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To support Hong Kong's sustainable development, the Government actively explores new land resources. One of the possible approaches is rock cavern development.

Being different from“Underground space”, which includes purpose-built, underground rock caverns as well as other large basement-type excavations formed by "cut and cover" methods. “Rock caverns” refer to large man-made spaces in rock. The development of the latter is a method to relocate existing facilities above ground level. These facilities are mostly obnoxious like sewage treatment works, columbarium niches, or uses which are suitable for the development of rock caverns like file rooms, warehouses and data centres etc. This approach can cater part of the demand of lands under the shortage of spaces for future development.

Although spaces gained from rock cavern development cannot be used for residential use, it can be a tool to relocate existing government facilities and free the sites to build housings. The Government is now initiating six rock cavern development projects and it is estimated to have 45.2 hectares of land spared in total.

Cavern construction is a mature technology that has have continually improved in its application. There has been successful local examples of accommodating different facilities in rock caverns, including the Stanley Sewage Treatment Works completed in 1995, as well as Island West Refuse Transfer Station and Kau Shat Wan Explosives Depot both completed in 1997. Also, in 2009, the University of Hong Kong reprovisioned the Western Salt Water Service Reservoirs in rock caverns to release the site for its Centennial Campus development. These projects have demonstrated that rock caverns can provide new land resources in a safe way.

According to the findings of the study on “Enhanced Use of Underground Space in Hong Kong” completed by the Civil Engineering and Development Department (CEDD) in March 2011, Hong Kong is particularly suitable for developing rock caverns from the geological perspective. The study has recommended a feasibility study on the relocation of Diamond Hill Fresh Water and Salt Water Service Reservoirs to caverns, with a view to releasing the 62-year-old existing site for housing and other welfare service uses. The relocation site has been initially proposed at the hillsides north to Chuk Yuen North Estate, Wong Tai Sin. The project is expected to be commenced in the second half of 2021 and completed in 2027. The new reservoir will then be Hong Kong’s first reservoir in caverns.

Existing Diamond Hill Fresh Water and Salt Water Service Reservoir

Diamond Hill Fresh Water and Salt Water Service Reservoirs (DHSRs) are located at Shatin Pass Road at Tsz Wan San, which occupies a footprint of about three hectares.

The existing Diamond Hill Fresh Water Service Reservoir (DHFWSR) was commissioned in 1957 with a capacity of 23,524 metre cube. At present, fresh water is delivered from Sha Tin Water Treatment Works via Lion Rock High Level Fresh Water Primary Service Reservoir to DHFWSR. It provides fresh water supply to Wong Tai Sin area.

The existing Diamond Hill Salt Water Service Reservoir (DHSWSR) was commissioned in 1957 with a capacity of 21,836 metre cube. At present, sea water is extracted from the sea water intake at the Tai Wan Salt Water Pumping Station and pumped through diameter nominal 800 millimetres and diameter nominal 900 millimetres salt water mains to DHSWSR for supply to the middle and eastern part of Kowloon area.

Proposed Relocation Site

It is proposed to have the relocation of the DHSRs at the hillsides north to Chuk Yuen North Estate, Wong Tai Sin, where is now zoned as Green Belt (GB) site. The geology of the proposed relocation site, belonging to hard granite with no obvious weak zones and faults, is most suitable for construction of large caverns. In addition, the majority of the area belongs to government land. With appropriate measures, the traffic impact arising from the construction and operation stages of relocation of the DHSRs could be minimized.

Brief Description of the Project

The relocated DHSRs will be constructed in a series of caverns linked by a vehicular access tunnel and an emergency exit to Ma Chai Hang Fresh Water Service Reservoir and Shatin Pass Road, respectively. The relocated DHFWSR and DHSWSR will be constructed with two and three compartments respectively while the existing Diamond Hill Fresh Water and Salt Water Pumping Station will be split into DHFWPS and DHSWPS when relocated. The proposed storage capacity of the relocated DHFWSR and DHSWSR is 10,000 metre cube and 19,000 metre cube respectively.

Ancillary facilities will be constructed near the tunnel portal including transformer room, switch room, emergency generator room, administration building, control room, ventilation building, and pumping station control room.

Project Schedule

Construction of the project is tentatively scheduled to commence in the second half of 2021 for completion by about 2027. Tentative programme for commissioning of the relocated DHSRs and terminating the operation of the existing DHSRs will be undertaken in 2027. The Environmental Impact Assessment study of the project was started in the middle of last year and will be completed in the fourth quarter of this year.

Possible Environmental Impacts and Mitigation Measures

Air Quality
Construction activities such as tunnel and cavern excavation, cutting, filling, rock crushing, stockpiling, construction vehicle movements may generate dust emission. Therefore, with the implementation of dust suppression measures as stipulated in the Air Pollution Control (Construction Dust) Regulation, dust generation is expected to be minimal during construction phase.
Construction activities such as construction of the relocated DHSRs, tunnel and cavern excavation using drill-and-blast methods, and material transportation, etc. may produce noise. Measures include the use of quiet powered mechanical equipment (PME), adoption of temporary noise barriers; and good construction site practices to minimize the noise impact from general construction activities will be implemented. If necessary, during construction phase to ensure compliance of the relevant criteria of Environmental Impact Assess Ordinance-Technical Memorandum.

The proposed tunnel and cavern and portals location are outside Lion Rock Country Park, including GB sites. The majority of construction activities will be carried out in caverns or in urbanized areas. Construction of emergency exit, vehicular access tunnel and ventilation shaft(s) (if any) may contribute to a direct loss of habitats, especially the encroachment of the proposed emergency exit on woodland and stream habitats where fauna species of conservation importance were identified during feasibility stage. A ventilation system with inlet and exhaust locating within the tunnel portal is proposed, this can further reduce the potential woodland habitat loss during the works.
It is expected to have indirect effect on the surrounding habitats and associated wildlife due to disturbance from construction works (e.g. construction dust, noise, silty run-off). The proposed tunnel and cavern will be installed with water-proof lining to prevent infiltration of groundwater infiltration into the tunnel and cavern. Therefore, drawdown of stream courses locating above works area and groundwater table are considered unlikely, and thus unlikely to cause indirect ecological impacts.

Future Development of the Original Site

The Government expected to have four hectares of land spared after the completion of the project to build at least 2,500 residential flats. Besides, at the southern part of the site, 54,000 square feet and 32,000 square feet of land will be reserved to house the existing soccer pitch and to build Government, Institution or Community (GIC) sites like healthcare facilities etc. respectively.


Rock cavern development is taken as a long-term measure to supply lands. As one of the Pilot Projects, it is hoped that the construction works can be completed smoothly. When the feasibility study is done, it is planned to have a systematic relocation programme for suitable Government facilities and provide new land resources to Hong Kong.

Environmental Protection Department
Official Website of “Relocation of Diamond Hill Fresh Water and Salt Water Service Reservoirs to Caverns”

Complimentary copies available to members of the following associations:

The Hong Kong Construction Association
Macau Coustruction Association
Hong Kong General Building Contractors Association
Hong Kong Institute of Utility Specialists
China Hongkong Society for Trenchless Technology Association
Hong Kong Construction Materials Association Limited
Contractor's Authorised Signatory Association
Hong Kong Construction Machinery Association