Cleaning up Hong Kong’s harbour by building big and digging deep

A major civil engineering scheme has recently been completed to improve the water quality of Victoria Harbour between Hong Kong Island and the Kowloon peninsula. It has involved creating the city’s largest sewage treatment works and its deepest sewage tunnel. The £1·6 billion project, commissioned at the end of 2015, complements an earlier stage completed in 2001. All harbour area sewage is now delivered by way of the combined 44·6 km long, 160 m deep sewer tunnel to Stonecutters Island sewage treatment works before being discharged into the harbour. This paper describes the many daunting design and construction challenges, which included keeping the first stage operational as work progressed, and the numerous innovations adopted to overcome them.