5. FACTORS AFFECTING DESIGN AND LAYOUT
Practical limits for alignment of berths
5.1 The seaward limit for the alignment of the quaywall is determined largely by the availability of fill to reclaim the area behind it, the time that the reclamation would take to consolidate and the cost of the structure required for the depth of water and existing seabed conditions. In this respect the Container Committee's layout for the Terminal shows an alignment of seawall which in view of the very large amount of fill required is considered to be about the practical seaward limit for the wall alignment.
5.2
The landward limit for the wall alignment is determined by the presence of the existing breakwater, the dredging needed and the minimum requirement of land area for the Terminal. The limit of alignment as determined by the position of the breakwater and Mong Chau is shown on Drawing 8. Depending on the other factors any alignment between these two limits will be practicable.
Availability of Filling Material
5.3
5.4
In deciding on the most practical layout for the Terminal one of the most important factors is the availability and cost of filling material for reclamation purposes. If there is a scarcity of free material from site-formation works and the cost of gaining of filling material is high and has to be included in the cost of the project, the amount of reclamation to be carried out must be reduced as far as possible. On the other hand if there is an abundance of free material then the fullest use must be made of it.
In assessing the availability of fill for the terminal the following sources of supply have been investigated:-
(a) Material from areas where site development will go ahead whether or not the terminal
is built.
(b) Material from sites not planned for development in the near future but which could
be reserved as borrow areas.
(c) Public dumping.
(d) Incinerator ash.
(e) Dredged material.
Dredging of Berths and Approaches
5.5
5.6
In selecting an economic alignment for the quaywall the amount and cost of dredging required to give the necessary depth of water at the berths and in the approaches should be balanced against the amount and cost of reclamation needed for the Terminal itself. Also it should be ensured that the depth of water required can be attained by dredging without encountering bedrock as this can only be removed at great expense. The cost of dredging will be influenced by the depth to which it must be taken, the distance to the spoil-dumping area, the suitability of the dredged material for reclamation purposes and the time allowed for completion of the work. The area to be dredged must for the sake of economy be kept to a minimum but must provide easy access for vessels to the berths from the deeper water.
At Kwai Chung, the site investigations carried out indicate that the nature of the seabed was such that dredging to -40′ C.D. and in some places to −50′ C.D. could be carried out without encountering rock except at positions close to Tsing Chau and Mong Chau. Should however a berth and approach to it be required with a seabed level of −50′ C.D., then considerable dredging would also be required off the south-east corner of Tsing Yi to provide a similar depth of water in this area of the main approach channel.
Area Required
5.7
In the Container Committee's 1966 Report they recommended that each berth should have:-
A working apron and container-marshalling area of about
A packing-station area of about
A lorry park and circulation space of about
Making a total of approximately
:
:
8
acres
6 acres
6 acres
20 acres
12