Hong Kong Water Supply Plover Cove Part 3 Reservoir Construction
Tymon Mellor: Implementation of the Plover Cove scheme was intended to be undertaken in a number of stages. The first stage captured available water resources in the New Territories and a new treatment plant at Shatin. The second stage would cover the construction of the main reservoir with subsequent stages capturing water resources within the Sai Kung peninsula.
With the implementation of Plover Cove Stage 1 in 1960 and the new Mainland water supply from Shenzhen Reservoir also in 1960, the territory had addressed the immediate water crisis with a cost-effective water sources. However, with continued rising water demand and concern on overreliance on the Mainland source, in early 1963 approval was given to implementation of the reservoir at Plover Cove.
The provision of water from Shenzhen Reservoir in 1960 provided some initial relief to the ongoing water crisis, but it was clear that additional storage capacity was required in the territory. In January 1963 the Government made the decision to proceed with the construction of the Plover Cove Reservoir. A spokesman confirmed that the decision “was taken as a result of the continued increasing demand for water throughout the Colony, and after consideration of various alternative means of meeting this demand, including the conversion of sea water to fresh water by the use of nuclear power”[i]. The scheme was to cost HK$641m and would treble the storage capacity, making the territory self-sufficient into the late 1970s[ii].
The 1963 water shortage in the territory forced the British Government to consider the possibility of acquiring additional water supply from Mainland sources. However, the British were concerned that relying on the Mainland water supply would put them in a difficult position if the Chinese “might seize the opportunity to make political demands”[iii]. The provision of water from the East River scheme in February 1965 was welcomed, but reinforced the need to strengthen domestic supply with the implementation of the Plover Cove and High Island schemes.
The importance of the self-sufficiency became apparent in 1967 when the supply agreement was for the HK Water Authority to send a request for water supply commencing on the 1st October, 1967, the start of the ‘dry season’. The request was sent on the 13 September, for 62.5million gallons a day[iv] but there was no response from the Mainland authorities. With the Cultural Revolution taking told and fighting with anti-Maoist elements, Guangzhou was in turmoil. The People’s Liberation Army were taking control and the influential Mayor of Canton, Mr Tsang Seng had been arrested but was released, so it was not clear who was in charge, and the situation was also hindered by erratic communications[v].
With ongoing water shortages, earlier in the year the Government had requested to commence the water supply early, with the provision of 2,000 million gallons a day from July, 1967[vi]. There had been no response from the Mainland authorities, thus there was doubt if the scheduled supply agreement would stand.
On the 29th September, it was still not clear if the water would be supplied, but three local organisations with contacts in Guangzhou ‘hinted’ that the water would be supplied[vii]. With the only news coming out through returning citizens, there was little the Colonial Government could do but wait. At 9am on the 1st October, a representative from the Shum Chun Water Authority telephoned the HK pumping station at Muk Wu to confirm that the facility was ready to receive the water and an hour later at 10am, water was supplied from the Shenzhen Reservoir[viii]. The Director of Public Works commented “The fact that we didn’t get the additional water we asked for in July, August and September was a surprise to me and something of a shock and one had a feeling that it might happen on October 1”[ix].
The new schemes would ensure that the Colonial Government would not be put into the same situation again.
Plover Cover Stage 2
The Plover Cove scheme was conceived as a multistage project, with the commencement of the Stage 1 works, the remaining works were undertaken as a single scheme and the stage 2 and 4 developments of the Sai Kung peninsula were deferred.
The remaining works to be implemented consisted of a number of elements: the tunnel from the Tai Po Tau pumping station to the reservoir, the Plover Cove Reservoir, a new cross harbour pipeline, and ancillary infrastructure.
Plover Cove Reservoir
The original plan was to enclose the whole of the bay using shorter dams to link up the islands of Yim Tin Tsai, Ma Shi Chau, Pak Sha Tau and Pak Ying Tsui. However, this strategy would result in significant areas of farm land and villages along the Ting Kok Road being lost to the reservoir[x]. The scheme was revised to constructing a main dam 2,100m long between the promontory at Tai Mei Tuk and Harbour Island. Two subsidiary dams, 200m and 265m long would close the gap between Harbour Island, Tung Tau Chau and the peninsula to create the reservoir. The island of Tung Tau Chau was reduced by blasting to form the foundation of a 240m wide spillway to provide an overflow to the reservoir when it became full. The main dam had a crest level of 12.2mPD and the spillway was set at a level of 8.2mPD giving a nominal storage capacity of 30,500 million gallons.
The reservoir received water from the extensive catchments, enlarged through the use of supply tunnels and from the ‘northern sources’ delivered through the tunnel from Tai Po Tau. The term ‘northern sources’ primarily covered Mainland supplied water but also includes water from New Territories rivers.
When water was drained from the reservoir, the water flow in the Tai Po Tau tunnel was reversed to supply the Tai Po Tau pumping station. When the reservoir was too low for gravity flows, low-head pumps at Tai Mei Tuk raised the water level above the tunnel portal weir[xi].
The design of the dam had to accommodate: the local geology, the impact of typhoons with storm surges of up to 4.3m, permeability of the dam/foundation materials, and reverse loading when the seawater level was higher than the reservoir. However, the biggest problem for the designers was how to address the problem of water salinity, as no one had tried to convert a sea water inlet into a fresh water dam and nobody wants to drink salty water.
Plover Cove had a number of villages around the coast line, all with a long history, some stretching back over 12 generations. The villages were primarily fisherman and farming families, for example in the village of Kam Chuk Pai, all the residents were from the Wong clan and other than Sam Mun Tsai, the villagers were mostly from the Lee clan.
|Sam Mun Tsai[xii]||35 (400 people)||Yim Tin Tsai||Jul 1965|
|Chung Pui[xiii]||28||Tai Po||Nov 1966|
|Chung Mei||11||Tai Po||Nov 1966|
|Wang Leng Tau||31||Tai Po||Nov 1966|
|Kam Chuk Pai||34||Tai Po||Nov 1966|
|Tai Kau||21||Tai Po||Nov 1966|
|Siu Kau||30||Tai Po||Nov 1966|
The residents of Sam Mun Tsai were fisher families and were moved to new Government built buildings on the hillside of Yum Tin Tsai, where the site would be named Sam Mun Tsai. The new village had a pier, a typhoon shelter and a school for the 100 or so children. The original village had to be cleared early as the site was required for the construction of one of the subsidiary dams.
The six other villages were not directly impacted by the construction works but would have been inundated with the higher water levels but more significantly, they posed a health risk as their occupation may result in pollution of the reservoir water. The Government constructed 13 six storey blocks comprising of 122 shops and 488 flats on new reclamation in Tai Po.
All the villagers were relocated on the last weekend of November, 1966. For the more remote villages, boats and military personnel assisted with moving the possessions to the road head at Tai Mei Tuk. The 1,069 new residents quickly settled in to Tai Po, enjoying the convenience of an urban environment. In April 1967, with the imminent closure of the dam, the villagers returned to the new lake to remove their fishing boats. With the assistance of Government loans for motor boats, many of the villagers continued fishing while others took up employment in local carpet factories or working in the construction industry[xiv].
Construction of the dam required around 8.5 million cubic metres of fill material, and since the sea bed mud was unsuitable, a search was undertaken to identify sites to source the fill material. The preferred fill material was decomposed granite, found on the hillsides along with rock for the foundation and sand for drains. Suitable sources for the decomposed rock were identified close by at Shuen Wan, Ma Liu Shui, Cheung Kang, White Head and Lok Wo Sha. Sand was to be dredged from coastal sites around Tolo Harbour and a new quarry was opened up at Turrent Hill at Shek Mun.
The borrow site at Ma Liu Shui would become the site for Chinese University, and the excavation by the Plover Cove project assisted in the preparing of the site. The White Head site would go on to supply fill material for the Shatin new town reclamation while stripping of the material from the Lok Wo Sha hills was said to have impacted the fung shui of the adjacent villages, bringing bad luck on the families. Insensitive reinstatement of the sites with non-native pine trees did not help the situation.
The decomposed granite was found to be typically 15m deep at the borrow sites, and it was removed and transported to the dam by truck or barge, depending on the location.[xv].
As part of the design development, a test mound was constructed in 1961 near the main dam site to try out different construction methods. The sea bed mud was dredged to understand how different slopes would perform. A slope of 1 vertical to 1.5 horizontal proved to be the most effective arrangement. An attempt to achieve an impermeable foundation by dumping large rocks into the existing mud provide unsuccessful, confirming that the mud would need to be removed ahead of foundation construction.
The tunnel between Plover Cove and the Tai Po Tau pumping station, completed in stage 1 was 9.7km long, ranging between 8m and 9m in diameter. In addition, tunnels were constructed to source water from the new Lau Shui Heung and Hok Tau irrigation reservoir, 3km long and the river at Nam Chung, 3.8km long. Access into the hillside required the construction of three access tunnels, a total length of 1.4km and 5.3m in diameter, and these were also used to intercept three local rivers. A short tunnel was also required on the west wall of the reservoir, 120m long, to be used during construction to pump out the sea water into the Tolo Channel.
The contract for the construction of the tunnels was awarded in early December 1963 to a Swedish firm, Svenska Entreprenad Aktiebolagat Sentab in partnership with local partner Gammon for HK$96.5 million[xvi]. The tenderer proposed to utilise the European practice of sprayed concrete to provide initial rock support rather than the established practice of ribs and lagging.
The 3.8km long 3.6m diameter tunnel from Nam Chung broke through in June 1965 after around 12 months of excavation. The main 9.7km tunnel broke through in August 1966 completing the tunnelling works after removing 1 million cubic metres of rock, drilling 1600km of holes and expending 1,000T of explosives[xvii].
The main tunnel was lined and the smaller tunnels were generally unlined with only concrete in the invert to provide access and to improve hydraulic performance.
Cross Harbour Pipeline
Along with the new water supply, an upgrading of the trunk distribution mains was undertaken. This included the laying of nearly 50km of large diameter water mains and a new 1.05m diameter cross harbour pipeline between Whampoa and North Point.
The contract for the construction of the dams was awarded in December 1963 to Societe Francaise d’Enterprises de Dragages et de Travaux Public known now as Dragages for a price of HK$1,247 million. Dragages were gaining a positive reputation in Hong Kong having recently completed the Shek Pik reservoir on Lantau. Recognising the importance of the project, Dragages proposed an incentive bonus of HK$10 million to complete closure of the dam ahead of programme in October 1966[xviii]. However, the project was hit by a number of delays, and closure was not achieved until early January 1967[xix], and so there was no bonus.
Work commenced on site in early 1964 with completion planned for 1967. The first task was to remove 5.4million m3 of sea-bed mud for the main dam site. This material was on average 12m deep but with a maximum dredge depth up to 29m below sea bed level. The dredged material was taken by barge, 2km away to be dumped in the small bay between Yim Tin Tsai and Ma Shi Chau. Extensive dredging was not required for the subsidiary dams[xx].
The large dredging equipment was shipped in from Europe, including the ‘Haiphong’ which had previously been use on the construction of Kai Tak runway, the purpose made ‘Biarritz’, equipped with two grabs, each with a capacity of up to 18 cubic metres and a capacity of up to 920 cubic metres per hour, and two floating grab dredgers. The dredging operation had been designed to minimise the impact on the Tolo Harbour oyster beds and no adverse effects were reported. However, problems were experienced with maintaining the excavated trench. Soft material would flow to the trench up to depths of 1.5m. Initial efforts to remove the fluid material were unsuccessful, but it was discovered that if the material was left for a month, it would be sufficiently consolidated to be removed by the grab dredgers.
The fill material for the dam required 1.7 million cubic metres of sand to form drains within the dam, to reduce the pore water pressure within the fill material. This material was to be sourced locally but although the identified deposits had 2.2 times the net requirements, there were significant losses resulting in a shortfall of material requiring the on-site crushing of rock to make up the shortfall.
Decomposed granite formed the main fill material for the dam requiring 5.9 million cubic metres. The initial borrow-pits provided less suitable material than expected requiring the opening of the Lok Wo Sha and Cheung Kang sites.
Around 1 million cubic metres of rock fill was required for the embankment, primarily to protect exposed surfaces from wave action in the form of rip-rap and also to support the dam closure operation.
To provide water cut-off, fissure grouting was required primarily at the dam abutments and below the dam base. The grout holes were spaced at 3m centres and extended 60m below the foundation into the rock. In total around 18.3km of drilling was undertaken for the cementitious grout material.
Placing of fill material was undertaken as a marine operation from December 1964 and completed at the end of 1966 using the two floating dredgers and the ‘Biarritz’. Placement of the sand fill and rock covering commenced in May 1965 and May 1966 respectively.
Closure of the main dam was the most critical stage of construction. Extensive studies had been undertaken on how best to complete the works to minimise current velocities through the gap. The closure gap was located central to the dam and the closure process required the dam to be complete to the high tide level, with the gap complete to slightly below the low tide. In the first week of January, 1967 rock fill was then placed in the gap to close the dam.
With the completion of the two subsidiary dams, work commenced within a month on pumping out the sea water through the tunnel on the west side. The plan was to pump out the sea water to around -9mPD leaving sufficient water to avoid disturbing the seabed mud. However, with a prolonged drought it was decided expedite the programme by removing all the water leaving the reservoir dry by May, 1967 and allowing works to progress in the dry.
Impounding began in June 1967 and by the start of the dry season on the 1 October, the reservoir, primarily thanks to tropical storms Iris and Kate had impounded almost 11,000 million gallons. With a continuing water shortage, brackish water from the reservoir was introduced into the distribution system on the 5th October, 1967 using a temporary pumping system until the main plant was completed. In early 1968 with the dry season coming to an end, work commenced on pumping out the remaining brackish water so that the reservoir could be filled with fresh water over the wet season. Using two pumps at the Tai Po Kau pumping station, 75 million gallons a day was drawn down so by the end of April, the reservoir was down to 2,500 million gallons and ready to receive the summer rains.
During the pumping operations, work continued to complete the dams, placing the rip-rap protection and completing all the concreting works. With the completion of the permanent pumping equipment at Tai Mei Tuk in early December 1968, water was drawn from the reservoir, and diluted with other local sources to reduce the saline content and introduced into the supply system.
A number of studies were undertaken to assess and minimise the environmental impact of both the reservoir construction and operation. To control plant and insect growth in the reservoir, 636,500 fish, mainly silver, mud and common carp, were introduced until a natural fish population developed[xxi].
Construction of the reservoir and associated tunnels had taken five years and required the mobilisation of up to 4,500 workers. On the 20 January, 1969 Governor Sir David Trench formally opened the HK$520 million scheme. He used the occasion to also announce that the capacity of the reservoir would be increased by 10,000 million gallons by raising the hight of the dams by 3.6m and an even larger scheme was under development, the High Island Reservoir in Sai Kung.
Upgrading of Plover Cove
During the construction of the reservoir, it had become apparent that the storage capacity of Plover Cove would not address the increasing water demand. Whilst studies were to be undertaken into the site of new reservoirs, in March 1967 the designers of Plover Cove, then known as Binnie and Partners with Scott Wilson Kirkpatrick and Partners, were asked to report on raising the reservoir water level to increase capacity by 10,000 million gallons. After some development it was confirmed that the levels would be revised from +8.2mPD to +13.4mPD, increasing the capacity by 13,000 million gallons or 60 million cubic metres, giving a total capacity of 230 million cubic metres.
In January, 1969 the ‘go ahead’ was given to raise the height of the three dams and work started immediately. To raise the water level 5.2m, the crest of the main dam would be raised 3.7m through the provision of additional rockfill and decomposed fill material, separated by a precast concrete retaining wall giving a new crest level of +15.8mPD. The subsidiary dams were raised in a similar fashion.
The spillway crest was originally to be raised with a concrete weir, but an alternative design utilising a siphon type spillway was eventually adopted. This required the construction of 64 concrete units dowelled into the existing spillway structure.
The works were all completed in 1973.
The Future Of the Water Supply
During the 1960s and into the 1970s the government embarked on a number of new initiatives to address the continued water shortage, including salt water flushing, desalination of seawater and the construction of ever larger reservoirs. High Island Reservoir would be the final local water supply scheme, as the future of the territory’s water supply would be from the north.
[i] New Reservoir for Colony, South China Morning Post, 12 Jan 1963
[ii] The Roots of Regionalism : Water Management in Postwar Hong Kong, 2017 David W Clayton.
[iii] The Changing Nature of Border, Scale and the Production of Hong Kong’s Water Supply System since 1959, 2013 Nelson Lee.
[iv] Optimism on Water from China, South China Morning Post, 16 Sep 1967
[v] China May Resume Water Supply, South China Morning Post, 28 Sep 1967
[vi] Govt to Ask China for reply to Water Request, South China Morning Post, 29 Jun 1967
[vii] Strong Hints China Will Supply Water, South China Morning Post, 29 Sep, 1967
[viii] Colony Welcome Water From China, South China Morning Post, 2 Oct, 1967
[ix] Colony Welcome Water From China, South China Morning Post, 2 Oct, 1967
[x] Investigation and Design of the Plover Cove Water Scheme, S E H Ford, S G Elliott, ICE, 1965
[xi] Investigation and Design of the Plover Cove Water Scheme, S E H Ford, S G Elliott, ICE, 1965
[xii] Villagers Move to New Homes, South China Morning Post, 13 Jul 1965
[xiii] Traditions and Heritage in Tai Po, Tai Po DC, Aug 2008
[xiv] Final Plover Cove Exodus Begins, South China Morning Post, 4 Apr 1967
[xv] Investigation and Design of the Plover Cove Water Scheme, S E H Ford, S G Elliott, ICE, 1965
[xvi] Big Contract Let for Plover Cove Scheme, South China Morning Post, 6 Dec 1963
[xvii] Fina Blast Links Up Tunnels, South China Morning Post, 3 Aug 1966
[xviii] Plover Cove Contract, South China Morning Post, 28 Dec 1963
[xix] Major Stage in Plover Cove Project Complete, South China Morning Post, 5 Jan 1967
[xx] Construction of Plover Cove Dams, S G Elliott, S E H Ford, J Oules, Commission Internationale Des Grands Barrages, 1967
[xxi] Hong Kong Annual Report 1969
This article was first posted on 24th December 2021.