Hong Kong Water Supply – Tai Lam Chung Reservoir
Tymon Mellor: The construction of Tai Lam Chung Reservoir in the 1950s was at that time, the largest and most expensive construction project yet in Hong Kong, but when a half page article[i] about the construction of the 12km of tunnels was published in 1956 the photo they used focused on the ever-running supply of water at the site. The Colony’s rapidly increase in the post war population was out stripping the supply of water resulting in severe shortages, leading to a water supply restriction of 3 hours every other day for much of May 1956[ii] and the people were suffering. Pressure was on the Government to supply more water, and Tai Lam Chung would be the solution.
Tai Lam Chung Valley Scheme
In 1938 the opportunity to use the Tai Lam Chung valley as a new reservoir was identified and site investigation along with detailed surveys were initiated to assist in the development of the scheme. The initial site for the dam was rejected when faulted rock was located and the dam had to be repositioned to an area of good geology. In August 1939 a proposal for the scheme was submitted to the Secretary of State for the Colonies in London and which requested the appointment of a Consulting Engineer to develop the scheme.[iii]
Messrs Binnie, Deacon and Gourley were appointed by the UK Government to provide advice and develop the scheme. The company was respected in Hong Kong as they had been responsible for the design and construction of Shing Mun Reservoir, which was up until then the largest reservoir in Hong Kong. The Consulting Engineer submitted a report to the UK Government in December 1940, proposing a reservoir of 6,000 to 7,000 million gallons at Tai Lam Chung, twice that of Shing Mun or Jubilee Reservoir[iv].
The Consulting Engineer proposed that the project be implemented in two stages. The first stage would take around six years to complete which was for a new reservoir and 16km of supply main to Lai Chi Kok. The scheme consisted of a mass gravity masonry dam around 30m high and around 300m long with three of four subsidiary dams. A tunnel to the south-east would convey the water to Castle Peak Road and pipes would transfer the water to filter beds situated near Tsuen Wan. The scheme would nearly double the Colony’s water resources upon completion[v] and was estimated to cost between $64 and $96 million.
The proposed location of the main dam was around 500m south of the actual final dam site. The second phase of the development would include expanding the supply including augmentation of the catchment area with extensive catchwaters, double the area draining into the reservoir. The full implementation was estimated to take a total of 11 years. However, all work on the project was abandoned during the Pacific War.
In 1947, with rising demand for water, work recommenced on the scheme with surveys and extensive drilling to confirm the ground conditions. By February 1948 two proposals had been developed, based on different locations for the dam. The pre-war scheme, with a 61m high dam located at the “lower site”, and a revised scheme with a 58m high dam at the “waterfall site”, higher up the valley. Both schemes provided a similar storage capacity but the lower site was located in an area of weak rock requiring the dam foundations to be at least 18m deep. The upper site provided more competent rock foundation but required a longer cut-off wall to prevent water passing below the dam[vi].
The pre-war water supply system had a capacity to support around 1 million people, but following the liberation of Hong Kong the population quickly grew, reaching 2 million by 1951. It became necessary to restrict the hours of water supply to maintain a sufficient supply throughout the year. From 1948 during the dry season and by 1950 throughout most of the year[vii] restrictions were implemented to reduce demand to match the supply. This situation could only be resolved through a new water source and additional storage capacity.
Progress on the Tai Lam Chung reservoir had stalled. As noted by the Financial Secretary C G S Follows in Legco[viii] in 1950, there were a number of problems with the scheme, but the two holding the scheme up were the expense and funding. The project estimate was an initial cost of $64 million increasing to $100 million for the full scheme. Funding was a problem, “Naturally this could not be financed from Revenue, and I am touching later in my speech on the difficulty of raising loans”, but a more immediate problem was the programme as it would take seven years before any water was available. Given these limitations, faster solutions were required. Options considered included a stripped down version of the scheme allowing early commissioning of scheme and the use of chemicals to create artificial rain, mitigating the risk of delays in the onset of the rainy season.
In early 1951, the Public Works Department developed a new scheme, reducing the costs and allowing rapid construction of the scheme. In June 1951 H J F Gourley, the UK Government’s advisor, visited Hong Kong to review the scheme. He provided a positive review and by August, 1951 the scheme had been approved and funding identified from the Colony’s Development Fund was in place. Messrs Binnie, Deacon and Gourley were appointed to design and supervise the works using local contractors to complete the works[ix].
The revised scheme was developed from the original proposal, but adopted a scaled down solution to provide early water supply with the option of raising the dam and enlarging the reservoir at some future date. The dam would be located at the waterfall site, a structure some 39m high creating a reservoir with a capacity of 1,150 million gallons. The dam would be designed to allow a future extension taking it to a full height of 54m and enlarged the reservoir capacity to 4,000 million gallons.
From the draw-off tower, water would be conveyed by a series of tunnels and large diameter mains to supply a new pumping station at Tsuen Wan, where the water would be raised through a 760mm pipe to a new treatment plant, then conveyed to a new supply reservoir on the hills above Lai Chi Kok. The project cost was estimated at $40 million and was to be completed with 3.5 years.
An interesting feature of the project was the provision of 14km of catchwaters on the south facing slopes of Tai Mo Shan, feeding into a small reservoir or settlement basin at Sham Tseng. The discharge from the settlement basin was to connect into the main supply tunnel through a drop shaft. With this arrangement, it was assumed that with the higher elevation of the settlement basin in times of low demand surplus water flows would discharge back into the reservoir[x].
Tai Lam Chung Arch Dam
The new dam would not be the first at the site. Back in 1933, the designers of the Shing Mun Reservoir scheme, Mr G B Gifford Hull of Sir Alexander Binnie, Son and Deacon were looking at the design for the new dam, and one of the options under consideration was a concrete arch dam. This was a new approach to dam design, utilising a thin concrete arch structure to retain the water. The engineering world was trying to understand how a dam of this nature could be designed to accommodate the changing stresses and achieve the necessary watertightness.
Ultimately, the selected Shing Mun dam site was not suitable for an arch dam, but the complications of the dam’s structural behaviour remained a problem to be solved.
Following the end of the Pacific War, the now promoted Brigadier G B Gifford Hull returned to Hong Kong in October 1952[xi] to supervise the construction of the new Tai Lam Chung dam. It would seem however that he still had an interest in concrete arch dams and undertook a full scale trial at the site of the proposed Tai Lam Chung Dam.
As reported a few years later in 1956[xii], a full scale model, 10m high and 17m long was constructed from concrete 150mm thick at the base and 100mm for the top 5m. The results of the trial confirmed a simplified approach to dam design, and this was then adopted for a small concrete arch dam on Hay Ling Chau. The location of the original trial was identified on the survey map of the river ahead of construction of the main reservoir.
With approvals and funding in place in November 1951[xiii] work started on the construction of an access road into the valley and the erection of the construction workers’ accommodation. This included seven European style bungalows and dormitories, washing and eating facilities for 700 workmen along with a small site hospital. A concrete jetty was constructed off the headland to the west of the Tai Lam Chung valley for the delivery of materials and connecting access roads.
In January 1952 a specialist team lead by the Government malariologist commenced anti-malarial work in the areas surrounding the working area. They sprayed the area with a “mosquito destroying powder” (DDT) and constructed land drains to remove standing water.
In March 1952 tenders were called to establish and operate a stone quarry for the project. This would allow stone to be stockpiled, ready for use once the dam construction contract was awarded. The dam was estimated to require 153,000 m3 of concrete and was to be faced with pre-cast concrete blocks.
By August 1952 the design and specifications for the dam had be completed in London and sent to Hong Kong allowing tenders to be called for the main dam works[xiv]. To expedite the construction works, the Government had already ordered 500T of 914mm steel pipe along with critical construction plant including a concrete batcher, a rock crusher, and a 10T overhead cableway.
Supervision of the works would be undertaken by Brigadier G B Gifford Hull, representing the consulting engineers of Binnie, Deacon and Gourlie. As a respected engineer in the Colony, Brigadier Gifford Hull’s return to Hong Kong made page 5 of the South China Morning Post[xv].
In early December, 1952 the contract to construct the dam was awarded to the Major Contractors Ltd for just over $7 million. The company was a joint venture of local construction companies comprising of Hong Kong Engineering and Construction Co, Lam Wo and Co and Cheong Hing Co., their chairman being Mr Lawrence Kadoorie.
Within two months, the contractor had mobilised 200 workers and had their own plant on site. The topsoil had been stripped from the quarry and dam site allowing excavation for the dam foundations to commence.
The new design adopted much of the original arrangement, a dam at the waterfall site, with tunnels and pipes connecting to a new pump station at Tsuen Wan. The shaft and connection to the Sham Tseung settlement basin was removed and replaced with a tunnel from the basin to the new reservoir. The new filter beds were to be constructed on the hillside above the Tai Po Road feeding the new service reservoir at Lai Chi Kok, and then onto another new service reservoir behind King George V School.
In March 1953, the Governor Sir Alexander Grantham made the first of many visits to the site to see progress on the excavation of the dam foundations along with the quarry and stockpiling of rock for the future dam construction. By the summer of 1953 good rock had been reached suitable for the dam foundation, and with 650 works on site, good progress was being made. However, the concrete batcher had not yet arrived from the UK on time preventing the start of the major concreting operation. The equipment would not arrive until the end of the year, nearly 18 months after procurement. Preparation works continued with the stockpiling of rock, installation of a railway to deliver rock from the quarry to a crusher, and the installation of an inclined conveyor to take the rock to the concrete batcher located on the hill beside the dam. From the concrete batcher, 3 m3 skips would be delivered with the 10T cableway to the location of placement.
By the summer of 1953 it was clear that the reduced Tai Lam Chung scheme would not meet the growing water demand. In November 1953 approval was given to expand the scheme to incorporate the full dam development, including the full height dam, doubling the capacity of the treatment plant and additional service reservoirs. This would add a further 12 months to the construction programme and bring the project cost to a forecast of $60million[xvi].
In May 1954 the Governor paid a visit to the site to see the progress of the works; the dam was now some 12m above the river bed but progress was limited as key equipment parts from the UK were still on order. This would ultimately delay the project by a further 6 months.
By the time that the Governor paid his next visit in April 1956, the dam was progressing well and over 32km of catchwater had been completed. After visiting one of the completed tunnels, Mr Lawrence Kadoorie proclaimed it to be “one of the major engineering achievements in the Colony”[xvii]. To mitigate programme delays, the labour force had been increased to 1,200 workmen on site, and productivity increased by up to 25% following the introduction of a bonus scheme.
Impounding of the reservoir commenced in July 1956 holding over 1,362 million gallons[xviii] by the end of that year. With completion of the supply tunnels, pumping station and treatment plant, the reservoir began supplying water to the network on the 7 March 1957[xix] when Lady Patricia Lennox-Boyd, the wife of the Secretary of the State for the Colonies opened a valve at the Tsuen Wan treatment works connecting the water supply to the distribution network.
A formal opening ceremony was held on the 7 December, 1957 where the Governor unveiled a granite plaque at the reservoir celebrating the completion of the dam. The reservoir with a capacity of 4,507 million gallons was complete but work would continue for another three years extending the catchwater system and improving the supply network.
What’s in A Name
At the time of the opening, there was discussion on the correct name for the reservoir. The District Office advised that the area of the dam was Tai Lam, thus the official plaque provides the name Tai Lam Reservoir. However, the term Tai Lam Chung Reservoir had been adopted by all.
The waterfall dam was planned to be constructed in two phases, the first stage being 46m high and 250m wide. The second stage would raise the height to 61m high and 366m long. Next to the dam was an earth embankment dam, 24m high and 335m long. This arrangement would provide for a storage capacity of 1,000 million gallons for stage 1 and 5,000 million gallons for stage 2[xx].
The stage 1 work involved the removal of 20,000m3 of soil and decomposed granite, excavation of 30,000m3 of rock and the placing of 140,000m3 of concrete, along with stone facing material.
The waterfall dam required the construction of a cut-off wall below the dam to prevent water flowing below the structure. The excavation was 3m deep and 2m wide at the base. It was excavated using blasting then filled with a high quality concrete. The dam was mass concrete with large rocks or ‘plums’ embedded to reduce the volume of concrete, and this construction method was known as cyclopean rubble.
The contractor had not planned to incorporate ‘plums’ within the concrete but was persuaded to adopt the approach by the supervising consultant. This required a re-configuration to material handling but with a 20% replacement factor, it provided a significant saving in cement and resulted in a denser concrete. To meet the programme the contractor needed to place an average of 210m3 of concrete per day. To allow for disruption this required a concrete batcher capable of producing 30m3/hr. The rock crusher and concrete batcher were ordered to achieve this value with contingency, but in the early periods they failed to meet the needs and required modifications to achieve the required production.
The 10T cableway was supplied by J M Henderson & Co Ltd and was designed to carry 3m3 skips with a hoisting speed of 1.3m/s and a travel speed of 5m/s allowing the cableway to handle the planned 30m3/hr.
The up and down stream face of the dam was planned to be faced with pre-cast concrete blocks. However, it was found that with abundant cheap labour available, finished granite blocks were cheaper to produce and so was adopted instead.
In addition to the main waterfall dam, three subsidiary dams were required in adjacent valleys. To improve construction access, the Government built a new road to serve the construction works and the village of So Kun Wat. The secondary dams were of a gravity earth embankment type with a concrete core wall as waterproofing. The highest dam was 21m and all three required around 37,000m3 of fill.
Quarries, Crushers and Concrete Mixers
For the main construction material, two quarry sites were explored, one adjacent to the valley access road, below the dam site and one above the dam to the southeast. The upper site was the initial favourite but with a detailed review of the logistics associated with siting a crushing and concrete plant and delivering the concrete to the cableway, the upper site was deemed impractical, and the lower site, Quarry No. 1 was developed.
From the quarry, tracks were laid to the crusher and 0.76m3 side tipping cars were used to transport the rock. The little quarry trains were pulled by Fordson Major tractors, both cheaper and easier to dispose of at the end of the job than the traditional diesel locomotive.
The crushing plant was located to the west of the main dam, at the foot of the adjacent hillside, a 760mm conveyor set at 20 degrees raised the crushed rock 52m to the concrete batcher on the hill. The belt could move 100T/hr sufficient for the needs of the crusher.
The 30m3/hr concrete batcher was located on the hillside to the west of the dam. It was positioned below the cableway, allowing the direct loading of skips and minimising the travel time for the wet concrete.
Derricks cranes were provided around the site and on the dam to lift materials into place, two 7T travelling, two 3T static cranes and one 5T unit[xxi] were utilised.
Tender for the supply tunnels was called in April 1954 and the contract was awarded in July 1954 to Major Contractors Ltd for just over $6 million. The design of the works had been revised to minimise the length of pipeline and extending the tunnels, requiring the construction of 8.2km of rock tunnel and 174m of pipeline in two short sections.
The supply line consisted of four separate tunnels, allowing driving to be undertaken from both ends, resulting in eight working faces with the longest tunnel being just under 3,300m.
Tunnel 1 connected the dam site to a portal at Sham Tseng, where a short section of pipe connected to Tunnel 2, passed behind Shan Tseng to the portals by the stream and to provide access to Tunnel 3. This tunnel connected to the rear of Tsuen Wan, but to improve construction efficiency a shaft was sunk at Ting Kau allowing the tunnel excavation to progress from two more faces.
The tunnels passed through predominantly hard rock, requiring the face to be blasted with 2.2kg of TNT. The tunnels were 2m in diameter but were generally larger due to over-break. Where unlined, only a concrete floor was placed but in areas of weak ground a concrete lining was provided reducing the tunnel to 1.75m diameter. Excavation required the drilling of 15 to 25 holes in the face and blasting 1.5m of rock. With five blasts every two days progress of 3.8m/d was achieved with a crew of 16 workers. A total of 384 workmen was required for the tunnel works, living in make shift accommodated at each portal.
After nearly two years of tunnelling, the final tunnel broke through in June 1956.
The supply tunnels were commissioned in March 1957 but in April 1958 a serious leak was detected and estimated to be losing one million gallons of water a day[xxii]. The leak was close to the Sham Tseng tunnel portal in an area of poor ground. The concrete lining was found to be cracked due to movement of the surrounding rock. The damaged concrete lining was cut away and holes drilled into the bed rock to grout up joints and to prevent further movement. The lining was replaced and the tunnel re-entered service in mid May 1958.
Further leaks occurred and after unsuccessfully trying to seal the leak from the outside, the tunnel was emptied on the 12 March 1959, restricting water supplies to the colony to 3 hours a day. Over a 120m section of the tunnel, radial grouting was undertaken to seal the rocks, but as a precaution, the section was also lined with a 914mm steel pipe to preclude future problems. The works were completed on the 2 April, 1959 and water supply hours were increased to 8 hours a day on the 4 April, 1959[xxiii].
Lam Tei Tunnel
With the development of Yuen Long and Tuen Mun, a new water tunnel was required to provide the necessary supply to the new San Hui treatment plant. In 1966 work commenced on the 4km long tunnel between Tai Lam and Lam Tei at a cost of $7 million. The tunnel broke though in April 1968 and the completed treatment plant commissioned in 1970[xxiv].
Pumping Station and Treatment Works
Tenders for the construction of the new treatment work at Tsuen Wan were issued in February 1954 and work commenced later in the year. The facility was designed to handle 20 million gallons a day. Water from the new reservoir would be chlorinated at the dam site before travelling through the tunnels and pipe line to the pump station and the treatment works. With the expansion of the reservoir, additional pumps had to be installed to cope with the additional supply. The facility was commissioned in March 1957 with a capacity of 40 million gallons a day.
The design of the treatment plant had allowed for a staged completion, but with the expansion of the reservoir, the full facility was constructed in one go. Construction of the rapid gravity filters was completed in November 1955 and an adjacent five million gallon service reservoir commenced later in March 1956.
In addition to the dam and filtration plant, the scheme required the construction of five new service reservoirs, including a covered reservoir at Lai Chi Kok peninsular with a capacity of 10 million gallons and on the hillside west of Ma Tau Wei Road. A new service reservoir was constructed at Diamond Hill and a new service reservoir at Ma Tau Wai, adjacent to KGV school.
The new reservoirs were connected with over 8.5km of steel pipeline up to 760mm in diameter, with installation commencing in March 1956 and was completed within nine months.
Catchwaters & Irrigation Reservoirs
To capture as much water as possible, 24km of catchwaters were identified to enlarge the reservoir catchment area but these were expanded to around 40km in total. The first section of catchwaters to be developed included the stilling basin at Sham Tseng, fed by a 2.3km catchwater along the southern slopes of the hills[xxv] in 1955.
With the expansion of the catchwater system the reservoir direct catchment area of 1,600 hectares was expanded by a further 3,300 hectares. The catchwaters were typically 4m wide and 2.2m deep, but varied in size depending on the volume of water to carry. Where it was not possible to establish a cutting, tunnels were constructed, typically around 3.2m in diameter. Thirteen tunnels were driven with a combined length of 8.2km, the longest Tunnel 1 being 1,980m long.
The implementation of the extensive catchwater system intercepted water supplies that would otherwise have flowed into agriculture land. To avoid disrupting the farming operations, a series of irrigation reservoirs were constructed to ensure a continued supply and to mitigate droughts. These reservoirs include the Sham Tseng settlement basin, Wong Nai Tun, Ho Pui and the Tsing Tam reservoirs and which are the subjects of a future article. The design of the reservoirs was such that once full, all additional water would overflow and be carried to the Tai Lam Chung reservoir.
Two villages were impacted by the works, Kwan Uk Tai and Tai Lam, a total of 37[xxvi] families. The villagers were traditional rice farmers producing between 1.1T to 1.5T per acre depending on the quality of the land. Negotiations for the relocation of the villages commenced in July 1948 and the villagers moved out in August 1956 with the filling of the reservoir. The Government proposed to relocate the villagers to new agricultural land but the villagers requested that they be moved to a new development in Tsuen Wan. The resultant purpose built building known as Tai Uk Wai was provided on Chung On Street at a cost of $1.2 million[xxvii]. The building was designed to house all the villagers with accommodation for 175 people consisting of 52 flats and 27 shops and the ancestral temple of the Cheung clan of Tai Lam. The living accommodation was granted in exchange for the houses and building land surrounding the original villages and the shops would provide compensation for the lost farming revenue.
Following the relocation of the villagers, discontent of the arrangements emerged, and in January 1957 a number of the villagers applied to the Compensation Board on the grounds that the resettlement had not accommodated the necessary Fung Shui arrangements[xxviii] and additional compensation was required. During the hearing the former farmers had forgot they had agreed to all arrangements and were now unwilling to accept alternative farm land in Yuen Long or move out from the new accommodation. They just wanted more. I have been unable to locate the result of the hearing.
Tai Uk Wai was demolished in the late 1990s to be replaced with the new Blue Yard development.
The final cost for the Tai Lam Chung project was $30 million for the reservoir and distribution system, $10 million for additional catchwaters and $5 million for associated projects. A total of $45 million with all work completed by 1961.
Even before the completion of the reservoir, it was clear it would not solve the Colony’s water supply problems. Thus, in 1955 investigation work commenced in the Shek Pik valley in Lantau to see if it would be suitable for a large reservoir and by 1958, surveys were undertaken at Hebe Haven and Plover Cove, the subjects of a future article.
South China Morning Post
Hong Kong Heritage Organisation
Annual Departmental Report – Director of Public Works
[i] South China Morning Post, 27 May 1956
[ii] Hong Kong Annual Report, 1956
[iii] Public Works Report 1939
[iv] South China Morning Post, 15 May 1947
[v] Hong Kong Annual Report, 1947
[vi] South China Morning Post, 1 July, 1948
[vii] Hong Kong Annual Report, 1950
[viii] Hong Kong Legislative Council, 29 March 1950
[ix] South China Morning Post, 29 August 1951
[x] South China Morning Post, 29 August 1951
[xi] South China Morning Post, 21 October 1952
[xii] Concrete Arch Dams, A P Goudy, The Engineering Society of Hong Kong, Session 1956-1957
[xiii] South China Morning Post, 17 November 1951
[xiv] South China Morning Post 23 August, 1952
[xv] South China Morning Post, 30 September, 1952
[xvi] Savingram, to the Secretary of State for the Colonies, 27th November 1953
[xvii] South China Morning Post, 19 April 1956
[xviii] Hong Kong Annual Report, 1956
[xix] Hong Kong Annual Report, 1957
[xx] Construction Plant for the Tai Lam Chung Dam, W Phillips, The Engineering Society of Hong Kong, Session 1955-1956
[xxi] South China Morning Post, 11 August 1955
[xxii] South China Morning Post, 25 April 1958
[xxiii] Hong Kong Annual Report 1959
[xxiv] South China Morning Post, 2 April 1968
[xxv] South China Morning Post 13 September 1955
[xxvi] Tai Lam Chung Level of Water, DCNT 17 July 1956
[xxvii] South China Morning Post, 9 August, 1956
[xxviii] South China Morning Post, 10 January 1957
This article was first posted on 22nd July 2020.
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