Hong Kong Water Supply – Plover Cove Pt 2 Construction of Stage 1

Tymon Mellor: In 1961 the Plover Cove scheme had developed from a simple water supply reservoir into an integrated water management scheme, linking local sources with the new Mainland water supply. The scheme would also go on to provide the first road tunnel through Beacon Hill as a by-product of the new supply pipeline. This one scheme was about to change the nature of the New Territories from an isolated rural community to become the water supply hub for the urban population and enabling the establishment of the new towns.

Staged Development

With the development of the integrated water scheme, the proposed new storage reservoirs at Hebe Haven and Plover Cove would be linked with provision for the new northern water sources, notably the new supply from Shenzhen. To expedite development of the project, the design consultant, Messrs Binnie, Deacon & Gourley and Messrs Scott & Wilson, Kirkpatrick & Partners divided the scheme into stages, allowing early start on construction while allowing time for further development of the more complex structures. The final implementation sequencing being:

Stage 1 – development of the northern sources requiring the construction of the tunnels and infrastructure from Tai Po Tau to Shatin;

Stage 2 – development of Plover Cove reservoir and associated tunnels;

Stage 3 – development of Hebe Haven reservoir and associated tunnels;

Stage 4 – development of eastern catchment area and dredging of Hebe Haven.

With the construction of the water collection and treatment facilities being managed by the consulting engineer, construction of the new water supply infrastructure from the Shatin treatment works, including the new Lion Rock tunnel and service reservoirs, was undertaken by the Waterworks Office.

Plover Cove Pt 2

Implementation of the Stage 1 works would provide an additional 20 million gallons a day and an additional 30 million gallons a day with the northern sources. Full implementation of the scheme would provide an additional 117 million gallons a day with an additional 37 million gallons a day from the northern sources.

Stage Description Yield (mgd) Capital Cost (HK$ millions) Implementation (years)
Without Northern Source Northern Source
Preliminary Investigations 9
1 Tai Po Tau – Shatin 20 30 121 3.5
2 Plover Cove – Tai Po Tau 45 7 900 5-6
3 Hebe Haven 24 140 4
4 Eastern Catchments 25 150 4
Hebe Haven dredging 3
Total 117 37 720 8-12 years

Northern Sources

In the effort to find additional water supply, it was recognised that the River Indus, in the north of the territory, may provide a suitable source, but it was remote from any water supply infrastructure. In 1960, with the agreement to provide water from the Mainland, a new 1.2m steel main was installed from the border to the Tai Lam reservoir catchwater, a length of some 16km to transfer the water into the supply network. As the new water main passed the River Indus, a temporary pumping station was constructed allowing water from the Indus to be added to the supply. Water from the Indus source commenced on the 7th October, 1960 and then from the new Shenzhen reservoir on the 5th December, 1960[i].

This arrangement relied upon there being spare capacity in the Tsuen Wan Filter treatment plant for the additional water. However, within 12 months it was clear the filtration plant could not accommodate the additional supply and a temporary pumping main was installed to transfer excess water to the Shing Mun reservoir South Conduit and using the spare capacity at the She Lei Pui plant[ii]. This was only a temporary fix, and the northern sources needed to be integrated into the new Plover Cove scheme.

Stage 1 Works

The Stage 1 works included all the infrastructure to support the delivery of water from the northern sources and the mountain streams along the route between Tai Po Tau and Shatin. This included:

  • Water transfer system from the mainland and the River Indus;
  • 13km of water tunnel and intakes between Tai Po Tau and Shatin;
  • Lower Shin Mun Reservoir;
  • Shatin Treatment works with a 80 million gallons a day capacity;
  • Lion Rock tunnel;
  • Transfer mains; and
  • Service reservoirs.

With funding of $100 million, works commenced on the Stage 1 works in November 1960 with the scheme to be completed and commissioned in 1965.

Slide2

Computer Design

The design of the scheme was undertaken at the head office of Binnie, Deacon and Gourley in London. Here, the team had access to an early digital computer and used this to establish the best dam elevation, reservoir capacity and tunnel size taking account of hydraulic efficiency and cost[iii]. The actual computer used is not described. However, a paper published in 1958 on slope analysis by other engineers from Binnie, Deacon and Gourley describe the use of a DEUCE (Digital Electronic Universal Computing Engine) computer, manufactured by English Electric[iv]. The machine was valve based and utilised punch cards for input and output, and 33 machines were sold between 1955 and 1964 before it was discontinued.

Slide13

For interest, the first computer in Hong Kong was installed by CLP in late 1963 when it took delivery of a NCR315 system. This was a second-generation system using printed circuit boards and transistors, and the machine was used to generate customer bills[v].

Tau Pass to Tai Po Tau

A new tunnel, 2.2km long was constructed from the pumping station at Tai Po Tau to Tau Pass, intercepting rivers along the route. In addition, at the northern end of the tunnel, the tunnel was sized to accommodate the northern sources, saving around $1.5 million on providing a dedicated pipeline to the Tai Po Tau pumping station.

Slide3

The tunnel was excavated from the pumping station in hard rock as it passed through the adjacent hillside and into the valley. With the reduction in ground cover a cut and cover solution was adopted. A trench was excavated for the construction of the tunnel along with three intake structures and the connection to the northern sources pipeline.

Slide4

Tai Po Tau Pumping Station

The Tai Po Tau pumping station provided a central collection point for the different water sources, pumping the water through the new tunnel to Lower Shing Mun Reservoir or directly to the Shatin Treatment works.

Water from the northern sources arrived through the Tau Pass tunnel, and water from the adjacent Lam Tsuen River was collected from a pool created with an inflatable neoprene dam, Fabridam, supplied by Firestone Tire and Rubber Co[vi]. The neoprene dam was inflated by air from an adjacent control structure creating a dam 3.7m high. In the event of heavy rain, the dam could be deflated to avoid flooding upstream and this was a cheaper solution than a sluice gate structure. A similar structure was provided at Tau Pass and the River Indus to impound water for the pumping stations.

Slide5

The facility was also designed to accommodate the future tunnel to the proposed Plover Cove reservoir.

From a central collection point, the water passed through a buried culvert to the central pump sump within the pumping station where four pumps with a capacity of 15 million gallons a day and two secondary pumps of 7.5 million gallons a day provided a nominal design capacity of 60 million gallons a day.

Construction of the pumping station was awarded to Paul Y Construction Co and construction work commenced in 1961, by 1963 the facility was ready for the installation of the pumps and Fabridam. These were installed in 1964 and commissioned on the 1st March 1965 to take advantage of the new water being supplied from the new East River Scheme transferring an additional 62 million gallons a day[vii].

Slide6

Tau Po Tau to Shatin Tunnels

From the Tai Po Tau pumping station, a tunnel 11.25km long was constructed to the new Lower Shing Mun Reservoir and Shatin Treatment works. The tunnel passed through granodiorite, rhyolite and granite rock and was excavated using drill and blast techniques. The tunnel, ranging in size from 3m to 7m diameter, was generally unlined with just a concrete invert to improve water flows and to avoid silting. The tunnel was designed to operate under full flow with a pressure head of between 1.5m to 76m, depending on the inflows. In areas of poor ground, the tunnel was fully lined to both support the rock and protect against possible damage from the water pressures. Where the ground was very poor, a concrete circular section was constructed.

In addition to the main tunnel, three branch tunnels of total length 5.09km and ranging in size of 1.7m to 3.2m were constructed to collect water from remote streams.

Slide7

Along the tunnel alignment, as it passed a mountain stream, drop shafts were constructed to collect water from the catchment area, with the ten shafts ranging in diameter from 2m to 4.6m depending on the volume of water expected. The shafts varied in depth between 70m to 110m deep and were designed to minimise the entrapment of air as the water descended down the shaft. A build-up of air within the tunnels could result in the explosive release of pressure at the tunnel portals. It was known that if the water descended down the shaft in a vortex, it would allow the air to be released. Modelling was undertaken at the UK Hydraulics Research Station in Wallingford[viii] at scales of 1:10 and 1:20 to establish the optimum configuration to create the vortex and to ensure it was maintained over the full depth of the shaft.

At the top of the shaft, a small dam with sluice gates was constructed to create a pond of water that would overflow into the drop shaft. The intake structure created the vortex ensuring the water clinging to the sides of the shaft releasing the entrapped air as it fell.

At the base of the shaft a de-aeration chamber was constructed. This structure had a large cross section with baffles, reducing the speed of the water, allowing air bubbles to rise to the surface and be released into the air through a vent pipe to the side of the drop shaft[ix].

Slide8

The contract for the construction of the tunnels was awarded to Hsin Chong – Kumagai Gosho, with work commencing in March 1962. Work was disrupted by Typhoon Wanda in August 1962 but the contractor mobilised additional resources and the tunnel broke through on programme in late March 1964[x].

Slide9

Lower Shing Mun

The Lower Shing Mun reservoir, is located down-stream of the Shing Mun reservoir in a steep sided valley impounded by a rockfill gravity dam. The reservoir receives water from the local catchment area, from Shing Mun reservoir and from water delivered through the tunnel from Tai Po Tau. The main function of the reservoir is to balance flood flows from these sources with the demands of the Shatin Treatment works. The optimum capacity of the reservoir, the siting and height of the dam, the sizes of tunnels and the pattern of operation of the reservoir relative to various draw-off rates were established through computer modelling. The results indicated that the reservoir with a capacity of 910 million gallons would fill and empty rapidly as the demand fluctuated.

Details of the construction will be addressed in a separate article.

Shatin Treatment Works

The Shatin Treatment works were located at the foot of Beacon Hill, adjacent to the KCRC line and Beacon Hill tunnel. To create the site for the facility, decomposed granite hills were removed and a existing stream diverted around the proposed facility. The treatment facility had a designed throughput of 160 million gallons a day, and the configuration allowed it to be constructed in two stages. The first stage would treat 60 million gallons a day with provision to take surge flows of up to 80 million gallons a day for short periods.

Slide12

A central control room was provided to manage the operation of the treatment works, the tunnel, pumping station, valves and intake structures using a supervisory system to feed a working mimic panel. In the days before computers, information and instructions were converted into a digital code and transmitted through telephone-line to the control centre. Over seven hundred monitoring points were scanned regularly with priority for alarm signals. Two 4-track recorders were provided with the ability to select any 8 out of 140 inputs selected through a plug board. Flows, levels and other information on the state of the scheme could be record and information printed out on two typewriters. A line printer record alarms and operational changes, such as pumps started and valves opening, as they occur. Extensive use was made of magnetic flow meters for accurate gauging of raw and treated waters; with the unit at Tai Po Tau measuring the direction of flow.

The chemicals needed for the plant operations were initially to be delivered by road, but there was provision for a chemical house with railway siding and connection to the KCRC to allow chemicals to be delivered in bulk and unload in a secure environment. However, this was never constructed.

Slide10

The contract for the construction of the treatment plant was awarded in November 1960, to Wan Hin & Co Ltd. The initial works included the site clearance and stream diversion followed by construction of the civil engineering infrastructure. By the end of 1963, installation of the equipment and plant had commenced. Sourcing quality sand at economic prices for the filter beds proved to be a problem. A UK sourced hydraulic classifier was mobilised to produce sand from local sources, but this had only limited success and sand had to be procured from Japan at greater costs.

The facility was commissioned in August 1964 using water from Lower Shing Mun Reservoir. With the completion of the tunnel to Tai Po Tau in March 1965, water from the northern sources commenced supply in 1966 when the intake structures were completed[xi].

Slide11

In addition to the new civil works, the existing power supply system had to be upgraded to support all the new infrastructure. The Kowloon 33kV electrical power supply was extended through the KCRC tunnel to supply the new treatment works.

Lion Rock Tunnel

The Lion Rock tunnel was required to transfer the water from the Shatin Treatment works to the new service reservoirs in Kowloon. The initial water tunnel was enlarged to accommodate both the large diameter water mains and vehicular road traffic. Details of the design and construction will be covered in a future article.

Stage 2

With the formal commissioning of the Stage 1 works in October 1966, all attention turned to the progress of Plover Cove reservoir and the new cross harbour pipeline.

Images

Hong Kong Image Database

Sources

[i] Waterworks Office, Annual Departmental Reports, 1960-61

[ii] Waterworks Office, Annual Departmental Reports, 1961-60

[iii] Investigation and Design of the Plover Cove Water Scheme, Stanley E H Ford and Stanley G Elliott, ICE 1965

[iv] The place of digital computers in civil engineering, Robert K Livesley, ICE 1960

[v] The Computer Age in Hong Kong: Dynamic Past, Hesitant Present, What Next?, Anthony O, 2013

[vi] Application of inflatable dam technology problems and countermeasures, Paul W M Tam, Can. J. Civ. Eng. 1998

[vii] Hong Kong Annual Report, 1965,

[viii] Technical Problems in Plover Cove Scheme Being Solved, SCMP, 31 Dec 1963

[ix] Investigation and Design of the Plover Cove Water Scheme, Stanley E H Ford and Stanley G Elliott, ICE 1965

[x] Plover Cove Tunnel Broken Through, SCMP 3 April, 1964

[xi] Plover Cover, Water Supplies Department

This article was first posted on 26th August 2021.

Related Indhhk articles:

  1. Hong Kong Water Supply – Plover Cove Part 1 Scheme Development
  2. Plover Cove Reservoir – photographs of official opening 1969
  3. Plover Cove Reservoir – 1977 Water Supplies Dept report
  4. Plover Cove Reservoir – 50th anniversary of relocation of residents from Sam Mun Tsai
  5. Q&A48 T.O.Morgan, Director of Water Supplies – imagined Plover Cove Reservoir while swimming in the area

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