Spatial variability of relative density of sandy seabed surface sediments in an energetic nearshore zone estimated from a portable free fall penetrometer

Many nearshore environments are characterized by energetic hydrodynamic conditions and active sediment transport processes. This impacts coastal erosion and vulnerability, as well as engineering activities in the coastal zone. Friction angle and relative density are key parameters affecting sediment erodibility and soil behavior. However, they have rarely been quantified due to the increased complexity of extracting high quality samples of cohesionless sediments under energetic hydrodynamics. In this study, variations in relative density across and along the sandy nearshore zone of Phipps Peninsula in Yakutat, Alaska, were estimated using a portable free fall penetrometer. Preliminary results suggest significant variations in relative density (Dr = ~20-95%) of sandy surface sediments along four cross-shore profiles (distance to shoreline approximately 200-550 m). These variations were associated with the expected wave impact on the seabed and local sediment transport processes, suggesting also a relationship to water depth and wave height.