STREAM MORPHOLOGY
Stream morphology (fluvial geomorphology) is the study of how the watershed
and stream channel change over time and space. Today we will use stream
tables as a model to learn about rivers and how they behave.
Models are used extensively in science to accurately depict processes and
mechanisms that we can not readily observe in the field. Today you will recreate
many fluvial processes on a small scale, and observe processes that you may
not be able to see outside!
Important Stream Variables
Discharge, Velocity, Gradient, Path, Morphology, Material
Predictions
How does a stream’s velocity change as discharge increases or decreases?
How does the gradient of the stream affect erosion rates?
How do meanders and straight stretches affect the velocity of the stream?
Do different materials change the erosion and deposition along a stream?
Experiment Procedure
1. Let’s test three different discharge amounts to see how the stream
changes, 1) ½ bottle, 2) 1 bottle , 3) 1 ½ bottle.
2. Set the slope of stream table to 1 block.
3. What natural event are we modeling when we change the discharge?
4. What changes when more discharge is added in each of the 3 trials?
MAKE SURE TO REBUILD CHANNEL BETWEEN EACH TEST!!!!
5. Let’s test three different stream gradients (slopes) to see if the velocity of
the stream changes, 1)1 block, 2) 2 blocks, 3) 3 blocks.
6. Set the discharge to be the same each of the three times, ½ bottle.
7. Does the water move faster or slower as the gradient increases?
8. Where would you find streams with steep, medium, and shallow gradients?
MAKE SURE TO REBUILD CHANNEL BETWEEN EACH TEST!!!!
8. Let’s test different stream paths to see if velocity and erosion changes
along the stream path.
9. Set the stream discharge to ½ bottle and slope to 1 block.
10. In your stream table make two meanders in the stream.
11. Now let’s look at the erosion and deposition along a stream. Where is the
sediment being eroded, where is it being deposited? DRAW A PICTURE
12. Use the three different grain sizes and other materials to see which the
water erodes away first. Record what you find below. Which material
erodes easily and which material is more difficult to erode?
Review
Look back at your predictions, were they correct? Explain in words &/or drawings
DAMS & STREAM MORPHOLOGY
Both human and natural dams can drastically reshape a river system. Dams
affect the geomorphology of river systems in three major ways;
1. Create a reservoir
2. Regulate and control discharge levels
3. Change sediment levels
Part 1: Experimental Procedure
1. Build an earthen dam in the middle of the stream table. Make sure the top
of dam is 2 cm below stream table edge, and add your town below the
dam.
2. Add water to fill reservoir behind dam (only 2/3 of the way).
Questions
3. Right now the dam is holding and everything is good in the town. Let’s think
of some changes that have occurred to the river.
4. Since putting the dam in how has the shape of the river changed above
and below the dam? Did you have to change the shape of the river to insert
the dam?
5. Before the dam, the river moved naturally and had floods and droughts,
now the discharge only changes slightly. Do you think the river will be the
same shape as it is now in 1000 years?
6. Before the dam sediment was carried downriver, where is that sediment
now?
7. What type of natural dams are there? What could dam a river that occurs
naturally?
Part 2: Experimental Procedure
8. Now add water to the reservoir, a little at a time. Watch what happens as
the water gets too high for the dam!
Questions
9. Dams usually fail by 1) having soft or weak spots give out, OR 2) storing
too much water and being overtopped by water. How did your earthen dam
fail?
10. After the dam failed, is the river shaped like it was before the dam?
Part 3: Experimental Procedure
11. Like before create a dam in the middle of your stream table, but this time
use the plastic to make a more secure dam.
12. Add water to fill reservoir (only 2/3 of the way!)
13. Now add water to the reservoir and watch what happens!
Questions
15. How did your dam fail this time?
16. What could cause such a large amount of water to fill the reservoir above
the dam?
17. Although most dams are safe, do you think putting a dam on a river is a
good idea or a bad idea? Explain your reasoning using complete sentences
and vocabulary!