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Beach erosion occurs when waves, currents, and storms remove sand faster than natural processes can replace it, gradually narrowing the shoreline and threatening buildings constructed close to the water. Coastal engineers have tried several approaches to slow this process, including building rock walls, known as seawalls, and periodically pumping sand from offshore deposits onto the beach in a process called nourishment. While seawalls can protect the structures directly behind them, studies have shown that they often accelerate erosion on neighboring stretches of beach by altering how waves interact with the shoreline. Sand nourishment avoids this side effect but must be repeated every few years, since the newly added sand erodes at the same rate as the original beach material.