Relating Geotechnical Sediment Properties and Erodibility at a Sandy Beach

Abstract

Geotechnical sediment properties, morphological change, and hydrodynamics were measured as part of the During Nearshore Event Experiment (DUNEX) in October 2021 at the sandy Atlantic side beach in Duck, North Carolina. In this study, direct relationships were explored between in situ soil properties and direct erodibility measurements in the context of morphological change. Moisture content, grain size, total density, relative density, void ratio, and sediment strength were compared to bed-level change using ground-based LiDAR and erodibility parameters from laboratory jet erosion tests (JETs) conducted along a cross-shore transect stretching from the dune toe to the lower intertidal zone. Directly relating changes in sediment properties to changes in morphology from LiDAR proved inconclusive due to the complex interactions between sediments, hydrodynamics, and morphology, even on a local scale, but initial observations and possibly impacting factors were discussed. Void ratio and total unit weight correlated well with the detachment rate coefficient from JETs, with denser sediments testing as less erodible. In situ sediment strength measurements related—as expected—to total unit weight, void ratio, and water content, with increases in firmness factor associated with increases in total unit weight, void ratio, and water content. These strength measurements were also found to have a correlation with the detachment coefficient from the JET, with stronger/firmer sediments being less erodible than weaker ones.