Coastal protection structures are constructed to protect harbors and infrastructure from ocean waves and erosion. The document discusses five common types of coastal protection structures: seawalls, bulkheads, groins, jetties, and breakwaters. Seawalls run along shorelines and are designed to withstand wave action through curved or stepped faces. Bulkheads retain earth and come in gravity or anchored sheet pile designs. Groins reduce erosion by altering currents and waves, while jetties extend into water to block sandbar formation and currents. Breakwaters shelter areas in three forms: offshore, shore-connected, or rubble mound.