Maintenance dredging of the Port Hacking estuary, with sand nourishment of Cronulla and North Cronulla beaches.

Port Hacking estuary

Project timeline

Project start: January 2023

Expected completion: May 2023

Project background

Since 1998, Port Hacking navigation channels have been restored by removing between 60,000 – 110,000 cubic metres of marine sand dredged approximately every 5-years (1998, 2003, 2007, 2012). This sand has historically been relocated and placed nearshore at Cronulla Beach (Bate Bay).

Removal of sand has not occurred for 10-years since 2012.

Project scope

The proposed scope of maintenance dredging will involve the removal of around 60,000 cubic metres of clean marine sand. This sand will be beneficially used for nourishment of currently eroded Cronulla and North Cronulla beaches through nearshore (underwater) placement at Bate Bay.

Project Timeline

The dredging contract is expected to be awarded in June 2022.

Every effort has been made to facilitate dredging works commencing in 2022. However, due to high demand for this type of dredging methodology and a limited market of suppliers, dredging works can only commence at the end of January 2023.

July 2021                         Funding Agreement signed

Oct 2021 – April 2022     Review of Environmental Factors (REF) Regulatory Agencies consultation

Dec 2021                         Expressions of interest – dredging contract

March – April 2022          Request for Tender – dredging contract

May 2022                         Tender evaluation Submission of required approval applications

July 2022                         Contract Award

Jan – May 2023               Dredging works

June 2023                         Project completion

Navigation depths

The dredge design depth for navigation channels east of Shiprock Aquatic Reserve (Areas 1, 2, 3, 4 and 8) is -2.5 m below Chart Datum.

The dredge design depth for navigation channels west of Shiprock Aquatic Reserve (Areas 5, 6 and 7) is -2.0 m below Chart Datum.

Impacts during construction

Funding

In accordance with Council’s dredging policy, financial responsibility for dredging of navigation channels where the bed of the waterway is owned by the NSW Government, rests fully with the NSW Government given it has the administrative responsibility for safe navigation and receives all revenue from the use of the waterways.

Transport for NSW has committed grant funding of up to $2.5 million through the Boating Now Program for Council to manage and deliver this project.

Each year, more than two million people use NSW waterways, such as Port Hacking, for recreational activities such as swimming, boating, jet-skiing, fishing and more.

However, much like roads, rail and airways, marine areas also require regular management and maintenance.

Since 2012, clean marine sand has accumulated within the Port Hacking navigational channels and currently constrains reliable navigable access to various marine infrastructure and waterway locations for recreational vessels.

Dredging is the removal of sediment (gravels, sand, silts and clay) from navigational areas such as channels, river entrances harbours, marinas and berth pockets.

There are two main types of dredging:

  1. Mechanical dredging uses mechanical means to excavate sand or sediment. Typical mechanical dredges included a bucket-ladder, grab or clamshell, and backhoe dredge.
  2. Hydraulic dredging utilises pumps and water flow to suck sediment from the river or sea-bed. Typical hydraulic dredges include plain suction, cutter suction and trailing suction hopper dredgers.

A trailing or plain suction hopper dredge will be used for the Port Hacking navigational dredging project.

Dredging to ensure that channels, berths or other port areas are maintained at their designed dimensions (source: National Assessment Guidelines for Dredging, 2009).

For Port Hacking, dredging will restore the navigational channel design depths and widths previously established and maintained in past dredging programs.

A trailing or plain suction hopper dredge is proposed to undertake dredging, similar to what has occurred previously in 2012 and 2007. These vessels have equipment and technology specifically designed to reduce impacts on the environment. Like an underwater vacuum cleaner, suction tubes equipped with a drag head are lowered onto the seabed.

A suction pump system vacuums the sand and water mixture into the vessel’s hold, or ‘hopper’. Once fully loaded, the vessel sails to the approved nearshore placement area, before placing sand through the bottom of the dredge vessel via its split hopper.

Sand nourishment of beaches at Cronulla boat in water

While Bate Bay is a “closed” system (no net loss of sand from within the embayment), there is still significant erosion that occurs at the southern beaches due to the longshore sediment transport within the Bay (see image below). As a result of this continuous erosion and due to the lack of a current natural source of sand to replenish the loss, significant beach nourishment operations have occurred in the past 50 years to maintain beach width and amenity.

Around 60,000 cubic metres will be placed in the nearshore active coastal system at North Cronulla and Cronulla beaches (at water depths of -5.0 to -9.5 m) to provide additional sand supply to these beaches and a buffer against future erosion events.

Port Hacking Dredging FAQ diagram beaches