Morphological change and sand transport mechanisms in the dynamic dune complex of South Beach State Park, Oregon

摘要

Shoaling within the jettied inlet at Newport, Oregon has increased by 30% since 2011. The U.S. Army Corps of Engineers (USACE) hypothesize that this shoaling is associated with increased rates of aeolian sediment transport to the navigation channel from the dynamic dune field at South Beach State Park (SBSP), located adjacent to the south jetty at Yaquina Bay. Needing to maintain the channel at depths suitable for large-draft ships, USACE is considering installing sand fences along the south jetty to reduce the volume of sediment being blown into the navigation channel, thereby allowing for more efficient spending of limited dredging funds. To optimize the design of the sand fence system, here we explore local sediment transport mechanisms by 1) quantifying inter-decadal coastal change patterns at SBSP; 2) comparing recent seasonal to interannual morphometric variations to inter-decadal trends; and 3) quantifying the relative role of environmental forces on promoting sediment transport from the dune field to the inlet. Rates of shoreline progradation, dune accretion, and rate of growth of foredune height have all increased since 2009, especially close to the jetty. These increases were found to be a response to the 2009-2010 El Nino, an increased northern gradient of wave-driven alongshore sediment transport from 2010-present, and larger aeolian sediment transport rates to the north from 2010-present. Aeolian sediment transport flux from the dune complex to the inlet is aided by three distinct sediment corridors. Coastal change analyses suggest that the corridors originally developed as a response to the 1997-1998 El Nino and persisted due to subsequent slow vegetation spreading rates, and high recreational foot traffic. Because the dune system has experienced increased rates of accretion since 2009-10, the corridors have more efficiently transported sediment to the inlet.