The hilly and hard rock terrain of Hong Kong makes it highly suitable for developing rock caverns, particularly on the urban fringes. The Government is actively exploring the use of rock cavern development to expand the land resources of Hong Kong and as one of the viable sources of long-term land supply.

With its urban setting, the released site of the existing Diamond Hill Fresh Water and Salt Water Service Reservoirs (DHSRs), covering around four hectares of land, is suitable for housing development. Besides, by following the “single site, multiple use” principle, part of the released site could be used for re-provisioning of the football pitch and its supporting facilities which are currently on the existing DHSRs, and providing some “government, institution or community” facilities including public car park, medical and health service facilities, etc.

Works for “Relocation of Diamond Hill Fresh Water and Salt Water Service Reservoirs to Caverns” commenced in late 2022 for completion in second half of 2027.


Project Information

This project is to relocate the existing Diamond Hill Fresh Water and Salt Water Service Reservoirs and associated facilities to caverns so as to release the existing site for housing and other uses beneficial to the people’s livelihood while continuing to ensure a reliable, adequate and quality supply of water.

The works mainly comprise:-

(1) construction of a caverns complex inside the mountain body at the south of Lion Rock of about 1.1 hectares in total area and about 156,000 cubic metres in total volume for accommodating the relocated Diamond Hill Fresh Water and Salt Water Service Reservoirs and associated facilities;

(2) site formation works at the access tunnel portal area near Ma Chai Hang Pumping Station, and construction of an access tunnel of about 780 metres long to connect the caverns complex;

(3) construction of the relocated Diamond Hill Fresh Water and Salt Water Service Reservoirs and the associated facilities (including two pumping stations) in caverns;

(4) installation of ventilation facilities and other associated electrical and mechanical (E&M) facilities in caverns and access tunnel, and at the access tunnel portal area;

(5) laying of fresh water and salt water pumping and distribution mains of about 13 kilometres in total length with diameters ranging from 250 millimetres to 800 millimetres in caverns, access tunnel and Wong Tai Sin district for connection with the existing water supply network;

(6) carrying out other related works including utilities diversion, landscaping works, etc.; and

(7) implementation of environmental mitigation measures and related environmental monitoring and audit programme for the works.


Ground Investigation Works at Lion Rock

To facilitate the tunnel and cavern construction works, the Water Supplies Department carried out ground investigation works at Lion Rock with the aims to facilitate the contractor of better identifying the ground condition in advance, commencing the cost savings design works and minimizing the associated construction risks.

Since the proposed tunnel and caverns in this project are underneath Lion Rock, while all the required ground investigation stations were in remote area, there was no proper road and access in the vicinity of the ground investigation stations. Lifting of equipment and materials to the designated ground investigation stations by helicopter was the most efficient and practicable way to carry out the works.

It is important for the contractor to ensure the lifting load would be kept below the safe lifting load of the helicopter in each flight (800 kilograms per lift). Prior to the commencement of each helicopter lifting operation, a loadmaster checklist and lifting schedule would be prepared by the contractor to ensure safe helicopter lifting operation. Due to the heavy weight of the equipment and materials, the helicopter is required to shuttle along the flight path.

During each lifting operation, the helicopter would hover in the air at the designated pickup point for around 5 to 10 minutes to load the equipment and materials. The nearby area would be temporarily closed and accessible only by certified ground crew.

The ground investigation works and helicopter lifting operations were completed by June 2024.


Commencement of Tunnel Construction

Due to the soft geological conditions in the initial section of the tunnel, pre-excavation grouting and the installation of temporary supports are required before tunnel excavation to ensure construction safety. The tunnel construction machinery was transported to the tunnel entrance near Lion Rock Park at the end of October 2024.

To facilitate the tunnel excavation, temporary supports installation works for the tunnel are necessary. Firstly, probe holes drilling will be carried out to access the geological profile and groundwater conditions ahead prior to commencement of excavation. If the water inflow rate exceeds the allowable limit, pre-excavation grouting will be carried out to control groundwater ingress in advance of the excavation works to enhance the construction safety. Subsequently, an advance full-face grouting will be conducted at the tunnel entrance. Soil nails will then be installed to stabilize the excavated face. Lastly, canopy tubes and steel arch ribs will be installed to support the upcoming excavation area.


Water Mains Laying

Water mains are being laid at Chuk Yuen Road, Shatin Pass Road, Lung Fung Street, Sheung Fung Street and Tsz Wan Shan Road to connect the relocated service reservoirs with the existing water supply network. Open trench excavation for water main laying works at some locations is in progress while excavation and lateral support works for trenchless excavation is in progress at other locations.



Source of Information & Picture: “Relocation of Diamond Hill Fresh Water and Salt Water Service Reservoirs to Caverns” Website of Water Supplies Department