The Sun.
London, England, 1855-01-15 00:00:00

INSTITUTION OF CIVIL ENGINEEES.

Both evenings (Dec. 12 and Jan. 0), wore entirely de-
voted to the discussion of Mr. P. W. Barlow's paper " On
some peculiar features of the Water-bearing, Strata of the
London Basin."
It was urged, that the term "water-bearing strata"
should be more clearly defined, and it should bo shown
whether it meant the chalk, through the fissures of which
the major portion of the water percolated, or the sands
which were entirely saturated with water.
The views expressed some time since, by the Bev. Mr.
Cluttorbuck, in his communications to the institution in
1812 and 1843, were insisted on as having been confirmed
by subsequent investigations. Professor Ansted's paper
" On the absorbent properties of chalk," was also quoted
in aid of the proposition of its retentive properties, and it
was shown that the action was chiefly by capillary attrac-
tion, and existed to such an extent that chalk would contain
one-third of ita bulk and one-fourth of its weight of water.
Hence it was argued that nearly all the chalk was super-
saturated with water "in situ," but nevertheless it did not
follow that it could be drained, except through the fissures
and layers of flints.
It was admitted that the indications of Mr.
Dickenson's rain-gauge might not be critically ac-
curate ; but they were so far correct as that they
served to inform him what supply of water ho might
expect in the river. The rate of evaporation from the sur-
face, both by sun and wind, required to be watched care-
fully. If it wore possible to evaporate clown to about six
feet beneath the surface, very little, if any water, falling
as rain, would reach the lower beds. After a dry summer
the earth required 3 inches of rain to compensate for the
previous evaporation, and it was only after that quantity
had fallen that there was any surplus moisture for re-
plenishing the springs.
The details were given of the experiments made and the
effect produced by the pumping at the well sunk by the
Grand Junction Canal Company, near Tring. The depth
oft
down rut.;
eweliwas 7Lo feet, with
withwthwenocabobry meanse-huls of
wentgnhiaet
level,
power and two pumps of 12 inches diameter and 6-feet
stroke, the water was intended to be pumped for the
use of the canal. The results of the experiments tended to
demonstrate, not only that the water in the adjacent wells
was reduced, but that the river was lowered and a pond in
the vicinity disappeared; but on arresting the pumping,
the water resumed its original level in all. It was urged
that the sources of the river were in the upper part of the
chalk, and therefore that if the well was puddle(' and
close-ateined, so as to exclude the top-water, no effect
would be produced ; this, however, on trial, was not found
to be the ease, as on the resumption of pumping a repeti-
tion of the same results was observed. It was also stated
that the well at the Croydon Waterworks, also sunk into
the chalk, had similarly affected the river IV
The accuracy of this statement was impungssi —it was
urged that the quantity of water pumped had not been
stated, and it had not been shown that there had been a
failure in the attempt to render the steining of the well
impermeable. It was indispensable to make wells water-
tight at the upper portions, in order to prevent them from
injuring other wells of less depth in the vicinity. It was
stated to be practicable to obtain a large supply of water
from the chalk, by the same system as had been employed
for procuring a supply of fresh water at Grimsby for the
use of the dock. It was also stated that a large quantity
of water was obtained from the chalk, at Woolwich, for
the supply of that district, without acting detrimentally
upon the neighbouring wells.
The peculiar features of the absorption of water in va-
rious parts of the course of the Lea and the reappearance
of the springs at other spots were noticed, and analogous
instances quoted--such as the river Mole, which partially
disappeared at several places in its channel, and after a
subterranean course of some distance through the porous
strata and fissures again rose to the surface.
Many celebrated springs owed their origin to this cause ;
the water when once it was absorbed finding its way into
various open strata, or fissures and beds, and only again
appearing at some fault, or where, by denudation, or other
cause, the porous strata appeared at the surface.
The great variety in the quality of the chalk was in-
sisted on, as necessary to be considered, in assuming it
to be a useful water-bearing stratum. In reality the qua-
lity varied infinitely, from an open texture, broken up and
mixed with heterogeneous materials, to a close compact
substance, almost of the density of stone; its distance
from the surface and the thickness of the bed, varying
almost to the same extent ; its capacity for water-bearing,
or rather for water-yielding, would, it was argued, be also
as various and uncertain.
It was contended that the sands underlying the chalk
would be found the most certain sources of water supply.
The condition of the strata at Grimbsy were different to
those of the London basin; and iu the latter locality, some
years ago, in any well of moderate depth,water was certain ly
met with, whereas at present it was only found at consider-
able depths,and was only obtainable by grea,t pumping power.
The water was nowchieflyfound in the fissures and flint beds,
and, but little in the solid chalk, beyond that held in
suspension, and which it was difficult to extract. Water
might be found in sufficient quantity, in the chalk, for the
supply of two, or three suburban parishes near the metro-
polis, but the conditions were very different from those of
iillounsdooryn ittos etlrfP
u ntod it, tanwy aßsiis.thr osno gulry.
ecfoonrt ean
Idaerdg
et
shuapt
pi
itywbays
Artesian wells. The district to the south-east of London
was comparatively intact, but it could only be proved, by
experiment, to what extent it was capable of furnishing a
large supply; although it was admitted that a large quan-
tity of water was wasted by the springs running into or
rising in the river, which might probably be beneficially em-
ployed. The case of the well now being sunk at Hampstead
was quoted : that well had been sunk at a spot 172 feet above
Trinity H. W. mark, with the intention of procuring a
supply of water from the chalk, which was found at a
depth of 320 feet from the suarnfadcoc.omTpahreacthivaellky
(wheys
;corn-
and the mass, and not in
thpact,
Hints hard,
weref r e edfi rs ot
rmi b fissures,tth
layers. After sinking 218 feet an the chalk boring was
commenced, and had proceeded until a total depth of 1,13 J
feet had been arrived at, traversing a thickness of 510 feet
of chalk, the subjacent gault, and into the red clay, pre-
sumed to overlay the lower green sand, in which it was
anticipated a supply of water would be found. Little or
no water had, however, hitherto been yielded in all this
deep boring.
The influence of swallow-holes, in admitting streams into
permeable strata, was noticed, as also that the lower
green sand must evidently be the source of many of the
springs, having the appearance of arising from chalk ; as
the rain was rapidly absorbed at the denuded out-crop of
those sands, and the water frequently passed from them
through the fissures in the chalk, and appeared to proceed
from the latter stratum.
It was contended, that the antipyclipamtteihgd quantity of water
to be derived from the chalk, and evenhe
might
fromfor
super-saturationt
the
the
rs greenfew
years
sands,be le
wasconeexiaagegraerbite, (b 1 ;ut by degrees
the supply
would be reduced, and the supply would depend on the
percolation of the annual rain-fall. The best accredited
experiments, upon 'various soils, showed that not more
than four inches of rain infiltrated through the strata and
flowed outwards in the shape of springs. Beyond that
quantity then any supply must be derived, by pumping,
from the constant quantity held in suspension in the
various strata, and that source of supply, it was argued,
would be soon diminished in certain localities.
It was admitted that water was obtained from chalk,
chiefly, if not entirely, by infiltration through the fissures,
and the layers of flints; and that although chalk was a
rapid absorbent of moisture, it did not readily part
with it again, nor in its normal condition would it
afford a free passage for water ; therefore it
could not be correctly denominated a water-bearing
stratum ; whereas sand would bo correctly so termed.
The chalk was, however, in certain districts so intersected
by fissures, and bad such numerous layers of flint that
practically the effect of a water-bearing stratum was ob-
tained ; and hence the excessive pumping from one well
would affect all around, as also the sources of the streams.
In other districts the chalk possessed such a density that
all hope of obtaining water from it was vain. The quality
of the chalk under London was as various as the depths
at which it was reached from the surface. The same pe-
culiarities exhibited themselves at Paris, where in one
situation water was reached at 574 feet, whilst at the
Puits de Grenelle it had loam necessary to go as deep as
1,800 feet.

Sand was, on the contrary, essentially a water-bearing
stratum ; the facility of yielding moisture depending gene-
rally on the size, and therefore the collective compactness,
or openness, of the grains. It was as susceptible of sate-
ration as the chalk, but not as capable of retention of mois-
ture. In some districts the lower tertiary sands were
mixed with clay, which interrupted the flow of water,
whilst in others they afforded a free passage.
The intermittent character of the flow from the well at
Grenolle wa.i mentioned, and was shown to arise chiefly
from stoppagCs of the pipe by sand, although the quantity
of water delivered was undoubtedly influenced by the fall
of rain on the out-crop of the tertiary strata, into the basin
of which the well was sunk. Artesian wells were not
sufficiently universal iu their application, and could scarcely
yet afford correct data as to the character of the flow, but
instances were cited of one well of that kind, stated to
have been sunk in the 12th century, and another about a
century old, the supply from both of which was now, ap-
paroltly, undiminished in quantity and unchanged in
quality.

It was contended that the dry character of the chalk in
certain localities was an indication of its being really a
water bearing stratum, as it was submitted that ts layers
of flints, and its numerous fissures, afforded the most rapid
means of percolation.
In reasoning from results obtained 'by gauges it was
necessary to observe the character of the ; if the
rain fell gently, the evaporation might be so great that
none would percolate ,- or during a storm it might all run
off tho surface ; therefore the question could only be solved
by observation for a long period, and over an extensive
area of out-crop. It was also necessary to observe the
swallow holes, and numerous depressions in the chalk dis-
tricts, as by them great quantitioe of water were convoyed
to the lower strata.
It was mentioned that the lower green sand stratum had
been reached in the Hampstead well at a depth of 1,150
feet from the surface, and a very short time would now
demonstrate the correctness or the fallacy of the views as
to the quantity of water to be obtained from those strata.
There was great difference iu the condition of chalk, with
or without flints, and it was contended that in some cases
the latter contained a larger amount of water than the
former. The lower beds appeared to b© saturated with
water which had percolated from rain or melted snow, and
was only arrested by the clay, and hence the accumulation
in the chalk, until the water rose to such a height as to
flow out as springs.
The wells under London did not now yield more than
eight millions of gallons per day, and the water-level had
been gradually sinking. In the year 1824 the water, when
Naveiht hti
on
,611.0 t
hfiene too ff
eheitg
olaf-
n waternot a ffme catrekd, bybut
p omwp iint gd,
the same level.
ilionseottore

There could not be any doubt of the south-eastern dis-
trict, mentioned in the paper, being very full of water,
but it might be anticipated iat it was there, as in other
districts, an accumulated store, which, when heavily drawn
upon and not adequately replenished, would after a time
fad as other stores had done. Few questions wore snore
hd ioffip led tthtaot ttrhe
ea tr
shiaant
sthati
ill:sods et
irgcaotnsi
o ind earnaat i oonf,
oabne de
rivta
tNivoans
would be annually laid before tho