3。2Model Selection

(c) Offshore resultant-wave roses

Fig。 2   Offshore wave roses。

shows that the dominant resultant-wave direction is south-westerly。

2。4Tide Levels

The astronomical  tidal  level variation  at the study

As waves approach the study site, they are affected by headlands, shallow water areas and complex seabed contours。 A one-dimensional model is not capable of dealing with such complex bathymetry and topography。 A two-dimensional spectral wave model has, therefore, been adopted for the study。

The MIKE2I SW model developed by DHI was used to transfer offshore waves into the study site [1]。 It is a third generation coastal wave model, which incorporates the latest developments in wave generation, wave refraction, shoaling, wave breaking, other shallow water effects, wave-wave interaction and wave-current interaction。 It has been successfully used in many similar situations throughout the world and is widely accepted by the industry。

Table 1   Water levels at the study site。

3。3Model Setup

The model area was chosen to ensure that it covers the study site and the surrounding area so that the impact of headlands and nearshore bathymetry is included in the simulations。

The east and west boundaries were set at distances far enough from the study site so that there is sufficient distance for waves to stabilise before they interact with the sea bed contours near the site。 The south boundary was set at the  offshore  data point。 The north boundary was set at a sufficient distance from the study site in order to avoid any boundary effects。 Overall the area covered by the model was approximately 45 km • 50 km。

A flexible (triangular) mesh was used in the study。 A high resolution was maintained within the shallow water areas as well as at the study site where changes in wave conditions take place quickly within short distances。

Bathymetric data were obtained from C-Map [4] which provides digital data from Admiralty Charts [5]。 The model bathymetry is illustrated in Fig。 33。44 Model Input Conditions

A water level of +0。74 m was adopted for all model runs。 This is the mean of HHWL and MHWL plus an allowance of 0。5 m for future sea level rise。

The model was used to transform the 10。83 years of offshore time-series wave to inshore location。 Model runs were carried out separately for wind-waves and swell-waves。 In the case of wind waves, winds were applied across the model to simulate the local contribution from wind in wave generation。 The time-series wind data was applied during the transformation of the wind-waves。 No wind was included into the model during the transformation of swell-waves。

3。55 Model Results

Model results (wave heights and directions) were extracted  for  the  entire  modelling  area。  The  wave

height contours were superimposed with wave direction vectors。 Samples of two-dimensional offshore-inshore wave transformation plots are shown in Figs。 4 and 5 for wind-waves and swells, respectively。

The model results were extracted at selected locations within the navigational areas and along the jetty of the proposed dry bulk terminal。 Examples of the model results at the study site are shown in Figs。 6 and 7 for wind-waves and swells, respectively。

4。Downtime Assessment  Technique

Operational downtime may be defined as the number of days per year when wave conditions at the loading and unloading berths exceed a given height Preliminary Assessment  of Operational Downtime of Sea Ports and Berthing Facilities through i2 I

Numerical Modelling

4。11 Definition of Wave Heights