Harbour resonance

Harbor resonance is the amplification of long-wave energy inside a basin when the period of incoming infragravity or long waves matches a natural oscillation period of the harbor, set by its plan geometry and depth. The amplified standing wave drives strong horizontal currents at the antinodes even when the vertical sea-level change is small, so moored ships range and break mooring lines while the water surface barely moves. Resonant periods run from tens of seconds to hours. Layout design detunes the basin from the local long-wave climate and adds energy-dissipating or absorbing boundaries to damp the response, per PIANC guidance on moored-ship motions.