Observation summary - Group 1

Initial Test: (Jan 12)
Parameters:  Sediment supply: None
                   Stream Velocity: 35
                   Gradient: 2 deg.
                   Initial channel shape: None
                   Base Level: 3.6 cm

Hypothesis: The water will create initial channels then create sub channels similar to a braided stream. Because we are starting with no particular calculated measurements this will probably happen instead of sustaining a true meander.  
Observations: We began the experiment and the water flooded toward the North. (Jan 14) No significant change.  Water flooded on the North side, slight headward erosion at basin. Base level rose.



Test 2: (Jan 14) 
Change: We are going to increase the velocity by 50% to 52.5 to help move the sediment.
Hypothesis: The increase in water velocity will increase the depth of erosion and move more sediment to allow lateral migration.
Observations:  Initially when changing the velocity it was noted that sediments were transported more rapidly. (Jan 19) A straight, shallow channel formed, most defined closest to the water input. Splays developed downstream. Riffle pools of swirling water and sediment were created in turbulent areas. (Jan 21) No change since last observations. The stream table must have reached equilibrium.

Test 3: (Jan 21)
Change: We are going to add sediment input.
Hypothesis: The increase of sediment input will help our stream become more as a real meander by shaping the stream better.
Observations:  We developed a system to input sediment into our stream table. (Jan 24) Our channel has now been filled from the additional sediment. The water flows on top of the sediment now.  Large fan deposits of coarse material and some fine grained flood deposits can be noted.

Test 4: (Jan 24)
Change: Lower base level
Hypothesis: This will cause heavier erosion because the stream can now erode deeper.  We hope this will also help to develop channel migration and continue in developing stream features.
Observations: As we lowered base level, there was immediately heavy erosion at the head of the river with headward erosion (down cutting). This erosion went on steadily for 30 minutes (about 1 1/2 ft) until it began to slow.

U. of NE - Omaha Experiment - WWL

Below is a link to stream table experiments done by UN-O. There are some interesting results.

http://maps.unomaha.edu/maher/geo101/tablea.html

Sediment Input - David Little

I've added extra sediment to the sediment input device twice now. It stopped flowing yesterday about 7 pm after we started the sediment feed at 3 pm. I left it overnight. Today I added sediment at 2 pm and at 6 pm. It appears that while sediment isn't being added to the system, the water flow digs a pit at the head of the channel and then prefers to take the channel closer to the seats in the classroom. When sediment is being added, the pit is first filled in, and then the water tends to take the straight channel.

One problem with the sediment feed is that the end with all of the sand in it sinks into the water-logged table. This makes the sediment stop going into the table earlier than it normally would. If we find a way to prop it up it would work for longer periods of time.

One problem we may run into soon is that we're running out of sediment to add to the table. I may go to Prof. Little's place tomorrow to help get some new sediment to add to the container. The bedforms are migrating well as long as sediment is being fed into the system. They are filling in one side of the channel (and there is a little bit of erosion on the other side of the channel!) but using up a lot of our sediment.

Martell and I were thinking that it might be good to decrease base level just a tiny bit. Not much at all, but with the water table high enough that much of the table is flooded, it's hard to get any bank erosion in the main channel we're hoping will migrate. A very small drop in base level may restrict the water more to the channel. This will hopefully increase erosion and deposition in that channel, and we won't lose as much sediment and water flow to other parts of the table. If that doesn't yield good results after a few days, then maybe Wednesday or Friday of this next week we may want to re-start the table with a sediment feed from the very beginning.

Literature - WWL

Several references have been added to the library. Some by you and some by me. Please take time to check them out.

University of MN Experiment (Braided to Meandering) - Prof. Little

Below is a link to an experiment conducted by The St. Anthony Falls Hydraulics Lab (under the direction of Tal and Paola) at the University of Minnesota studying the influence of vegetation (alfalfa) on the transition between braided and meandering stream patterns. The interesting thing here is that the change is from braided to a more meandering-like pattern.

http://faculty.gg.uwyo.edu/heller/SedMovs/Tal.htm


Details on the experiment can be found in:

Tal, M., and Paola, C., 2007, Dynamic single-thread channels maintained by the interaction of flow and vegetation: Geology, v. 35, p. 347-350.

Sediment modeling - David Little

If anybody can find a good place to order melamine plastic medium. The best video we've seen for modeling meandering uses this with kaolin clay. I've seen stream tables that use only melamine and those aren't cohesive enough for meanders. So if anybody can find a good place to order this, that'd be great.

-David

Helpful Videos - David Little

Here are a few videos from YouTube that are helpful in studying stream table meanders. There are a few more that I've found, but these are some I've found with the most data from the posters.

This first video was one that was viewed in class. Initially the video did not have any information posted, but after three of us posted comments and I sent an email to the museum exhibit people, they posted the following in the video description:

"The table is 7 feet long and 30" wide, minimal slope.

12 gallons per hour flow.

Over 100 iterations of material testing went into making this video."

http://www.youtube.com/watch?v=LOXWqBoxPZM

This next video has a channel pattern that has both meandering and braided elements. The most interesting thing is the meandering initiation in the first few seconds of the video.

http://www.youtube.com/watch?v=ZBoeI3ZX7us

This next video is one of a large series by the poster. I'm going to try to contact him at some point, as he seems to have taken careful notes in his experiments. This particular video appears to have decent meanders in it, though I don't see much migration. We should take the time to view more of his videos in order to watch migration. In the video description the poster wrote the following:

Meandering experiment with diatomacious earth and kaolinite clay
discharge = 15 ml/s
slope = 2%
material = DE:KC - 4:1"

http://www.youtube.com/watch?v=Y1X4aAfHpzw

Posting Guidelines - David Little

Before you do something to the stream table, please make a post about it here. When you post, write just a little bit about what you were experimenting with (i.e. discharge or sediment input) and place the names of whoever was involved in the title. If there are any good links to videos or files that are helpful for study or experimentation, post links or embed them here.

-David