THE MECHANISM OF SEICHES IN TABLE BAY HARBOR, CAPE TOWN

Abstract

Surging in Table Bay Harbor is shown to be favored by the peculiar location of the harbor within Table Bay and of Table Bay within the South Atlantic Ocean, and by the fortuitous fact that both the external and internal dimensions of the 'harbor accentuate the development of seiches. The roadstead comprising a three-sided quasi-basin permits resonant augmentation of several bay-seiches, notably those of about 11 and 5 1/2- minutes period, and certain harmonics among these are stimulated sufficiently to communicate themselves into the docks and achieve resonance there also. The periodicities of oscillations found by observation are explained theoretically and confirmed in model experiments. The largest basin of the harbor, during its construction period, exhibited different oscillating properties from those in evidence today. The differences are explained on the basis of the changing dimensions in shape and depth of the enclosed body of water. Model experiments again confirm the general mechanism of behavior.