Internal Tides and the Spread of River Plumes in the Trondheim Fjord
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The Trondheim Fjord receives a substantial amount of freshwater during the year, with a mean runoff of 725 m3s-1 and a spring flood maximum of up to 6430 m3s-1. How this freshwater spreads and mixes with the ambient presents one of the great challenges in understanding the dynamics of fjord circulation. This problem is approached in the present thesis by performing high-resolution numerical simulations of the physics and circulation of the Trondheim Fjord. The model used is the Navy Coastal Ocean Model (NCOM). An introductory study is carried out for a river discharge into an idealized basin. The simulations are compared with results from previous studies where laboratory models have been applied to study similar problems. In the next study the Trondheim Fjord is simulated for different scenarios that include the forcing of river discharges, tides and the effect of the Coriolis force. The simulations show that the river plumes in the fjord are affected by the rotation of the earth, which is to be expected from earlier studies. Further, the internal tide has in certain cases a great influence at the freshwater flow near the surface. These results are used to explain earlier observations of the hydrographic conditions and currents in the Trondheim Fjord. The NCOM model has also been configured to reproduce the physical circulation in the Trondheim Fjord for a period in April 2002. Different types of data and observations from this period are used to evaluate the model results. Findings from earlier studies are also considered and compared with the results from the high-resolution simulations.