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Abstract: Torrey Pines State Beach, a site with large seasonal fluctuations in sand level, received a small shoreface beach fill (about 160,000 m3) in April 2001. The 600 m-long, flat-topped nourishment pad extended from a highway riprap revetment seaward about 60 m, terminating in a 2 m-tall vertical scarp. A 2.7 km alongshore span, centered on the nourishment region, was monitored prior to the nourishment and biweekly to monthly for the following 2 years. For the first 7 months after the nourishment, through fall 2001, significant wave heights were small, and the elevated beach fill remained in place, with little change near and above Mean Sea Level (MSL). In contrast, the shoreline accreted on nearby control beaches following a seasonal pattern common in southern California, reducing the elevation difference between the nourished and adjacent beaches. During the first winter storm (3 m significant wave height), the shoreline retreated rapidly over the entire 2.7 km survey reach, forming an alongshore-oriented sandbar in 3 to 4 m water depth [Seymour, R.J., Guza, R.T., O''Reilly, W., Elgar, S., 2004. Rapid erosion of a Southern California beach fill. Coastal Engineering 52 (2), 151–158.]. We show that the winter sandbar, most pronounced offshore of the nourishment, moved back onto the beach face during summer 2002 (following the usual seasonal pattern) and formed a wider beach above MSL at the site of the original nourishment than on the control beaches. Thus, the April 2001 shoreline nourishment was detectable until late fall 2002, persisting locally over a full seasonal cycle. In an extended 7-year time series, total sand volumes (summed between the back beach and 8 m water depth, over the entire 2.7 km reach) exhibit multi-year fluctuations of unknown origin that are twice as large as the nourishment volume. [Copyright &y& Elsevier]

Abstract: A four-year time series of nine airborne LiDAR surveys were used to assess the roles of wave attack and rainfall on the erosion of 42km of southern California seacliffs. Nine continuous seacliff sections, separated by coastal lagoon mouths, all show maximum seacliff erosion in the rainiest time period (when wave energy was not particularly elevated), and in most sections the squared correlations between rainfall and erosion time series exceeded 0.8. Although rain and associated subaerial mechanisms such as groundwater seepage triggered most of the observed seacliff failures, wave attack accelerated seacliff erosion, with erosion rates of cliffs exposed to wave attack five times higher than at adjacent cliffs not exposed to waves. The results demonstrate the importance of both waves and rain in the erosion of southern California seacliffs and suggest that the combined influences of marine and subaerial processes accelerate the erosion rate through positive feedbacks. [Copyright &y& Elsevier]

Erosion of a 2.5 km-long sedimentary coastal cliff by waves and rainfall is explored with three years of weekly observations. A truck-mounted lidar resolved the fronting beach and convoluted surface of the ~10–25 m high cliffs. Volumes of 4362 cliff erosion events ranged up to 885 m3 (mean 3.3 m3). The three-year cumulative erosion was clustered and alongshore variable. Cliff base wave impact heights were estimated with a wave model and empirical runup formula, and validated with cliff base observations. Cliff erosion rates, incident wave heights, wave-cliff impacts, and rainfall were all elevated during winters. The high temporal resolution of the multiyear dataset is unique, and allows separation of erosion from waves and rainfall by, for example, isolating time periods with no rainfall and high wave runup. Upper cliff erosion was best correlated with rainfall (r2 = 0.57), and lower cliff erosion with wave impacts (r2 = 0.56). • 3 years of high temporal (~weekly) and spatial resolution lidar observations. • High spatio-temporal data used to separate and quantify erosional cliff processes. • Waves and rainfall are correlated with lower and upper cliff changes, respectively. • Erosion was concentrated at hot spots at a range of temporal and spatial scales. [ABSTRACT FROM AUTHOR]