Dream Table - Subsidence - Group 1

The above sketch is a mock-up of the way we can show subsidence on our stream table we are developing. We want to have some sort of poles with a wider surface on the end. These will hold up a rubber membrane which the sediment is on. The poles can be adjusted so that they can move up and down. A simple way would be if the poles were screws and they were attached to a board farther down. This would give us the ability to simply screw up or down the poles. We would want the bottom of the box accessible so we could do so. I am sure there is a way to make the poles move vertically with some motor as well. We still need to decide how many sections/poles of the stream table we would want to be able to move.

Dream Stream Table - Group 1

As our stream table is doing fairly well and now we mostly have to wait and see what happens next we have began to develop our future stream table. Some things we want to develop/incorporate into the table are as follows:

-Box

-Sediment supply

-Water supply

-Wave/Tide generator

-Base-level control

-Camera mount

-Uplift/subsidence mechanism

-Gradient control

Continuation of Setup 3 - GROUP 1

(pictures to come soon)

2/25 

Results: With our new sediment input we created splays formed and the channel as filled. We dredged the channel and fixed our sediment input so there would be less sediment feeding into the system. We really need to remove some of the large pebbles which on this scale act as large boulders. The small stream simply cant carry them and can not erode further where they are. We removed a few boulders very carefully as to not harm the system.

2/27

We have ran the system without any changes with our current set up and it seems to be doing very well. It is very very slowly meandering and the meander is even moving downstream! Real rivers take a long time to meander and change course and the same is try for out stream. This is where patience needs to come into our experiment. 

3/1

The nozzel of the sediment feed has fallen off sometime while no one was present which allowed all the sediment to dump into the sream at once. The channel is filled again with sediment. It seems like channel is trying to make a comeback so we will try to leave it run without any input of new sediment (this way the stream can erode and carry the excess sediment in the channels). 

3/2

The stream was not able to make as good of a comeback from our catastrophe the day before as we hoped. We are dredging it once again to get rid of the sand that filled the channel. We didn't change anything else and we began the water again. Right away the stream began to make sand bars and thalwags once again.

Overall the stream table is doing quite well.  It is slowly meandering down the stream toward the basin. There are steam like features forming as well, like the thalwags, sand bars, splays, etc. 

 

Stream Table – 3.4 – Group 2

We did not have to start over on the stream table!  We dredged the white sand that had dumped on the table out of the stream, and removed it from the table.  The stream appears to have continued to meander, and has found its way to the cut banks again.

The black spot in at the head of the table is the plastic

 bottom of the table.  It is also where the water is 

being dribbled on the table.

The white sand is what is being deposited. 
The cut banks are brown/rocky cuts in the white sand.

A new sediment shaker has been designed, and is being implemented in this version.  The last sediment shaker had good concepts, but it was not consistent in its deposition of sediment, we would often walk in to observe it and no sediment would be coming out of the pinch point.  The new sediment shaker uses the angle of repose to control the amount of sediment being fed into the stream instead of a pinch point.

The red cup holds the sand and has a straight, stiff tube 

epoxied to the bottom.  The silver thing strapped on to the cup 

via the black band is a motor with a spinning fan at the 

bottom to shake the cup. There are springs on the three 

posts that also allow the cup to shake.

The delta has migrated channels over the last day:

Yesterday:

In this picture the main channel is flowing toward the 

bottom-right-hand corner of the photo (north-west).

 Today:

In this picture the main channel is flowing toward the
top-right-hand corner of the photo (south-west).

Catastrophic Stream Failure! – Group2

The stopper/pinch-point at the end of the sediment feed shaker slipped off, and allowed the contents of the shaker to pore out onto the table.

Pictures below (taken 11:20 3/1/2011):

This may mean that we may have to re-level the table and start over.

One good thing is the migration of the delta at the end of our stream:

Stream Table 3.3 – Group 2

Stream has cleared its self out.  The sediment shaker has been modified, a pen has been taped to the feeder tube to straighten it (to help avoid clogs), and the pinch on the tube has been lowered to the end of the feeder tube.  The sediment shaker was on this morning (2/28/2011), but was not flowing, so I (Sara) tapped the end of the feeder tube a few times, and it started slowly flowing again.

Pictures of the altered sediment shaker:

Pictures of the meander on the stream table:

Stream Table 3.3 – Sediment Shutoff Again – Group 2

Stream table sediment feed was accidently turned back on this morning, creating many splays (or at least highlighting them) and a small alluvial fan.  At 10:20am both group leaders made an executive decision to turn off the sediment feed, increase the stream velocity to encourage the stream to clear its self out, and dredged the channel to remove the alluvial fan.

 

Stream before dredging:

Stream after dredging:

Stream Table 3.3 – Sediment Shutoff - Group 2

Stream sediment was shutoff on  2/24/2001 around 6:30pm.  The stream had too much sediment, and was starting to fill.  Goal of cutting off sediment is to allow the stream channel to clear its self out.

Picture of stream table with full channel, notice splay:

Stream table 3.3 - Group 2

New sediment shaker put in yesterday on the 24^th.  New sediment shaker should help avoid the creation of alluvial fans at the start of the stream by keeping a slow and constant feed of sediment onto the stream channel.

Picture of sediment feeder:

Picture of stream meander around 1:30pm on 2/24/2011:

Setup #3, Test 2 - Group 1

Feb 18, 2011
We began a new test today by dredging a new channel with a bend at the beginning to help with our sinuosity. We dug the channel with our fingers.

Initial results: With our larger, deeper channel our water flow became restricted to the channel and is no longer saturating the flood plain. Sediment is being transported. Sand bar developed on the inside of the channel. There are small amounts of sediment now being deposited on the inside of the river bends.

The bend we created. Note the sand bar developing in the stream.

 Feb 23, 2011
It seemed as our system has reached a point of equilibrium. Cut banks have developed on the outside of our bends. Thalwegs formed. There is no more flow of sediment flowing at this time,  which we need in order to develop our stream. Our sand bars are still intact.

We began to input more sediment (70 grit sand). A sand wave began to move through our stream.  We are currently working on a new way to input our sediment.

Setup #3, Test 1 - Group 1

Feb 16, 2011

We restarted our stream table completely once again. Out gradient is now 2 degrees with a 1-2 cm soil/mud to the top of the plane for cohesion. We created a small straight channel with the end of a spoon to be able to direct the water in the beginning. Our base level is about 1 cm beneath the top of our sediment. Picture of our setup is below. 

Initial resutls: All the soil surrounding the stream began to saturate and a marsh like feature formed. We dredged the channel to make it a bit deeper in order to meet our annual flow and to prevent flooding on the floodplain. 

Feb 18, 2011- The table was still marshy and saturated. 

Sediment Tests - Group 1

3:1 Test
We set up a new stream table test and began it on February 2.  We have a 1 degree gradient, cut a small channel into the middle to help start directing the flow, and had out sediment input a 3:1 ratio of sand to mud. We made a new sediment input so it could run longer without adding more sediment. This consisted of a flower box holding the sediment instead of a small tupperware.

Two days later there was an alluvial fan. Even though it was a perfect alluvial fan this is not what we wanted. The water would flow over the alluvial fan with no channel. We thought this might have happend becaue we had too much sand in our sediment.

2:1 Test
We wanted to try a new sediment input so we re-leveled it and set it up the same as at the beginning of our last test (3:1 Test). The only thing we changed was our sediment input ratio. We mixed new sediment so the ratio is now 2:1 sand and mud.

On the 7th another alluvial fan was created. It was slightly different from our first alluvial fan, where as our sediment was sorted and a great floodplain was developed.

 

2:1 Test
Feb 9, 2011
We kept our table the same today, as in we did not regrade or change anything besides our input. Our input is now 2 mud: 1 sand. We sifted our mud so it would be fine and all of the same size. We used find sand that we purchased, 70 grit.

Immediate results: The finer sediment we used this experiment made it looked like a mud flow for a time. Small channels began to form in our alluvial fan left from the last experiment.

Feb 11, 2011
Our stream made a path to the right of the table and formed an angle at the side and flowed toward the basin from there.

Turning off water supply - David Little

I turned the water supply off at 8 pm last night. The sediment had been flowing onto the table at a high rate for five straight hours. It's been feeding at a faster rate than the previous mechanism did. Because it was running low on sediment, there wasn't any more to replace it with, and the sand was just depositing in a fan on the table, I decided to turn it off.

Stream Table: Version 2 – Group 2

New Parameters:

A mixture of sediment, 3 parts sand to 1 part mud (3:1 mix), has been spread 1-2 mm thick on the re-leveled surface of the stream table.  The 3:1 mix will also be what will now be fed into the stream.  This is to help encourage meanders and less stream piracy.

A one degree slope has been given to the new table surface, to encourage meanders to form by decreasing the river profile.

New sediment hopper!  The new hopper is larger and should reduce the periods of time where there is a shortage of sediment entering the stream and discouraging stream piracy.

Water meets drop-off edge as the graded profile drops down to the basin.  This should prevent entrenching of the river. (Over all, we raised the water table significantly.)

A shallow path for the river channel has been carved to encourage it to start its formation in the center of the table, instead of the edge where it has no room to migrate.

Predictions:

Less stream piracy, more meanders.  We feel that the changes my still need tweaking to provide the best results.

Conclusion of Change 4: Sediment – Group 2

Conclusion:
                -      Putting sediment in encouraged channelization

                                       -        Formation of unstable meanders

                                       -        Stream Piracy occurred – the stream started on the northern side 

                                   of the table and migrated/pirated its way southward.

      Ideas if we start over with the stream table:

  -          Adjust bedding angle from 2 degrees to 1.

  -          Lower and calculate the actual flow rate

  -          Increase size of sediment container/feed hopper to decrease

                  maintenance times

  -          Raise base level a bit from its current lowered state

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