Boat Harbour Development Case Study

Shell Cove Boat Harbour Development, NSW
Greg Britton1
Director, Haskoning Australia (a company of Royal HaskoningDHV), Sydney, Australia

1

Abstract
Shell Cove is a large scale, masterplanned, beachside, urban development originally approved in the 1990s located on the New South Wales South Coast in the Shellharbour City region (Figure 1).
The Boat Harbour element of the project is proposed to be developed in three stages and includes an Inner
Harbour, Outer Harbour, Entrance Channel linking the Boat Harbour to the sea across Shellharbour South
Beach, a Breakwater and a Groyne. Substantial excavation/dredging is required to create the Boat Harbour, much of which is within an area of actual and potential acid sulfate soils.
A
range of modifications were made to the original Boat Harbour design to enhance the technical, environmental and social outcomes. These modifications included rotation of the Boat Harbour planform (as one component of the management of acid sulfate soils), re-design of the Breakwater and Groynes, and deletion of a proposed Boat Harbour flushing pipe system. An extensive Construction Environmental
Management Plan (CEMP) and Operational Environmental Management Plan (OEMP) were developed to ensure achievement of the enhanced outcomes. Construction of Stage 1 of the Boat Harbour commenced in early 2013.
Keywords: coastal structures, acid sulfate soils, water quality, environmental management plans.
1.
Introduction
Shell Cove is a large scale, masterplanned, beachside, urban development originally approved in the 1990s located on the New South Wales
South Coast in the Shellharbour City region
(Figure 1).
The project comprises the development of approximately 3,000 dwellings, a championship 18 hole golf course, a 300 berth
Boat Harbour, commercial development including a town centre, hotel and business park and associated open space, environmental and social provisions. changes to statutory legislation since the original design. The Boat Harbour element of the project is proposed to be developed in three stages and includes an Inner Harbour, Outer Harbour,
Entrance Channel linking the Boat Harbour to the sea across Shellharbour South Beach, a
Breakwater and a Groyne.
Substantial
excavation/dredging is required to create the Boat
Harbour, much of which is within an area of actual and potential acid sulfate soils.
Patterson Britton & Partners (Patterson Britton) were appointed by Australand Corporation (NSW)
Pty Ltd (Australand) in May 2003 to evolve the conceptual design for the Boat Harbour prepared in 1996, which formed the basis for the original
Development Application (DA), to a final detailed design and documentation stage.
The Brief prepared by Australand included a Value
Management protocol involving review of all elements of the original design in respect of, among other issues, buildability, cost implications, environmental and ecological outcomes, aesthetics, risk management, construction schedule, impact of the conditions of consent and

Figure 1 Shell Cove Location Plan

The review conducted by Patterson Britton led to recommendations to modify the original design in a number of ways. The recommendations were accepted by Australand and led to preparation of a technical report to support a Section 96 (s96) modification application under the
NSW
Environmental Planning & Assessment Act, 1979 to modify the original consent [1]. The key modifications included:



rotation of the Boat Harbour planform; design modifications to the Breakwater and
Groynes;



deletion of the Boat Harbour flushing pipe system. 

Construction of Stage 1 of the Boat Harbour commenced in early 2013. Completion of the Boat
Harbour is scheduled for before 2020.
2.
Rotation of the Boat Harbour Planform
The method of management of acid sulfate soils
(ASS), comprising both actual acid sulfate soils
(AASS) and potential acid sulfate soils (PASS), proposed in the Environmental Impact Statement
(EIS) involved reburial of the materials, both below the bed of the Boat Harbour (by over-excavation) and within burial pits adjacent to the Boat Harbour under the future land platform. Removal and transport of the materials to the disposal areas was proposed to be by use of a cutter-suction dredger pumping the ASS as a slurry through a pipeline.
This wet method of removal and transport of ASS was proposed in order to reduce the risk of oxidation of the ASS.
Two main geotechnical issues were identified with the ASS management strategy proposed in the
EIS based on field and laboratory investigations undertaken by Coffey Geosciences on behalf of
Patterson Britton:



the lengthy time necessary to achieve adequate consolidation of the hydraulically placed ASS material in the burial pits under the future land platform and hence the time delay before commencement on the development of public and private infrastructure, estimated to be from 4 to 70 years; the shallower rock levels determined over the site compared to those adopted in the EIS, which substantially restricted the opportunity for reburial of ASS below the Boat Harbour and significantly increased the required lateral extent of burial pits under the future land platform thereby exacerbating the consolidation issue above.

Rotation of the Boat Harbour by approximately 15o in an anti-clockwise (westerly) direction
was proposed in order to reduce the quantity of ASS that required excavation and management (Figure
2). In addition, it was proposed to ‘consolidate and cap’ (not remove) insitu ASS located outside (to the east) of the footprint of the rotated Boat
Harbour. These avoidance measures reduced considerably the quantity of ASS to be excavated and managed, from the figure of approximately
640,000 m3 in the EIS to a figure of approximately
340,000 m3. This led to considerable cost savings and reduction in environmental risk.

Figure 2 The location of the original Boat Harbour planform (in blue) and the rotated planform (in green) superimposed on the lateral extent and thickness of ASS on site.

The reduction in the quantity of ASS to be excavated and managed also meant that it was possible to avoid the need for creation of burial pits located under the future land platform. This had the major advantage of de-coupling the consolidation behaviour of the excavated ASS from the schedule for development of the land platform. The rotation of the Boat Harbour planform also provided an advantage for buildability and construction sequencing. The western section of the Inner Harbour was now able to be excavated in non ASS, immediately winning material for beneficial reuse in the ‘consolidate and cap’ strategy and delaying the introduction of ASS management measures.
Testing was also undertaken to determine the rate of oxidation of the clayey textured ASS when exposed to air.
This involved recovery of representative samples and monitoring in the laboratory of the acidification of the samples over time. This testing showed that it would be possible to adopt an ‘in the most’ technique for excavation and transport of the ASS, using conventional earthmoving equipment, rather than use of a cutter-suction dredger pumping the ASS through a slurry pipeline. This significantly reduced the estimated consolidation times for the ASS placed below the over-excavated Boat Harbour, again achieving significant schedule benefits.
Drilling and blasting may be necessary in order to achieve sufficient storage capacity for the ASS below the Boat Harbour, beyond the base of the rippable rock. Studies have shown that drilling and blasting would satisfy vibration criteria and, with suitable controls in place, air overpressure criteria.

The Northern Groyne and Southern Groyne had several purposes; to protect the channel and berthing areas from wave action, to prevent sediment infilling of the channel (Northern Groyne) and to maintain a sandy beach south of the entrance (termed Harbour Entrance Beach). The
Northern
and
Southern
Groynes were approximately 230 m long and 180 m long respectively and extended out to a common water depth of approximately -4 m AHD.
The primary armour on the Breakwater and the
Southern Groyne included artificial concrete armour units (hanbars) in addition to rock. Primary armour was located along the crest of each entrance structure. As such, pedestrian access along the structures would not have been possible.
A range of modifications were proposed to the
Breakwater and the Northern and Southern
Groynes with the aim of achieving a functional design outcome at least equivalent to the EIS design (eg wave height attenuation and overtopping performance), but having a reduced environmental impact and providing improved public access. The proposed modifications were supported by the results of an extensive program of numerical modelling, two dimensional (2D) and
3D physical modelling, analytical calculations, and a specialist navigation assessment. A wave rider buoy was installed locally and utilised in the calibration of the numerical and physical modelling.
Wave rider buoy data was also available from the offshore Port Kembla and offshore Sydney wave rider buoys.
The
proposed breakwater modifications were (Figure 3):

and

groyne


Early findings from the Stage 1 excavation works indicate that the rock below the Boat Harbour may be rippable to a deeper level than initially thought, at least in the western section of the Inner
Harbour, reducing dependency on drilling and blasting. Design Modifications to the Breakwater and Groynes
The entrance configuration for the Boat Harbour proposed in the EIS comprised a Breakwater, a
Northern Groyne and a Southern Groyne (Figure
3).

realignment and shortening of the Breakwater by 50 m, thus reducing the visual impact of the structure; 

adoption of a ‘berm type’ design for the
Breakwater rather than a conventional rubble mound design so as to avoid use of artificial concrete armour units such as hanbars, thus reducing the visual impact of the structure and allowing efficient use of local quarry materials; deletion of the Southern Groyne, thus reducing the extent to which structures cover natural rock reef ecology, reducing the visual impact of the entrance structures, and reducing the amount of construction activity in the vicinity of
Aboriginal middens located south of the entrance channel;

3.

The Breakwater was approximately 565 m long and extended offshore into a water depth of approximately -10 m AHD.
It had two main purposes; to protect the entrance navigation channel and berthing areas from wave action and to provide a physical barrier to sediment movement which would otherwise cause infilling of the channel.





provision for pedestrian access and maintenance vehicle access along the crest of the Breakwater and the Northern Groyne, thus enabling greater public accessibility and providing straight-forward access for any required maintenance following severe storms;

Figure 3

Proposed modified breakwater and groyne design (in black) superimposed on the EIS design (in red).
Aboriginal middens are shown hatched and shaded.

Figure 4 View of the 3D physical model testing of the entrance configuration conducted in the wave basin at UNSW
Water Research Laboratory



slight modification to the head of the Northern
Groyne, thus providing greater wave protection to the Access Channel and to the boating facilities located upstream.

Construction of the Stage 1 section of the
Breakwater and Northern Groyne, which are located across the sandy beach above high water mark, is now underway. These works are being constructed within a temporary steel sheet pile cofferdam which incorporates temporary rock and sand ground anchors.
Deletion of Boat Harbour Flushing Pipe
System
The EIS proposed a flushing pipe system for the
Boat Harbour on the basis that, adopting conservative assumptions, a pump may
be required at the ultimate urban development stage to assist natural tidal flushing of the Boat Harbour and ensure adequate water quality. The concept of the flushing pipe system was to pump ocean water into the Inner Harbour of the Boat Harbour
50% of the time, during ebb tides.

The results of the reassessment showed that:



predicted nutrient concentrations within the
Boat Harbour without any pump assisted flushing are less than the default trigger values in the ANZECC/ARMCANZ (2000) Guidelines for estuarine waters and, accordingly, there is considered to be a low risk of algal blooms occurring in the Boat Harbour in the no pump case; 

the predicted concentrations of labile
(bioavailable) copper in the Inner Harbour without any pump assisted flushing satisfy the
90% of species protected level in the
ANZECC/ARMCANZ (2000) Guidelines;



the flushing pipe system simply increases the rate at which copper is transported from the
Boat Harbour to the adjacent coastal waters, it does not alter the total amount of copper released to the environment. For this reason copper concentrations increase in the adjacent coastal waters in the pumping case;



in the no pump case, the majority of the copper ends up in a low-bioavailability form bound to sediments on the bed of the Boat Harbour.
The predicted concentrations of copper in the sediments are not considered to be of concern and disturbance of the sediments by maintenance dredging would not be expected to be required for at least 200 years.

4.

The problematic water quality parameters were nutrients and copper. The sources of nutrients were urban runoff during rainfall events, vessel sewage and vessel bilge water. The main source of copper was copper-based antifouling paints applied to the hulls of vessels.
Predicted concentrations of nutrients and copper in the Boat Harbour and adjacent coastal waters were reassessed as part of the Value Management process using a range of models and, in the case of copper, updated copper leaching rates and an improved understanding of the fate of copper in the water column (Figure 5).

Introduction of a flushing pipe system was considered to have a number of adverse environmental and economic impacts, as follows:



the power consumed by the system would be approximately 503,700 kWh per year. This is equivalent to approximately 531,000 kg of greenhouse gas emissions per year based on

information available
Greenhouse office;



from

the

Australian

it would introduce significant quantities of chlorine into the Boat Harbour as a result of the need to dose the flushing pipe system with chlorine to prevent biofouling within the pipe;



the flushing pipe system would transfer greater quantities of copper to the environmentally valuable adjacent coastal waters;



the annual operating and maintenance costs are high, at approximately $515,000 per year.

Figure 5 Fate of copper in the water column and predicted long term average copper concentrations in the Inner Harbour

5.

Construction Environmental Management
Plan
(CEMP) and Operational
Environmental Management Plan (OEMP)
A detailed CEMP and OEMP have been prepared to address the requirements of the development consent and development concurrence conditions.
The CEMP and OEMP comprise a total of 13 individual management plans and include extensive monitoring provisions.
The development is subject to an Environment
Protection Licence (EPL) issued by the
Environment Authority – NSW.
The EPL addresses a range of environmental issues with particular emphasis on the management of surface water quality and impacts on the adjacent coastal waters. Figure 6 Marine water quality and aquatic ecology sampling sites

6.

References

[1] Patterson Britton (2005), Shell Cove Boat Harbour :
Section 96 Modification of Consent 95/133 – Support
Information, Issue No 4, December 2005.