PRELIMINARY DATA ON SEASONAL SEDIMENTATION ASSOCIATED WITH A LIVING SHORELINE RESTORATION PROJECT IN AN URBAN SOUTHERN CALIFORNIA ESTUARY

Estuaries in Southern California are particularly vulnerable to sea level rise as they are constrained by urbanization and/or steep topography which limits upland habitat migration. Therefore, estuarine habitat resilience and sustainability in Southern California are primarily dependent on building elevation capital through increases in sedimentation. To address this issue, resource managers in California are increasingly pursuing living shorelines restoration projects as means to minimize shoreline erosion and promote sediment deposition. In this project, we will present preliminary data characterizing seasonal sedimentation associated with a living shorelines restoration project in Newport Bay, Newport Beach, California. Living shorelines were installed in 2016-2017 at four different locations in the estuary, with three different configurations (oysters only, eelgrass only, and oysters and eelgrass combined) and a control site with no modifications at each location. These preliminary data reflect comprehensive sedimentation monitoring that include quantifying bimonthly sediment deposition using sediment tiles and characterizing newly deposited sediment properties including sediment texture and composition. Initial results reveal that the combination oyster/eelgrass living shoreline configuration promoted the highest sediment deposition on average. These preliminary results also reveal that sedimentation was higher in the spring months (March-June) than the winter months (January- March). This is unexpected, as the majority of Southern California’s precipitation (and runoff) occurs during winter months, although precipitation was negligible (max monthly precipitation was 2.5 cm) and increases in streamflow minimal throughout the study period. This may indicate that sediment supplied to this section of the bay comes from marine sources driven by marine processes rather than fluvial sources. Further characterization of the sediment deposited may help to distinguish these sediment sources. Our goal through this project is to determine whether living shorelines are effective at promoting sedimentation up shore within the estuary and therefore may be a useful management tool to address the potential for intertidal habitat loss due to sea level rise in the region.