An introduction to the Hele-Shaw beach experiments

The sea, as well as being a destructive force can also be constructive and can move great quantities of sand often forming a beach. Waves can move material both up and down the beach, leading to the construction of sloping beaches. Wave-sand dynamics are studied via experiments. The tank is narrow, just over one-particle diameter wide, creating a quasi-2D set-up also geared towards mathematical modelling. There is strong two-way feedback between the free-surface waves and the beach morphology. The waves transport the particles, changing the basal topography, causing the waves to transform from rolling to breaking. ``All'' classical breaker types (plunging, collapsing, spilling and surging) are observed on a time-scale of about a second. Finally, on longer time-scales many steady beach morphologies are observed, including dry and wet beaches, dry berms/dunes, and bars. The highlight being dry dunes which have dynamic waves crashing on the seaward-side and quiescent water on the far side.