Lagunitas Creek Watershed Sediment Monitoring Data Collection Methods

Prunuske Chatham, Inc. and Balance Hydrologics, Inc. collect field data for the San Geronimo Bedload Sediment Reduction Program.  Annual data collection includes: changes in streambed elevation, embeddedness, bed surface composition, and bed core composition.  Prunuske Chatham, Inc. retains Balance Hydrologics, Inc. to collect the streambed surface, rock type composition, and bed core data. 

 

Change in streambed elevation is conducted at each established monitoring site in the basin.  Cross-sections are annually surveyed.  Mean streambed elevations are compared to the most recent previous survey of the same cross-section and are reported as mean change in streambed elevation.. 

 

Embeddedness is a visual measurement of the average proportion of rock particles, larger than 45mm, that are buried in finer sediments on the streambed surface.  Measurements of embeddedness are reported in increments of 10%.

 

Bed surface composition data collection is based on a modified Wolman pebble count methodology.  The pebble count involves a systematic collection of rocks from the streambed surface.  Collected rocks are measured for mean diameter.  Surface particle size distribution is determined from the data.  The median (d50), d16, and d84 particle sizes are reported in annual monitoring reports.

 

Bed core composition data is collected for pool-tails at Lagunitas Creek monitoring sites.  Bed cores are taken at locations across established cross-sections after the bed-surface layer is removed.  A 15-cm diameter thin-walled cylinder is driven into the substrate a minimum of 4-inches deep.  The substrate is removed from the samples and dry-sieve analyzed to determine the particle size distribution.  Annual monitoring reports contain the median (d50), d16, and d84 particle sizes.  Prunuske Chatham, Inc.(2000) and Balance Hydrologics, Inc. (2002) report that bed cores are not taken in areas where spawning might occur and are not intended to be used to characterize spawning habitat.