Interactions between waves, beaches, and coastal cliffs

Eroding coastal cliffs threaten infrastructure, public safety, and recreational resources around the world. Beaches are a primary natural defense to wave attack on coastal cliffs, while the eroding cliffs provide sand to the beach. On the urbanized southern California shorelines, cliff erosion has sometimes been accelerated by long-term shortages in the beach sand previously supplied by (now controlled) rivers in flood. Rising sea levels, changes in storm tracks (e.g. rainfall and waves), seawall construction, and ongoing beach replenishment projects will all influence cliff erosion. The cliff and underlying shore platform are the boundaries for beach erosion and retreat. Detailed field studies of the feedbacks between shore platforms, waves, beaches, and cliffs are rare, and needed to improve predictions of the coastal response to sea level rise.

The Scripps Coastal Mapping Program uses ground based mobile lidar to map beaches and cliffs, monthly, over 10s of km of coast. These observations include time series of beach nourishments, cobble exposure, beach sand levels, shore platform exposure, and cliff morphology. Three years of weekly lidar observations over a few km of coastline in Del Mar, CA, coupled with modeled incident wave conditions and backshore wave height observations, are used to explore the details of wave-beach-cliff interactions. The time period evaluated includes a sequence of large coastal landslides and erosion events that elevated cliff retreat rates above previous periods.