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

     3.3.   Option C1 - Wall and Embayed Beach

Option C1 involves the construction of an erosion protection wall along the length of the Noosa River Spit with the formation
of a short embayed beach to provide recreational amenity. For the purposes of the model, the groynes were fully emergent
and extended out to the centre of the existing channel. See Figure 20.




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Figure 20: Sketch of works forming Option C1

Given the full protection of the majority of the shoreline with hard erosion protection measures, the key area of concern in
this case is the proposed beach area between the two groynes. Numerical modeling [Figure 21 and Figure 22] showed
similarly low velocities would be experienced in this area on the flood tide. however on the ebb tide [most critical for erosion]
it showed only a small region (-30m in length) adjacent to both groynes where velocities were lowered. The remainder of
the beach between the two groynes was subject to higher than existing velocities [up to 0.8 - lm/s]. This is a significant
increase [by up to 0.5m/s].

In the main channel, velocities were generally the same on the flood and ebb tides, although the areas of high velocity
adjacent to the northern and southern shoals were increased in size. Velocities adjacent to the shore at the end of the
Noosa River Spit were decreased on the flood tide and increased on the ebb tide [although this location would be protected
by rock wall as part of this option].

In the medium term it is likely that the southern channel will once more become dominant. This will result in a deepening of
seabed levels adjacent to the ends of the groynes and an increase in velocities in the southern channel. Velocities adjacent
to the structure and within the embayment will change in response to the change in the channel configuration. While it is
possible that widening of the channel may result in a reduction to the velocity spike shown by the modelling, it could easily
result in further increases in velocity.

The potential impacts of Option C1 [wall & embayed beach] include:
               •    Within embayment
                         •    Increased erosion
                         •    Increased potential for breaching of Noosa River Spit in an already vulnerable location
               •    Where walls are located [majority of foreshore]
                         •    No further erosion
                         •    Complete loss of beach
                         •    Complete loss of recreational amenity
                         •    Adverse public perception

While it may be possible that groynes could effectively be used to protect the area directly adjacent to the rock wall. the
proposed layout does not appear to be effective and it is clear that the creation of a stable beach in this location would
require either many more groynes at much closer spacings [which is less desirable for recreational beach amenity] and/or
much longer groynes [which would result in channel closure without substantial dredging to relocate the existing channel].