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WATER SUPPLY AND DISTRIBU

TION.

CONFERENCES ON THURSDAY AND FRIDAY, JULY 24 AND 25, 1884.

Sir FREDERICK ABEL, C.B., D.C.L., F.R.S., in the chair.

THE CHAIRMAN, in commencing the proceedings, said the active interest displayed by his Royal Highness, the President of the Society of Arts, on this subject, had led the Council to hope that it might have been in his power to open the proceedings; indeed, at one time, there was no doubt that this Conference would have been the opening one of the series arranged by the Executive Council of the Health Exhibition, and that his Royal Highness would have presided, at any rate, over a portion of the proceedings, when that unexpected calamity occurred which had so deeply afflicted the Royal Family and the nation. The fact that even quite recently the Prince had fixed the present date for this Conference was an indication that, had it been possible, he would have marked his sense of its importance by attending at the opening. In 1878, his Royal Highness addressed a letter to the Council of the Society of Arts, calling attention to the importance of the subject of water supply; pointing out that whereas various large towns were at that time incurring heavy expenditure to improve their water supply, smaller towns, and particularly villages, were left to shift for themselves; and suggesting that it might be desirable to discuss fully the question how

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far it might be possible to apply the great natural sources of water supply according to some national comprehensive scheme. The Council of the Society, acting on that suggestion, issued inquiries and invitations for papers, and received more than twenty papers in response, some written by men of eminence who had devoted a great deal of attention to this subject. Those papers, and the topics arising out of them, were very carefully discussed, and the general conclusion arrived at was that local conditions and circumstances presented such very considerable variations that it appeared impossible to devise any comprehensive national scheme for the supply of water to communities. But a resolution was passed that it was desirable to memorialise the Government to appoint a small permanent Commission to collect facts connected with the water supply throughout the kingdom, in order to utilise the natural resources, as indicated by his Royal Highness, according to some general system for the benefit of the country as a whole. That suggestion was not acted upon, but, nevertheless, the discussion which took place in 1878 had been fruitful of beneficial results, and it was quite certain that the subject of improved water supply had made an important advance since that time. The influence of polluted water in promoting the spread of epidemics had become more thoroughly understood and recognised, and the mischievous effects of using water derived from surface wells, and from the careless storage of water in houses, arising out of intermittent supply and other circumstances, had received much public attention; but there could be no doubt that many points bearing upon the supply of wholesome water still required further elucidation. Many interesting discussions connected with one branch or another of this subject had taken place since 1878, and probably none were more interesting than those connected with the questions as to what constituted a good water for drinking and domestic purposes, and how a sufficient quantity might be ensured. It was scarcely necessary to remind the audience that amongst the most intelligent men who had given attention

to this subject there had existed, and still remained, diversities of opinion on some important points more especially connected with the question of how the purity of water was affected, and how it was re-established if the water were once polluted. Thus some authorities had maintained that no river which had been in any way polluted could ever be fit for use afterwards, or, at any rate, that the time when it might become fit for use as potable water was very remote; but that, on the other hand, it was only necessary to sink wells deep enough in order to obtain water absolutely free from injurious organic contamination, so that water could be furnished in any degree of abundance by means of artesian wells. On the other hand, there were authorities, not less well recognised as possessing special knowledge and experience, who had maintained that it was quite erroneous to suppose that river water, when it became polluted by sewage, was thereby rendered permanently unfit for potable purposes; that a river had only to flow a comparatively short distance for its self-purification to take place, a purification which, although it might vary in degree according to circumstances, must ultimately he carried out to a sufficiently perfect extent to render the water absolutely wholesome. Probably the truth lay between the extremes; in fact, it was already recognised that it did so, and there were indications that amongst the most extreme exponents of either view there was a tendency to an assimilation of opinions. These subjects had been lately so warmly fought out on many battle-fields that the weak points on each side had become more and more apparent to advocates and adversaries alike; and, therefore, there was a hope that something like that unity of view might, before long, be arrived at, without which any real progress cold hardly be looked for. There was probably no subject which could be selected for discussion which involved so many considerations of primary importance as that of water supply. On the one hand, there were geological, medical, chemical, and engineering considerations; and, on the other hand, there were financial, legal, municipal, and it might be even

political considerations. As the Society met on this occasion, in conference in connection with the Health Exhibition, he thought they were primarily concerned with the first-named set of considerations, and their hands would be quite full enough if they limited themselves to these, avoiding, as much as possible, any discussion on the extremely debatable ground of financial or legal questions. They would now at once enter upon the consideration of the first branch of the subject, viz., the Sources of Supply.

I. SOURCES OF SUPPLY.

ON THE AREA OF CHALK AS A SOURCE OF WATER SUPPLY.

By W. WHITAKER, B.A., F.G.S.

Of the Geological Survey of England.

IT is only of late years that we have had the means of measuring the area of the great water-bearing formation of the south-east of England that can be reckoned on as a gathering-ground with certainty; and now we can do this for only a limited part of the chalk tract. As it will be a long time before we can do it for the whole, even so far as the London basin is concerned, I have not hesitated to bring forward the subject in its present imperfect state.

On ordinary geological maps, including the greater number of those as yet issued by the Geological Survey, the chalk, beyond the parts where it is covered by the eocene tertiary beds, is shown as bare, except for outlying patches of those tertiary beds (mostly on the high grounds), and for strips of alluvium (or marshland) along the bottoms of the chief valleys. For some years past, however, the Geological Survey has carefully mapped those varying deposits of clay, loam, and gravel, and sand, usually

grouped under the name of drift, which cover, in a more or less irregular way, the various divisions of the tertiary beds and the chalk, and which have a marked effect on the nature of the country where they occur to any great extent.

It follows that it is only in those parts of the chalk tract where the Geological Survey has mapped the different divisions of the drift, that we are able to tell, with an approach to accuracy, over how much of the surface the rain has a more or less free access to the chalk, and can therefore sink into it, and add to the supply to be got from it at lower levels.

In the course of a somewhat prolonged and detailed examination of this question, I have constructed a set of maps for the purpose of showing over what areas the chalk is bare, over what areas it is covered by beds of a permeable character (allowing of the sinking of water through them to the chalk), and over what areas it is cut off from the reception of water through being covered by impermeable beds. This may seem, on first thoughts, a simple matter; but, on trial, it is hardly found so, and instead of confining myself to three colours, one for each of the three areas above noticed, I was obliged to use a fourth, for various beds of a doubtful character, either from their being of a mixed composition, or of a changeable one, at this place permeable, at that the reverse.

With these four colours I was at first content; but the fact that in some areas where the chalk is protected by impermeable beds, the water flows over the surface until it reaches the chalk, and then sinks into that rock, has led me to show those areas by a lighter tint, as they contribute somewhat to the water in the chalk, and should, therefore, be distinguished from tracts that do not.

Beyond these five divisions the maps now exhibited do not go; but it may, perhaps, be needful to make a sixth, and to mark off from the rest of the bare chalk those parts where the base of the formation, the chalk marl, is so clayey as to be out of the question of water supply. This tract, however, would be a very narrow band along the outer edge of the chalk.

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