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.