Pebble #1 Exercise
To conduct an abbreviated Rosgen Level II Wolman Pebble Count at the monumented cross section on the single threaded Ouachita River Reach.
- 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.