Variations due to seasonal cycles were also measured. Accretion/deposition rates of +/- 0.5 cubic yards per foot of beach were noted. The response to Spirit fast ferry wakes was less than this seasonal variation.

Location of Beach Transects in the Study Area

The graphic below shows changes in the upper beach (above the 5 foot contour relative to mean lower low water) at two beach transect locations on Point White, Bainbridge Island.

The photograph shows the nature of the beach at Transect 4A. Transect 4B is located a few 100 ft to the northeast of 4A. The location of Transect 4A is shown in the map. The general location of both transects is represented in the map below.

The line graphs on the right show the beach volume change measured over time relative to May 2000 at the two transects (4A and 4B). The colored bars indicate the alternating periods of fast (yellow) and slow (light blue) WSF Chinook class ferry operation on the route. The red bar indicates the interval of trials with the research vessel Spirit in 2005.

The blue line indicates the beach volume change relative to May 2000 in the interval 2000-2002. The magenta line indicates the beach volume change relative to May 2000 for the interval August 2004 to January 2006.

No profile surveys were collected during the first interval of Chinook class fast ferry operation (1998-1999). The first survey was measured near the end of a period of slow Chinook class ferry operation (May 2000). No profile surveys were collected between 2002 and 2004.

During the period of fast operation of the Chinook and the Snohomish (May 2000 through October 2001), the beach eroded rapidly in the first 3-6 months and then approximately stabilized. The survey data collected as part of the research study (2004-2006) indicates that this beach has approximately recovered to the pre-May 2000 baseline condition.

The measurements also indicate that the beach exhibited a minor, to insignificant, response to the trial wakes from the high speed research vessel, Spirit (February-April 2005).

A seasonal cycle of +/- 0.5 cubic yards per foot of beach is evident in the volume change measurements from both transects. The erosion response of 1.3 cubic yards per foot to Chinook class fast ferry wakes is significantly larger than the seasonal variation.

The response to Spirit fast ferry wakes is smaller than the seasonal variation.

The upper photograph at left shows the condition of a beach on Bainbridge Island to the northeast of Transect 4. The profile measurements and photographs confirm that the beach lost approximately 4 feet of sediment within 3-6 months of WSF fast POFF operation (Chinook and Snohomish).

The lower photograph shows that the beach in this area has recovered to pre-Chinook levels.

The conclusion is that the beach was significantly impacted by the wakes from Chinook and Snohomish.

No response to Trial Wakes

This graphic shows the same location as in the previous slide showing before (left) and after (right) photos for the interval of trials with the research vessel Spirit in 2005.

The photograph on the left is from February 28, 2005 (prior to the start of Spirit trials). The photo on the right is from April 19, 2005 (near the end of the Spirit trials).

The beach profile surveys indicate that the beach at this location has been relatively stable for the past year (Aug 4, 2004 to July 22, 2005).

The conclusion is that Spirit trials did not significantly impact this beach at this location.

  Beach Response to Spirit Trials

Survey data collected (2004-2006) at two beach locations on Point White, Bainbridge Island, indicates that this beach has recovered to pre-May 2000 baseline conditions. Furthermore, our measurements indicate that the beach exhibited a minor, to insignificant, response to the trial wakes from the high speed research vessel, Spirit (February-April 2005).