Embedded Files
Introduction
In the Fiesinger Lab 101 we were able to capture some fluvial geomorphic processes using a Emriver Em2 Stream Table. It was really cool to be able to control the hydrology of the system and see the different processes at such a small scale. It was crazy to see how fast things could happen and how fast a river system can change based off small adjustments. The Alpha thermoset plastic modeling sediment is 60% lighter than sand, making the processes happen quicker. The different colors represent the sediment size.
Flume Controls
To control the water discharge (Q) we used the flow controller located at the downstream side of the flume. We were able to adjust the amount of water being discharge by simply turning a knob on the flow controller. Using this controller, we were able to create different water processes.
The slope of the Emriver Em2 Stream Table has a standard box slope of 3.5 degrees, but to control the slope of the flume we could place a block on the downstream side of the table or raise and lower the standpipe. Another idea is the increased amount on sediment on either side of the table. Both the slope and the water discharge control the sediment discharge.
To control the sediment discharge (Qs) with the flume you had to adjust the slope or the water discharge. An increase in slope would increase the amount of sediment discharge. An increase in water discharge would increase the amount of sediment discharge as well. When you increase both the water discharge and the slope of the flume it will lead to high sediment discharge.
The profile of the stream was fun to play with. To control this, we could place the sediment where we wanted, create our own channels using our hands, control the water discharge, change the slope, etc. The possibilities are endless when controlling the profile of a stream. To create deeper channels for the flume we might increase the sediment, increase slope, and increase water discharge. For shallow areas we might slow the water discharge and decrease the slope.
The base level of the flume was essentially the standpipe. The standpipe is like the "hollow plug" located on the downstream side of the flume. We could change the base level of the stream by raising and lowering the standpipe. When we would raise the standpipe, it would decrease the slope of the flume and begin to create a little reservoir. When we lowered the standpipe, the slope would increase causing an increase in sediment and water discharge.
Fluvial Geomorphic Processes
These photos show the fluvial geomorphic processes of bank erosion, bed erosion, deposition, and sediment transportation. Bank erosion is caused by the flow of the water hitting the bank. Bank erosion depends on the sediment, vegetation, and velocity of the water. Bed erosion in this photo was seen when we put a culvert/bridge into the flume. There was a hydraulic jump from the object to the stream bed. This caused bed erosion that eventually created a pool. Sediment deposition was seen when we raised the standpipe. Sediment was being transported from the stream and depositing near the base level. This sediment deposition caused a delta at the base level.
Fluvial Geomorphic Mechanisms
Meandering
The image to the right sort of shows a meandering stream. The water flows from side to side and contains bends and curves. The water flows slower on the inside of the bends and faster on the outside of the bends. The outside bends tend to cause faster bank erosion due to the high flows.
Avulsion
Avulsion is the process of the water cutting back at the bank trying to create a new channel. It is simply the water trying to find the fastest path of travel. In the image to the right, you can see the little head cuts from the mainstream.
Grain Size Sorting
This image to left shows the grain size sorting of the stream bed. The color-coded media helps distinguish the particle size. Average particle sizes for the different colors are: Yellow: 1.4 mm, White: 1.0 mm, Black: 0.7 mm, Red: 0.4 mm. Size particles are sorted by the flow of the river and its river profile.
Braiding and Chute Dissection
To the left we are able to see braiding and chute dissection. Braiding is the when the stream channel is separated by smaller channels. These braided channels are usually temporary because they are separated by sediment deposits and overtime, they become uniform. Chute dissection is the little run-offs from the stream. Overtime they become disconnected due to sediment deposits. As you can see the chute (black sediment) was disconnected by the sediment deposit (white and yellow sediment).
Structural Forcing
The image to the left shows structural forcing. In this case it was the woody debris and as you can see the sediment deposit in front and side of the structure. Structural forces the channel to form different fluvial geomorphic units. Structure like rocks, debris, anthropogenic features, etc. all effect the fluvial geomorphology.
Events
The events we witnessed in this experiment were small flood, big flood, and channel realignment. When we created a small flood there was more processes and mechanisms happening. When we created a big flood even more processes and mechanisms occurred. I remember when we created the big flood the culvert/bridge we put in place was absolutely destroyed. There was a lot of bed erosion at the end of the culvert. The impact of a small flood does not affect the streams geomorphology as much. The stream we created handled the small flood pretty well, but the event of a big flood changed the river system majorly. There are processes and mechanisms you see above happened rapidly. In this experiment we witness overbank flow, bank full flow, and base flow. We witnessed overbank flow when we increased the flow control. Overbank flow created new channels and created braiding. Bank full flow was seen when we did the small flood. It caused a lot more bank erosion than the simple base flow. We could really see the base flow after the small flood and big flood. We were able to see the foundation of the stream and its structure. The role of hyporheic flow in this experiment created new channels. Water seepage happened just about everywhere within the flume. To me it seemed it created a lot of the avulsions within the stream. Recession limb flows created sediment deposits. I noticed this when we created a big flood and suddenly decreased the flow control. The sediment nearly "stopped in its tracks". This experiment was really fun, and it was really cool to see these events at such a small scale.
Page updated
Google Sites
Report abuse