How do waves help build the barriers that enclose coastal lagoons?

Waves play a fundamental role in creating the barriers that enclose coastal lagoons by acting upon an adequate supply of bottom material, typically sand.1

These barriers form in areas where the coastal slope is flatter than the equilibrium slope required by long constructive swells—the waves that build up the foreshore in front of their breakpoint. By depositing material on this gradient, waves build up an equilibrium profile that eventually rises above the sea level. This accumulation can be further elevated by wind to form dunes.12

Additionally, waves contribute to the formation of these barriers through the transport of material along the shore. This process can create a spit, which may extend across a bay to become a bay-mouth barrier, effectively enclosing a lagoon. Once the barrier is established, it protects the land behind it from the open ocean, allowing a lagoon to persist as long as the barrier maintains its elevation relative to rising sea levels.234