Stream Table 2011

This course was last taught Winter 2011. That semester, research was conducted using a small (~0.5 X 1.5 m) commercial table with limited capabilities. The goal was the same, to create a sustainable migrating meander and was accomplished on a limited basis (i.e. a single migrating meander bend near the head of the table). Toward the end of the semester, the 2011 group developed ideas for what they called the "Dream Table." In conjunction with the Department of Mechanical Engineering at BYU-Idaho, a preliminary version was constructed and used for the first time this semester (Winter 2013). To see work done by the 2011 group, click here.

Feedback and Collaboration

We welcome feedback and collaboration with others working on or interested in this topic.

Monday, October 28, 2013

EXPERIMENT 3


Hypothesis

Carving an initial channel that has a single bend near its head and then runs in a straight line to the end of the table will encourage development of a meandering pattern.

Set up (Fig. 1)

Bed fill:
Fine-grained (0.70 mesh) quartz sand
Bed thickness:
Not recorded
Bed gradient:
0.5⁰
Base level:
5 - 6 cm below bed surface (estimated)
Discharge rate:
45 mL/s (estimated)
Sediment feed rate:
0
Shape of initial channel:
R/w = 4 cm
Depth of initial channel:
0.5 cm
Width of initial channel:
2 cm
Discharge stage:
Bankfull
Adjustments from Experiment 2:
· Based on a USGS study using a larger table, we scaled our channel gradient to be 0.5⁰.
· Using a published formula relating curvature radius to channel width for natural streams, we adjusted the width, depth, and curvature of our initial bend.
· We began the experiment with a pre-carved channel extending the full length of the table, following an initial bend (Fig. 1a).  This seems to be a characteristic of all successful experiments for larger tables.
· A rock was suspended from the base-level hose to try and increase stability.
Procedure:
· Discharge was started and allowed to flow uninhibited for the duration of the experiment.


Figure 1: Initial carved channel with bend.


Observations

1) Upon beginning the experiment, the discharge began to scour the channel floor and deposit within the channel immediately downstream, creating a blockage to flow and causing overbank flooding with subsequent sheet flow across the floodplain (Fig. 2).


Figure 2: Flooding and subsequent sheet flow.


Interpretations

1) The discharge velocity was too high entering the channel, causing erosion and chute development. The additional sediment from from the chute then decreased flow velocity, causing deposition within the channel.  In-channel deposition decreased channel cross-sectional area, restricting the flow and leading to flooding and sheet flow across the sand-bed surface.


Technical Issues

The discharge rate needs to be adjusted to decrease the amount of initial erosion.  We continue to have problems with maintaining a stable base level.




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