Work

Internal hydraulics and solitary waves in a realistic laboratory model of the Gibraltar Strait

Year: 2026

Type: article

Abstract: We present the first laboratory investigation reproducing realistic internal solitary waves (ISW) in a rotating, tidally forced exchange flow over complex bathymetry, using the Strait of Gibraltar as a dynamically consistent prototype. The experiments reproduce strongly nonlinear ISWs consistent with field observations and resolve their generation, propagation, and hydraulic evolution throughout the tidal cycle. The results reveal fundamentally different generation mechanisms during spring and neap tides. During spring tides, ISWs are generated by the release of an internal hydraulic jump at Camarinal Sill following flow reversal, producing strongly nonlinear bores that may subsequently evolve into solitons. During neap tides, the hydraulic jump remains persistent and weakly nonlinear bores instead arise from nonlinear steepening of the internal tide. Spring-tide internal waves are strongly nonlinear and generate intense Kelvin–Helmholtz instabilities and vigorous mixing, whereas neap-tide internal waves remain weakly nonlinear and are dominated by Holmboe instabilities with substantially weaker mixing. The experiments further demonstrate that maximal exchange in the Strait is maintained during the experiments but does not imply a complete independence from the Mediterranean Sea boundary conditions throughout the Strait. Instead, the spatial extent of the controlled region evolves with the background flow, governing the subsequent evolution of spring-tide internal waves. A simple two-layer hydraulic criterion successfully predicts the bore–soliton transition, identifying local hydraulic criticality as the primary control on wave morphology despite the strongly three-dimensional character of the exchange flow.

Source: Deep Sea Research Part I Oceanographic Research Papers

DOI: 10.1016/j.dsr.2026.104753

Authors: Axel Tassigny, Lucie Bordois, Xavier Carton, Samuel Viboud, Thomas Valran, Maria Eletta Negretti