1841.] 



THE CIVIL ENGINEER AND ARCHITECTS JOURNAL. 



evaporation, and we are therefore justified in assuming that tlie quantity wliich 

 descends upon the surface of tlie chalk finds its way, with very shglit diminu- 

 tion, into tlic fissures helow. The lower beds of the cretaceous group, and 

 the gault which immediately succeeds it, again present an impermeable stra- 

 tum of clay, causing the water to accumulate tlirough the lower regions of 

 the more porous chalk. An enormous natural reservoir has thus been formed 

 and the level up to which it may be considered as quite full of water is the 

 lowest point where it can find a vent and overflow, therefore, as the chalk 

 communicates under the coasts of Norfolk, Suffolk, and Essex with the ocean, 

 tliis level, in the present ease, may be considered to be the same as the mean 

 height of the sea. 



That there is, however, an extensive accumulation of w.ater above tbis level 

 will be obvious, when it is considered that the friction, which from the na- 

 ture of the small fissures and pores must exist, will necessarily prevent the 

 water from exerting rapidly its hydrostatic pressure, and as for this reason it 

 cannot flow off with sufficient velocity, the higher parts of the chalk belt 

 which surround the London clay being saturated, will allow of its escape to 

 the surface wherever it can find a nearer and more ready vent than its sub- 

 terranean one. 



The greater or lesser facility, which from lines of fissures soft strata and 

 pores, the water may encounter in flowing towards the centre of the basin, 

 ■will also govern its surface, and cause it to assume an inclination, the angle 

 of which will represent the friction, and in this manner we may readily ac- 

 count for the different levels, which often appear anomalous, at which the 

 water will he found to stand in wells. 



The foregoing remarks will now enable me, I think, to show that the pro- 

 posal of perforating the tertiary clays for the purpose of obtaining the water 

 for the general supply of the inhabitants of London, would not have been at- 

 tended with the advantages which at first sight it would appear possessed of: 

 it may indeed be urged that a reference to the section, shews us London 

 situated nearly over the centre of the basin to which it gives its name, and 

 that we may consequently infer, that wells sunk through eocene strata into 

 the chalk, will derive their supply immediately from that portion where the 

 greatest accumulation of water exists by my own shewing. But it will be 

 found that this very circumstance throws a material difficulty in the way of 

 any attempt to supply the inhabitants of the Metropolis from this source, and 

 one which has been found frequently confirmed, when private individuals 

 have sunk deep wells in London. The objection is, that whenever a large 

 quantity is extracted, the wells in tlie vicinity, which derive their water from 

 the same strata, are very sensibly affected ; and, for this reason, that although 

 a constant supply will always, as I have shown, find its way down, to take 

 the place of whatever water we may pump away, this cannot flow in so quickly 

 from the obstructions of the stratification, but that the level, for some dis- 

 tance round this focus, will be temporarily reduced. In other parts of the 

 district, as will be readily understood, this would not he the case ; or if so at 

 least in an inferior degree, as a well would not here derive its share from 

 every side of the basin at once, but only from that portion situated immedi- 

 ately above it. At Watford, for instance, a well would only be fed from the 

 chalk which intervenes between that place and the great outcropping Chiltern 

 ridge, and so in any other part of the belt. I may also here add, that the 

 sheet of water in the deeper part of the chalk, can only l)e affected to an iu- 

 sensible degree by such a well, which at most would merely deprive it of the 

 supply from a very trifling part of the great circle which erery where else 

 would remain untouched. 



The company which had been based on the Artesian project, proljahly soon 

 obtained facts which proved that their proposal could not be established 

 without such interference with private interests, as they undoubtedly fore- 

 saw, would have great weight with the House of Commons ; and they must 

 also have taken into account the expense of forcing the requisite quantity of 

 water to the elevation necessary for the high services, in addition to which, 

 it must be borne in mind, that after perforating say two hundred feet of clay, 

 the water under London by no means rises to the surface. As might have 

 been readily foreseen, this idea was after some time, abandoned ; and it is 

 not surprising, that its originator, Mr. R. Paten, should have turned his at- 

 tention to other endeavours. 



The abundance of the springs which overflow into the Colne valley, above 

 Watford, and the apparent purity of the water, had long attracted his atten- 

 tion, and now led him, in connexion with some other gentlemen, to make 

 various experiments to ascertain whether a sufficient quantity for the de- 

 mands of the Metropolis, could be obtained in that neighbourhood, at a small 

 depth beneath the surface ; and whether this might be effected without in- 

 juring the existing interests in the vicinity, \nien it was found that the re- 

 sult more than confirmed their most sanguine wishes, 1 was requested to 

 examine whether the experiments were well grounded, and to advise as to 

 the means of carrying the plan into effect. 



I had for a length of time been acquainted with the various proposals which 

 have been submitted to the public, and was aware of the objections which 

 could with justice be urged against them. It was therefore not without plea- 

 sure that I undertook the examination of a plan, which I at once saw might 

 be possessed of advantages, which were not before contemplated. 



It will be my endeavour, in the remainder of this Report, to show how far 

 the hope of obtaining the necessary quantity of water at Watford is weU 

 founded ; to describe the experiments which have been made for the purpose 

 of acquiring practical data, to explain the proposed method of procuring the 

 water and conveying it to London ; and lastly, to submit such remarks ag 



will enable you, in my opinion, to present the project before parliament, with 

 a confident reliance that it cannot but deserve its attention and support. 



As I have already described at some length the geological features of the. 

 country surrounding London, I am not called upon to add much to my former 

 explanation on this head, and shall confine myself here to stating, that as re- 

 gards the more inmiediatc object now in view, we may look upon the Colne 

 valley as marking in a great part of its length, on the one side the escarp- 

 ment caused by the outcroj) of the plastic clay, whilst on the other, the coun- 

 try rises gradually to the north-western boundary of the chalk strata, the 

 Cbiitern Ridge. 



An attempt to fix positive quantities, by any line of argument, is naturally 

 attended with considerable difficulty ; nevertlieless, the following considera- 

 tions will give some idoa of tl'.e volume of water tliat can be derived from 

 the chalk of the Colne valley. 



The surface oi" country which has its drainage into the Verulam and Colne 

 above Watford, may be taken at 113^ square miles. If, then, we assume that 

 the annual fall of rain amounts to twenty inches, which you will find a low- 

 average, the result will be 141 millions of cubic feet of water per twenty-four 

 hours, falling on the surface. Of this quantity, Mr. Telford found that the 

 Colne carried off at Watford, thirty cubic feet per second, or about 2; mil- 

 lions per twenty-four hours ; as this was however in a dry season, it will 

 be safer to assume Dr. Thompson's calculations, with respect to the annua! 

 quantity of water flowing off by streams and springs, which he was led to 

 fix at four inches, and tbis would give us for the area drain'ed l)y tlie Colne, 

 not quite three millions per day. 



There remain then IH millions of cubic feet per twenty-four hours, either 

 to be again evaporated, or to find their way into the earth. In an eariier 

 part of this Report, you will remember that I showed that the porous nature 

 of the soil, in a chalk district, prevents the evaporation to a great extent ; 

 nevertheless, if we assume that with the portion which enters into animal and 

 vegetable life, one-third of the entire quantity falling, disappears in tlsis man- 

 ner, we still shall have upwards of 6\ milhons of cubic feet, or 42 milUons of 

 gallons per twenty-four hours, suppljing the sheet of water under that por- 

 tion of ihe chalk surface. 



Mr. Telford's examination of the body of water flowing off liy tb.e Colne 

 river, having been made at a period of unusual drought, when the surface 

 water might be considered to have nearly disappeared, we shall, I think, be 

 correct in assuming that two millions at least of the quantity he measured, 

 had issued from springs. In order therefore to represent the total subter- 

 ranean flow, we shoiJd add these two millions to the former Ci. These in- 

 deed would form no part of the supply to the deep, but would designate that 

 supply which has been already explained, cannot find its way to the lower 

 depths, owing to friction, and other impediments, and therefore seeks a 

 readier vent at a higher level. 



It was important that this should be set in its proper light, as the evident 

 inference we may draw is, that we cannot, by pumping from a lower level, a 

 quantity small in comparison to the accmnulation of water, produce any visi- 

 ble effect upon the springs which feed the Colne. 



I am quite confident that my views as regards the manner in which the 

 water finds its way into the strata of the chalk, will not for a moment be 

 called in doubt by any scientific person, but that which may by sucii a one 

 be considered in the hght of a received axiom, and |)roved by numerous cor- 

 responding facts bearing thereon, with wiiich he will be already acquainted, 

 will require more lengthened demonstration to the general public, with wliom 

 an appeal to experience will have far greater weight than any abstract rea- 

 soning. To these then the experiments which have been made, will afford 

 far more conviction than any argument however well founded. 



The alluvial bed, which covers the bottom of the Colne valley, rather ex- 

 ceeds twenty feet in thickness, after wliich we reach the chalk : proceeding 

 about five feet lower, abundant springs of water are encountered, which in- 

 crease in magnitude and force as we continue to descend. 



It was therefore in the first place necessary to ascertain that these did not 

 derive their supply directly from the river, which, had it been the case, would 

 have affected the various mills in the vicinity ; and it was also desirable to 

 have direct proof of the quantity which might be calculated on being obtain- 

 ed. In order to obtain positive e\idence on both these points, a well was 

 sunk in Bushey Hall meadows, near the Colne, to a depth of about 34 feet. 

 Two small steam engines were then set up temporarily, for the purpose of 

 working four pumps, of which two were 13 inches in diameter, with a length 

 of stroke of 20 inches, and the others were 13s inches in diameter, with a 30 

 inch stroke. One of the engines might be calculated to produce from 27 to 

 30 strokes of the smaller pumps per minute, the other lietween 17 and 20 

 strokes of the larger pumps. The water of the well was now repeatedly 

 pumped out, as low as the power of the engines admitted, and the height of 

 the Colne at those times carefully noted, and it soon became ol.nious that the 

 height of the springs could in no degree be said to aft'ect the level of the 

 river, thus shewing that all direct communication between the two might be 

 considered as cut off by a bed of puddle or clay. The next object of enquiry 

 was as to the supply which a well might be expected to yield, and the result 

 of a careful experiment, made under my direction, and confirming those pre- 

 viously conducted by Mr. Paten, satisfied me that after the water had for 24 

 hours been kept at the lowest level to which the power of the pumps would 

 reduce it, (about 2S feet below its surface when undisturbed,) it rose in the 

 well with a velocity equal to 202 feet per second, thus yielding 174,500 

 cubic feet, or 1,091,000 gallons per 24 hours. As this was obtained in a 



