1843.] 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



351 



the level will then be raised in proportion to the quantity of water which 

 passes through the sand into the chalk beneath it, the elevation of level ex- 

 tending towards the river in a ratio increasing with the distance from the 

 river ; the fixed summit will remain unaltered, until the level at the point of 

 irruption has attained aii elevation at which the water can flow towards the 

 south. After a period of protracted drought the level will decline in the 

 same ratio as it had risen, until it assumes a line in which little or no varia- 

 tion can be traced. In a given line from the Colue at Watford, to the vil- 

 lage of Bushey, 1J miles distant, in the autumn of 1841, the level was found 

 to rise from the river, at a regular inclination, to a point within the outcrop 

 of the clays. After heavy rains, the level, near the swallow-hole which re- 

 ceives a large body of water, began to rise rapidly, the fixed summit level not 

 being affected till the level, at the point of irruption, rose above it ; the total 

 rise at the point of irruption was 20 ft., and at the fixed summit 2 ft. The 

 position of the summit level had then varied from the fixed summit to the 

 point of irruption ; coincidental!}- with this elevation the level under London 

 rose also, and began to decline at the same time that the level, at the point of 

 irruption, sank below the fixed summit. The subsidence of the level at the 

 point of irruption, was — in April, 4 ft.; May, 3 ft.; June, 2 ft.; July, 1ft.; 

 August, 9 in.; September, Gin. ; in October, and to November 8th, 14 in. ; 

 the average inclination, from the fixed summit to the river, then being about 

 15 ft. in the mile. The subsidence of the level to this inclination, was coin- 

 cident with a visible defalcation in the product of the springs discharging 

 themselves into the river Colue. In the autumn of 1842, and in the prece- 

 ding spring, similar effects were observed, both as to the rising of the level 

 at the point of irruption, and the coincident elevation of the level under 

 London. This oscillation of level has been traced at various points, both to 

 the east and west of that here described. It is probable that near the junc- 

 tion of the Colne and the Vtr, the level dips directly from the level of the 

 latter river, at a point where the plastic clay extends itself under the Colne 

 to the margin of the Ver. This suggests the probability of that to which 

 the author alluded in his former communication — namely, the possibility of 

 connecting a periodical defalcation observed in the waters of the Ver or the 

 Colne, at those seasons when the water is short, with the exhaustion of 

 water under London. The evidence in favour of this supposition has been 

 strengthened, during the past year, by a repeated coincidence of variation in 

 the London level with the supply of water in the river. The height of the 

 water in the river (about 210 ft. above Trinity high-water mark) gives the 

 same average inclination of level towards London as observed in other places, 

 and strengthens the probability that the supply of water to the river may be 

 affected at this point by the London pumping, the daily increasing demand 

 of which will, if (as is contended) there be any ground for this supposition, 

 very soon put this question beyond a doubt. 



Remarks. — Mr. Dickinson said, that Mr. Clutterbuck's observations had 

 been caused by a project for obtaining a supply of water for the metropolis, 

 from wells to be sunk in the valley of the Colne. It had been stated, in 

 support of the plan, that the rapidity with which the rain water percolated 

 into the bowels of the earth, in a great measure prevented evaporation, and 

 hence it might be assumed, that the quantity which descended upon the sur- 

 face of the chalk found its way, with very slight diminution, into the fissures 

 below. This reasoning was not in accordance with the deductions Mr. 

 Dickinson had drawn from an extended series of observations, and, fearing 

 that his mill property might be injured by the diminution of the supply of 

 water, he had opposed the project. He had found it necessary, several years 

 since, to investigate strictly the nature and extent of the supply of water to 

 the springs and rivers of the chalk district, for which purpose he had a 

 common rain gauge, which was corrected by observations upon that kept in 

 the same district by the Grand Junction Canal Company; he also fixed a rain 

 gauge on the principle suggested by Mr. Dalton, which demonstrated the 

 quantity or proportion of the rain falling on the surface, which descended so 

 far into the earth as to be beyond the reach of evaporation, and, therefore, 

 must be calculated to reach the internal reservoir of the country whence the 

 springs were fed. This gauge demonstrated that the greater part of the 

 rain that fell on the surface, was either consumed by vegetation or evapo- 

 rated. It furnished information of the most valuable kind, both as regarded 

 his mills and business, and as to any engineering operations, having reference 

 to the perennial supply of water in the springs and rivers of the district. 

 Mr. Dickinson presented a tabular statement of the comparative result of 

 his two gauges for the last eight years, pointing out, as was generally the 

 case, that none of the rain-water penetrated to the springs between the 1st 

 of April and the 30th of September. He also stated that the indications of 

 the gauge were not only certain, but that they preceded generally by about 

 two months, any thing that could be deduced from the observation of wells, 

 with reference to the effect upon the rivers ; and that, as to the latter, the 

 only guidance to be derived from the state of the wells, was from those in 

 the higher range of the chalk, because, along the valleys where the streams 

 flowed, the level of the wells continued nearly the same throughout the 

 year. 



Mr. Clutterbuck perfectly agreed with Mr. Dickinson as to the satisfactory 

 results yielded by Dalton's rain-gauge ; but he had, from the first, expressed 

 an opinion, that the same practical results might be obtained by a periodical 

 measurement of the wells, in any part of the chalk district. If a line was 

 taken, extending from the river or vent to a point midway between the 

 rivers Gade and Ver, or any others, and observations made during different 

 periods of the year, and the same periods of different years, the height to 



which the water rose or fell, would indicate the quantity which had actually 

 percolated to the water level, and would give the relative quantity to be de- 

 livered out by the springs. The ratio of alternation throughout the line 

 would be maintained with such undeviating regularity, that by the measure- 

 ment of the wells at the two extremes, the rise or fall of all'between them 

 might be calculated with the greatest exactness. He had chosen, by way of 

 illustration, a portion of the line, of which a section, three miles in length, 

 was given, extending in a direction north aud south between the rivers Gade 

 and Ver, a locality whence a considerable portion of the water, which in 

 part moved the machinery at Mr. Dickinson's mills, was derived. He took 

 the seasons which govern the supply of water, as shown by Dalton's gauge. 

 In the season 1840-41, the gauge indicated the percolation of less than 5 in. 

 of rain, a quantity which must be far short of that which found its way to 

 the water level. The gauge recorded no percolation of water immediately 

 after the melting of the snow on the 16th of January, 1841, within a month 

 of which time the level rose in some localities more'than 15 ft. To make a 

 proper estimate of the quantity of water to be delivered from the springs, 

 it was necessary to ascertain the state of the level before the percolation 

 commenced; to this the rain gauge was no guide; but by Mr. Clutterbuck's 

 observations he was enabled to determine the exact re'lasive depression of 

 the level. The first day taken was September 13th, 1841, between which 

 period and November 8th, the level rose at one point 18 ft., and at other 

 points in due proportion, which distinctly proved that " the indications of 

 the rain-gauge do not precede by two months any thing that can be deduced 

 from observations on wells." His next observation was February 14th, 

 1842, showing the highest point at which he measured the level, giving a 

 total rise of 34 ft. ; though from observations elsewhere it must previously 

 have risen even higher, and have fallen to that point in consequence of the 

 accelerated drainage caused by the breaking out of springs at higher levels, 

 when the water in the chalk attained a certain elevation. On the 7th of 

 May the level had fallen considerably, and on the 24th of October had de- 

 clined to within a few inches of the same level as in the September of the 

 previous year. In the season 1841-42, Dalton's gauge indicated the perco- 

 lation of 17-98 in. of rain; in 1842-43, 10-64 in. ; but from the causes be- 

 fore alluded to, and from the rain not having percolated till a later period, 

 the level continued to rise till May, consequently the quantity of water then 

 in the chalk was greater in proportion, than as 10 to 17. He conceived 

 that the great practical question was, what supply might be reckoned upon 

 from the 1st of May to the end of October ? The reply to this was, he con- 

 tended, more distinctly given by his observations than by the indications of 

 Dalton's rain gauge. With reference to the rapidity with which the water 

 found its way from the surface to the level, except when there was a great 

 quantity of rain within a veryshort period, the percolation would be gradual, 

 as indicated by a steady and progressive rise in the wells, which he had as- 

 certained to amount sometimes to 1 or 2 in. in a day in the upper district, 

 and continued generally to the beginning of May. In the neighbourhood of 

 the swallow-holes the level rose very rapidly: a well sunk 50ft. in the 

 chalk, in which the water stood at 40 ft. from the surface, was affected 

 within 15 hours after a late heavy rain commenced ; the quantity of rain, 

 which amounted to 1 in. in 12 hours, appeared to have retarded by a fort- 

 night the exhaustion of that portion of the level to the south of the Colne, 

 which is fed by the irruption of water through the swallow holes. On a 

 former occasion, between the 10th and 25th of November, 1842, there fell 

 on the surface 3-88 in. of rain ; the level near the swallow-holes rose 6 ft. 

 within the same space of time. When the water had reached the level, the 

 influence of one part on another was very rapid : thus when the distant level 

 was raised, as Mr. Clutterbuck had described, there was a simultaneous rising 

 of the level under London. The continuity of the level, as shown iu his 

 section, was the best evidence in favour of the supposition, that the water 

 to London was mainly supplied from the source to which he had attributed 

 it. He had not met with any evidence iu favour of the supposition that a 

 distinction was to he drawn between the water from the chalk and that from 

 the sand ; he believed that it was all derived from the chalk, whence it rose 

 into the sand, to which there appco :edno impediment. At the points where 

 the water broke through the sand, it invariably sunk into the subjacent 

 chalk, a space being left between the bottom of the sand and the top of the 

 water; following the water level, it might be traced in the chalk, and rose 

 into the sand when the surface of the chalk sunk below the inclination 

 at which the water level dipped towards London : from whence he in- 

 ferred that the whole level of water might be called the " Chalk water 

 level." 



Mr. Simpson reiterated his opinion respecting the waters iu the sand and 

 in the chalk being different. He had seldom found the water from those 

 strata stand at the same level, and in the majority of instances, the water 

 from the chalk rose to higher levels than that from the sand. Towards the 

 west of London, prior to 1830, there were numerous cases of overflows from 

 bore-holes ; and he believed, from an account drawn up by him from actual 

 inspection of the wells when they were sunk, or soon afterwards, and which 

 he presented to the Institution, it would be found that in the majority of 

 instances of overflowing wells the water proceeded from the chalk. This 

 paper gave an account of 67 wells, detailing in several cases the various 

 strata passed through, and in all, the total depth, the levels at which the 

 different qualities of water were met with, the quantity of water yielded, 

 and the height to which the main supply rose in the well. He had found 

 from recent inquiries, that in many of these wells the water had now ceased 



