does not flow in a truly straight line (use a piece of string to measure the length of the river).
Show all the steps in your calculations and the conversion factors you use.
NOTE: You will have to extrapolate the elevation of the source of the river, unless one of your contours is crossing it.
5. Give the answer obtained in question 4 as meter per kilometer.
6. In question 4 you have calculated the average gradient. However, you can see from the topographic profile that the slope of the river varies.
Where is the gradient steepest? Show this with an arrow on your profile.
What is the gradient for this part (reach) of the river (in feet per mile)?
7. Give the answer obtained in question 6 as meter per kilometer.
8. What is the total relief shown on the map?
9. Give the general orientation followed by the river on the island as it is draining into the ocean (from its source to its mouth) both as an azimuth and as a compass point.