Development Application - Part 2 of 2 - Report & Plans · OPW11/0116

5.   CONSTRUCTION MATERIALS

A number of construction materials were considered, including:
    •   Rock - suitable
    •   Sand-filled geotextile containers [both smaller units and mega-containers] - suitable
    •   Concrete walls - not flexible enough to accommodate erosion
    •   Concrete modules - not in keeping with the natural visual appeal of the area
    •   Reef balls - unlikely to be effective
    •   Combination

     5.1.   Sand-filled geotextile containers

Construction of submerged structures using sand-filled geotextile mega-containers is not common, but has been undertaken
successfully in the past. This would be achieved by:
     •      Excavating / dredging to the design base level [within tolerance] and with suitable batters - material to be used for
            construction [filling of containers], beach nourishment and backfilling, as required.
     •      Container to be rolled out and anchored in place using barge-mounted equipment and divers
     •      Fill the container using dredge or jet pump
     •      Seal container with closures using divers

Construction of structures using smaller 2.5m3 sand-filled geotextile containers would require creation of a working platform
with a sand stockpile for filling and stockpiling of containers. These could then be placed either onshore using excavators or
in submerged locations using barge mounted excavators. For greater depths, slings can be used, but placement accuracy is
lower.

The manufacturer advises that the 1209RP geotextile has an official lifetime when fully exposed to UV conditions of 25
years, which is considered to be conservative. As the structure will be submerged a large part of the time, the geotextile
promotes the ingress of sediment into its structure and will likely provide a suitable substrate for marine growth (all of which
will reduce the UV reaching the geotextile), it is anticipated that the actual lifetime of the structure could be longer.

     5.2.   Rock

Construction of structures using rock would require importing of material. Importing by truck would result in a significant
impact on Hastings St and require clearing of a significant access track (700m x 3m = 2100m2) along the length of Noosa
River Spit, a designated koala habitat area. This is generally considered to be undesirable and should not be considered
providing that costs for delivering the rock by barge are acceptable.

     5.3.   Comparison

A comparison of sand-filled structures and rock is presented in Table 1.

Table 1: Advantages & disadvantages of rock & sand-filled aeotextile containers
            Sand-filled Geotextile Containers                                                  Rock
Advantages                                                        Advantages
•   Stable with suitable container sizes                          •     Stable with adequate rock sizes
•   Can be designed to allow for scour                            •     Can be designed to allow for scour
•   Flexible to accommodate additional scour if necessary         •     Flexible to accommodate additional scour if
•   Easily removed / modified / extended if necessary                   necessary. Easily topped up.
•   Uses local materials [no need to import materials]            •     Easily extended
•   Uses floating plant [no access issues]                        •     Robust [no potential for damage]
•   User-friendly                                                       Voids may create habitat
•   Substrate may provide
•   Cost
Disadvantages                                                     Disadvantages
•   Vulnerable to damage from vandalism / vessel impact               Import of materials required
    even with robust RP geotextile. Higher maintenance.               If importing by truck, need for clearing and traffic
•   Replacement cost [25year lifetime]                                issues along Hastings St
                                                                  •   Less user-friendly
                                                                  •    Cost
                                                                  •     More difficult to remove