Hong Kong Water Supply – The Tai Tam Tuk Scheme First Section
Tymon Mellor: With the memory of severe water shortages fresh in the minds of the Hong Kong residents and with the political will to address, once and for all the limited water supply to the city of Victoria, in 1902 the Public Works Department embarked on the Tai Tam Tuk Scheme. Unlike all the previous reservoir schemes, this proposal included the provision for a site investigation to confirm the best location for the dam.
Tai Tam Proposals
In August 1894[i], the Colonial Adviser to Hong Kong, Osbert Chadwick submitted a report on the water supply to Hong Kong. In the report he noted that schemes to construct additional reservoirs above the existing Tai Tam Reservoir had been explored, but he considered the better solution would be to construct a new reservoir below the existing dam at around the 30 mPD contour and use steam power to pump the water up to the existing conduit.
Chadwick’s proposal was not readily adopted and the Director of Public Works, Francis Cooper in his report of 1896[ii] proposed a number of options including those identified by Chadwick, but the focus was on extending the catchwater system, new dams at Wong Nei Chong Gap, and a possible new dam above the existing Tai Tam Reservoir.
Using the existing supply infrastructure was the most cost effective arrangement and thus, locating a new reservoir above the existing Tai Tam Reservoir had the advantage that it could feed into the existing supply culvert. Three dam sites were identified. Dam Site 1 had a capacity of 70 million gallons with a catchment of 220 acres. Dam Site 2, to the north was a smaller catchment of only 60 acres and a storage capacity of 40 million gallons. Dam Site 3 was below the existing Tai Tam Reservoir while still able to discharge into the existing culvert had a capacity of 20 million gallons. This would become Tai Tam Byewash.
Sites 4 and 5 were located below the supply culvert and if adopted would require the impounded water to be pumped uphill. This approach was not favoured by Cooper who noted; “I merely place the outline of the project for the record”.
The immediate supply and storage problems were addressed with the construction of Wong Nei Chong Reservoir starting in 1897, and Tai Tam Byewash commenced in 1901 along with extensions to the catchwater system.
The rainfall of 1901 was a record low, and exposed the limitation of the Tai Tam catchwater for the Tai Tam Reservoir did not fill up during the summer rains. As Osbert Chadwick noted in his report of April 1902[iii] in relation to Cooper’s proposed reservoirs located above Tai Tam Reservoir; “Consequently, the additional reservoirs would not have filled, and the water-supply for the water-year 1901-2, would not have been increased, by their construction, by a single gallon.”
Osbert Chadwick once more presented a report to the Legislative Council recommending the following measures:
- Install a pump in the Tai Tam River below the existing dam, transferring the river water to the Tai Tam dam;
- Locate a new dam below the existing dam to take advantage of the increased catchment area;
- Explore the opportunity to use the recently acquired New Territories for water gathering and reservoir sites.
Further details on the proposals were presented in a second report by Osbert Chadwick later in April 1902[iv]. He proposed to construct one or more low-level reservoirs with a capacity of around 400 million gallons at the head of the Tai Tam Tuk Estuary to capture all the waters from the river. A pumping station would be constructed on the foreshore where there was at least one fathom of water depth at low tide to allow the delivery of coal for the pumping station. Three engines would be required, two operational and one on stand-by, each capable of lifting 1,250,000 gallons in 24 hours.
To convey the 2,500,000 gallons a day, a single 530mm (21”) or two 380mm (15”) diameter pipes would be provided.
He recommended that an immediate start be made on surveying the area, installing a gauging weir to measure the existing water flow, and commence the procurement of the pumping engines and pipes. With these in-place, they could commence operation drawing water from a temporary dam.
Tai Tam Tuk Investigations
Following water shortage the previous year, work on developing the Tai Tam Valley commenced in 1900 with a detailed survey of the valley along with the planning of new reservoirs. However, the engineer heading the scheme, Mr Crook[v] was transferred to Gibraltar and work was suspended.
Following Osbert Chadwick’s proposals in 1902, work commenced on a detailed contour survey of the Tai Tam basin to establish the drainage area, roads and pumping mains. In the same year, two small dams were constructed across the river to measure the dry-weather flow of the river and hence the capacity of the catchment to feed a future dam.
Following construction problems experienced on previous reservoir projects, the Public Works Department decided to undertake a detailed investigation into the ground conditions at each of the three identified sites during 1902 to 1904. Trial pits were excavated on the hillsides to locate the rock head and establish if suitable foundations could be located for the dam without having to undertake deep excavations.
To establish the nature of the ground, a series of brick wells or shafts were constructed in the shallow waters of Tai Tam bay. Using two barges equipped with boilers, steam winches and derricks were mobilised to support the construction of a brick shaft within the shallow waters. A brick shaft was constructed above a cast iron ring and this was then lowered through the water and sunk into the seabed. By excavating the soft material from inside the shaft, the brick shaft would descend into the sea bed. As the structure descended into the soft soil additional brick layers were added. With an internal size of 1.7m (5’8”) excavation was undertaken by hand or using a grab bucket operated by the steam winches. The wells were kept dry by bailing the water out or using a pulsometer pump[vi] driven by the steam from the barge boiler.
The work was difficult and dangerous with many of the workers suffering from a severe type of malaria.[vii]
The initial wells were sunk on the most southernly dam location. Well 1 reached a depth of 10.8m below sea level by the end of 1902 but was abandoned when it became out of plumb (no longer vertical) before reaching bed rock.
Well 2 was then commenced but had initial problems descending into the soft material, the friction on the brick structure was so high that additional loading, ultimately reaching 200 tons had to be applied. However, the shaft was sunk to a depth of 14m (46’) when rock was encountered on the 17th May, 1903. The shaft excavation passed through clay and silts intermingled with shells and layers of sand. Just before reaching rock, a layer of densely packed beach boulders was encountered of about 0.6m deep along with a large volume of water. It was not possible to pump the shaft dry precluding a detailed inspection of the final rock foundation.
Work commenced on Well 3 and at 12.8m down the excavation encountered the same strata of boulders found in Well 2. Excavation continued through the boulders and after a further 3m, sand was once more encountered. In the middle of October, 1903 the rock head was finally encountered at 17.9m, but it was impossible to pump the shaft dry so the nature of the rock was ascertained by feeling the rock and breaking off pieces to be compared with the bed rock at the sides of the bay. Over the bottom of the shaft, the rock was found to be dipping steeply to one side, indicating highly variable rock head depth.
The findings of Well 3 raised doubt on the reliability of the Well 2 findings, thus excavation of Well 2 recommenced and the rock at the base of the shaft was found to be a large boulder. After great difficulty removing the boulder, the rock head was eventually reached in early 1904 at a depth of 18.9m to 19.8m.
In addition to the sinking of wells, Norton Tubes, a hollow tube that was driven into the soft material was used to establish the rock head. Over 171 “prickings” were undertaken in 1903 over the site of the dam, and indicating rock head was located at around 12m collaborating the initial findings of Well 2.
With the results of Well 3 and revised results of Well 2, it was decided to abandon the dam site due to the challenges associated with having to construct a deep excavation to ensure the dam would be founded on a stable rock head.
A second site 213m inland was then explored[viii], and three wells were sunk along the possible location of the dam site, wells 4, 5 and 6. These confirmed bed rock at 13.7m to 16.5m, similar to the original site.
Given the problems of locating suitable foundations in the delta area, the team then undertook investigations at the original site proposed in Francis Coopers report of 1896[ix]. The site was located on land where the Tai Tam River joined the bay. Trial pits were undertaken to locate the rock head and confirm the location for the dam. The results were positive and the site was chosen for the dam, similar to the original proposal but higher, allowing the impounding of 0.9 million m3 or 194 million gallons.
With agreement on the proposed dam arrangement, the site investigation works were completed on the 10th October, 1904[x].
A number of the wells remain in place to this day, however Wells 2 and 3 collapsed after being crushed by vessels during sand quarrying in the shallow water in the 1960s [xi].
Tai Tam Tuk Scheme – First Section
With the initial results of the investigation works indicating problems with the selected low-level site, a scheme was developed based on the 1896 high-level reservoir Site 4. The proposal was submitted to the Secretary of State for the Colonies on the 23rd October, 1903[xii]. The proposal was estimated at $780,000 and included:
- A dam to impound 194 million gallons set below the original Tai Tam dam in a side valley, to be called Tai Tam Intermediate Reservoir;
- A pumping station near the shores of the bay with two engines, each capable of delivering 1.25 million gallons a day;
- 2km of new road alongside the reservoir;
- Access roads;
- 2km of 450mm diameter rising main; and
- 2km of temporary suction main from a small temporary dam to be used before the main dam is complete. The pipe subsequently being used to duplicate the rising main.
Tai Tam Temporary Pump
In Osbert Chadwick’s 1894[xiii] report, he also noted that even without a reservoir, it would be possible to construct a weir and install a pump in the existing river, to transfer some 30 to 40 million gallons of stream water into the main Tai Tam Reservoir, allowing it to remain full between the October and January season.
In 1903 in order to supplement the Tai Tam water supply, a temporary dam and temporary pumping plant was installed. A Worthington engine and boiler were obtained and located in a building below the junction of the three principle branch valleys. Cast iron pipes were located to create a 2km rising main allowing the water to be delivered to the entrance of the Tai Tam tunnel. On the 1st November, 1903 the pump was commissioned and by the end of the year had transferred around 20.75 million gallons[xiv].
Each year, in times of water shortage, the pumping system was used to transfer water back into the system, typically in the dry season, during the adjoining first and fourth quarters.
|Year||Volume (million gallons)|
With the end of the dry season in sight and the imminent commissioning of the new pumping systems the facility was de-commissioned in May 1907, the pump was dismantled and the rising mains removed[xv].
Tai Tam Intermediate Reservoir
Approval for the construction of the Tai Tam Intermediate Reservoir was given by the Secretary of State on the 1st January, 1904. Construction tenders were sought on the 1st February, 1904 and on the 16th March, 1904 the construction contract was awarded to Kang On for the construction of the concrete and masonry reservoir to impound 194 million gallons, access roads, new pumping station on the west shore of Tai Tam Bay, a 450mm rising main from the pump station to the Tai Tam gauging basin and a 450mm suction main from the existing dam to the pumping station.
With over 1,000 workers on the site, good progress was made in the first year with the works, despite heavy sickness during the summer months. By the end of 1904 over 10,000 cubic yards had been excavated for the dam foundations and 1,500 cubic yards for the over flow channels. The ground was described as “red earth, rotten rock with soft clay seams, hard rock with a few clay scams to a bottom of very hard rock with a few clay seams through which a little water percolates”. Quarrying of rock for the dam dressing or finish and concrete commenced at Tai Tam and Stanley.
In January 1905 excavation of the dam was sufficiently advanced to allow the placement of foundation concrete and construction of the dam along with the stone facing. By the end of the year, the dam was sufficiently complete to commence impounding 10 million gallons of water. During the early part of 1906 good progress was made on the dam with the top within 1.4m of the overflow level. However, during the summer, progress was slowed by sickness of the workers and a typhoons hitting the territory on the 18th and 29th September, 1906 destroying all the mat sheds and the scaffolding. With the increase in the dam height, the volume of water impounded increased to 120 million gallons.
By the end of 1907 construction of the dam was complete with the valve house finished in 1908. The completed dam had a capacity of 196 million gallons and 213 million gallons with the installation of 0.76m high boards on the overflow. The construction utilised 18,750m3 of concrete and 1,700m3 of masonry. The total cost of the works was $896,139.64 (silver dollars).
Tai Tam Pumping Station
Work on the new pumping station site commenced on the 4th April, 1904 with the levelling of the site and the formation of the reclamation using 14,000 cubic yards of soil and rock which was excavated from the hill-side. The completed reclamation was used to store materials including 1,000 tons of 450mm cast iron pipe until the new access roads were completed.
On the 1st August, 1904 the pump and engine along with two boilers supplied by Messrs Tangyes of Birmingham arrived in the Colony. These were stored in temporary mat sheds until the new pump house was ready for installation in 1906. The boilers were set in place in early 1906 and installation of the engine commenced in July 1906 with the second unit in October. By April, 1907 the first engine was ready for testing with the second unit ready by May, 1907. During the initial testing of the pumping main, a valve on the main burst requiring replacement of the substandard parts. The pumps commenced operations on 23rd March, 1908[xvi] when water was required to supplement the dwindling supply.
In December 1907 a contract was let to Messrs Wilks and Jack for the installation of lighting within the building.
The engines were a triple-expansion, condensing arrangement with a pumping capacity of 1.25 million gallons a day running at 24.5 revolutions per minute. Each engine drove three 12-inch diameter rams with a 30” stroke. The rams were drive by a crack shaft powered by piston rods from each of the three cylinders.
A similar motor arrangement was installed a few years on at the Psych Bend Pumping Station in Victoria and has recently been renovated. The building is very similar to the Tai Tam structure but in this case, the pump is a centrifugal type rather than piston type.
The building looks remarkably similar to the Hong Kong structure, down to the 5T overhead travelling crane.
New roads were constructed to provide access to the new facilities requiring the construction of four large bridges, three cuttings over 18m deep, and numerous retaining walls. Buried below the new road was the 3.1km long pumping rising main, and the 450mm diameter cast iron pipes were laid in 3.6m long lengths weighing 965kg and taking 16 ‘coolies’ to carry. The suction main at 2.2km long connecting the new reservoir to the pumping station used the same pipework as the rising main.
Delay of Second Section
With the completion of the site investigation at the end of 1904 for the larger reservoir, both of the estuary sites were rejected due to the depth of the bed rock. The third site, located just below the village of Tai Tam Tuk was selected for the dam and work commenced on preparing the design and tender documents. However, due to financial constraints[xvii], the project was suspended in 1907 with the completion of the Tai Tam Tuk Intermediate Reservoir providing a temporary respite from water shortages. However, it would not be long before water shortages and the adoption of the intermittent supply would once more became part of the daily routine.
[i] Water Supply of Victoria, Hong Kong, 7th August 1894 by Osbert Chadwick
[ii] Report on the Water Supply of the City of Victoria and Hill District Hongkong, by Francis A Cooper, Director of Public Works, 9th May 1896
[iii] Preliminary Report on the Sanitary Condition of Hongkong, 10th April, 1902 by Osbert Chadwick
[iv] Report on the Water-Supply of Hongkong. Mainly with Regard to the Full Development of the Supply from the Taitam-Tuk Valley, 18th
[v]Report of the Director of Public Works, For the Year 1900
[vii] Report of the Director of Public Works, For the Year 1902
[viii] Report of the Director of Public Works, For the Year 1903
[ix] Report on the Water Supply of the City of Victoria and Hill District Hongkong, by Francis A Cooper, Director of Public Works, 9th May 1896.
[x] Report of the Director of Public Works, For the Year 1904
[xi] The Four Brick Wels at Tai Tam Harbour, By Ir Dr S W POON, Ir K Y MA, Ir K F MAN, T W TSIN and Dr Y DENG, http://www.hkengineer.org.hk/program/home/articlelist.php?cat=article&volid=152
[xii] Report of the Director of Public Works, For the Year 1903
[xiii] Water Supply of Victoria, Hong Kong, 7th August 1894 by Osbert Chadwick
[xiv]Report of the Director of Public Works, For the Year 1903
[xv] Report of the Director of Public Works, For the Year 1907
[xvi] Report of the Director of Public Works, For the Year 1912
[xvii] Report of the Director of Public Works, For the Year 1907
This article was first posted on 22nd December 2019.
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- John MacNeile Price, Surveyor General of Hong Kong, the Tai Tam reservoirs
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