Video Observations of Shoreline and Sandbar Migration at a Wave Dominated Beach: Northern Monterey Bay, California

Beach morphology in northern Monterey Bay adjusts to seasonal and interannual trends in wave climate. Cross-shore elevation profiles are characterized by beach erosion and offshore sandbar migration during high-energy winter wave events. This is followed by natural beach replenishment and shoreward sandbar migration during calmer summer conditions. An Argus video monitoring station was installed in 2017 at Sunset State Beach, a sandy barred beach in the northern Monterey Bay of Central California to continuously measure shoreline and sandbar positions. Nearly two years of observations were considered with the aim to improve our understanding of the interactions between sandbars and shorelines under various wave forcing.

Shoreline and sandbar positions were extracted from rectified time-exposure image mosaics. Time-series of both shoreline and sandbar positions show strong seasonal signals and evidence of wave-driven erosion and recovery within the study area. Sunset State Beach exhibits an equilibrium shoreline response to wave forcing while the sandbar appears to be more sensitive to small changes in wave conditions. The sandbar likely buffers the shoreline from smaller wave events until it loses functionality as natural armoring during winter wave conditions. Observations show that most shoreline erosion occurs following the first large wave event of the winter season, though further erosion or subsequent recovery will occur according to wave characteristics during the rest of the winter. This work reveals higher nearshore morphological variability than previously observed in the Monterey Bay and offers insight into the impact of wave forcing and shoreline-sandbar interactions on shoreline change.