See links below. 

The following are Conclusions from the Cardno, CSIRO and Water Technology  Reports,

Cardno Report:   March 2011

Conclusions

 The conclusions are the following:

 1.   The Great Sands as a region is stable on a timescale of human lifetime, but there are areas of mobile sand which are continually changing.

 2.   There are no identifiable changes in the stability of the Great Sands as a region which can be attributed to channel deepening activities.

 3.   There are no identifiable changes in the Great Sands that are attributable to CDP activities that are inconsistent with SEES predictions. Apart from the shipping channels which were dredged, there are no areas which have plausibly changed depth due to the CDP.

 4.   The LADS survey data identifies areas of mobile sand waves, particularly in South Channel, east of Schnapper Deep and in the west on the southern side of the channel. Mobile sand is also identified north of Popes Eye, in Symonds Channel and east of Pinnace Channel. The locations of these areas are consistent with the sediment transport modelling originally undertaken for the SEES and the post dredging refined sediment transport modelling.

 5.   Analysis of the LADS survey data shows there are no identifiable changes to Mud Islands or Swan Island that are attributable to CDP activities.

 6.   The analysis of beach profiles taken from the LADS surveys does not identify any changes in the beaches which can be attributed to CDP. The LADS analysis shows that there is accretion on a number of beaches and very little erosion.

 7.   The comparison of wave heights from modelling before and after dredging shows there is no significant difference in the wave heights off Portsea and adjacent areas in the pre and post-dredging scenarios.

 8.   Further comparison of wave height patterns, and therefore wave energy patterns, in this section of the Bay also does not reveal any significant differences for the pre and post-dredging scenarios.

 9.   Analysis of the measured sea-level and wave data in 2009 shows there were several events of exceptionally high sea-levels accompanied by high wave-conditions emanating from Bass Strait. This combination of naturally occurring extreme weather events is the most plausible explanation for initiating beach erosion on the Nepean Peninsula including the localised area of erosion on the Portsea Front Beach. The refined sediment transport modelling indicated less impact upon sediment transport in the Great Sands from deepening of the channels than was predicted for the SEES. This is consistent with the LADS survey data.

 10.Any observable effects of sediment transport in the dredged areas are likely to be limited to the sand-wave fields in South Channel West and South Channel East, east of Schnapper Deep.

 11.  The pattern and rate of change on beaches in the southern part of Port Phillip Bay during the past 2 years (during and post CDP) is consistent with that documented over the past 150  years.

CSIRO Report:  April 2013

Conclusions

 The major conclusions drawn from this and other studies that were available to the OEM are;

 1.     While beaches do experience significant natural variability the record of shoreline position based on sparse historic photographs is not sufficient to distinguish between differences in tidal elevation, short term storm response, seasonal variability and longer term changes.

 2.     Following the CDP changes in sea level, currents and large scale sediment transport pathways were assessed to be minimal.

 3.     Wave heights at Point Nepean and water levels at Hovell Pile in 2009 were the highest at the 0.05%, 0.1% and 0.5% exceedance level in 8 year record from 2003-2008 and coincided more frequently with higher sea levels associated with storm surge and astronomical tides.

 4.     In a numerical study of wave propagation from Bass Straight through the Entrance and into Port Phillip Bay, Cardno (2011) reported no change in wave conditions following the CDP. The model results did suggest a focussing of wave energy towards the Portsea region and very minor increases in wave height at Portsea (less than ~3%) post-dredging that were considered insignificant. Results of ray tracing analysis (reported in OEM’s third dot point) showed waves reaching Portsea did not pass over the dredged channel. However, given the very localised nature of the erosion at Portsea small changes to the model through various parameter settings, different formulations of wave physics and bathymetry could change the local wave conditions.

 5.     Wave modelling reported by Water technology (2013) also shows a focussing of wave energy towards Portsea Beach but, in contrast to Cardno (2011), a comparison using pre and post CDP bathymetries shows a 7-10% increase in significant wave height. When the significant wave height outside the entrance is 2m the corresponding wave heights at Portsea before and after the CDP are 0.32m and 0.35m respectively.

 6.      A change in the local wave conditions is the likely cause of the erosion at Portsea, however the absence of long wave records at Portsea beach that predate the erosion event and CDP do not allow this to be quantified. Evidence suggests that naturally occurring storm events produced high sea levels and waves that were a primary mechanism for enhanced erosion. However, evidence from wave modelling studies also indicates that it is conceivable that the CDP may have increased the height of waves impacting the beach at Portsea and therefore some degree of attribution to the CDP is possible. In this regard it is therefore also conceivable that the CDP may have not only contributed to the erosion that has been observed, it may have impeded subsequent recovery of the beach. The limited number of wave modeling scenarios considered and the uncertainties associated with assumptions used in the modeling lead to only moderate confidence in the modeling results. Higher confidence in the wave modeling results could be achieved by

a.     providing more evidence of wave model validation using additional wave data collected at Portsea  since the CDP,

b.     investigating the sensitivity of the findings to model resolution under a greater range of tidal, sea level and wave conditions.

 7.     In summary, this review concludes that it is not possible to attribute the erosion observed at Portsea to a single causal factor since a range of factors operating on different time and space scales may be contributing. It is conceivable that the CDP has contributed to the erosion. However the extent of model investigations is not sufficiently detailed to ascertain if this is the case and if so what fraction of the changes in wave height can be attributed to the CDP.

Water Technology Report:  March 2013

Conclusions

The following summarises the main conclusions from the review and analysis of wave transformation processes through Port Phillip Heads:

 1.   The analysis undertaken in this review predicts that the main change to wave transformation processes following the completion of the CDP has been associated with an increase in the total internal reflection of wave energy along the bathymetric discontinuities created by the CDP dredging. The analysis predicts the total internal reflections are predominately occurring along the bathymetric discontinuities created at the ‘Entrance Approach Channel’, ‘South Channel West’ and the ‘South Channel Sediment Traps’.

 2.   The absolute magnitude of the changes in significant wave heights predicted due to total internal reflections are relatively small and vary from a few centimetres to up to 0.1m locally under average type ocean wave conditions. Absolute changes in mean wave directions of greater than 50 are predicted adjacent to the bathymetric discontinuities created by the CDP.

 3.   In relative percentage terms, the predicted changes to wave transformation processes associated with the CDP dredging result in predicted local increases in significant wave heights between approximately 7-10% at Portsea Front Beach, and a relative decrease of between 5-7% is predicted for Lonsdale Bight. Significant, percentage changes to wave heights are also predicted immediately adjacent to the bathymetric discontinuities associated with the CDP dredging.

 4.   The non-linear relationship between wave height and wave energy yields predicted percentage changes in wave energy density locally of 15-20% at Portsea Front   Beach, with corresponding decreases of 10-15% in Lonsdale Bight. 

 5.   Testing of incident wave directions representing the majority of the incident wave energy at Port Phillip Heads found that the extent of the changes identified were insensitive to incident wave direction and the testing suggests that the predicted changes to wave transformations associated with the CDP exist under the majority of incident wave conditions.

 6.   Modelling analysis using the series of Post CDP bathymetric scenarios derived from various surveys of the study area showed that the predicted changes to wave transformation associated with the CDP were able to be reproduced with reasonable consistency across these surveys and time periods following the completion of the  CDP.

 7.   The modelling analysis using the series of Post CDP bathymetric scenarios showed that over time, natural variations in bathymetry can result in additional changes to wave transformation processes, however, testing of the 2010 NO CDP bathymetric scenario showed that these changes could be clearly distinguished from the predicted changes associated with the CDP bathymetric changes.

 8.   The various sources and contributing factors that influence the level of certainty that can be prescribed to the findings of this analysis have been reviewed. A number of sources of uncertainty were identified that relate to the schematisation of the bathymetry, the numerical modelling scheme and the specification of the ocean wave boundary conditions.  However, these sources of uncertainty are generally expected to result in an underestimation of the changes identified in this analysis

9.   The major source of uncertainty that could influence the relative significance of the main changes to the wave transformations predicted in this analysis is considered the extent to which tidal currents intensify and subdue the total internal reflections from the bathymetric discontinuities created by the CDP. The net impact of tidal currents on the percentage change in wave conditions will be related to the extent of asymmetry between flood and ebb tide current speeds at these locations.

Below is our letter of the 13th March to Ms Kelly Crossthwaite;   DELWP

Dear Ms Crossthwaite

 Thank you for your letter dated 25 February 2015. I have discussed it with David Syme, Chairman of the Portsea Foreshore Advisory Group (PFAG), as our two organisations represent the strongest body of community interest and opinion in relation to the present situation at Portsea. We think it is important that we advise you of our continuing concerns about the efforts to date to rescue the Portsea front beach.

You may be aware that prior to the change of Government, Ryan Smith as Environmental Minister was very supportive of the ongoing drive to find and install a viable, long term solution for re-establishment of the Portsea Beach. Many senior people in your Department, including Rodney Warren and Travis Dowling, were genuine in their efforts to achieve this.

Since the change of Government in 2014, we have become aware of one policy change which appears to have been made, but which is inconsistent with the apparent legal obligations enjoyed by, most relevantly, the lessee of land in the Point Nepean National Park with a lease for the development of commercial undertakings in that park.

Whilst we are very appreciate of the support and goodwill exhibited by your department to date, it is worrying to our community that major projects committed to by the previous government are to be abandoned or are under some other form of threat. Accordingly we ask for your assurances that the plans to rectify the issue at Portsea Beach by the new Government are not under any such threat.

As outlined in your letter we have noted with concern that no variation of the Worley Parsons contract, as previously discussed in our recent meeting, could be initiated to include finding solutions to the problem. This decision was based on advice from your legal department.

However your department did agree, within the original scope of the tender, to examine sand drift from the Nepean Bay coastline to the offshore sand shoals, sand shoal dynamics and migration patterns and near-shore and beach dynamics.

Studies to date by Water Technology and Worley Parsons have reached the same conclusions with where the refraction is occurring. We must emphasise that unless the additional data is essential to identifying a solution to diverting the wave pattern it is therefore wasteful of public funds. These funds ought to be applied directly to finding a solution.

As the prevailing wave pattern was first observed in 2009, we think it is irrefutable that these conclusions have taken far too long to reach. We are adamant that finding a solution to what is plainly an environmental disaster, needs to be fast tracked as the community has lost patience and will require far more aggressive activity by its representatives.

 For these reasons we are requesting that steps be taken immediately to address all matters that are required:

• First, find and publish a suitable solution
• Second, obtain from the Government these assurances:

o   that these steps will be agreed to within a stated time frame;

o   that works required will be funded by the Government; and

o   that finally, when the works are completed and are successful, that all remedial works that have been done at Portsea to primarily protect the assets behind the dune are removed and the beach bought back to its original condition, a beach that was known as one of the most iconic front beaches in Australia.

Yours sincerely

Colin Watson  :   President  Nepean Ratepayers Association

David Syme:  Chair  Portsea Foreshore Advisory Group