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Home Background Chronology Key Issues Engineering Report Legal Advice Magnetic Harbour 1998 Nelly Bay Proposal 1995 Magnetic Quay 1989 Magnetic Keys 1986 Win-Win Alternative EIA Process Public SEIS Responses State SEIS Response Federal SEIS Response Public FEIS Responses Nelly Bay Photographs Corporate Information State Marine Park Great Barrier Reef Region Photo: Brahminy Kite © Ian Montgomery www.birdway.com.au	Engineering Report: Proposed Construction of Canal Estate Nelly Bay 1. Introduction Following is a discussion of some engineering and related issues involved in construction of a canal estate at Nelly Bay. Initial construction at Nelly Bay started in 1988 and was abandoned in 1990 for financial reasons, leaving breakwater walls and some earthworks around the periphery. The site presently can be described as an 'eyesore', and represents a considerable degradation of the original amenity and environmental values of the area. This paper was prepared without reference to the most recent EIS for proposed redevelopment of the Nelly Bay site. It is intended to provide background information and opinions based on experience from geotechnical assessment of earthworks generally. It also reflects the writer's experience from 1995-present with the canal estate at Raby Bay, near Brisbane, which includes both short-term construction-related issues and long-term maintenance issues. Raby Bay is constructed in an area of clay materials (mostly derived from volcanic rocks), whereas Nelly Bay is likely to involve a mixture of clays, sands, and coarser materials. While the materials have an important influence on the manner in which engineering can be done, the underlying principles are material-independent. The following discussion of both materials and underlying principles is addressed particularly to readers who do not have a background of professional training and experience in earthworks construction. 2. Materials Issues 2.1 Materials to be Used at Nelly Bay The materials will be sands, clayey sands, and silts together with coral rubble and rock sourced at site. Much of the coral rubble and rock will be obtained by underwater blasting for the entrance channel. In addition, fill material of various gradations may need to be imported to the site. Most of the materials are likely to be of fair to reasonable quality, geotechnically speaking, and certainly stronger and easier to place and compact than the clays found at Raby Bay. Nelly Bay is a geologically recent embayment beach sequence with two important distinctions: the terrestrial sediment input from overland runoff (principally Gustav Creek, prior to urban development), and the fringing coral reef. Over the Pleistocene period (the age of glaciations) the coastline has changed dramatically, for example until about 12,000 years ago the coast was many kilometres seawards of its present location. As the sea level rose, the coastline sediment sequence was driven westwards. The immediate geological profile at Nelly Bay is thus granitic bedrock which is weathered and incised and overlain by a sediment 'layer cake' which is likely to vary laterally over small distances due to seasonal activity of the Gustav Creek drainage system. Apart from the presently known deposits of potentially acid sulphate soils, there may be many other pockets not just at the immediate present tidal zone. Some of any such pockets may have already been disturbed by construction (dredging) to date, but this is unknown. It does mean that any dredged or excavated material which is removed from an anaerobic saturated state to a subaerial state as fill, may potentially require ASS treatment. The Bulk Earthworks Matrix described in the Thiess document of June 1995 may not be correct in terms of quantities for the latest proposal, but the sourcing is undoubtedly current. There will definitely be a requirement for some imported fill, including topsoil for landscaping. The current level of ASS survey is not necessarily sufficient to identify the overall extent of the potential problem, if fill from excavation is to be used above low water springs level. Experience from detailed review of construction records for the Raby Bay Canal Estate is that fill sourcing will vary, and quality will vary more than the construction specification would indicate. It would be impossible, in my opinion, for fill to be controlled to the standards required for such a contained site unless truly Level 1 earthworks supervision (AS 3798-1996) was in place. The ASS question is of great importance, given the damage that has already been done to the fringing reef and the necessity to minimise future damage no matter what construction options are adopted. 2.2 Environmental Management Constraints Noise, dust, and siltation are inevitable at any earthworks construction site. There is now a body of good information on best practices which, if adhered to or enforced, should lead to acceptable levels of disturbance due to noise, dust, and siltation. Construction traffic will create disruption to the local road network, particularly when imported materials are being hauled. This can also lead to noise and dust nuisances well away from the site itself. Unfortunately the previous construction activity at the site has severely degraded the amenity and environmental values of the area with respect to its pre-construction state. The soils, beachfront, and fringing reef are all sensitive to disturbances. Because the general area has outstanding natural attributes, it should be a goal of any construction activity and post-construction facility to restore the former conditions to the greatest possible extent. It would not be technically feasible to remove the present constructed forms without creating additional negative environmental impacts particularly to the beach area and fringing reef. However, such impacts should also be compared to the impacts of completing the marina basin and in particular the negative impacts of construction of the access channel. 2.3 Stability of Canal Banks and Revetments The stability of all embankments and slopes should be explicitly checked during design. The basis for design calculations, and the criteria used for stability, should be explicitly included in design documents and reports submitted for approvals. For most of the situations and materials that can be determined and interpreted from the information to date, it is not expected that stability design will be difficult. Longer-term stability of the constructed landforms will depend as much on good construction practices as on acceptability of design. At Raby Bay there has been a continuing history of instability despite designs being acceptable and approved. The causes are related to the swelling properties of the clays but are not well understood, and research work is continuing. At Nelly Bay the most likely causes of instability following end of construction are likely to be internal erosion and collapse. The former will happen if filters and other controls are not adequately designed to prevent seepage water from eroding and transporting fine soil particles, while the latter will happen if materials are not adequately compacted (to design specifications). Revetments are defined here as the parts of the wetted slopes that are deliberately designed and constructed to resist erosion. The proposed revetments at Nelly Bay are rip-rap rock. This will require geofabric and possible sand bedding filters to prevent internal erosion of the fill behind the revetment. Materials that are suitable for Nelly Bay conditions are readily available. However, it is often the case that such filter systems are not adequately designed or constructed, with a reliance on unrealistic specifications or installation 'to manufacturers recommendations' which are not followed. As noted above, the Nelly Bay fill materials are not likely to exhibit the poor engineering characteristics of the Raby Bay materials. Provided that there is adequate sampling and testing, and that the design basis is properly set out and reviewed prior to approval, instability is not expected to be a concern for Nelly Bay unless construction standards fall below specification requirements. Having Gustav Creek discharge into the proposed marina basin is a fundamental design weakness, given that the access channel leads through an already damaged reef. The alternative would be to construct a stream diversion, which would involve large-scale foreshore disruption and which may be difficult and expensive to stabilise against flooding. Sedimentation from Gustav Creek may have some stability implications. If a sedimentation basin is constructed, with the intention of periodic clearing, then this will probably involve disturbance of the ASS area. If there is no explicit sedimentation control, then periodic maintenance dredging will be required with the spoil either being used for nearby beach replenishment, pumped out to sea, or loaded-out for remote disposal. 2.4 Performance of Foundations on Filled Ground Construction processes for reclamation fill lead to many implications for subsequent foundation performance. Usually there will be some post-construction settlement, although this will be minimised if the fill compaction control is really good. However buildings are very sensitive to such movements and building owners insist on extremely fine tolerances with respect to cracking, loss of alignment, etc. The degree of settlement depends on the fill material consistency and depth of filling, as well as on the degree of compaction achieved. In practice, the degree of settlement must be expected to vary a lot, and in ways that are not easily predictable. In order for owner expectations to be fulfilled, there will be a requirement for testing and engineered design of foundations to provide support to buildings. This may involve cost premiums for piles or stiffened rafts, even though the reclaimed land may be very expensive to begin with. Many owners will not understand this, and may accept compromises on development costs which lead to building damage, poor relationships with builders and local authorities, and litigation which should have been unnecessary. Such histories are part of the Raby Bay experience, even though the majority of buildings there have been well designed and perform to expectations. Part of the problem may be attributable to the hype which surrounds the marketing of reclaimed land, in order to make the high purchase costs attractive. Some of the building-related problems at Raby Bay have been significant, but have been incorrectly associated with the engineering of the fill for the estate. The blame has generally lain with cost-cutting and unreal expectations, or a failure to appreciate realities that exist but which do not fit the marketing image of a high-value estate. Questions may then arise about the competence of local authorities that provide development approvals. There will always be a market for lowest-common-denominator engineering, and local authority approval relies upon engineering advice without necessarily being able to determine if it is adequate or not. If the advice is inadequate, it not only may lead to specific performance problems, but will also reflect poorly on the majority of engineers who would have provided much better advice. 2.5 Cyclone Impacts Because the area is subject to cyclone activity, any development would have to be designed for appropriate levels of potential impact. The longer-term responsibilities of the local authority and the private landholders must be considered in relation to the consequences of such impacts. A severe cyclone event will create damage, and appropriate design will only limit damage to (hopefully) acceptable levels. A high-value coastal canal estate will have public infrastructure (roads, storm-water, sewerage, electricity reticulation, and communications lines). The local authority will be responsible for all of the canals and waterways, as well as the roads, drainage, and sewerage. In the event of a severe cyclonic impact, the surrounding region will also be impacted. The demand for repair works and the costs of such repairs will place severe strain on local authority resources. In the case of a canal estate at Nelly Bay, the demands may be locally severe, and the responsibilities of private landholders would be limited to structures on their land. The wider community would have to provide resources for restoration of public infrastructure. For a canal estate, the component of public infrastructure is significantly higher and more damage-prone than for the surrounding land-based community. This requires forethought and planning to determine whether the additional responsibilities of a canal estate are a justifiable risk and cost that the local authority should be prepared to accept on behalf of the wider community. 3. Underlying Principles 3.1 Role of Engineer Professional engineers may undertake a number of roles for a reclamation-type development. The designer is responsible for fulfilling normally accepted standards of safety, function, and fitness for purpose. The specifier has to document the intention of the design in such a manner that there can be a fair and enforceable contract to construct the facility using suitable materials and methods. The certifier provides a legally binding opinion that the actual materials and works comply with the specification. Provided that the design has been adequately prepared, and that the materials and methods comply with the specification, the risk of failure (ie loss of function or fitness for purpose) is normally acceptably low. Usually reductions of risks are directly proportional to the care (and money) spent on addressing risk minimisation. However, there will always be uncertainty about the quality of design detailing, material variability, and works practices. The risk of failure is closely linked to the quality control or quality assurance used for all aspects of the project. 3.2 Process of Engineering Inputs to Design, Specification, and Certification The designer of a reclamation project is normally a civil engineer who is dependent on inputs from other discipline specialists. Examples relevant to Nelly Bay include the distribution and potential severity of oxidation of acid sulphate soils, the distribution and strength variability of in situ sediments and fill materials, and the prediction of wave climate or cyclonic conditions. Typically all such specialist information includes reasonable assumptions and representative data, but can never exhaustively eliminate uncertainty. It is normal practice to utilise quality assurance systems as an efficient method for minimising risk. These systems rely on a chain of compliance with recognised (community accepted) standards. If acting for the project developer, there will always be pressure on the designer to reduce compliance costs. For a reclamation development, the bulk of the work involves naturally variable materials under conditions where supervision can never be absolute and compliance testing is both expensive and tedious. These conditions always lead to the risk that corners will be cut, and reasonable assumptions made instead of more detailed investigation, design, or testing. 3.3 Specification and Intent versus Practicality and Guarantee Engineers refer to the term design intent. Specifications are developed to describe this, but to allow as much flexibility as possible in how this is achieved. In practice, this means that there may be opportunities for such activities as: • use of non-specification materials when the inspectors testers or certifiers are otherwise engaged; • failure to achieve adequate compaction everywhere, and even conspiracy to achieve it only in areas that will be scrutinised and tested; • actions to minimise testing and scrutiny by creative interpretation of the wording of the specification (engineers are not generally perfect writers, can be guilty of cutting corners with preparation of specifications, and may not recognise that a problem has been created); • making contingency decisions as a result of bad weather, breakdown of equipment, lack of sufficient quality of suitable fill (etc), that violate the spirit of the design intent but which help to bring the project in on time and within budget. One of the frequently encountered problems at Raby Bay is the misunderstanding that compliance with specification provisions is a guarantee of performance. It is impossible to make such guarantees, but it is human nature for developers and marketers to sell-up the virtues of a package by implying things that cannot be implied. All that engineers can do is minimise risks (that are known) and apply prudence and judgement where the risks are not clearly known. Engineers are trained to do this far better than non-engineers. However engineers typically are put in the defacto role of environmental managers, and may then apply judgements and values outside of their area of expertise. There are standards for earthworks construction that should be used for any proposed construction activity at Nelly Bay. Given the sensitivity of the site, and its previous history, the only appropriate standard is the so-called Level 1 which requires full-time supervision by suitably trained and accredited testing authorities and/or construction engineers. The scale of the site is relatively small, so Level 1 supervision is unlikely to be efficient and would therefore be much more expensive than the developer would prefer. However, no other means can be foreseen whereby the likely scale of construction can be achieved successfully, and the previous construction episode is sufficient proof that very high standards are mandatory. 4. Precautionary Principle For Environmental Management The commonly stated version of the precautionary principle is that where there are threats of serious or irreversible environmental damage, lack of full scientific certainty should not be used as a reason for postponing measures to prevent environmental degradation. In applying this principle, public and private decisions should be guided by (1) careful evaluation to avoid wherever practicable serious or irreversible damage to the environment (2) an assessment of the risk-weighted consequences of various options. It is considered that the current Nelly Bay situation already represents serious and irreversible environmental damage. Intervention measures, for example construction of a facility or rehabilitation of the site in some manner, are therefore urgently required to restore amenity and minimise future environmental risks. No matter what intervention takes place, there will be high costs and environmental impacts. The issues are therefore about the form that intervention should take, how the construction and future maintenance costs should be met, minimising the short-term negative environmental impacts, and maximising the long-term environmental gains. There is a strong case for applying the precautionary principle to the Nelly Bay situation in order to restore values to the degraded environment and enhance the amenity that has been adversely impacted. This would involve consideration of environmental, maintenance, and cost issues in a systematic manner considering long-term as well as short-term constraints. Rather than start the process by searching for a development solution that satisfies particular cost-revenue constraints, a range of options should be evaluated using objective management criteria. All options would have to be evaluated as legitimate options to a completed development in order for any choice of action to be justifiable in environmentally sustainable terms. Economic criteria including capital and maintenance cost issues would form part of the risk-weighting process. In broad terms, four options need to be evaluated: • do nothing; • complete some form of constructed development; • abandon a fully developed canal estate, with retention and possible modification of those elements already constructed but which would be too difficult, too costly, or too environmentally degrading to deconstruct; • fully deconstruct the existing works and rehabilitate the site; Adoption of the precautionary principle to guide the process means elimination of the 'do-nothing' choice, or its use only as a benchmark for comparing the benefits of the other choices. If a canal-style facility is constructed within the existing breakwater walls, the Gustav Creek mouth area would require creative and expensive engineering to develop a construction and long-term maintenance plan that would not lead to future facility and neighbouring reef damage from siltation. All the landscaping of the reclamation area would require watering and fertiliser application, the runoff from which is potentially fatal to a range of marine organisms. The final civil engineering design would therefore have to include the constraints of managing sediment inputs, capturing runoff, intersecting seepage, and eliminating nutrient loading to the canals and hence the marina mouth and reef flats. The design would also have to be maintainable at an acceptable cost for an indefinite future period. Alternatives to construction of a canal estate development would involve some deconstruction of the current breakwater structures and rehabilitation of the beach and foreshore. This would also restore the Gustav Creek mouth area, and would probably result in enhanced tidal water circulation and minimal future maintenance requirements. Foreshore maintenance similar to other parts of the Magnetic Island coastline would be involved. At Raby Bay (and at other canal estates, it is understood) a rates levy is used by the local authority to fund maintenance works including drainage management and dredging. The intention of a rates levy is to raise funds specifically for the maintenance requirements of the development, without imposing on ratepayers elsewhere who would gain no benefits from it. This intention has been broadly accepted at Raby Bay and in the surrounding shire, even though it was opposed by a small proportion of owners who took the view that such costs should not have been necessary, or should have been included in the purchase price. A rates levy could be considered as part of the funding mechanisms for both development and deconstruction options. The current development proposal documentation should be sufficiently detailed to enable risk-weighted consequences to be evaluated for the choice to complete a constructed development. Because there is presently no documentation of the scope and likely impacts of choices involving deconstruction, further discussion of deconstruction is set out below. 5. The Options for Decontruction 5.1 Basic Approach An experienced civil engineer will automatically assume that the costs and impacts of deconstruction will exceed the costs and impacts of the original construction. There are many reasons for this, not the least of which is that structures that are built to last are implicitly difficult to pull down. For example, experience with repairs to failed concrete walls along canal frontages at Raby Bay Canal Estate is that rebuilding costs are at least twice the cost of initial construction, and this is with minimal removal of materials. The deconstruction option should not be passed-over just because it does not meet the automatic assumptions of experienced engineers. Whether or not it has merits at the end of the process, evaluation must be based on detailed arguments and credible costings. The final choice of action can then be based on the balance of risk-weighted economic and environmental arguments. Following is Table 1 which is a preliminary framework for discussion of the issues involved in deconstruction. It is not a credible engineering plan, or a sufficient basis for costing. To develop plans and costing for deconstruction, it is estimated that experienced civil engineers would require at least four person-weeks of full time work to expand the table into a program of activities and tasks, generate the necessary breakdown of cost details, prepare plans, and assemble a reliable cost estimate. This would be the minimum effort necessary before the deconstruction option could be seriously evaluated. At least an additional full time person-week would be necessary to generate an outline specification for the works involved. Further detailing, drawings, and related documentation including detailed specifications would be necessary prior to deconstruction works being ready for tendering. In terms of funding for deconstruction options, it must be recalled that the Commonwealth Government permitted a private development to proceed at Nelly Bay without securing necessary insurances against construction failure. The public (rightfully) expected that such security would have been obtained as a normal standard of responsibility. It can therefore be argued that the Commonwealth Government in particular should now accept some responsibility for costs of actions to restore an acceptable environment in the locality. There may also be a role for the State Government to contribute in some manner. It may be the case that the deconstruction option would be too difficult, environmentally destructive, and expensive alongside construction options. It will not be possible to reverse all of the environmental impacts of the failed development, so even if deconstruction is taken seriously it will not mean a return to the preconstruction state. The best outcome to be expected from full deconstruction would be as close to the pre-constructed state as can be physically achieved. For this reason, it may well be that partial deconstruction offers a compromise that is far more attractive when evaluated using the precautionary principle. 5.2 Partial Deconstruction Compromises As an alternative to complete deconstruction, forms of compromise between deconstruction and a fully-developed canal estate could also be examined. In the same manner as above, these would have to be evaluated technically prior to being accepted or dismissed on environmental or cost grounds. Scenarios would need to be developed as starting points for partial deconstruction compromises, in order for stages and methods to be identified for evaluation. Suggestions for significant objectives are: • freeing the discharge from Gustav Creek (which may also have implications for channel margin developments and catchment management improvements); • restoration of public access that would enhance the amenity of the foreshore area; • determination of whether any harbour, mooring, or sheltered anchorage is to be included; • minimising further disturbance of coral reef areas and encouraging reef revitalisation. It is understood that some coral recruitment has occurred within a few years in the cleaner water areas surrounding the present structures at Nelly Bay. This suggests that there is considerable potential for creating long-term high value recreational assets relating to reef experiences. It also implies that issues of water circulation and sediment discharge from Gustav Creek are keys to enhancement of the environmental values of the near-shore area. Questions of public access, harbour, mooring, and sheltered anchorage require community and professional advice. It is expected that the latest proposal for development is based on such advice. It is also expected that it would be structured on achieving a revenue base (land sales and marina/harbour activities) to pay for development and operation costs, routine infrastructure maintenance, plus profits for the entrepreneur and facility operators. Any compromise between development and deconstruction would have to meet equivalent cost-revenue criteria, or seek shortfall funding. The Commonwealth Government's role in creating the situation leading to the present development impasse should not be overlooked. The challenge now is to conduct a balanced evaluation of all options using the guidance of the precautionary principle, and if necessary to develop justifications for approaches to State or Commonwealth Governments to cover any shortfall funding. 6. Summary and Conclusions The present situation at Nelly Bay challenges conventional notions of development costs and environmental values. It is not expected that a simple solution satisfactory to the broader community will be easily achieved. However, given the outstanding environmental values of Magnetic Island generally, application of processes under the guidance of the precautionary principle must offer the best chance for outcomes that will be both acceptable and sustainable. This discussion has included some comments and opinions on the realities of earthworks construction for a canal estate. While every effort (and cost) can be directed to achieving the design intent, there are many practicalities which mean that the outcome may result in maintenance costs and outcomes that are less successful than expected. Trapping the discharge from Gustav Creek, and further damaging the reef areas, are examples of issues where technical solutions can be imposed that are not necessarily valuable considering longer-term risk-weighted consequences. Much of the previous debate about the Nelly Bay development debacle has involved a polarisation of views and attitudes. The situation now is that there is an opportunity to use best-practice principles to guide a planning process that will result in the best achievable result for the environment. Experience has been that broadly acceptable and successful planning processes do not necessarily (or often!) start with a clear concept of what the preferred outcome will be. Considering that the same environmental values are the core of all parties' interests in the area, the most responsible course now would be to initiate a responsible and comprehensive best-practice process. John V Simmons Principal, Sherwood Geotechnical and Research Services 16 Erinvale Street, Corinda, Qld 4075 .................................................... Home \| Contact Us \| Resources \| Sitemap Nelly-Bay.com © 2006. All Rights Reserved – Nelly Bay Engineering Report

Engineering Report:

Proposed Construction of Canal Estate Nelly Bay

1. Introduction

Following is a discussion of some engineering and related issues involved in construction of a canal estate at Nelly Bay. Initial construction at Nelly Bay started in 1988 and was abandoned in 1990 for financial reasons, leaving breakwater walls and some earthworks around the periphery. The site presently can be described as an 'eyesore', and represents a considerable degradation of the original amenity and environmental values of the area.

This paper was prepared without reference to the most recent EIS for proposed redevelopment of the Nelly Bay site. It is intended to provide background information and opinions based on experience from geotechnical assessment of earthworks generally. It also reflects the writer's experience from 1995-present with the canal estate at Raby Bay, near Brisbane, which includes both short-term construction-related issues and long-term maintenance issues. Raby Bay is constructed in an area of clay materials (mostly derived from volcanic rocks), whereas Nelly Bay is likely to involve a mixture of clays, sands, and coarser materials. While the materials have an important influence on the manner in which engineering can be done, the underlying principles are material-independent. The following discussion of both materials and underlying principles is addressed particularly to readers who do not have a background of professional training and experience in earthworks construction.

2. Materials Issues

2.1 Materials to be Used at Nelly Bay

The materials will be sands, clayey sands, and silts together with coral rubble and rock sourced at site. Much of the coral rubble and rock will be obtained by underwater blasting for the entrance channel. In addition, fill material of various gradations may need to be imported to the site. Most of the materials are likely to be of fair to reasonable quality, geotechnically speaking, and certainly stronger and easier to place and compact than the clays found at Raby Bay.

Nelly Bay is a geologically recent embayment beach sequence with two important distinctions: the terrestrial sediment input from overland runoff (principally Gustav Creek, prior to urban development), and the fringing coral reef. Over the Pleistocene period (the age of glaciations) the coastline has changed dramatically, for example until about 12,000 years ago the coast was many kilometres seawards of its present location. As the sea level rose, the coastline sediment sequence was driven westwards. The immediate geological profile at Nelly Bay is thus granitic bedrock which is weathered and incised and overlain by a sediment 'layer cake' which is likely to vary laterally over small distances due to seasonal activity of the Gustav Creek drainage system.

Apart from the presently known deposits of potentially acid sulphate soils, there may be many other pockets not just at the immediate present tidal zone. Some of any such pockets may have already been disturbed by construction (dredging) to date, but this is unknown. It does mean that any dredged or excavated material which is removed from an anaerobic saturated state to a subaerial state as fill, may potentially require ASS treatment.

The Bulk Earthworks Matrix described in the Thiess document of June 1995 may not be correct in terms of quantities for the latest proposal, but the sourcing is undoubtedly current. There will definitely be a requirement for some imported fill, including topsoil for landscaping. The current level of ASS survey is not necessarily sufficient to identify the overall extent of the potential problem, if fill from excavation is to be used above low water springs level.

Experience from detailed review of construction records for the Raby Bay Canal Estate is that fill sourcing will vary, and quality will vary more than the construction specification would indicate. It would be impossible, in my opinion, for fill to be controlled to the standards required for such a contained site unless truly Level 1 earthworks supervision (AS 3798-1996) was in place. The ASS question is of great importance, given the damage that has already been done to the fringing reef and the necessity to minimise future damage no matter what construction options are adopted.

2.2 Environmental Management Constraints

Noise, dust, and siltation are inevitable at any earthworks construction site. There is now a body of good information on best practices which, if adhered to or enforced, should lead to acceptable levels of disturbance due to noise, dust, and siltation.

Construction traffic will create disruption to the local road network, particularly when imported materials are being hauled. This can also lead to noise and dust nuisances well away from the site itself.

Unfortunately the previous construction activity at the site has severely degraded the amenity and environmental values of the area with respect to its pre-construction state. The soils, beachfront, and fringing reef are all sensitive to disturbances. Because the general area has outstanding natural attributes, it should be a goal of any construction activity and post-construction facility to restore the former conditions to the greatest possible extent. It would not be technically feasible to remove the present constructed forms without creating additional negative environmental impacts particularly to the beach area and fringing reef. However, such impacts should also be compared to the impacts of completing the marina basin and in particular the negative impacts of construction of the access channel.

2.3 Stability of Canal Banks and Revetments

The stability of all embankments and slopes should be explicitly checked during design. The basis for design calculations, and the criteria used for stability, should be explicitly included in design documents and reports submitted for approvals. For most of the situations and materials that can be determined and interpreted from the information to date, it is not expected that stability design will be difficult.

Longer-term stability of the constructed landforms will depend as much on good construction practices as on acceptability of design. At Raby Bay there has been a continuing history of instability despite designs being acceptable and approved. The causes are related to the swelling properties of the clays but are not well understood, and research work is continuing. At Nelly Bay the most likely causes of instability following end of construction are likely to be internal erosion and collapse. The former will happen if filters and other controls are not adequately designed to prevent seepage water from eroding and transporting fine soil particles, while the latter will happen if materials are not adequately compacted (to design specifications).

Revetments are defined here as the parts of the wetted slopes that are deliberately designed and constructed to resist erosion. The proposed revetments at Nelly Bay are rip-rap rock. This will require geofabric and possible sand bedding filters to prevent internal erosion of the fill behind the revetment. Materials that are suitable for Nelly Bay conditions are readily available. However, it is often the case that such filter systems are not adequately designed or constructed, with a reliance on unrealistic specifications or installation 'to manufacturers recommendations' which are not followed.

As noted above, the Nelly Bay fill materials are not likely to exhibit the poor engineering characteristics of the Raby Bay materials. Provided that there is adequate sampling and testing, and that the design basis is properly set out and reviewed prior to approval, instability is not expected to be a concern for Nelly Bay unless construction standards fall below specification requirements.

Having Gustav Creek discharge into the proposed marina basin is a fundamental design weakness, given that the access channel leads through an already damaged reef. The alternative would be to construct a stream diversion, which would involve large-scale foreshore disruption and which may be difficult and expensive to stabilise against flooding.

Sedimentation from Gustav Creek may have some stability implications. If a sedimentation basin is constructed, with the intention of periodic clearing, then this will probably involve disturbance of the ASS area. If there is no explicit sedimentation control, then periodic maintenance dredging will be required with the spoil either being used for nearby beach replenishment, pumped out to sea, or loaded-out for remote disposal.

2.4 Performance of Foundations on Filled Ground

Construction processes for reclamation fill lead to many implications for subsequent foundation performance. Usually there will be some post-construction settlement, although this will be minimised if the fill compaction control is really good. However buildings are very sensitive to such movements and building owners insist on extremely fine tolerances with respect to cracking, loss of alignment, etc. The degree of settlement depends on the fill material consistency and depth of filling, as well as on the degree of compaction achieved. In practice, the degree of settlement must be expected to vary a lot, and in ways that are not easily predictable.

In order for owner expectations to be fulfilled, there will be a requirement for testing and engineered design of foundations to provide support to buildings. This may involve cost premiums for piles or stiffened rafts, even though the reclaimed land may be very expensive to begin with. Many owners will not understand this, and may accept compromises on development costs which lead to building damage, poor relationships with builders and local authorities, and litigation which should have been unnecessary. Such histories are part of the Raby Bay experience, even though the majority of buildings there have been well designed and perform to expectations. Part of the problem may be attributable to the hype which surrounds the marketing of reclaimed land, in order to make the high purchase costs attractive.

Some of the building-related problems at Raby Bay have been significant, but have been incorrectly associated with the engineering of the fill for the estate. The blame has generally lain with cost-cutting and unreal expectations, or a failure to appreciate realities that exist but which do not fit the marketing image of a high-value estate.

Questions may then arise about the competence of local authorities that provide development approvals. There will always be a market for lowest-common-denominator engineering, and local authority approval relies upon engineering advice without necessarily being able to determine if it is adequate or not. If the advice is inadequate, it not only may lead to specific performance problems, but will also reflect poorly on the majority of engineers who would have provided much better advice.

2.5 Cyclone Impacts

Because the area is subject to cyclone activity, any development would have to be designed for appropriate levels of potential impact. The longer-term responsibilities of the local authority and the private landholders must be considered in relation to the consequences of such impacts. A severe cyclone event will create damage, and appropriate design will only limit damage to (hopefully) acceptable levels.

A high-value coastal canal estate will have public infrastructure (roads, storm-water, sewerage, electricity reticulation, and communications lines). The local authority will be responsible for all of the canals and waterways, as well as the roads, drainage, and sewerage. In the event of a severe cyclonic impact, the surrounding region will also be impacted. The demand for repair works and the costs of such repairs will place severe strain on local authority resources.

In the case of a canal estate at Nelly Bay, the demands may be locally severe, and the responsibilities of private landholders would be limited to structures on their land. The wider community would have to provide resources for restoration of public infrastructure. For a canal estate, the component of public infrastructure is significantly higher and more damage-prone than for the surrounding land-based community. This requires forethought and planning to determine whether the additional responsibilities of a canal estate are a justifiable risk and cost that the local authority should be prepared to accept on behalf of the wider community.

3. Underlying Principles

3.1 Role of Engineer

Professional engineers may undertake a number of roles for a reclamation-type development. The designer is responsible for fulfilling normally accepted standards of safety, function, and fitness for purpose. The specifier has to document the intention of the design in such a manner that there can be a fair and enforceable contract to construct the facility using suitable materials and methods. The certifier provides a legally binding opinion that the actual materials and works comply with the specification.

Provided that the design has been adequately prepared, and that the materials and methods comply with the specification, the risk of failure (ie loss of function or fitness for purpose) is normally acceptably low. Usually reductions of risks are directly proportional to the care (and money) spent on addressing risk minimisation. However, there will always be uncertainty about the quality of design detailing, material variability, and works practices. The risk of failure is closely linked to the quality control or quality assurance used for all aspects of the project.

3.2 Process of Engineering Inputs to Design, Specification, and Certification

The designer of a reclamation project is normally a civil engineer who is dependent on inputs from other discipline specialists. Examples relevant to Nelly Bay include the distribution and potential severity of oxidation of acid sulphate soils, the distribution and strength variability of in situ sediments and fill materials, and the prediction of wave climate or cyclonic conditions. Typically all such specialist information includes reasonable assumptions and representative data, but can never exhaustively eliminate uncertainty.

It is normal practice to utilise quality assurance systems as an efficient method for minimising risk. These systems rely on a chain of compliance with recognised (community accepted) standards. If acting for the project developer, there will always be pressure on the designer to reduce compliance costs. For a reclamation development, the bulk of the work involves naturally variable materials under conditions where supervision can never be absolute and compliance testing is both expensive and tedious. These conditions always lead to the risk that corners will be cut, and reasonable assumptions made instead of more detailed investigation, design, or testing.

3.3 Specification and Intent versus Practicality and Guarantee

Engineers refer to the term design intent. Specifications are developed to describe this, but to allow as much flexibility as possible in how this is achieved. In practice, this means that there may be opportunities for such activities as:
• use of non-specification materials when the inspectors testers or certifiers are otherwise engaged;
• failure to achieve adequate compaction everywhere, and even conspiracy to achieve it only in areas that will be scrutinised and tested;
• actions to minimise testing and scrutiny by creative interpretation of the wording of the specification (engineers are not generally perfect writers, can be guilty of cutting corners with preparation of specifications, and may not recognise that a problem has been created);
• making contingency decisions as a result of bad weather, breakdown of equipment, lack of sufficient quality of suitable fill (etc), that violate the spirit of the design intent but which help to bring the project in on time and within budget.

One of the frequently encountered problems at Raby Bay is the misunderstanding that compliance with specification provisions is a guarantee of performance. It is impossible to make such guarantees, but it is human nature for developers and marketers to sell-up the virtues of a package by implying things that cannot be implied. All that engineers can do is minimise risks (that are known) and apply prudence and judgement where the risks are not clearly known. Engineers are trained to do this far better than non-engineers. However engineers typically are put in the defacto role of environmental managers, and may then apply judgements and values outside of their area of expertise.

There are standards for earthworks construction that should be used for any proposed construction activity at Nelly Bay. Given the sensitivity of the site, and its previous history, the only appropriate standard is the so-called Level 1 which requires full-time supervision by suitably trained and accredited testing authorities and/or construction engineers. The scale of the site is relatively small, so Level 1 supervision is unlikely to be efficient and would therefore be much more expensive than the developer would prefer. However, no other means can be foreseen whereby the likely scale of construction can be achieved successfully, and the previous construction episode is sufficient proof that very high standards are mandatory.

4. Precautionary Principle For Environmental Management

The commonly stated version of the precautionary principle is that where there are threats of serious or irreversible environmental damage, lack of full scientific certainty should not be used as a reason for postponing measures to prevent environmental degradation. In applying this principle, public and private decisions should be guided by (1) careful evaluation to avoid wherever practicable serious or irreversible damage to the environment (2) an assessment of the risk-weighted consequences of various options.

It is considered that the current Nelly Bay situation already represents serious and irreversible environmental damage. Intervention measures, for example construction of a facility or rehabilitation of the site in some manner, are therefore urgently required to restore amenity and minimise future environmental risks. No matter what intervention takes place, there will be high costs and environmental impacts. The issues are therefore about the form that intervention should take, how the construction and future maintenance costs should be met, minimising the short-term negative environmental impacts, and maximising the long-term environmental gains.

There is a strong case for applying the precautionary principle to the Nelly Bay situation in order to restore values to the degraded environment and enhance the amenity that has been adversely impacted. This would involve consideration of environmental, maintenance, and cost issues in a systematic manner considering long-term as well as short-term constraints. Rather than start the process by searching for a development solution that satisfies particular cost-revenue constraints, a range of options should be evaluated using objective management criteria. All options would have to be evaluated as legitimate options to a completed development in order for any choice of action to be justifiable in environmentally sustainable terms. Economic criteria including capital and maintenance cost issues would form part of the risk-weighting process. In broad terms, four options need to be evaluated:
• do nothing;
• complete some form of constructed development;
• abandon a fully developed canal estate, with retention and possible modification of those elements already constructed but which would be too difficult, too costly, or too environmentally degrading to deconstruct;
• fully deconstruct the existing works and rehabilitate the site;

Adoption of the precautionary principle to guide the process means elimination of the 'do-nothing' choice, or its use only as a benchmark for comparing the benefits of the other choices.

If a canal-style facility is constructed within the existing breakwater walls, the Gustav Creek mouth area would require creative and expensive engineering to develop a construction and long-term maintenance plan that would not lead to future facility and neighbouring reef damage from siltation. All the landscaping of the reclamation area would require watering and fertiliser application, the runoff from which is potentially fatal to a range of marine organisms. The final civil engineering design would therefore have to include the constraints of managing sediment inputs, capturing runoff, intersecting seepage, and eliminating nutrient loading to the canals and hence the marina mouth and reef flats. The design would also have to be maintainable at an acceptable cost for an indefinite future period.

Alternatives to construction of a canal estate development would involve some deconstruction of the current breakwater structures and rehabilitation of the beach and foreshore. This would also restore the Gustav Creek mouth area, and would probably result in enhanced tidal water circulation and minimal future maintenance requirements. Foreshore maintenance similar to other parts of the Magnetic Island coastline would be involved.

At Raby Bay (and at other canal estates, it is understood) a rates levy is used by the local authority to fund maintenance works including drainage management and dredging. The intention of a rates levy is to raise funds specifically for the maintenance requirements of the development, without imposing on ratepayers elsewhere who would gain no benefits from it. This intention has been broadly accepted at Raby Bay and in the surrounding shire, even though it was opposed by a small proportion of owners who took the view that such costs should not have been necessary, or should have been included in the purchase price. A rates levy could be considered as part of the funding mechanisms for both development and deconstruction options.

The current development proposal documentation should be sufficiently detailed to enable risk-weighted consequences to be evaluated for the choice to complete a constructed development. Because there is presently no documentation of the scope and likely impacts of choices involving deconstruction, further discussion of deconstruction is set out below.

5. The Options for Decontruction

5.1 Basic Approach

An experienced civil engineer will automatically assume that the costs and impacts of deconstruction will exceed the costs and impacts of the original construction. There are many reasons for this, not the least of which is that structures that are built to last are implicitly difficult to pull down. For example, experience with repairs to failed concrete walls along canal frontages at Raby Bay Canal Estate is that rebuilding costs are at least twice the cost of initial construction, and this is with minimal removal of materials.

The deconstruction option should not be passed-over just because it does not meet the automatic assumptions of experienced engineers. Whether or not it has merits at the end of the process, evaluation must be based on detailed arguments and credible costings. The final choice of action can then be based on the balance of risk-weighted economic and environmental arguments.

Following is Table 1 which is a preliminary framework for discussion of the issues involved in deconstruction. It is not a credible engineering plan, or a sufficient basis for costing. To develop plans and costing for deconstruction, it is estimated that experienced civil engineers would require at least four person-weeks of full time work to expand the table into a program of activities and tasks, generate the necessary breakdown of cost details, prepare plans, and assemble a reliable cost estimate. This would be the minimum effort necessary before the deconstruction option could be seriously evaluated. At least an additional full time person-week would be necessary to generate an outline specification for the works involved. Further detailing, drawings, and related documentation including detailed specifications would be necessary prior to deconstruction works being ready for tendering.

In terms of funding for deconstruction options, it must be recalled that the Commonwealth Government permitted a private development to proceed at Nelly Bay without securing necessary insurances against construction failure. The public (rightfully) expected that such security would have been obtained as a normal standard of responsibility. It can therefore be argued that the Commonwealth Government in particular should now accept some responsibility for costs of actions to restore an acceptable environment in the locality. There may also be a role for the State Government to contribute in some manner.

It may be the case that the deconstruction option would be too difficult, environmentally destructive, and expensive alongside construction options. It will not be possible to reverse all of the environmental impacts of the failed development, so even if deconstruction is taken seriously it will not mean a return to the preconstruction state. The best outcome to be expected from full deconstruction would be as close to the pre-constructed state as can be physically achieved. For this reason, it may well be that partial deconstruction offers a compromise that is far more attractive when evaluated using the precautionary principle.

5.2 Partial Deconstruction Compromises

As an alternative to complete deconstruction, forms of compromise between deconstruction and a fully-developed canal estate could also be examined. In the same manner as above, these would have to be evaluated technically prior to being accepted or dismissed on environmental or cost grounds.

Scenarios would need to be developed as starting points for partial deconstruction compromises, in order for stages and methods to be identified for evaluation. Suggestions for significant objectives are:
• freeing the discharge from Gustav Creek (which may also have implications for channel margin developments and catchment management improvements);
• restoration of public access that would enhance the amenity of the foreshore area;
• determination of whether any harbour, mooring, or sheltered anchorage is to be included;
• minimising further disturbance of coral reef areas and encouraging reef revitalisation.

It is understood that some coral recruitment has occurred within a few years in the cleaner water areas surrounding the present structures at Nelly Bay. This suggests that there is considerable potential for creating long-term high value recreational assets relating to reef experiences. It also implies that issues of water circulation and sediment discharge from Gustav Creek are keys to enhancement of the environmental values of the near-shore area.

Questions of public access, harbour, mooring, and sheltered anchorage require community and professional advice. It is expected that the latest proposal for development is based on such advice. It is also expected that it would be structured on achieving a revenue base (land sales and marina/harbour activities) to pay for development and operation costs, routine infrastructure maintenance, plus profits for the entrepreneur and facility operators.

Any compromise between development and deconstruction would have to meet equivalent cost-revenue criteria, or seek shortfall funding. The Commonwealth Government's role in creating the situation leading to the present development impasse should not be overlooked. The challenge now is to conduct a balanced evaluation of all options using the guidance of the precautionary principle, and if necessary to develop justifications for approaches to State or Commonwealth Governments to cover any shortfall funding.

6. Summary and Conclusions

The present situation at Nelly Bay challenges conventional notions of development costs and environmental values. It is not expected that a simple solution satisfactory to the broader community will be easily achieved. However, given the outstanding environmental values of Magnetic Island generally, application of processes under the guidance of the precautionary principle must offer the best chance for outcomes that will be both acceptable and sustainable.

This discussion has included some comments and opinions on the realities of earthworks construction for a canal estate. While every effort (and cost) can be directed to achieving the design intent, there are many practicalities which mean that the outcome may result in maintenance costs and outcomes that are less successful than expected. Trapping the discharge from Gustav Creek, and further damaging the reef areas, are examples of issues where technical solutions can be imposed that are not necessarily valuable considering longer-term risk-weighted consequences.

Much of the previous debate about the Nelly Bay development debacle has involved a polarisation of views and attitudes. The situation now is that there is an opportunity to use best-practice principles to guide a planning process that will result in the best achievable result for the environment. Experience has been that broadly acceptable and successful planning processes do not necessarily (or often!) start with a clear concept of what the preferred outcome will be. Considering that the same environmental values are the core of all parties' interests in the area, the most responsible course now would be to initiate a responsible and comprehensive best-practice process.

John V Simmons
Principal, Sherwood Geotechnical and Research Services
16 Erinvale Street, Corinda, Qld 4075