Ongoing Beach Nourishments in San Diego County, Ca.

Beach nourishment decisions are becoming increasingly difficult as seas rise and sediment supplies dwindle, but are better informed in San Diego County than many regions owing to long-term nourishment monitoring. Almost two decades (2001-2020) of wave and sand level monitoring at selected San Diego area beaches includes 6 beach nourishments: 1 in 2001, 3 in 2012, and 2 in 2018. Previous work showed that the 2012 nourishments, constructed with sand coarser than native, drastically increased subaerial retention times (along the backbeach) compared with a nourishment in 2001 built with a grain-size similar to native. In 2018, opportunistic nourishments of fine and medium grained sand were placed atop the coarser remnants of two of the 2012 nourishments. Preliminary analysis suggests that the coarser-grained nourishments continue to stabilize the beach, in conjunction with the larger, more recent, finer-grained placements. At Imperial Beach, the 2012 coarser-grained nourishment sand has migrated south several km, and accumulated on the north side of the Tijuana River mouth, where it appears (temporarily) trapped. Some sand may have also entered the dune fields north and south of the river mouth. Recent advances in survey technology (LiDAR and photogrammetric imagery) have increased temporal and spatial resolution and the monitoring domain, allowing a more complete investigation of nourishment evolution, including the backbeach, river mouth and dunes. Hourly wave estimates from a buoy-driven numerical model will be used to compare nourishment evolution models of varying complexity with observations. This research was supported by The Copley Foundation, USACE, and California Parks.