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Pebble #1 Exercise

Exercise Objective

To conduct an abbreviated Rosgen Level II Wolman Pebble Count at the monumented cross section on the single threaded Ouachita River Reach.

Exercise Process

Download the pebble image for analysis of the intermediate axis in ImageJ. Note the scale bar change with certain pebbles.
Identify the intermediate axis as neither the longest or shortest x, y, or z dimension of the pebble. Along the intermediate axis use ImageJ Analysis scale and measure tools to determine the longest path or maximum diameter across the pebble.
Record the measurement of maximum diameter along the intermediate axis.
Record the bed material type based on the following diameter size categories:
- Boulders - diameter 256-2048mm
- Cobbles - diameter 64-256mm
- Gravel - diameter 2-64mm
- Sand - diameter 0.062-2.0mm
- Silt/clay - diameter < 0.062mm

As an illustration of this technique, for Pebble #1 the intermediate axis is y, while x is the longest and z is the shortest. Maximum diameter along the y-axis is in the center of the pebble, and is approximately 10 mm.