Waves, Hydrodynamics and Sediment Transport Modeling at Grays Harbor, WA

Abstract : This numerical modeling study was performed for the purpose of addressing short- and mid-term dredge material management issues for the Federal Navigation Project at Grays Harbor (GH), Washington. Seattle District (NWS) is also currently evaluating GH navigation channel realignment in the Point Chehalis/Entrance reach because historic trends in survey data indicate this area is naturally scouring a new thalweg just north of the present channel. The realigned channel would take advantage of the thalweg, and a relocated channel is hypothesized to reduce annual dredging quantities. The impact of dredged material placement sites on channel maintenance is also examined. The three dredged disposal sites of interest considered in the present study are the Point Chehalis Disposal Site (PCDS), South Jetty Disposal Site (SJDS), and Half Moon Bay Beneficial Use Site (HMBBUS). The realignment of GH navigation channel is an attempt to establish optimal locations for the PCDS and SJDS. The key issues of interest to the NWS investigated in this study were: a) changes in waves and hydrodynamics at GH navigation channel over time scales of 0.5 to 5 years, b) consequences of channel realignment on waves, hydrodynamics and sedimentation of GH navigation channel, c) sediment transport pathways in the lower GH and at three dredge material placement (DMP) sites, and d) channel infilling estimates from frequently occurring, low energy storms and less frequent, but more energetic storms. These issues were examined for two channel alternatives: "Existing" and "Realigned" channel configurations. The Realigned channel was modeled with and without the Existing channel filled.