Seiches

A seiche is a standing wave oscillation in an enclosed or partially enclosed body of water, such as a lake, bay, harbor, fjord, or reservoir. The water sloshes back and forth between basin ends, producing stationary nodes (points of little or no motion) and antinodes (points of maximum displacement). Seiches range in period from minutes to many hours, depending on basin geometry and depth.

Seiches are generated by disturbances that displace the water mass, including persistent or sudden wind stress, rapid changes in atmospheric pressure, seismic activity, or incoming long waves such as tsunamis. When the period of the forcing matches a basin’s natural modes, resonant amplification can greatly increase wave amplitude. In the shallow-water approximation the fundamental period for a rectangular basin is approximately T = 2L / sqrt(g h), where L is basin length, h is mean depth and g is gravitational acceleration; higher modes have correspondingly shorter periods.

Impacts of seiches include strong currents, rapid changes in shoreline water levels, damage to moorings and small craft, and localized flooding. They are recorded in lakes and coastal basins worldwide, notably in the Great Lakes, parts of the Baltic Sea, and many enclosed harbors. Detection and monitoring use tide gauges, water-level sensors, and pressure recorders; modeling of basin resonances helps predict likely periods and potential amplification.

Understanding seiches is important for hazard assessment, harbor design and water-resource management in enclosed and semi-enclosed basins.