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Gallien, TW, O'Reilly WC, Flick RE, Guza RT.  2015.  Geometric properties of anthropogenic flood control berms on southern California beaches. Ocean & Coastal Management. 105:35-47.   10.1016/j.ocecoaman.2014.12.014   AbstractWebsite

Coastal flood riskfrom coincident high tides' and energetic waves is concentrated around low-lying urban areas. Municipalities construct temporary sand berms (also known as sacrificial dunes) to manage potential flooding, however the relationships between berm geometry (e.g., height, width and length) and performance are not understood. Concomitant pressures of sea level rise and urbanization will increase active beach berming. Effective future coastal flood risk management will depend upon optimizing berm efficacy relative to geometry, placement, and water levels. Here, 34 individual berms at seven southern California locations are characterized using 18 LiDAR datasets spanning nearly a decade. Three berm classifications emerged based on deployment duration: event, seasonal and persistent. Event berms, deployed to manage specific storms or high water events, are triangular in cross-section, relatively low volume (similar to 4 m(3)/m) and low crest elevation (similar to 5 m NAVD88). Seasonal berms are larger, volumes vary from 6 to 28 m(3)/m, and average crest elevations are between 5.3 and 6.4 m. A persistent berm, captured in all LiDAR data for that area, is the largest (48 m(3)/m), longest (1.2 km), and highest mean crest elevation (7 m NAVD88) of all study berms. Total water levels, estimated using observed tides and a regional wave model coupled with an empirical runup formula, suggest that overtopping is rare. Currently, event berms are vulnerable to wave attack only a few hours per year. However, even with modest sea level rise (similar to 25 cm) or El Nino conditions, exposure increases significantly, and substantial nourishments may be required to maintain current flood protection levels. (C) 2014 Elsevier Ltd. All rights reserved.

Young, AP, Guza RT, Dickson ME, O'Reilly WC, Flick RE.  2013.  Ground motions on rocky, cliffed, and sandy shorelines generated by ocean waves. Journal of Geophysical Research-Oceans. 118:6590-6602.   10.1002/2013jc008883   AbstractWebsite

We compare ground motions observed within about 100 m of the waterline on eight sites located on shorelines with different morphologies (rock slope, cliff, and sand beaches). At all sites, local ocean waves generated ground motions in the frequency band 0.01-40 Hz. Between about 0.01 and 0.1 Hz, foreshore loading and gravitational attraction from ocean swell and infragravity waves drive coherent, in-phase ground flexing motions mostly oriented cross-shore that decay inland. At higher frequencies between 0.5 and 40 Hz, breaking ocean waves and wave-rock impacts cause ground shaking. Overall, seismic spectral shapes were generally consistent across shoreline sites and usually within a few orders of magnitude despite the diverse range of settings. However, specific site response varied and was influenced by a combination of tide level, incident wave energy, site morphology, ground composition, and signal decay. Flexing and shaking increased with incident wave energy and was often tidally modulated, consistent with a local generation source. Flexing magnitudes were usually larger than shaking, and flexing displacements of several mm were observed during relatively large incident wave conditions (Hs 4-5 m). Comparison with traffic noise and earthquakes illustrate the relative significance of local ocean-generated signals in coastal seismic data. Seismic observations are not a simple proxy for wave-cliff interaction.