Island water supply - 1959
Val de la Mare Reservoir
When I last prepared a paper for this society the island was in the hands of a foreign power. The paper itself did not appear in the bulletin of the society until 1947, some few years after it had been written.
It is difficult after the lapse of 14 years or so to recapture the atmosphere of the days of the Occupation, but I find that I terminated my paper thus:
- "The need for future extensions has always been borne in mind, and the existing system is planned to form part of a harmonious whole, when the time comes to write 'finis' to the story of future developments."
I think that even at this time I looked beyond the depressing circumstances then existing, but it would be idle boasting if I said that I ever had any vision of Jersey as it now is in 1959.
I do not think I can do better as a start to this paper than to sketch the development of the water resources of the company. This introduction will form a sound basis for what is to follow, and underline the quieter tempo of the years preceding the post-war period.
The first works of the original company were near Vicart Mill, and consisted of a small reservoir into which the waters of the nearby St Lawrence stream could be diverted. Completed about 1865, these measures soon proved inadequate, and the Jersey Waterworks Company went out of existence in 1882.
The new company, The Jersey New Waterworks Company, started out by establishing a well and pumping station at Millbrook, and in 1899 the Millbrook Reservoir (12 million gallons) and slow sand filters (capacity 500,000 gallons per day) were built at this station. The well was abandoned, being unsatisfactory.
1911 saw the completion of Dannemarche Reservoir (28 million gallons), and in 1932 the Handois Reservoir (50 million gallons) was added. With this last construction it could be said that the St Lawrence Valley was fairly fully utilized.
In 1934 it was made possible to take the stream yield from the top half of the St Peter's Valley. To enable this to be done a pumping station and small reservoir were built at La Hague, and a 10-inch main was laid connecting this station with the Handois Works, to which station the water was pumped.
Up to 1934 all filtration and final treatment had been carried out at Millbrook.
During this year a modern rapid gravity filter plant and service reservoir were brought into use at Handois, the Millbrook station becoming secondary to the new addition. The plant added at this time was capable of an output of 1,400,000 gallons per day.
The construction of a pumping station and small reservoir in the Mourier Valley was started in 1939. The pumping main joining the new station to Handois was completed, and the other works were about half done when the German forces arrived in 1940. The partly finished pumping station was converted into a machine gun post, and the trench which had been prepared for the foundations of the dam was partially filled by the enemy forces. So it remained until the end of the war.
The curtain of occupation lifted upon conditions very different from those prevailing in 1940. Most of the materials required for waterworks construction were in short supply, as also was labour, until demobilisation got into full stride. The value of money had also changed considerably, so that any plans which had previously been made, based on pre-war estimates of cost, no longer had any validity.
The first obvious task was the completion of the Le Mourier Valley scheme, the second to review the likely needs of the island, and get the necessary works under way.
The Le Mourier works were completed in 1947, and in 1948 and 1949 similar small pumping stations were constructed at Tesson in St Peter's Valley and about half way up the Bellozanne Valley. The last two additions made available the stream yields of the lower half of the St Peter's Valley and the northern portion of Bellozanne. The completion of these smaller stations marked the end of a phase of development.
Thereafter the provision of storage facilities would be necessary, and every available acre of gathering area possible would be required to fill the reservoirs visualized for the future.
The two major problems which confront a waterworks authority when planning augmentation of supplies are usually how much to provide and when; and how much can properly be spent. In 1946 it was also necessary to find a reservoir site that was within the range of the money, materials and labour available, and upon which a dam could be completed in a reasonable space of time.
Study of yields
A comprehensive study of the probable water yields of all the gathering areas of the island was one of the first jobs to be put in hand. It was felt that this information would be useful not only for the immediate project, but for the further schemes which the future would probably require. All the valleys in which it appeared that storage reservoirs might be built were examined. Following this survey the potential holding capacity and the estimated costs of eight reservoir sites were calculated.
But although the storage reservoirs are an important part of any waterworks system, it must not be forgotten that pumping machinery, pumping mains, filtration plant and distribution mains are also required. The maximum day's demand for water in 1938 (the last full year before the war) had been 1,300,000 gallons. Clearly this was going to increase. It only remained to determine again - by how much and when.
The programme of capital works eventually approved as a first post-war measure consisted of:
- The construction of a new storage reservoir and pumping station at Grands Vaux, together with a trunk main to join Grands Vaux and Handois.
- New filtration plant and service and contact reservoirs at Handois to increase the output of this station from 1.4 to 2.8 million gallons daily.
- A new trunk main from Handois to Town increasing delivery capacity from 1.5 to 3.0 million gallons daily.
- Sundry smaller works, including new machinery at Millbrook and new pumping plant and mains to certain areas to which water is boosted or repumped.
The estimated cost of the new capital works was £450,000, and the actual cost was very near to this figure. The capital cost of all the works of the company completed before 1945 was approximately £320,000. This amount included offices, reservoirs, distribution mains, filtration plant and all. The cost of the new works more than doubled the capital expenditure which had been necessary up to then.
All the works scheduled in the programme outlined were completed by 1953. The overall picture at this stage is of five of the principal gathering areas of the Island linked together for waterworks purposes, with a combined area of 6,535 acres.
By arrangement with the Public Health authorities the Vallee des Vaux and two subsidiary valleys adjoining Grands Vaux were omitted from the general plan. It will be noticed that the south-easterly part of the St Peter's Valley is also left out.
Immediately after the completion of the Grands Vaux Reservoir, attention was given to the question of further storage. The previous approach to the problem had spotlighted two sites as being worthy of further consideration. The approximate estimated holding capacity and the estimated costs of the two schemes were:
- 100 million gallons £400,000
- 220 million gallons £600,000
The post war rate of growth of demand up to 1953 was vigorous, but not exceptional, and it seemed that the smaller of the two projects just mentioned might well be the next stage. In 1954, however, there was some indication of an increased tempo, and later in this year exploratory work was started in the larger valley, so that if the site conditions there proved favourable, this would be the scheme to be adopted. In 1955 the company started buying the land required for what is now the Val de la Mare Reservoir project. An aerial photograph of the whole site was taken in September 1955, and from this a picture of the valley with the proposed reservoir shown thereon was prepared.
The policy of the company was to acquire all the land required for the reservoir and forming the valley itself. It was also thought wise to purchase sufficient land to enable an access road to be made from the St Ouen's main road to the site. It will be observed that this policy did not make necessary the buying of good agricultural land.
Twenty-five different owners were discovered, some in England, some in Canada, and eventually in May 1957, but before all the land required actually belonged to the company, work was started on clearing the valley for the building of the dam.
The actual buying of the land was sometimes pleasant, sometimes frustrating. By and large, however, the owners were not too difficult and appreciated the public purpose for which the land was being bought.
St Ouen's Pond
The Val de la Mare streams feed St Ouen's pond, an old and historic feature of the Jersey scene. I would like here to mention and pay tribute to the public spirit and understanding shown by Guy Malet de Carteret, Seigneur of St Ouen, which made it possible for the reservoir project to go ahead, whilst at the same time preserving "La Mare au Seigneur".
The capital programme approved by the board of the company at this time consisted of the following:
- Val de La Mare storage reservoir (220 million gallons)
- Pumping Stations at Val de la Mare and La Hague. Capacity 3½ million gallons daily each
- Two untreated water trunk mains, one connecting Val de la Mare to La Hague, and the second duplicating the existing main between La Hague and Handois
- Completion of the new 18in trunk main between the Handois station and Kensington Place. The first half of this main (Handois-Millbrook) had been completed as part of the immediate post-war programme
- New trunk mains in Town and to the various suburbs. New booster stations
- Provision of new service mains to building sites goes on all the time in addition to the major capital programme. Older mains are replaced as occasion demands and opportunity offers.
The new reservoir at Val de la Mare is of gravity section and spillover type. It is being constructed in mass concrete and consists of 26 separate blocks each 22 feet wide. In between each block will be a copper strip embedded in bitumen. This articulated method of construction allows for movement caused by expansion and contraction, which can be considerable in a structure of this size. An inspection and drainage gallery 8ft high x 3ft 6in wide and 220 feet long, runs lengthways through the heart of the dam. A comprehensive system of under drains discharging to this gallery ensures that no dangerous uplift can develop. The maximum depth of water will be 76 feet, and as the deepest foundations are 55 feet below ground level, the total height of the structure (deepest foundation to crest) will be about 130 feet. It is estimated that some 30,000 cubic yards of excavation will be necessary, of which 16,000 cubic yards will be of rock. Some 50,000 cubic yards of concrete will be required for the construction of the dam.
Primary grouting, the injection of liquid cement under pressure, has been carried out to a depth of between 12 and 15 feet in the area of the deeper foundations. Secondary grouting to a depth of 60-80 feet is to be done under the "cut-off" portion of the dam.
The pumping machinery and mains will make it possible to transfer a maximum of 3½ million gallons of water a day to the new reservoir when available from the other gathering areas. The Val de la Mare area alone will probably not contribute more than 90,000,000 gallons per year. It will be possible also to pump a similar daily quantity from the reservoir either to Handois or to a new filter station which is now being planned.
About 50,000 cubic yards of spoil are being removed from the bed of the reservoir, and the area downstream of the dam is being filled, levelled and resoiled. Several minor valleys or re-entrants on the south-eastern side of the reservoir and access road are also being filled and levelled. The total area of recovered land will be about 15 vergees.
Extensive planting of trees and general beautification is to follow the engineering portion of the works. In a few years Val de la Mare should be as beautiful as any spot in the island, and perhaps more peaceful than some, because, except for public purposes, the company has never disposed of any of the large area of land which it holds for the purpose of public water supply. This is a policy which the present members of the board hope will always continue.
This business of supplying water for public needs is largely one of costs. Water has always been, and is today, the cheapest commodity in daily use in the home and elsewhere. But waterworks projects such as the building of reservoirs, and all the other engineering works which make up a modem system, are usually costly and call for long distance planning. Large extensions undertaken too far ahead of needs can impose heavy financial burdens upon those who use water. Even before the last war it was not particularly easy to decide the proper time to start on new capital expenditure.
It was, however, easier then than it has been in the last ten years, because the new works could be planned against a background of increased revenue. Since 1945 inflation has more than absorbed natural increases. The problem of cost and charges is thus as important as engineering detail, and I can assure all my listeners that the planning of the works now under construction and those considered likely for the future has been approached with this aspect taken very carefully into account.
The survey of potential reservoir sites which I mentioned earlier shows that there are still places in the Island where conventional storage reservoirs can be built.
The valleys in Jersey, however, are small but, nevertheless, require comparatively large barrages if a reasonable amount of storage is to be created. The cost of storage is consequently much higher than on the mainland. In spite of this, it was clear that to provide storage at Val de la Mare would be much cheaper than the alternative method of sea water conversion.
The board of the company have the question of new sources constantly under review, and indeed tentative plans to meet future requirements are already formulated. But these must remain to be dealt with in another paper.