Circulation, mixing, and exchange processes in the vicinity of tidal inlets: A numerical study

Abstract

The circulation in the vicinity of an idealized tidal inlet connecting a continental shelf and a coastal sound is examined. The circulation is forced by an M2 tide and a weakly buoyant discharge. The buoyant discharge forms a plume in the coastal ocean and induces a distinct anticyclonic circulation at the plume edge that is maintained throughout the tidal cycle. We focus on the plume's onset and its evolution over 5–10 tidal cycles. Over the timescales considered, the plume was roughly circular, slightly skewed in the along‐coast direction. The model solution yielded high vertical Ekman numbers Eϵ ∼ O(5) in the vicinity of the inlet mouth, decreasing seaward from the inlet to an order of magnitude smaller (Eϵ ∼ 0.25) at the seaward edge of the plume. Passive particles released in the region seaward of the inlet mouth were used to describe the exchange between the coastal region and the inlet. A marked asymmetry between ebb and flood flows is observed in the vicinity of the inlet, with jet‐like ebbing currents and weaker potential‐flow‐like flooding currents. Over a tidal cycle, net exchanges between the coastal ocean and the inlet are found to be spatially and temporally dependent; that is, particle trajectories depend on the release point and the time of the release in the tidal cycle. The near‐inlet residual circulation shows significant differences in the absence of stratification.