Groyne Field Sediment Budget

Waves rarely meet a beach head-on. When they break at an angle, the swash of each wave surges obliquely up the sand while the backwash drains straight back down the slope under gravity — and that asymmetry drags sediment steadily along the coast, a process called longshore drift. This simulation renders that mechanism directly: hundreds of sand grains zigzag along a stretch of coastline in real time, their net alongshore speed set by the same sin(2θ) law that governs the real CERC transport formula. Drop a field of groynes into the surf zone and watch the physical consequence play out as a live sediment budget — sand piles up in bright bars on the updrift face of each wall while the beach immediately downdrift is starved of supply and erodes toward exposed rock, exactly the trade-off coastal engineers have to weigh when they build one.