PO Box 162
BLUE WEDGES SUBMISSION TO PUBLIC INQUIRY: INVESTIGATION OF ‘SCOUR’ AT THE HEADS
This document has been prepared by Blue Wedges in response to recent studies investigating ongoing scour believed to have been caused by the Trial Dredge program in 2005 at Port Phillip Heads. It must be noted that the two week timeframe for the public submissions on this new and complex information is grossly inadequate, whereas the decision to allow the PoMC an extension of time for unfinished studies seems to be extraordinarily charitable.
This submission draws attention to the likelihood of undocumented instability of the rock formations at Port Phillip Heads, and the inadequacy of studies to predict its future behaviour. This matter has the potential for severe impacts on the Port Phillip Bay environment, coastal infrastructure and Commonwealth Heritage sites. In that context we ask: what is the design duration of the Great Ship channel? Is it designed to last 30 years (C.f. the bund to contain spoil on the northern DMG? By comparison the Dutch design seawalls to withstand one in 500 year events.
Some 2 years after the Trial Dredge operation, scour and disintegration of rock at the Great Ship Channel is still occurring. This has implications for the recovery rate of marine communities which existed in the area prior to the Trial; and also for the hydrodynamics of Port Phillip Bay.
- Recovery is highly dependent on the disturbance to the substratum – there is evidence of multiple successional stages present at some sites, indicating periodical, ongoing scouring effects;
- There are substantial ongoing rock fall processes occurring following dredging, with new rockfall material being derived from reef disintegration;
The implication of this uncertainty is that ongoing scour of the reef will cause changed tidal regimes and currents to erode areas of foreshore and the Great Sands and alter important habitats (such as Swan Bay and Mud Islands).
As a general principle, the greater the amount of scour the greater the potential for altered currents and tidal regimes, damage to coastal habitats, infrastructure and property.
Cardno Lawson Treloar (CLT) has been asked to consider any implications for the results in the original report if it is assumed that the Great Ship Channel scoured to depth of -22 CD . Additional modeling was carried out to investigate this situation.
The CLT report provides no background on why it may be assumed that scour would occur at the Great Ship Channel; or more specifically, why the depth of -22m CD was selected for study; nor if studies to determine for how long the continued disintegration of the rocks are proposed. Consequently, while the CLT report does shed some light on potential impacts of scour, it should not be relied upon to rigorously assess environmental risks or shipping safety.
On the basis of the modeling, CLT conclude that there is no appreciable difference in hydrodynamics of the existing case and the scour scenario. However, their reports do not present include charts which enable comparison of the effects of ebb-tide currents on the Great Sands in the ‘existing’ and ‘scour’ scenarios. In the absence of this information, it is not possible to conclude that significant erosion of the Great Sands will not occur.
Further, the CLT hydrodynamic modeling studies are based on one month of modeling and therefore cannot be seen as representative of all seasonal conditions.
Blue Wedges therefore contends that the CLT Hydrodynamic cannot be relied on to inform risk assessments for other disciplines such as fisheries, seagrasses, etc.
Examples of areas which would be effected by altered tidal regimes
Swan and Sand Islands north of Queenscliff are very low-lying and consist of sandy beaches backed by dune ridges and backshore depressions. Along the northern and eastern sections of the island, marshland fringes the coastal zone. Both islands are of biological importance as bird habitat. Coastal processes in these regions are influenced at present by dredging of the Queenscliff Creek. An altered tidal regime may increasingly erode the sandy beach and cause retreat of the marshland vegetation.
Areas of potential vulnerability are the southwestern sections of Swan Island, which is restricted Commonwealth land with important defence installations. The southwestern shoreline is subject to swell waves and is actively eroding but has recently been maintained by dredge spoil. The beach is backed by low-lying dune and backshore areas behind which is the main access road. Greenhouse changes may lead to accelerated erosion along this sector, with the possible threat to the main access road if the barrier breaches. Operational army buildings, gun placements of historical significance and telegraph poles, may also be threatened by flooding and wave attack on this actively eroding shoreline.
Global Warming and predicted sea level rise
The effects of altered tidal regimes can only exacerbate the effects of sea level rise resulting from global warming, adding to coats of coastal infrastructure maintenance.
For example, the Queenscliff entrance separating Sand Island from Queenscliff is presently dredged. Siltation may increase if greenhouse changes result in a greater body of sediment being carried through the Rip. From the boat pier south towards Shortlands Bluff, the beach is backed by low-lying dune ridges in the north and a vegetated cliff towards Shortlands Bluff. Erosion of this beach may result in inundation of the low-lying backshore area to the north and undercutting of the cliff to the south, threatening buildings situated at the base of the cliffs .
From Shortlands Bluff to Point Lonsdale, a long continuous beach runs along the length of Lonsdale Bay, backed by a grassy dune. Greenhouse changes may increasingly erode the beach leading to the undercutting and instability of the dune. The area of greatest impact may be at the central western section where the beach is very narrow and a rock rubble and wooden wall have been built to protect the dune from wave attack.
A seawall lines the beach towards Point Lonsdale backed by a vegetated bluff. The beach is narrow and groynes have been placed to try and halt sand movement. The beach may be increasingly lost with increases in wave attack against the seawall. At Point Lonsdale, the shore platform may become permanently inundated and the cliffs of dune calcarenite may be increasingly undercut and the seawall attacked. This beach would be subject to high energy wave activity and so erosion and retreat of the beach may be rapid.
Analysis of ‘Scour Assessment Report The Entrance’, SKM July 2007
Blue Wedges contends that the investigations in the ‘Scour Assessment Report The Entrance’, SKM July 2007 are inadequate for the purpose of drawing sound conclusions on the duration that scour might be expected to continue.
The modelling done by Raisbeck on rock fall only looks at the effects of gravity and slope on mobile rock. It does not estimate the impacts of tidal currents or swell. This is probably because there is not sufficient information about tidal currents over the range of depths being considered.
In order to assess the potential rock fall, scour effects and delamination of rock, plus the role of the 'hard cap' layer at RL-22m will require extensive research and analysis, and even then the risk will be uncertain as there are so many variables. Raisbeck has said that pieces of layered base-rock up to 2m wide and 250mm thick have been worked loose and flipped over by current and swell.
Much more detailed investigation is required in relation to the geology at the Heads; and other factors which contribute to instability of rock formations. In the absence of this greater detail the assumption that scour will not progress any deeper than -22m is mere speculation.
It appears dredging causes fractures in this relatively soft rock and this is then worked by the currents. But the rock is also naturally weak along joint lines and faults, and the rock is also variable and layered so that prediction of how it will behave when exposed to currents is difficult.
Calcarenite is basically sand that has been welded together usually by calcium dissolved in water that percolates down through more or less horizontal layers. This means layers of various hardness form, sometimes interleaved with pure sand.
The notion being put forward by PoMC that rock scour will not go more than 3m below the surrounding rock levels, or below RL-22m due to the "hard cap"
layer at that level is dubious. The "hard cap" is hardened calcarenite and has been scoured down to RL-25m in some places. The combined effects of delamination and rock scour has not been accurately assessed (if, indeed it can be). Currently, PoMC is saying scour could continue for 10 years (and maybe they are saying that because that is the span of the project).
Proximity of the Entrance to geological faultlines
Port Phillip Heads is located between two roughly parallel faultlines, with Selwyn’s Fault 22 kms to the east and the Bellarine Fault 5 km to the west. Five earthquakes with epicentres within 20 kms of the Heads were recorded between 1974 and 1982 (Atlas of Victoria. Victorian Govt. Printing Office. 1982). This indicates that earthquakes are very common within a short timeframe.
Seismic activity associated with the Bellarine Fault and Selwyn’s Fault has probably already fractured the rock formations in the Heads and that process is likely to continue into the future. There is no indication in the SKM Report that the impact of seismic activity on rock in the proposed dredging area has been considered in the project assessment.
Other factors which may contribute to weaknesses in the rock and therefore ongoing delamination and rockfall include historic blasting activities, the Trial Dredge program and any subsequent dredging.
Blasting might create weaknesses within a radius of the blast site, or further increase existing weaknesses in the rock e.g. by causing separation of rock layers. Similarly dredging might cause fractures below or beside the point of mechanical contact, which are then more easily mobilized by movement of tide and swell.
Channel deepening in 1902, 1912, 1923, 1945-77, 1981-87.
1902- 1200 tonnes dynamite used – 8590 charges used
1945-77- WWII mines and depth charges used – 100 plus blasts per year.
1902 - reduction of pinnacles
1923 - 37 ha leveled to new depth
A key assumption of the SKM Report is that the “hard cap” layer claimed to occur at -22m is relatively uniform across the area to be dredged. Given the geological instability and variability of the area, we question whether the data is adequate to support this assumption. We contend that it is quite probable that areas of scour could penetrate well beyond -22m. There are existing sites where this has already occurred.
Speculation on scour impact timeframe
This assessment dismisses the possibility of ongoing delamination and rockfall. The consequences of an error of judgement failing to predict a significant altered tidal regime would be catastrophic.
PoMC Consultants in a wide range of fields have been asked to comment on the implications of scour scenario to -22m. Generally they have concluded that risks are negligible or minor. The consultants were not asked to comment on a scour scenario beyond -22m.
We contend that scour to -22m is not necessarily the worst case scenario.
Because the degree to which the Entrance might scour out, and over what time span, is likely to remain uncertain, a full reassessment of bay-wide impacts should be made based on a revised worst-case scenario. Impacts include potentially escalating rates of delamination and scour in the Rip, bigger volumes of water in and out of the bay, extra flushing of the bay, bigger tidal ranges, bigger impacts on the Great Sands, more changes in currents and current speeds, etc., etc.,
The SKM report admits that mobile rock is accreting to the immediate south of areas of scour in mounds of up to 2m high. These mounds represent a hazard to shipping. Ongoing clean-up to remove these rocks, which are likely to result from major storm events, has not been costed.
The inadequacy of hydrodynamic investigations to assess the scour in the Rip and erosion in the Great Sands has major implications for a wide range of environmental values including adjacent Marine Parks, Ramsar sites, and Heritage-listed Commonwealth sites (see Appendix 1). The accretion of scoured rock (mentioned above) to the south of scoured sites, indicates that the ebb-tide current is stronger than the flood-tide. A nett loss of sand from the Bay (eroded from the Great Sands) is a probable scenario under these conditions.
The Shipping Channel in the Rip is at risk of ongoing scour and accretion of rock. The Southern Channel is at risk of increased influx of sand eroded from the Great Sands.
SEES process and extension of Public Inquiry afforded the PoMC
The PoMC entered into the Inquiry process in the full knowledge that their studies were incomplete. The matter of altered hydrodynamics was admitted in the opening days of the Inquiry but no detail was provided until July 30 (the second last day of the hearing).
As with information on studies relating to toxic sediments, the documents on rock scour were released after all public presentations had been delivered. Consequently, the public has been allowed less than 14 days to respond to a complex set of documents and effectively denied proper opportunity to appraise and respond to issues. The process has had no provision for expert witness assessments and presentations.
Further, we understand that the Independent Expert Group (IEG) has not been convened as a group to discuss this issue. At this stage we are unaware of any formal response from the IEG. To what extent has the IEG been consulted?
Public denied access to key information
In the course of this investigation a member of the public rang the Hydrographic Survey Office to request historical records of blasting, and other works in the Rip and was told that the information could not be accessed without approval from Mr Nick Easy, Executive General Manager Channel Deepening Project.
When phoned, Mr Easy asked if the request was in regard to the channel deepening inquiry and was told it was. Mr Easy then said that the request should be directed to Michael Crossman at Planning Panels Victoria as the Public Inquiry had said that all inquiries regarding the channel deepening project go through that office.
The Planning Panels Office was contacted and the response was that “The Inquiry advises that it is not in a position to become involved in your request for this material,
The withholding of this information effectively constrains the capacity of the public to undertake relevant research on the issue in question.
The information provided so far in the SEES and subsequent studies is insufficient to enable the Public Inquiry to make a confident assessment that major risks are avoidable.
 P. 20 Expert Witness Statement to the Public Inquiry (June 2007)
 P. 1 Supplementary Report – Entrance Channel Depth. Cardno Lawson Treloar. July 2007
 P 22. Victorian Coastal Vulnerability Study. Port of Melbourne Authority, 1992.
 P. 22 Victorian Coastal Vulnerability Study PMA 1992
 P.13 Scour Assessment report. The Entrance. SKM July 2007
 Jan Watson presentation at Field Naturalists Club of Vic Hall 11/4/2005
 Don Raisbeck SKM. PowerPoint presentation to Inquiry
 Email correspondence. Michael Crossman, 10/8/07
Swan Island is the largest emergent sand accumulation feature in Port Phillip Bay. The island, which has been built principally by wave actions rather than by aeolian forces, has played a major role in determining the pattern of sedimentation in Swan Bay and preserves geomorphological evidence of changing Quaternary sea levels. The eastern and northern shores of the eastern arm of Swan Island are of regional significance as an example of active coastal depositional and erosional processes. The patterns of erosion and accretion on these shores provide a good indicator of sand movements into Port Phillip Bay.
Swan Island and Naval Waters is an integral part of Swan Bay, an internationally significant wetland which is important as wader and waterfowl habitat, and provides important habitat for 46 water bird species: of which 26 species are listed under the Japan-Australia and China-Australia migratory bird agreements; and 8 species are listed under the Bonn Convention on Migratory Species.
During the migration season Swan Bay supports internationally significant populations of the eastern curlew (NUMENIUS MADAGASCARIENSIS), ruddy turnstone (ARENARIA INTERPRES), red-necked stint (CALIDRIS RUFICOLLIS), sharp-tailed sandpiper (C. ACUMINATA), curlew sandpiper (C. FERRUGINEA), and grey plover (PLUVIALIS SQUATAROLA). Nationally significant populations of the greenshank (TRINGA NEBULARIA), pacific golden plover (PLUVIALIS FULVA), double-banded plover (CHARADRIUS BICINCTUS), and lesser sand plover (C. MONGOLUS) also occur.
Sand Island is the most important high tide roosting area in Swan Bay and at high tide regularly supports half of the shorebirds in the Swan Bay - Mud Islands complex. Sand Island maintains a regular breeding population of the fairy tern (STERNA NEREIS) and provides the main roosting habitat in Swan Bay for the nationally endangered little tern (STERNA ALBIFRONS). Significant numbers of lewin's rail (RALLUS PECTORALIS) have also been reported from Swan Island.
The only Victorian record of the Sea Water-mat (LEPILAENA MARINA), rare in Victoria, is from the ZOSTERA MUELLERI meadows of Swan Bay (Stingaree Bight and along the western and southern shorelines of Duck Island & Swan Island). The Devious Sea-wrack (HALOPHILA DECIPIENS), rare Victoria-wide, occurs in the HETEROZOSTERA TASMANICA meadows of Swan Bay.
Communities dominated by moonah (MELALEUCA LANCEOLATA) only occur as remnants in the Swan Bay area, with Swan Island one of only two places with relatively pristine examples. The mosaics of wet and dry saltmarsh that occur extensively around Swan Bay, and on the islands, provide a good example of communities that were once more widespread. It has been estimated that since European settlement, some 75-80% of the saltmarsh that occurred between Melbourne and Pt Lonsdale has been destroyed.
Swan Island retains relatively undisturbed coast tea-tree (LEPTOSPERMUM LAEVIGATUM) and coast beard-heath (LEUCOPOGON PARVIFLORUS)/ beaded glasswort (SARCOCORNIA QUINQUEFLORA) woodland and saltmarsh communities. These habitats provide important winter feeding and roosting sites for the nationally endangered orange-bellied parrot (NEOPHEMA CHRYSOGASTER). These birds migrate from Tasmania each year to spend winter on the mainland, Swan Island is one of three major wintering sites on the Australian mainland and has supported up to 40% of the total population.
Ten historic shipwrecks are known to have occurred in the vicinity of Swan Island. The location of six of these wrecks are known within Swan Island's naval waters, these are Mountain Maid (1856), Will O the Wisp (1853), the Iza (1928), Countess of Hopetoun (1924/25), J-3 submarine (1926), and S.F. Hersey (1923). These wrecks contribute strongly to the maritime history of this part of Port Phillip Bay.
The area also contains a highly significant historic cultural landscape, the Swan Island Defence Precinct, a network of defensive fortifications built by the Colonial government in 1879 for Victoria's protection. This place is the subject of a separate Register of the National Estate listing (database number 019449).
It is possible that Indigenous cultural values of national estate significance exist in this place. As yet the Australian Heritage Commission has not identified, documented or assessed these values.
Swan Island is significant as a cultural landscape containing a rich collection of historic elements including fortification earthworks, battery emplacements, underground command centre and tunnel network, jetties and buildings relating to the early and important theme of coastal defence in south-eastern Australia. The island fort was developed from 1877 in response to fears of Russian invasion of Britain's colonies in the late nineteenth century. (Criteria A.3 and A.4)
The mud flats and seagrass communities of the area form the most extensive remnants of the communities which were once much more widespread in Port Phillip Bay. The wetlands of the area are of international significance and have been included in the Directory of Wetlands of International Significance under the Ramsar convention which designates sites of international importance especially for waterfowl habitat. The mudflats, saltmarsh, seagrass meadows and sand dunes within the area support a high diversity of fish species, wading birds and waterfowl including species protected under Japan Australia Migratory Birds Agreement and China Australia Migratory Birds Agreement international migratory waterbird treaties. It also provides an important breeding and nursery area for fish, crustaceans, molluscs and other marine organisms. Swan Island supports the largest known population of the Orange- bellied parrot, which listed as rare by the International Union for the Conservation of Nature in the International Council for Bird Protection bird red data book and as endangered by Council of Nature Conservation Ministers.