EXPERIMENT 8

Hypothesis

Adding a thin layer of kaolinite to the sand-bed surface will increase bank cohesion, decreasing rates of cutbank erosion and allowing point bar deposition to keep pace.

Set Up (Figs. 1a, b. c)

Bed fill:	Fine-grained (0.70 mesh) quartz sand with thin layer of kaolinite on surface in a narrow strip within and along the channel
Bed thickness:	5 - 6 cm
Bed gradient:	0⁰
Base level:	Even with channel mouth
Discharge rate:	45 mL/s (estimated)
Sediment feed rate:	~0.75 mL/min
Shape of initial channel:	Single semi-circular bend with a 10 cm radius, followed by a straight channel
Depth of initial channel:	~1 cm
Width of initial channel:	4 cm (estimated)
Discharge stage:	Bankfull
Adjustments from Experiment 7:	· Kaolinite added to surface within and along channel.
Procedure:	· Discharge and sediment feed were started and allowed to flow uninhibited for the duration of the experiment.

Figure 1a: Initial channel with a thin layer of kaolinite in a strip along either side.

Fig. 1b: Sifter used to apply kaolinite to bed surface.

Fig. 1c: Initial channel bend.

Observations

1) Kaolinite within channel quickly removed and transported to the basin (Fig. 2).

2) Development of a point bar and opposing cutbank (Fig. 3).

3) Widening of channel and transition into a well-developed braided channel pattern (Fig. 4).

Figure 2: Transportation of eroded kaolinite to the basin.

Figure 3: Development of a point bar and cut bank erosion on opposite side of channel.

Figure 4: Final braided channel pattern.

Interpretations (Each interpretation is tied by number to an above observation.)

1) Kaolinite as an unconsolidated powder is easily removed by flow within the channel.

2) Clay added to the floodplain surface became saturated, providing some increase in cohesion, allowing initial development of a weak meandering pattern and cutbank erosion temporarily slowed.

3) The thin layer of kaolinite did not sufficiently slow erosion to prevent significant widening of the channel.  Once widening exceeded the width of the  narrow band of kaolinite along the channel, the rate of erosion increased to rates of previous experience, transforming the system to a braided pattern.




Technical Issues

Continued problems with wicking of water into sediment feed.

Continued instability of base-leve control.