Observations of Tidal Circulation in Mamala Bay, Hawaii

by Peter Hamilton, (M.ASCE),

Document Type: Proceeding Paper

Part of: North American Water and Environment Congress & Destructive Water


A comprehensive measurement program, designed to study circulation processes and support hydrodynamic modeling, has been carried out in Mamala Bay on the south coast of the Island of Oahu, Hawaii. One of the overall goals of the study was to quantify the dispersion from two, deep-water sewage outfalls in the bay. Some of the tides show complex flow patterns with strong opposed M2 currents at the two headlands and a nodal point near the Honouliuli outfall. Large internal M2 temperature fluctuations are observed in the center of the bay in the depth range of the main thermocline. A consequence is that, even in the summer when the upper water column is stratified, the water column over the two outfalls can de-stratify almost every tidal cycle and allow waste plumes to surface. The mechanism for the generation of the M2 internal tide involves the convergence and merging of the barotropic tidal wave around the island as it propagates across the north central Pacific. Tidal flows are directed primarily along the isobaths and are about 180? out of phase between the east and west headlands. Internal tides are generated by the sinking and rising, in the center part of the bay, caused by the alternating convergence and divergence of the M2 tidal currents. This generation mechanism does not appear to have been described previously in the literature.

Subject Headings: Tides | Bays | Water circulation | Islands | Hydrodynamics | High-rise buildings | Flow patterns | Hawaii | United States

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