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

Preliminary design has been prepared [Figure 43].


  Rock Design                                               2m [barge construction]
                                                       OR 4m [land-based construction]
                  od lei
  HA                                                 Armour                     1V:1.5H
                                                      Rock
EA1




   Sand-filled Geotextile Container Design

         100yr flood level
 HAT


 LAT
                   Dredge
                                                                                         J W V.21-1
                                                                                              W_
                                                                RL-3.5m AHD
               Max -6.1 m AHD
                                                          18m

   Sand-filled Geotextile Container Design with Rock Armour




Figure 44: Preliminary design of training wall

Modelling was undertaken using emergent structures and, as such, the crest level must be above HAT with some allowance
for wave action. It is intended that the top of the training wall be at approximately 100yr flood height. Design of the structure
is such that it can accommodate any minor overtopping during events.

Preliminary design has allowed to take the closure to a depth of approx. RL-6.1 m AHD, over 1.5m lower than surveyed
maximum channel depths within the Noosa entrance (and 4-6m below current depths). The only location which is in excess
of this depth is adjacent to the water inlet for the sand recycling and this is not in close proximity to the structure. Still, given
the variability of the river and the proposed staging of the works, it is possible that at some point during the life of the
structure the training wall could be subject to undermining due to channel deepening or local scour. In the event that
monitoring identifies that levels are approaching the foundation depth directly adjacent to the structure, an additional
container or rock could be used to provide additional scour protection. The structure is flexible and can accommodate some
settlement, although this could result in lowering of the crest.

An 80m training wall has been allowed. This brings the structure to approximately low tide mark, beyond which construction
becomes impractical. Shoreward of low tide, it is anticipated that sand fill will be placed to allow for the construction of a
revetment wall detail [see section 6.3]. The placed fill on the eastern side of the training wall will be stable as this region will
be very well protected by the training wall.

The last 100m of the Noosa River Spit is low-lying and subject to inundation on king tides and during flood events. As such,
there is the potential for breaching at the shoreward end of the groyne during a flood event. To avoid this, it is intended to
link the proposed training wall with a location which is not subject to inundation during flood events.