Anthony Doherty (Jacobs), Matthew Sheppard (Jacobs)
The primary objective of the Lyttelton Harbour Wastewater project is to remove routine discharges of treated wastewater into Lyttelton Harbour. The project is an integral part of the Whaka-Ora Healthy Harbour Plan to restore the cultural mauri and ecological health of Lyttelton Harbour. This project removes the discharge of treated wastewater from Lyttelton Harbour and reduces the frequency and extent of wastewater overflows, resulting in an improvement of water quality within Lyttelton Harbour. This paper provides an overview of the scheme arrangement, operational philosophy, key challenges encountered and resolution of these challenges.
In 2009 Christchurch City Council (CCC) approved a joint working party recommendation to remove wastewater discharges into Lyttelton Harbour by pumping wastewater from Lyttelton, Governors Bay and Diamond Harbour to the Christchurch Wastewater Treatment Plant (CWTP) in Bromley. It was immediately obvious the project required significant capital investment. Consultation on the scheme, including public drop-in sessions, took place from September 2015 to March 2016.
Based on consultation feedback, a preferred approach was identified comprising the construction of submarine pipelines to convey untreated wastewater, approximately one metre under the seabed, from Diamond Harbour and Governors Bay to Lyttelton.
Wastewater would then be pumped to CWTP through the existing road tunnel via a new pump station at Simeon Quay in Lyttelton.
The project is being constructed in four stages and is now near completion. The various elements of the scheme include:
• The construction of 7 km of submarine pipelines from Governors Bay and Diamond Harbour to Lyttelton
• Decommissioning and converting existing wastewater treatment plants at Governors Bay, Diamond Harbour and Lyttelton into pump stations with overflow storage
• A new high-head terminal pump station in Lyttelton to pump wastewater through the Lyttelton road tunnel
• The construction of a 2 km pressure main from the Lyttelton pump / storage facility to the terminal pump station
• The construction of a 2 km glass reinforced plastic (GRP) pipeline through the air shaft of the Lyttelton road tunnel
• The construction of a 5 km gravity pressure main with a control valve station and an above ground stainless steel pipeline section from the Lyttelton Tunnel to Pump Station PS15 in Woolston
There have been a number of design and construction challenges encountered on this project and many lessons learned over the six year journey. The paper describes the key engineering design challenges encountered on this project and the innovations developed by Jacobs and CCC to overcome these challenges, including:
• Development of low complexity pumping and storage arrangements
• Use of high-head progressive cavity pumps
• A design that includes a combination of pressure and gravity pipelines
• Design of control valve arrangements that provide straightforward operation
• Specific odour treatment to mitigate any potential negative impacts on local communities
• Design and installation of high-pressure pipework in the Lyttleton tunnel
• Design and construction of submarine pipelines across Lyttelton Harbour
A key construction challenge was the ground conditions presented by the loess soils of Banks Peninsula and the constrained nature of the majority of the pumping and storage facility sites. Our approach to address this challenge will also be highlighted.