Asymmetric tide in Lake Vallunden (Spitsbergen)

We observed strongly asymmetric tide in a channel connecting the Van Mijen Fjord and Lake Vallunden in Spitsbergen. The channel is approximately 100 m long, 10 m wide, and 1–2 m deep. Asymmetric tide was also observed in the lake. The form of the semidiurnal tide is described by a combination of only three harmonics (<i>M</i>₂, <i>S</i>₂ and <i>M</i>₄) with different amplitudes and phases. The flood dominant form of the surface elevation in the channel (unlike the ebb dominant tide in the fjord) is formed over a horizontal distance of 50 m over a shallow bottom at the entrance to the channel. The tide in shallow places becomes asymmetric due to nonlinear effects caused by the influence of the bottom and especially by choking of the tidal flow over a sill that is located between the fjord and channel. We think that such a small distance, over which the form of the tide changes, is caused by the small scale of the channel related to the fjord. We suggest a numerical model related to these measurements