Rapid urbanization, change in land use and a substantial increase in the paved area of Hong Kong have resulted in a significant increase in flood risk in Northern Hong Kong Island. Floodings in the summer months cause traffic disruption, damage to property and in extreme cases potential risk to life. 

In response to this and to meet the community’s increased expectations for higher flood protection standards, the Drainage Services Department initiated the project. 

Arup is the consultant to the Hong Kong Drainage Services Department in carrying out the design, pre-qualification, tender and construction supervision for the Hong Kong West Drainage Tunnel. Hong Kong West Drainage Tunnel, the city’s longest facility of its kind, greatly alleviated flooding risks in Central and Western District and Wanchai District, minimising traffic disruption and disturbance to the public caused by flooding.

Furthermore, by deploying innovative techniques like concurrently carrying out tunnel boring machines excavation and adit blasting, the impact on residents, traffic and the environment during construction was minimised. 

Tunnel boring and excavation 

The main tunnels will be constructed by two tunnel boring machines (TBM). The horizontal adits will be constructed using the drill and blast method, carried out concurrently with the TBM excavation. 

Most of the dropshafts will be constructed using raise boring. Disturbance at ground level is minimised by drilling a small shaft from above that is then expanded to the required dimensions from below. 

Tunnel boring machine

The tunnel boring machine 'Oshin' is named after a symbolic figure of perseverance. 

Stormwater collection and drainage 

The tunnel will intercept surface stormwater runoff from an upper catchment area at the mid-level area of Hong Kong Island and discharge up to 240m3/s at the final outlet portal to the west. 

Stormwater will pass through a drainage system of horizontal shafts, 32 dropshafts up to 195m deep, an eastern inlet portal structure and over 30 other intake structures.