In a manner similar to that of surface waves on beaches, high-frequency interfacial waves (IWs) may break when approaching the 'internal coastline,' where the undisturbed pycnocline intersects the shoaling bottom. This process has been studied previously in idealized laboratory and numerical experiments but there are few field observations to document the properties of IWs shoaling on natural internal beaches. This paper presents observations of currents, density and turbulence collected inshore of the break point of an internal beach of the St. Lawrence Estuary. A series of large- and small-amplitude complex-shaped and unorganized internal boluses was observed. The structure of these boluses is discussed, along with their role in boundary turbulence and transport.
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