Technical note on possible hydraulic control of the exchange through the Oxdjupet passage in the Baltic Sea

Hydrographic data and ADCP current-meter records from a passage in the archipelago of Stockholm are analyzed to determine whether hydraulically controlled exchange flow took place. Initially the analysis was based on standard 2-layer formalism, showing that the flow was significantly subcritical during all the hydrographic surveys. Since, however, the presence of mixing and friction precludes an ideal 2-layer flow, the analysis was extended to encompass three layers. Within this framework two of the six surveyed hydrographic situations proved capable of sustaining marginally critical flow with respect to the wave mode analogous to that present in the 2-layer case. Since almost maximal 2-layer exchange was attained concurrently, this indicates that the flow could in fact have been critical on these two occasions.