Pebble Count

The composition of the streambed and banks is an important facet of stream character, influencing channel form and hydraulics, erosion rates, sediment supply, and other parameters. Observations tell us that steep mountain streams with beds of boulders and cobbles act differently from low-gradient streams with beds of sand or silt. You can document this difference by collecting representative samples of the bed materials using a procedure called a pebble count. The basic technique is known as the Wolman pebble count. It requires two people, one with a metric ruler and one is a recorder. The ruler-person walks the stream and randomly selects substrate material, while the other records the results of the measurements. Pebble counts can be completed using grids, transects, zig-zags etc. Whatever procedure you select be consistent.

Pebble Axis


Select the portion of the reach that you wish to measure (this may be the entire reach or riffles only). For stream characterization, sample pools, runs and riffles in the same proportions as they occur in the study reach. For other purposes, it may be more appropriate to use a random method, transects, or zig-zag pattern.

Most SOPs recommends collecting and measuring a minimum of 100 particles. Start at a selected point near the downstream end of the reach. Starting on the shoreline, take a step into the stream. Averting your gaze, pick up the first particle touched by the tip of your index finger at the toe of your wader. Measure the intermediate axis (neither the longest nor shortest of the three mutually perpendicular sides of each particle picked up). Continue across the channel in an upstream direction towards the opposite bank and repeat the process, continuing to pick up particles until you have the requisite number of measurements. Measure embedded particles or those too large to be moved in place.

Fine Gravel
Coarse Gravel
Woody Debris

Size Range
Very Small (Smooth Feel)
Very Small (Grainy Feel)
2 - 16 mm
17 - 64 mm
65 - 256 mm
257 - 1025 mm
> 1025 mm (or large solid surface)
Sticks, leaves, etc


There are several methods that can be used to perform pebble counts. The most straight forward approach is:

  1. Traverse across the stream perpendicular to flow using 10-meter transects (for 100-meter reach)
  2. Use a zigzag pattern
  3. Stratify the reach according to bed features and them proportionately (i.e. % riffles, runs and pools)

The pebble count is one of a variety of methods that can be used alone or in combination to evaluate sediment processes in small streams. Others procedures include BEHI-NBS, erosion pins, monumented cross-sections, habitat assessment, keeping photo-logs and more. In 2006 WIB created a protocol that incorporates many of these methods.


  • Zigzag Pattern

    Zigzag pattern illustration.

  • Data Sheet

    Pebble count methods field sheet.

  • Streambank/Sediment Monitoring

    Monitoring is an essential component of stream restoration because it allows stakeholders to see what progress is being made, provides load reduction estimates and provides information on the types of restoration that can best achieve project goals. However, obtaining quantifiable results from streambank restoration projects has been difficult. There are a wide range of monitoring techniques to document erosion or sedimentation, but often they are intended to provide data for project design not environmental results.