Table 2.2 Summary of Alternative Design Options
Design
Option |
Environmental
Benefit |
Environmental
Disbenefit |
Remarks |
Vessel
Type: |
|
|
|
Shallow draught vessel |
Minimize
catwalk / jetty length; Minimize
scale of dredging for approach channel & associated water quality impact.
|
|
Key
factors in determining the scale of dredging for approach channel are vessel
draught & length. Not
considered practicable due to adverse weather conditions and vessel stability
constraints. |
High manoeuvrability vessel / small size |
Reduce length of catwalk / jetty size; Minimize scale of dredging & associated water
quality impact. |
|
|
Jetty
Structure: |
|
|
|
Rubble
mound catwalk with openings in causeway under catwalk |
Openings
would enhance seawater circulation; Rubble mound foundations would provide habitat for recolonisation and would compensate for the loss of intertidal habitat; Rubble mounds would blend with rocky boulder shoreline. |
|
|
Open
bridge type structure (with piled support) for catwalk and jetty head |
Enhance
seawater circulation; Minimize
visual intrusion; Minimize
scale of dredging & associated water quality impact; Reduce
loss of intertidal, seabed habitat & benthic communities. |
Piling/
pile foundation would result in noise disturbance to dolphins, but bored
piling would minimize impact compared to percussive piling; Less
area for recolonisation by intertidal fauna; Disturbance
associated with greater maintenance activities. |
Higher
cost and maintenance requirements for piled support &
reinforced/prestressed concrete bridge catwalk. |
Construction
Method: |
|
|
|
Use of pre-cast structures for jetty &
catwalk |
Shorten
construction period & duration of impact. |
|
|
Underwater piling |
|
Mitigation may be required to
minimize noise impact on dolphins e.g. use of bubble curtain. |
|