Tidal and wind forced flow in clode sound: observations and numerical modelling

Timko, Patrick George (2004) Tidal and wind forced flow in clode sound: observations and numerical modelling. Doctoral (PhD) thesis, Memorial University of Newfoundland.

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Abstract

Clode Sound is a small fjord on the east coast of Newfoundland that contains a shallow sill and coinciding contraction. Studies of the hydrographic properties and currents in Clode Sound, Newfoundland during the summers of 1996 and 1997 indicate that considered as a two-layered model the tidally forced flow over the sill is supercritical during spring tides. Supercritical flow may lead to the formation of internal bores or internal hydraulic jumps that increase the vertical mixing as they propagate away from seaward side of the sill. Within the inner basin, there is little evidence of mixing below the level of the sill and the inner basin water, formed during the winter months, remains trapped. Fresh water inflow from the Northwest River is low but the combination of mixing and the input of solar radiation leads to the formation of a well-defined surface layer in which the water column is thermally stratified. On the seaward side of the sill, the surface layer extends below the level of the sill, within the inner basin the depth of the surface layer is limited by the depth of the sill. The model used to simulate the circulation of Clode Sound is based upon the Princeton Ocean Model (POM). Attempts to simulate the three-dimensional circulation using a static density field reveal that such a model is not capable of reproducing the tidal currents with Clode Sound. Models with a static density field show no significant difference to a model with constant density. The inability of the model to reproduce the tides leads to an imbalance of forces when wind stress is applied to the model. Further simulations in which temperature and salinity evolve within the model provide a much better result for the main tidal constituents. The inclusion of temperature and salinity mixing required very strong relaxation of the scalar fields and the model performance is evaluated with both a constant background density field and an evolving background density field. Wind stress applied to the mixing model leads to the rapid onset of numerical instability limiting the length of the model simulations. A comparison of the model simulations to the observations of 1996 and 1997 indicate that with both tidal and wind stress forcing the model, the model is able to reproduce the variability of the residual circulation but is unable to reproduce the observed velocity field .

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