Author: Fung, Yuk-ming
Title: Mathematical model study of tidal deformation in Tolo Harbour, Hong Kong
Degree: M.Sc.
Year: 1994
Subject: Tides -- China -- Tolo Harbour (Hong Kong) -- Mathematical models
Hong Kong Polytechnic -- Dissertations
Department: Department of Civil and Structural Engineering
Pages: 1 v. (various pagings) : ill. ; 30 cm
Language: English
Abstract: The objective of this study is to investigate the cause of the tidal deformation found within the Tolo Harbour. Such tidal deformation may be due to turbulent stress and bottom friction stress within the harbour, and also the seiching of the harbour. The tidal record obtained from the tide gauges at Tai Po Kau, Ko Lau Wan and Waglan Island showed that tidal deformation was found at Tai Po Kau and Ko Lau Wan respectively. A semiimplicit finite element scheme developed by Li (1986) was adopted investigate the tidal deformation phenomenon. A mathematical model with the finite element grid covering the Tolo area and Mirs Bay was established to compute the tidal circulation in Tolo Harbour. The accuracy of the model was confirmed by using the hourly tidal record at Ko Lau Wan as input at the open boundary of the model and comparing the simulated tide with the hourly tidal record at Tai Po Kau. A tide filter which based on the work of Dijkzeul (1984) was developed to filter both recorded and simulated tide into five principle tidal constituents :- diurnal tide, semi-diurnal tide, quarter-diurnal tide, sixth-diurnal tide and eighth-diurnal tide. The filtered tides of the tidal record showed that the tidal deformation was mainly due to the amplification of quarter-diurnal tide, sixth-diurnal tide and also the eighth-diurnal tide. The quarter-diurnal and sixth-diurnal tide have already been amplified at the Mirs Bay while the eighth-diurnal tide was amplified within the Tolo area. From the model, the resonant frequency of the Tolo harbour was found to be close to the period of eighth-diurnal tide. It was therefore believed that the amplification of the eighth-diurnal tide is due to seiching in the Tolo area. With the hourly tidal record at Ko Lau Wan as input to the open boundary of the model, the model can reproduce the similar tidal deformation occurred at the Tolo Harbour. However, when the tidal record at Waglan Island was adopted as input, the tidal deformation reproduced by the model was much less significant. Through the analysis of the simulated tide by means of the tide filter, it was found that the model cannot reproduce the similar amplification of the quarter-diurnal and sixth-diurnal tides as that found in the tidal record. The sensitivity study of the model showed that this was not due to the inappropriate estimation of the turbulent stress, bottom friction and the shallow water effect in the scheme. The amplification of the quarter-diurnal and sixth-diurnal tide is therefore probably due to the seiching in the area including Tolo area and Mirs Bay. It was believed that the imposition of clamped water elevation boundary condition at the mouth of the Mirs Bay led to the incapability of the model in reproducing this seiching effect.
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