Objectives #23 (November
By the end of today's class, you should be able to do the following:
w Review: Using topographic maps, determine the difference between steep and gentle slopes, find the elevation of a point, find the distance between two points, determine the direction a stream flows, identify a hill, a valley, a closed depression (basin), a stream, an intermittent stream, and a lake.
w Explain the terms meander, oxbow, and floodplain.
Complete the following three activities at your own pace. A handout with these activities appears here.
Sketch a profile illustrating a floodplain. Explain how a floodplain
would appear on a topographic map. Using topographic quadrangles
from two groups (named below), identify any floodplains you can see, and
also point out meanders, and oxbows.
ACTIVITY TWO: On the Galena, Illinois
quadrangle, find the word “RAWLINS” in the middle of the map. Between
the W and the L in RAWLINS flows an intermittent stream. Using tracing
paper, outline the watershed (drainage basin) for this stream. Follow
1) Place the tracing paper over the stream area and mark on the paper a few landmarks that appear on the map. When the paper slides around, you’ll be able to re-orient it using these landmarks.
2) Using blue pencil, trace the course of several streams that occur in the area, including the one we are working on.
3) Find the highest land between the streams and our stream of interest. Draw a very light line following the general location of this high area.
4) Now, get more precise: Locate the very highest places between the streams. Ask yourself, “If rain fell to the land surface here and started flowing downhill, which way would it flow?” If it goes in a direction that makes it end up in our stream of interest, it is part of that watershed! Draw the exact line showing the boundary of the watershed.
|ACTIVITY THREE: The
Preparation: Smooth the surface of the sand in the stream table. Make it reach the level of the metal plate on the upstream side, and gradually decrease until it ends at the tape mark on the side of the table. The surface should be perfectly smooth and even, like a perfect ramp.
Experiment A: Turn the water on by flipping the switch. Adjust the discharge by turning the valve until there is a small but continuous flow. This flow will create a stream. Carefully observe the stream for the next 5-10 minutes. It will change continuously during that time, and your job is to observe what happens.
w How does the stream channel form? What shape does it take? Does the shape change over time?
w Where does erosion occur? Where does deposition occur? Does this change over time? If so, how?
What feature forms where the stream
meets the ocean? Sketch it. Place a toothpick near the main channel in
this area. Watch it for a few minutes. What happens? If you build
your house on a feature like this, what is likely to happen to it?