A grain of sand on a beach does not stay put; it zig-zags along the shore, because waves arrive at an angle while the backwash runs straight down the slope. The more oblique the wave angle, the faster the longshore drift, and the longer the spit grows where the coastline bends. A groyne teaches coastal engineering’s expensive lesson: sand piles up thick on one side while the other is starved and cut back, so stopping erosion here simply moves it somewhere else.
A grain of sand on a beach does not stay put; it zig-zags along the shore, because waves arrive at an angle while the backwash runs straight down the slope. The more oblique the wave angle, the faster the longshore drift, and the longer the spit grows where the coastline bends. A groyne teaches coastal engineering’s expensive lesson: sand piles up thick on one side while the other is starved and cut back, so stopping erosion here simply moves it somewhere else.
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