APAC 2020 – Preview Paper: NSW Shell Cove Boat Harbour & Marina

As we all have to wait a few more months for our inaugural APAC 2020 Conference in Fremantle (30 Nov to 4 Dec), we thought we’d provide sneak previews of just some of the excellent papers being presented there…

NSW Shell Cove Boat Harbour and Marina

From design concept to delivery – challenges and successes.

Keywords: harbour, breakwater, marina, soil management, construction  

The Shell Cove Boat Harbour and Marina Project is one of the most significant recreational boating facilities proposed for the NSW coast, located approximately 100km south of Sydney, with a construction value of AUD$150 million plus.

The project incorporates an innovative Icelandic berm design breakwater with a purpose designed high quality public promenade along the crest. The harbour with its associated commercial, residential, public open space and boating infrastructure offers a variety of new opportunities for the region.

Design and delivery of the project – with its 270 berth marina, 120 vessel dry boat storage, 470m long Icelandic berm breakwater; 280m long groyne, constructed beach and other features, has been a challenging though rewarding project that has spanned nearly 15 years.

Overcoming site constraints, the design and construction of a navigation channel to the sea, sediment and stormwater management, satisfactory long-term water quality, and acid sulfate soils management, required innovative design and management approaches.

A total volume of 370,000m3 (bulked) of acid sulfate soils (ASS) within the excavation area posed challenges, necessitating changes in the original design plans. ASS were removed mechanically ‘in the moist’ – rather than the original hydraulic dredging – and reburied within an over-excavation of the Inner Harbour – with sand capping. Capping and consolidation of ASS also took place under future development areas; as well as their neutralisation and reuse in earthworks outside the harbour footprint.

A staged approach was taken throughout the project to enable construction in the dry of various infrastructure including the landward section of the breakwater and groyne, perimeter foreshore structures, 800m timber boardwalk, marina piling and boat launching ramp.

(Image) Staged construction works allowed multiple parts of the site to be developed in parallel, note the residential construction far left and boat ramp construction in the dry in foreground.

 A 5-year ARI flow criterion for management of stormwater quality was adopted for protection of the sensitive nearshore coastal environment during construction. Careful planning was required for the creation of diversion channels (and ‘switching’), stabilisation of channels, monitoring of initial flows/ultimate flows/detention storage, and avoidance of potential internal and external flooding impacts.

Design development included investigation of alternative innovative breakwater designs to achieve a fully rock design, for cost, aesthetic and access reasons. These alternatives included a mass-armoured berm structure, an S-shaped berm and an Icelandic type berm. Extensive 2D and 3D physical modelling was undertaken to prove hydraulic stability and overtopping performance before an Icelandic berm structure was finally adopted.

While construction works are still underway, and the challenging task of opening the harbour to the ocean lies ahead (currently planned for late 2020/early 2021), the project to date is considered a significant success.

(Image below) Aerial oblique view of the Boat Harbour showing breakwater and groyne in the foreground and Boat Harbour construction in the dry in the background

Greg Britton, Royal HaskoningDHV, Sydney, Australia