Non-linear dynamics and attractors for the entrance state of a tidal estuary
Many small estuaries comprise a tidal basin linked to the sea by a constricted entrance channel, itself formed by the tidal and fluvial flows. Its dimensions control the tidal, salinity and water quality regimes within the estuary. Methods of non-linear dynamics have been applied to discover and characterise the attractors for the entrance channel. An attractor (node) is a quasi-equilibrium state to which the estuary evolves over time. Two attractors have been identified, one in which the entrance is tidally dominated, known crudely from field studies of tidal prism-entrance area relationships, and a new attractor in which the river flow dominates the hydrodynamics but the small tidal flow dominates the evolution. Attractor methods provide a powerful new tool for understanding and managing estuaries.