384 



THE CIVIL ENGINEER AND ARCHITECTS JOURNAL. 



[November, 



be cotablishcd when more information is obtained, wiiieli will be best effected 

 bv keeping registers of the daily variations of wells in different localities, 

 aiid determining the height at which the water stands with reference to 

 Trinity high-water mark. Such ir^formation, if brought together, would well 

 repay the labour bestowed on its collection. 



The author's views were illustrated by a number of sketches and enlarged 

 diagrams of the geological formation of the district, &c. 



Jfemaris. — Dr. Bucklaud was desirous to bring the subject of Mr. Clut- 

 terbuck's paper before the Institution, because he was impressed with the 

 value of a systematic series of observations upon a matter so intimately con- 

 nected with' engineering as the tbeor)- of the causes of the supply of water 

 to springs and rivers, and the rise of water in Artesian wells. 



In his Bridgewater treatise, pi. C8 and pi. 69, he had illustrated by dia- 

 grams the causes of the accumulation of a subterranean reservoir consisting 

 of sheets of water diffused through strata of gravel, sand, and chalk within 

 the basin of London, and of the rise of water in wells and small perfora- 

 tions through the London clay, under the influence of hydrostatic pressure. 



Mr. Clutterbuek's observations and experiments confirmed the general 

 opinion as to the existence of these subterranean sheets of water in the 

 chalk basin, and indicated a connexion between their distant parts, by the 

 svmpathy he had observed between the sudden floods at Watford and certain 

 wells in London, the level of which had been carefully observed and found 

 to rise a few hours after the occurrence of the floods at M'atford. In London 

 also, he had confirmed observations already made upon deep wells at con- 

 siderable distances from one another, and found that any large quantity of 

 wafer taken from one well reduced the level of those adjacent. 



It had been questioned whether the communication between wells of this 

 kind took place solely through the medium of large cracks and fissures, or 

 whether the entire masses of the permeable strata, beneath the level of the 

 lowest springs which flowed from them, had all their pores and minutest in- 

 terstices so entirely filled with water, that any abstraction of this fluid from 

 one well was more or less rapidly replaced by a general flow towards it from 

 every part of the water-logged stratum of sand or gravel or stone in which 

 it was excavated ; on the latter hypothesis during such a flow the surrounding 

 wells would be affected in the direct ratio of their proximity to that from 

 which large quantities of water were taken. 



It had been found at Brentford fliat, as the number of Artesian wells in- 

 creased, the force and quantity of each became diminished ; a similar effect 

 followed in the case of adjacent wells in Lnndon ; the inference he would 

 draw therefore was that a very extensive supply for the metropolis could not 

 be obtained from deep wells of this kind, although a few wells might he sup- 

 plied abundantly. 



The district called the London Basin is made up of a contimious seam of 

 chalk from 300 feet to 500 feet in thickness, which on the S.E. of the Colue 

 is covered with beds of sand and gravel, alternating with plastic clay, and 

 over all these, a thick covering of London clay : whdst the country N. and 

 K.W. of the Colne is for the most part composed of naked chalk. Beneath 

 the whole chalk basin lies a sub stratum of clay or gault which is imper- 

 meable by water, and upholds the reservoir in question. Tlie valleys in this 

 chalk are traversed by the rivers Ver, Gade, and Chess, whose chief perennial 

 supply of water is from springs that issue out of the chalk ; in one of these 

 valleys Mr. Dickinson had proved by experiments made with Dalton's rain- 

 gauge (which, being buried 3 feet beneath the surface, received only such 

 water as descended more than that depth) that during about two-thirds of 

 the year the rain which fell rarely sank 3 feet into the earth ; but in No- 

 vember, December, January, and February it passed down into the subjacent 

 chalk, in proportions which accorded so constantly with the greater or less 

 amount of rain falling in these four wet months, that he had been accustomed 

 to regulate the amount of orders undertaken to be executed in his paper- 

 mills during the following spring and summer, by the indications on this 

 rain-gauge, of the quantity of water that descended more tlian 3 feet in the 

 preceding winter. 



The Colne is often flooded by the effect of sudden rain which is retained 

 upon the surface of the London clay ; but that portion of its water which 

 is derived from perennial springs is supplied from the overflowings of the 

 natural reservoirs, or subterranean sheets of water which fill the interstices 

 of the chalk, and also of the sand and gravel beds of the plastic clay for- 

 mation. The surface of this reservoir is marked by the outbreak of a suc- 

 cession of springs, at levels gradually rising as they are nearer to the upper 

 regions of the chalk; and as the entire supply of this subterranean stock of 

 water is derived from rain that falls on the surface of permeable strata within 

 the London basin, the abstraction of water from any part of this reservoir 

 would. Dr. Buckland conceived, diminish the quantity remaining to he dis- 

 charged by springs into the rivers in the vicinity of such abstraction, by the 

 total amount of water so transferred to any other than its natural channels. 



It was asserted that the surface of the water in this subterranean reservoir 

 did not maintain a horizontal level, but that it rose nearly 300 feet in four- 

 teen miles, between the town of Watford and the highest spring that issued 

 from the neighbouring chalk hills. The molecular attraction of the particles 

 of chalk tlirough which this sheet of water is diffused, and the obstruction 

 presented by friction to its descent through the numerous pores and miinife 

 crevices by which it has to pass in adjusting the line of its upper surface, 

 might account for this deviation from the level line which fluids assume, if 

 left to act freely in open spaces, or in large and continuous conduits; Mr. 

 Clutterbuek's repeated observations upon wells along the line in question 



must be considered to have proved the existence of this inclined level. His^ 

 observations were also very important, as to the floods at Watford raising in 

 a few hours the level of the water in deep wells in London, and as to the 

 eflfect of a steam-engine erected to pump water from a large experimental 

 well near \Yatford in lowering the water in smaller wells in that town and 

 the country adjacent to it. 



Mr. Dickinson had made very accurate observations upon the absorption 

 of water by the chalk, and was convinced of its being always in a wet state 

 almost amounting to saturation ; but few cre\ices and fissures exist in the 

 chalk of the district under notice, the rain therefore occupies a considerable 

 time in overcoming the molecular attraction of the pariicles through which 

 it passes. Wherever fissures exist at a certain depth below the chalk, they 

 become channels which collect and facilitate the flow of water to maintain 

 the springs ; the accumtdations of the winter rain sink slowly down in sum- 

 mer, and by a series of vents or springs furnish a supply for the rivers which 

 run in the deepest valleys of the chalk district ; a long cessation of rain 

 lowers the level of the water in the rivers, at an interval of some months 

 after the drought, and any extraordinary demand by pumping from the wells 

 in the chalk, would lower the water in the wells around, even at a consider- 

 able distance. 



From experiments with the rain-gauge buried 3 feet below the surface, he 

 found that but little rain penetrated to that depth until the months of No- 

 vember, December, January, and February — the total quantity per annum 

 was shown to vary between 17 inches and 6 inches, which latter amount 

 sufficed to fill the principal springs. He was induced to believe that if a 

 large supply of water was drawn from the chalk it would eventually have a 

 prejudicial effect in diminishing the water in the rivers of the district. 



Mr. Clutterbuck said that the sphere of his observations extended over a 

 line of wells 20 miles in length, and in the whole of them there was the most 

 perfect accordance between the alterations of level of the water and the indi- 

 cations of the rain-gauge, allowing the time necessary for the rain to sink 

 into the chalk ; as also there was between the fall and replenishment of the 

 wells at Watford and those in London, whence large quantities of water were 

 obtained by pumping ; he could always tell, by measuring the height of 

 water in one well of the series, what would be that of any other well along 

 the line ; he therefore was satisfied of the accuracy of the observations in 

 his paper. 



Mr. Dickinson observed, that he corld not satisfactorily account for the 

 greater amount of variation in the wells at the higher part of the district, 

 when compared with those of the lower part ; the alternations of the former 

 amounting frequently to 30 feet, while those of the latter were only 10 feet 

 iu the same time. 



Dr. Buckland believed this fact to arise from the hydrostatic pressure 

 being less interfered with by friction and capillary attraction, in the lower 

 part of the district than in the upper part. 



Mr. Clutterbuck accounted for the alternations of level in the sand springs, 

 being greater than in the chalk springs, by the relative degrees of opposition 

 the water met with, from the friction in passing through the two kinds of 

 strata. 



Mr. F. Braithwaite had made many borings and sunk several deep wells 

 into the chalk — he would instance particularly the wells at Messrs. Meux's 

 and Messrs. Reid's breweries, and that at Greenwich Hospital ; in these wells 

 he had used cylinders of iron to shut out the sand springs. He did not find 

 the chalk so spongy or saturated witli water as had been stated ; he imagined 

 that the supply of wafer was derived from tlie crevices in the chalk, and in 

 many instances water had not been arrived at, because one of these crevices 

 had been missed, whilst in a well of less depth nearly adjoining, in which 

 they had fortunately hit upon the crevice, a plentiful supply of v.-ater was 

 obtained. In the first and second beds of flints under London there was 

 very little water; from the third to the fifth bed the quantity increased, and 

 at 30 feet lower down a continuous fault or crevice was generally found 

 which conveyed a good supply of water — the rise and fall of water in wells 

 in the chalk did not accord with those of wells in the sand beds above the 

 chalk ; the alternations in the former amounting to only a few inches in a 

 given time, while those of the latter were as many feet. He placed great 

 confidence in the observations made by Mr. Clutterbuck. That gentleman 

 had told him accurately, from the variations of the well in the llampstead 

 Road, all the difl'erences of the quantity of water drawn from iMessrs. Reid's 

 well, arising either from an extra demand or from cessation in the pumping. 

 The brewers of London could be supplied by the water companies at a 

 cheaper rate than by pumping ; but as a large quantity was used for refri- 

 gerating the wort, it was important to have the wafer at a low temperature, 

 they therefore were obliged to pump it up at a great expense. The quantity 

 raised at Messrs. Reid's well was about 7,700 barrels of 36 gallons each per 

 day, which was calculated to be a suflicicnt supply for 5,000 families ; there 

 was already a decided diminution manifested in the supply from the sand 

 springs, and an extension of these eflfects might be anticipated from the 

 sinking of any large number of wells into the chalk. 



Dr. Buckland ascribed the difference of the supply of water in sand 

 springs, and in those originating in chalk, to the relative extent of surface of 

 the sandy and cretaceous strata in Hertfordshire, by which alone they receive 

 their respective supplies of rain water, the amount of sandy surface being to 

 that of naked chalk about as one to twelve. 



