Numerical modelling of hydraulic control, solitary waves and primary instabilities in the Strait of Gibraltar

A two-dimensional, vertical section of the Strait of Gibraltar is simulated numerically with the nonhydrostatic/ non-Boussinesq three-dimensional CROCO model to investigate details of small-scale dynamics. The proposed configuration is simple, computationally efficient and incorporates the configuration of sills characteristic of this region. Despite the shortcomings of a 2D representation, this configuration provides a realistic depiction of small-scale mechanisms in the strait during a typical tidal cycle: internal solitary waves generation and propagation, occurrence of hydraulic controls and hydraulic jumps at the sills and presence of active turbulent patches. In particular, the well-known eastward propagation of large amplitude internal waves is assessed using the Korteweg de Vries (KdV) propagation model for solitary waves. As a step towards establishing a realistic three-dimensional Large Eddy Simulation (LES), the sensitivity of the configuration to various choices (e.g., resolution, amplitude of tidal forcing or numerical schemes) is investigated. Our analyses indicate that the representation of small-scale dynamics in the Strait of Gibraltar can be much improved by increasing resolution and relaxing the hydrostatic assumption. Further studies are necessary to grasp the mechanisms of mixing and/or stirring induced by this fine scale process.