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

     3.8.    Option E - Combination

Upon review of modeling results for Options B, C & D, it was recognized that all the proposed strategies presented potential
benefits and drawbacks and it was decided to investigate a layout that combined aspects of all of these options [Figure 35].
Option E was developed to incorporate the benefits of all three considered strategies to provide a solution that provided the
greatest benefit with the least impact on the river. As such, Option E includes the following components:

     •      End of Noosa River Spit - Recreational benefits and creation of a beach is not desirable. Allowing further erosion
            is not desirable as this could have impacts on Munna Point. As such, the erosion limit control line has likely been
            reached and an erosion protection wall was included along this section.
     •      Upstream section - Modeling [section 0] showed that emergent training walls and groynes were very effective in
            reducing velocities in this location and providing a control point for the flood tide. Construction of training walls and
            groynes has been included.
     •      Central section - This section is very vulnerable and a key location for recreational amenity. Modeling [section 0]
            showed that the provision of upstream and downstream submerged closures provided substantial benefits in this
            location [the creation of a calm lagoon area and stable beach]. As there was potential for future river changes to
            breach the shoal between the upstream and the downstream closures, it was considered desirable to address this
            problem during the initial works rather than extend the structure as required at some point in the future. The
            potential impact on the river was also minimized with the inclusion of a single, curved closure that allowed a more
            natural channel alignment when the southern channel was dominant. Dredging for construction and use of
            material as nourishment was also included.
     •      Downstream section - this area is presently protected by the existing rock wall. To minimize the impact on the
            river and retain the rock habitat, this has been left in its present state [although it is noted that maintenance of the
            structure may be required if/when the channel deepens along this section].




Numerical modeling [Figure 36 and Figure 37] showed that the curved "closure' successfully created an enclosed lagoon
with lower velocities (typically <0.25m/s) on both ebb and flood tides. The upstream regions of the Noosa River Spit
experienced lowered velocities [<0.25m/s on both the ebb and flood tides] with slightly elevated velocities along a short
section between the closure and the first short groyne. Modeling did not show any inclination for the formation of vortices
adjacent to the training wall, although this may be due to the resolution of the model and the inclusion of nourishment.
Velocities adjacent to the existing rock wall were typically unchanged on the flood tide and lowered on the ebb tide.

In the main channel, velocities were generally the same on the flood tide. although there was minor increases to the size of
high velocity areas adjacent to the northern shoals and the velocities adjacent to the upstream closure were increased (0.1 -
0.5m/s) where the southern channel merged with the middle channel. On the ebb tide, velocities were very similar for the
bulk of the channel, but were slightly increased (by 0.1 - 0.3m/s in places) where the channel is narrowest between the
shoals. Areas of high velocity adjacent to the southern and northern shoals were increased in size. Velocities adjacent to
the shore at the end of the Noosa River Spit decreased on the problematic ebb tide.