Appendix A
Stability Analysis of a
Submerged Spur, North Jetty,
1
Grays Harbor, Washington
Introduction
This appendix documents results of an independent investigation of stability
of a submerged spur being considered as a sediment control structure at the north
jetty at the entrance to Grays Harbor, WA. The study was funded by local
interests (Coastal Communities of Southwest Washington) independent of the
U.S. Army Corps of Engineers (USACE) north jetty Operation and Maintenance
(O&M) study described in the main text of this report. The present study
included development of design waves, analysis of existing published data on
stone stability for submerged structures, and physical modeling in a large-scale
two-dimensional (2-D) wave flume.
A reconnaissance study performed in year 2000 for the U.S. Army Engineer
District, Seattle (NWS) by the U.S. Army Engineer Research and Development
Center, Coastal and Hydraulics Laboratory (CHL) and Pacific International
EngineeringPLLC determined that a submerged spur could be constructed in the
north jetty environment with a marine-based operation consisting of split-hull
bottom dump barges and tugs. The constructability analysis concluded that rock
size should be as small as possible for a marine hopper barge operation; barge
openings up to 8 ft can dump rock up to approximately 3 ft in diameter.
Furthermore, construction would be simplified greatly if a single rock gradation
can be used due to the difficulties with trimming and dressing of the structure in
the north jetty wave and current environment. A 3-ft diam maximum rock size is
small relative to the size of stone normally used in North Pacific Ocean jetty
construction. The small rock size and broad gradation raised concerns regarding
rock stability in the energetic wave regime at the north jetty, Grays Harbor.
Existing formulae and experimental data for submerged structure stability
were reviewed and evaluated. Calculations of crest stone sizes for the extreme
1
Written by Philip D. Osborne, Nels Sultan, and Michael H. Davies, Pacific International
Engineering, PLLC, Edmonds, WA.
A1
Appendix A
Stability Analysis of a Submerged Spur, North Jetty, Grays Harbor, WA
Previous Page
