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