Center for Marine Biodiversity and Conservation

Cardiff State Beach (CSB) in Encinitas, CA is a barrier bar, sandy beach in San Diego County along the west side of the San Elijo Lagoon. The beach has been nourished by sand placement several times over the past twenty years to enhance its width amidst erosive wave events. In addition, San Elijo Lagoon “bypassing” (dredging of sand from the inlet) has been routinely conducted and the resulting sand placed on the beach. CSB is also the location for a Living Shoreline project that built a vegetated dune system along the western edge of South Coast Highway 101. In the interplay between rising sea levels, changing wave climate and human management efforts, projecting beach width would enable an understanding of coastal sediment management practices needed to maintain beach width (“hold the line”). The objective of this capstone project was to use a sediment budget model created for Cardiff beach to project change in beach width for 2022-2050, assuming two strong El Nino winters and sea level rise scenarios outlined by the NOAA sea level rise technical report (2022). The model was then validated using a hindcast and then comparing to existing datasets from SIO and SANDAG surveys for the 2000-2020 period. Our preliminary results indicate a promising scenario of beach width increase for CSB during the period considered, even just with routine yearly bypassing. However, in the absence of human intervention in the form of added sand, El Niños and sea level rise take a toll on the beach width, decreasing it by ~25 m by the end of the three decades. The movement of sand between the dunes and the nearshore zone is a novel element of this model that needs to be assessed further during future El Niños or other highly energetic winter wave seasons. This work is intended to support the City of Encinitas and San Diego Association of Governments’ (SANDAG) beach monitoring program by providing future beach scenarios to enable decision-making around nourishment activities and coastal resilience.