THE 
DESIGNING AND CONSTRUCTION 
OF 
STORAGE RESERVOIRS. 
ARTHUR JACOB, B. A., 
LATE EXECUTIVE ENGINEER FOR IRRIGATION H. M 
BOMBAY SERVICE. 
NEW YORK: 
D. VAN NOSTRAND, PUBLISHER, 
23 Murray and 27 Warren Street. 
1 8 7 3. THE DESIGNING AND CONSTRUCTION 
OF 
STORAGE RESERYOIRS. 
Before entering upon such considerations 
as affect the selection of reservoir sites and 
their construction, a brief allusion to some 
of the most ancient works for impounding 
water may not be uninteresting. Of these 
the most prominent examples are undoubt- 
edly to be found in ELindostan, where the 
magnitude and antiquity of the storage 
works cannot fail to arrest attention. These 
great works, surpassing in their immensity 
what are conventionally esteemed to be the 
wonders of the world, the production of 
other countries and nations, took their ori- 
gin in the necessities of the people and the 
variableness of the climate of India, and 4 
were, in fact, great public works on which 
the welfare of the people mainly depended. 
The climate of India, although singularly 
uniform in some respects from year to year, 
is remarkably variable as regards the rain- 
fall ; and in order to guard against the dis- 
asters of famine and sickness, inevitably 
attendant on a scanty monsoon, the native 
princes were wont to make such provisions 
as large resources and an almost unlimited 
power enabled them, in order to obviate 
the difficulty that they had to contend with. 
The rain records of India for several 
years past show that a scarcity of rain is 
indicated by periods of about five years, or 
that every fifth or sixth year is marked by 
a scanty rainfall over certain districts. The 
recurrence of these periods is, of course, 
not very clearly marked, but still it is suffi- 
ciently so to warrant, -frith approximate 
correctness, the prediction of scarcity and 
famine ; and such deplorable recurrence is, 
as all are aware, now reigning in India, 
and visiting with destruction, by sickness 
and hunger, some thousands whose sole de- 
pendence is upon a fair season of rain, and 5 
the successful maturing of their little crop 
of grain. 
The natural expedient for guarding 
against the recurrence of these periodical 
calamities was evidently to be found in 
husbanding a scanty supply of rain-water 
for the purpose of irrigation, and this the 
people of India appear to have understood. 
They took advantage, in certain districts, of 
every nook and ravine, whether large or 
small, and converted them into storage re- 
servoirs by throwing across banks of earth, 
or bunds, as they are termed, producing, in 
certain districts, such an elaborate and 
complete system of irrigation as can only be 
compared, for cost and completeness, to our 
railway system in England. Taking four- 
teen districts in the Madras Presidency, 
where tank irrigation was most generally 
relied upon, the records of the Indian Gov- 
ernment show that there are no less than 
43,000 irrigation reservoirs now in effective 
operation, and as many as 10,000 more that 
have fallen into disuse, making a total 
number of 53,000 storage works. The ave- 
rage length of embankment is found to be 6 
about half a mile, the extreme limit of the 
series being a dam of the immense length 
of 30 miles. This ancient reservoir, called 
the Poniary tank, is no longer in use, the 
cost of maintaining such a length of bank 
in adequate repair having probably been 
found disproportionate to the advantage 
derived from the supply. The work, em- 
bracing an area of storage of between 60 and 
80 sq. miles, remains however as a record 
of what the Hindoos are capable of. To 
quote a second example, there is the Yera- 
num reservoir, now in actual operation as 
a source of supply, and yielding a net rev- 
enue of no less than £11,450 per annum. 
The area of the tank is 35 sq. miles, and 
the storage is effected by a dam of 12 miles 
in length. In order to bring the immensi- 
ty of this system of storage works within 
the reach of statistical minds, it has been 
calculated that the embankments contain 
as much earth as would serve to encircle 
the globe with a belt of 6 ft. in thickness. 
To show that these are not singular exam- 
ples, one other embankment of remarkable 
size may be alluded to. This embankment, 7 
of somewhat singular construction, was 
built on the island of Ceylon, and bears 
testimony that the Singalese monarchs 
were not behind their neighbors in public 
spirit or enterprise. The embankment was 
composed of huge blocks of stone strongly 
cemented together, and covered over with 
turf, a solid barrier of 15 miles in length,. 
100 ft. wide at base, sloping to a top width 
of 40 ft., and extending across the lower 
end of a spacious valley. 
Thus it will appear that the practice of 
embanking across valleys, for the purpose 
of retaining the surface water, has for ages 
been in operation. There is no doubt that 
the disposal of some of the most remarka- 
ble works in India is not what it might, with 
advantage, have been ; the fact remains, 
however, that the desired end was attained,, 
and if the earthworks were dispropor- 
tionately extensive, it was a source of satis- 
faction at least for the projectors to know 
that they cost,* as a general rule, little or 
nothing, the practice in those days being to 
press whatever labor was required, render- 
ing in return nominal wages or none at 
all. 8 
The two main questions that it is pro- 
posed to submit for consideration are, first, 
the selection of a reservoir site ; and, se- 
condly, the leading principles to be observ- 
ed in the designing and construction of 
storage works. 
The purpose or purposes for which the 
work may be required will, of course, af- 
fect materially the choice of a position, as 
well as the details of the structure itself; 
but certain general principles are available 
for our guidance in every case, after con- 
sidering which, it is proposed to dwell upon 
such points as apply to the special purposes 
for which reservoirs may be constructed. 
The first and most essential point for ac- 
curate determination by the engineer is 
undoubtedly the amount of rainfall, both 
maximum and minimum, that may be ex- 
pected in the district under examination ; 
and, having arrived at reliable data on this 
point, the next consideration will obviously 
be, what amount may be made available, 
due allowance having been made for evap- 
oration and absorption. When we know 
that the annual depth of rainfall taken all 9 
over the world varies, according to the lo- 
cality, between zero and 338 in. or 28 ft. 
deep (which excessive amount was on one 
occasion registered in the hill district of 
Western India), it will be obvious how 
little ground there will be for assumption, 
in the examination of any district hitherto 
unexplored, with regard to the question of 
its rainfall. In the examination of any 
given country, however, there are certain 
phenomena connected with the rainfall that 
will be found of almost invariable accepta- 
tion, and may with advantage be borne in 
mind. 
The rainfall will, as a general rule, be 
greatest in those districts that are situated 
towards the point from which the prevail- 
ing winds blow. If Great Britain for in- 
stance be taken, the western districts will 
be found the most rainy. The very reverse, 
however, of this phenomenon is noticed in 
the neighborhood of mountain ranges. If 
the wind prevails from one side rather than 
from the other, it is found that the greatest 
rainfall is on the leeward side of the range,, 
and the probable solution of the matter is, 10 
that the air, highly charged with moisture, 
is carried up the hills by the wind until it 
comes into a cold region of the atmosphere. 
Condensation of the watery vapor immedi- 
ately takes place, and the result is a fall of 
rain on the side of the mountain range re- 
mote from the prevailing wind. 
To this cause may also be attributed the 
fact that the rainfall is always greatest in 
mountainous districts, while it by no means 
follows that elevated plains are more abun- 
dantly supplied with rain than land lying 
nearer to the sea level. The principles are 
remarkably exemplified in the southern 
part of the Bombay Presidency, where the 
author has had occasion to study the sub- 
ject of rainfall. The Western Ghauts run 
parallel to the coast, rising to a height of 
4,500 ft. above the sea, and form the west- 
ern support of the great table- land of the 
Deccan, the mean elevation of which may 
be taken at 3,000 ft. In the rainy season 
the south-west monsoon, blowing from the 
sea, impinges against the ghauts, and while 
passing onwards to the Deccan, parts with 
its moisture to the average annual amount 11 
of 254 in. On a spur of mountain that 
runs eastward, the pluviometers are found 
to register but 50 in.; and about 40 miles 
farther inland the rainfall is not more in 
some places than 15 in., which is consider- 
ably less than that registered in the lower- 
lying districts of the Presidency. 
In civilized countries like our own much 
valuable information is as usually avail- 
able regarding th9 rainfall, if not ap- 
plying actually to the district under exam- 
ination, then probably to some neighbor- 
ing districts, enjoying the same physical 
characteristics; but when any project of 
great importance is in contemplation, it will 
not be sufficient to take the returns of ad- 
joining districts as accurate information of 
the rainfall at the exact locality fixed upon 
for the construction of the works. It will 
be necessary to establish rain-gauges at 
different points over the catchment basin 
of the valley from which it is intended to 
obtain the supply; and daily observations 
of these gauges must be taken for compari- 
son with a series of simultaneous observa- 
tions taken and recorded at the nearest sta- 12 
tion at which the rainfall has been regu- 
larly and carefully noted. It is evident 
that a comparison of the several observa- 
tions taken over the area of water-shed with 
those registered at the permanent station, 
will convey a just estimate of the amount of 
maximum and minimum rainfall that may 
be relied upon. 
The amount of rain falling upon the 
ground is not, however, the point to be 
determined, though it will aid considerably 
as a guide to the engineer. A considerable 
quantity of all the rainfall is either absorb- 
ed by the ground or evaporated before it 
reaches the point at which it can be made 
available for storage. Regarding, then, first 
the question of absorption, it must be ap- 
parent that no two districts, unless they are 
exactly identical in soil, inclination of sur- 
face, and under similar circumstances of 
cultivation, can give on examination the 
same comparative result of rainfall and 
evaporation. If one district or unit of area 
be similar to the other in all respects but 
the surface inclination, that which has the 
greatest slope will, as a rule, give the larg- 13 
est percentage of water available for stor- 
age, because of course there will be less 
time for the rain to be absorbed. Again, 
the degree of cultivation will materially af- 
fect the result when two areas, otherwise 
precisely similar in their physical conforma- 
tion, come to be compared one with the 
other, it being evident that an open and 
well-drained soil will be more favorable to 
the retention of water falling upon it than 
compact and impervious land. In every 
case the physical features of a district will 
each and every one of them force itself on 
the attention, as influencing the conclusion 
to be arrived at. If any general rule can 
be applied, it may be said that the greater 
the slope of the valley, the more rapidly 
it will throw surface water off; the more 
denuded the surface is of soil of any kind, 
the less will the escape of rain-water be re- 
tarded ; and the more compact the rocks 
composing the geological structure of a dis- 
trict, the better will the circumstances be 
for impounding water. The volcanic rocks 
and those of the granite order will be as fa- 
vorable as any that could be desired; 14 
while, on the other hand, porous rocks, 
such as the sandstones, chalk, etc., are too 
absorbent to offer the desired conditions for 
storage. It is not here asserted that all 
the water absorbed by porous rocks is ne- 
cessarily intercepted from passing away to 
contribute to storage supply; much of it 
may be lost by evaporation and absorption 
by vegetables, but a considerable portion 
will often be found to contribute in the 
form of springs, if the disposition of the 
strata be favorable. 
As a further source of loss, evaporation 
from the ground as well as from the sur- 
face of the reservoir, must be taken into 
consideration. The circumstances attending 
the latter source of loss will be considered 
further on, as this does not affect the ques- 
tion of how much of the total rainfall may 
be made available. 
The question how much water will be 
evaporated at any moment from the surface 
of land is one involved in considerable diffi- 
culty ; and so many disturbing elements 
enter into the solution of the problem, that 
its accurate determination may beregarded 15 
as hardly possible of attainment. The hy- 
grometric state of the ground’s surface, the 
aspect of the sky, the amount of wind, and 
the temperature, will all, in their degree, 
exercise a sensible influence on the amount 
of water that the ground will give off from 
its surface; so that, in fact, it is doubtful 
whether any reliable and philosophically 
correct conclusions can be arrived at. The 
resultant facts from such experiments as 
have been carefully conducted afford, after 
all, the only data for the engineer to arrive 
at any general conclusion by; and for form- 
ing a rough estimate for the probable avail- 
able rainfall of a district, the following 
proportions of available actual rainfall may 
be accepted as furnishing general data ; but 
they are not meant to obviate the necessity 
of a careful and specific examination of the 
circumstances likely to affect the design of 
any particular work : 
Steep surfaces of granite, gneiss, and slate 100 
Moorland and hill pasture 60 to 80 
Flat cultivated country 40 to 50 
Chalk 0 to 0 
In order to arrive at more specific, and 
truly reliable results, the engineer will have 16 
to make a series of accurate observations 
on the discharge of the stream or streams 
that carry away the rainfall of a district ; 
and by doing so, and at the same time 
comparing the result with the amount of 
rain registered by the gauges—which 
should also, of course, be kept with accura- 
cy in the locality under examination—an 
approximately true estimate of the avail- 
able rainfall will be arrived at. 
If there is time in the preparation of a 
project to make the necessary examination 
of a district, it is evident that the results 
will speak for themselves ; and there will 
be no necessity to enter into abstract specu- 
lations concerning the theory of the influ- 
ences affecting loss by either evaporation or 
absorption. 
In proportioning the size of a storage 
reservoir to the area of the catchment bas- 
in, the engineer will, of course, in the first 
instance be guided by the requirements of 
the work. The object of the undertaking 
may be any one of the following : 
To husband a scanty rainfall. 
To check the injurious effect upon the 
country by floods. 17 
To add to the discharge of a stream, by 
preventing the escape of the flood waters. 
The amount of storage will always be 
part of an engineer’s data in designing 
works. It will either be his object to store 
the whole of the water that the drainage 
area will afford, which will be the case in 
impounding water for irrigation, for exam- 
ple ; or a certain fixed demand, governed 
by the want of a town or other require- 
ments, will determine the amount of the 
rainfall that it will be necessary to retain 
for supply. In England the demand for 
water supply may be reckoned at from 150 
to 180 days, depending on the amount and 
the constancy of the rainfall; as a rule, the 
six months’ supply will be the safest to 
adopt. The following Table, extracted 
from Mr. Beardmore’s work, shows the pro- 
portions that have been observed in design- 
ing some of the best constructed reservoirs. 
(See Table A.) 
From this it appears that the proportion 
between the amount stored and the total 
rainfall varies between one-half and one- 
fouith. 18 
Table A. 
Locality. 
Height 
above Sea. 
Drainage Area. 
ft. ft. 
sq. m. 
Bann Reservoirs, 1837-38... 
400 to 2800 
5.15 
Greenock, 1827-28, fiat moor 
512 to 1000 
7 88 
Bute, 1826 
200 to 350 
7 80 
Glen corse, Pentland Hills .. 
734 to 1600 
6.00 
Belmont, 1843, moorland... 
850 to 1600 
2.81 
“ 1844, “ 
“ 1845' “ 
“ 1846' “ 
Rivington Pike, 1847 
800 to 1545 
16.25 
500 to 1800 
Turton and Entwistle, 1836 
500 to 1300 
3.18 
“ “ 1837 
Bolton Watenvork® 
800 to 1600 
.80 
Ashton 1 ‘ 1844.... 
800 
.59 19 
Table A —Continued. 
576.7 
548.2 
100 2 
40.7 
K) |_* k-1 
foP 
OHMtCOOOCJtO „ 
O W M GO O O 03 05 P 
Total Discharge for the 
Year. 
181.3 
172.3 
125.2 
65 5 
MMMMWMHMW O 
-i • 
05 C5 M C5 C O' O 
. • 
Discharge per Square 
Mile. 
ptviCDMv|C0OWM05OW05M00 g* 
O'MOOOOiOMtOW^WOOO 
Representing Rainfall 
per Ann rm. 
• 
© • X 05 to O’ w» CO OI O CO M c?« o t>0 S3 
O • WtOWOiC'OOOO^O^CO 
Registered Rainfall per 
Annum. 
31.43 
25.6 
21.0 
• • • • o 
• • • • • 
to • • • to • CO On M Mj 
© * • • 05 • 00 C5 3. P 
C5 • • • 0005* OO 
• • • 05 • 63 
Reservoir Room per 
Square Mile. 
1-J • \M 
1 1 • CC\ 
—1 09 
• • • 03 • 
SC: : : g: 
Proportion of Storage to 
available Rainfall. 20 
The rule suggested by Professor Ran- 
kine “ for estimating the available capacity 
required in a store reservoir, that founded 
upon taking into account the supply as well 
as the demand,” is probably the best that 
can be adopted in designing waterworks for 
the supply of a town; “for example, 180 
days of the excess of the daily demand 
above the least daily supply, as ascertained 
by gauging and computation in the manner 
above described.” In order that a reser- 
voir of the capacity “ prescribed by the 
preceding rule may be efficient, it is essen- 
tial that the least available annual rainfall 
of the gathering grounds should be suffi- 
cient to supply a year’s demand for water.” 
In calculating the capacity of a storage re- 
servoir, the consideration of the surface 
evaporation must not be disregarded, espe- 
cially when the works are designed for 
tropical or very dry climates. The amount 
of loss will in some cases be very consider- 
able, for whatever depth of water be assum- 
ed to pass away into the air, it must be re- 
garded as extending over the whole surface 
of the reservoir ; or, in fact, the cubic quan- 21 
tity will be equal to the product of the 
depth evaporated away and the mean sur- 
face area of the reservoir as the water rises 
or falls throughout the year. Some have 
gone the length of asserting that the amount 
of evaporation from the surface of large and 
deep bodies of water is probably nothing at 
all, or, at any rate, not worthy of considera- 
tion ; whilst others assume a much larger 
amount of loss than appears to be support- 
ed by observation. The following extract 
from the article “Physical Geography,” 
published by the Society for Promoting 
Useful Knowledge, expresses intelligibly 
the conditions that tend to promote evapora- 
tion : 
“ Other things being equal, evaporation 
is the more abundant the greater the 
warmth of the air above that of the eva- 
porating body, and least of all when their 
temperature is the same. Neither does 
much take place whenever the atmosphere 
is more than 15 deg. colder than the sur- 
face upon which it acts. Winds powerfully 
promote evaporation, because they bring the 22 
air into continual as well as into closer and 
more violent contact with the surface acted 
upon, and also, in the case of liquids, in- 
crease by the agitation which they occasion, 
the number of points of contact between the 
atmosphere and the liquid. 
“In the temperate zone, with a mean 
temperature of deg., the annual evap- 
oration has been found to be between 86 
in. and 37 in. At Cumana, on the coast of 
South America (N. lat'. with a mean 
temperature of 81.86 deg., it was ascertain- 
ed to be more than 100 in. in the course of 
the year; at Guadaloupe, in the West Indies, 
it has been observed to amount to 97 in. 
The degree of evaporation very much de- 
pends upon the difference between the 
quantity of vapor which the surrounding 
air is able to contain when saturated and 
the quantity which it actually contains. M. 
Humboldt found that in the torrid zone the 
quantity of vapor contained in the air is 
much nearer to the point of saturation than 
in the temperate zone. The evaporation 
within the tropics, and in hot weather in 
temperate zones, is on this account less 23 
than might have been supposed from the 
increase of temperature.” 
Thus it appears that evaporation, under 
highly favorable conditions, may take place 
to the extent of 9 ft. in depth—an allow- 
ance that will demand careful consideration 
in designing storage works. In India, 
where from the extreme dryness of the at- 
mosphere the evaporation is found to be 
considerable, the usual allowance made by 
engineers for the evaporation from the sur- 
face of storage reservoirs is at the rate of 
| in. of depth per diem for eight months in 
the year. Regarding the results that have 
been arrived at in Bombay, this allowance 
would appear to be about double what is 
necessary, for the observations extending 
over five years give a mean daily evapora- 
tion of less than \ in. In Bombay, how- 
ever, the atmosphere is much more humid 
than that experienced on the great table- 
land of the Deccan ; and in Madras, where 
reservoirs are the specialty, it is probable 
that the actual loss is not far from being a 
mean between the two fractions. In Great 
Britain the mean daily evaporation is found 
to average less than the tenth of an inch. 24 
In estimating the quantity of storage 
water that will result from the drainage of 
any particular district, it will be essential 
to consider carefully the geological disposi- 
tion of the strata characterizing the locality 
in which it is contemplated to establish the 
works. This, although a matter that may 
influence the effectiveness of an undertaking 
to the extent of success or failure, will ap- 
pear to the purely practical man to imply a 
degree of refinement that is uncalled for. 
There will be no difficulty, however, in 
showing that the geological conformation 
of a district may be such as, on the one 
hand, to materially contribute to the effi- 
ciency of a storage reservoir, or on the oth- 
er to prove so defective that no engineering 
skill or pecuniary outlay could remedy it. 
A condition of geological structure perhaps 
the most favorable that could be imagined 
is that shown in Fig. 1. This diagram 
represents a geological section taken at 
right angles, or nearly so, to the axis of the 
valley that it is proposed to convert to the 
purpose of storage. This somewhat peculiar 
structure is what is geologically termed syn- SECTION ACROSS SYNCLINAL AXIS. 
Fig. 1. 26 
clinal, the beds inclining away from the 
axis of the valley, and is the result of an 
upheaving force having taken place under- 
neath the points of greatest elevation. Sub- 
sequent to the upheaval and consequent 
displacement of the strata, the process of 
denudation has taken place, cutting the up- 
per beds, and leaving the outcrop exposed, 
not only inside the basin, but in the adjoin- 
ing valleys at 0 and 0. Now, it is evident 
that if the highest ridges bounding the val- 
ley be taken to mark the line of water- 
shed, and therefore limiting the area of the 
catchment basin, it is possible that the esti- 
mate of the amount of supply may be found 
far short of what the district will yield. A 
certain proportion of the rain falling upon 
the outcrop at the points 0 0 will be ab- 
sorbed by such of the strata as are porous, 
and the water, percolating through the bed- 
ding, till an impervious stratum is met 
with, will find its way down the course of 
the stratification, till it ultimately reaches 
the reservoir in the form of springs, and 
contributes more or less to the maintenance 
of the supply. The converse of this condi- SECT!OX ACROSS ANTICLINAL AXIS. 
Pig. 2. 28 
tion of things will be readily understood by 
reference to Fig. 2. It also represents a 
section taken directly across the valley of 
the proposed reservoir. Here the strata of 
the earth’s crust incline against each other 
consequent upon some disturbing force 
having taken place to elevate them, and 
are said to be anticlinal to the axis of the 
valley. In order to account for the forma- 
tion of a valley on the summit of the ridge, 
that at first was thrown up, it is to be un- 
derstood that the upper beds suffered frac- 
ture in the process of upheaval, and subse- 
quently were exposed to denudation. These 
valleys of elevation are evidently not to be 
desired as situations for the establishment 
of storage reservoirs. The area of the 
gathering grounds will be much more lim- 
ited than the extent of the watershed would 
appear to indicate ; and cannot safely be 
relied upon to give an estimate of the quan- 
tity of water that the valley will afford. A 
certain amount of water will undoubtedly 
pass over the surface in times of heavy and 
continued rain, before it can be absorbed ; 
but there is no doubt that of all the water 29 
absorbed by the ground, by far the greater 
portion will follow the inclination of the 
strata, and come out as springs in the ad- 
joining valleys. 
Fig. 3 shows a geological section that 
combines in it favorable and unfavorable 
conditions for the storage of water. On one 
side the outcrops of the strata are found to 
extend beyond the highest point of water- 
shed line, whilst on the other side the strata 
incline away, producing such a condition 
as would favor the escape from the valley 
of the water absorbed. 
Certain rules are in general use for esti" 
mating the quantity of the total rainfall 
that will be lost by absorption and evapo- 
ration, with a view to determining the 
proper proportion to be observed between 
the reservoir and the area of the catchment 
basin. Two-thirds of the whole fall is 
sometimes taken to represent the loss that 
may be expected from the drainage of any 
district, in general terms, one-third being 
assumed as the amount that may actual- 
ly be intercepted for utilization. Some au- 
thors leave a much smaller margin, and VALLEY OF DENUDATION. 
Fig. 3. 31 
state that fully two-thirds of the total rain- 
fall may fairly be taken as available for 
storage. This is a large discrepancy when 
the application of the rules is taken to be 
general; but when the statements are ap- 
plied to separate districts and different 
countries, there is nothing irreconcilable in 
them. General rules are undoubtedly of 
much value if they be received with quali- 
fication, and are not adopted as of absolute- 
ly universal application. They cannot, 
however, with safety be substituted for 
specific investigations, when so much de- 
pends on starting with accurate data. 
RESERVOIR SITES. 
The special requirements of each partic- 
ular case will, as a general rule, go far 
towards determining the selection of a site 
for the establishment of storage works. 
Assuming, however, that there is a consid- 
erable extent of country situated advanta- 
geously in relative position to the locality 
at which it is proposed to utilize the water, 
and that there is a choice of ground, the 
point to be considered chiefly will be the 32 
nat ral lie of the country. To throw an 
embankment across a valley at any point 
without due regard to the configuration of 
the ground would most probably result in 
an expensive and ill-designed scheme ; 
for under such circumstances the cost of the 
dam would bear a very large proportion to 
the quantity of water stored. It will rarely 
happen that, in the examination of the re- 
sources of any particular piece of country, 
some special features will not present them- 
selves, favorable to the situation of storage 
works. The most advantageous disposition 
of the ground will be when two spurs of 
high land approach each other, forming a 
narrow outlet for the stream, and leaving a 
wide space above above them in the valley 
for storage. Such a configuration is not 
uncommonly met with at the junction of 
two streams, as shown in Fig 4. This is 
merely a sketch from memory, by the 
author, of a reservoir that he designed in 
India for purposes of irrigation; and it will 
be evident that the disposition of the 
ground was singularly favorable in every 
respect for the construction of a large IRRIGATION RESERVOIR. 
Fig. 4. 34 
storage work. The area of the reservoir, 
as designed, was about three square miles, 
and the maximum depth 90 ft., the area of 
the catchment basin being about 60 square 
miles. Such favorable situations for storage 
are of somewhat rare occurrence ; for when 
the contour of the land is what is desirable, 
it may be that the area of water-shed is 
not adequate, or possibly the geological 
condition of the ground may be unfavorable, 
or the materials for the construction of a 
sound bank are not available. In examin- 
ing large tracts of country in India, with a 
view to the establishment of irrigation re- 
servoirs, the author found that more reli- 
anco was to be placed on a careful exami- 
nation of the map in the first instance, 
than on the common plan of making per- 
sonal explorations of the country. A good 
map will show at a glance, especially if the 
hill-shading has been carefully engraved, 
the points at which the supply will be found 
sufficient to justify the undertaking; and 
will probably furnish a pretty true indica- 
tion of sites at which embankments may be 
advantageously constructed. 35 
In tropical climates, where the rainfall is 
in places very scanty, and where the land is 
not of great value, it not unfrequently hap- 
pens that such situations prove available 
for the establishment of large storage 
works as would not under any circumstan- 
ces be made available in England. These 
sites are to be found, not at the head of a 
valley, but at some considerable distance 
down the course of a stream, where, the 
general inclination of the country being 
slight, a low embankment serves to store a 
very large area of water. The apparent 
disadvantages of such a site for storage are 
the large area of land swamped and lost to 
the cultivator and to Government, and the 
great surface exposed to evaporation under 
a tropical sun and the influence of a dry 
wind. In India, the first objection is one 
of comparatively little moment, considering- 
that in those districts where irrigation is 
most required the value of land is very 
trifling. From Is. to 2s. is about an average 
rent per acre, where land is under dry 
crops; but when water is available, the 
cultivators can, with profit, afford to pay 36 
80s. per acre. It is therefore evident that, 
so far as Government is concerned, there is 
no sacrifice in the matter, but, on the con- 
trary, an unspeakable benefit is conferred 
on those landowners who hold farms below 
the reservoir ; and an ample supply of water 
is stored in the dryest seasons to mature 
those crops whose failure almost inevitably 
reduces the people to the verge of starva- 
tion. The evaporation from these lakes is, 
beyond question, a source of very consider- 
able loss, and one that admits of no possible 
abatement. Estimated as above, at about 
half an inch vertical for eight months of the 
the loss frequently amounts to one- 
third of the whole body of water stored. 
As a set-off against this and other objec- 
tions, the facilities for constructing these 
reservoirs of great extent, are considerable. 
In the first place, the embankments, being 
very low, are rapidly and cheaply construct- 
ed by native workmen ; and when finished, 
the head of water even at the deepest point 
is not sufficient to try the work to any great 
extent. Further, the greater the extent of 
the reservoir, the less inconvenience is ex- 37 
perienced from silting. The streams, owing 
to the suddenness of the rainfall, come down 
heavily charged with earth in suspension, 
the mass of which is deposited like a minia- 
ture delta at the influx of the reservoir, in- 
stead of passing on and resting near the 
embankment, as invariably occurs in reser- 
voirs of small extent. The immense con- 
sumption of water necessary to confer any 
appreciable benefit by irrigation is of itself 
the strongest argument in favor of these 
broad and shallow reservoirs ; for it is not 
possible to find in the upper part of a valley 
such sites as would store the requisite quan- 
tity of water without an embankment of 
excessive dimensions; and moreover, the 
catchment area in such situations is not 
usually sufficient to serve, with a scanty 
rainfall, for the supply of a very large re- 
servoir. It is not, of course, maintained 
that this mode of storing water is by any 
means applicable in England, for the cir- 
cumstances and requirements in each case,’ 
are wholly dissimilar. 38 
SUPPLY. 
The reservoir site being supposed every- 
thing that could be desired, as regards the 
disposition of the ground, the supply will 
next engage attention as a matter of course. 
Assuming that the gathering grounds 
are sufficiently extensive, it is presumed 
that the reservoir will be constructed to 
contain sufficient water to meet the maxi- 
mum demand, whatever that may be calcu- 
lated at; and in order to determine with 
accuracy what capacity the reservoir will 
have with different heights of embankment, 
it will be necessary to carry out certain level- 
ling operations over the ground. The least 
elaborate manner of proceeding will be to 
run a series of cross-levels through the 
valley, referring all to the same datum, and 
by comparing these levels to ascertain what 
the average depth will be for a given height 
of bank. Having decided the height of the 
water-level, the next operation will be to 
contour round the basin, and to survey the 
boundary-line. In this way may be acquir- 
ed sufficient knowledge as to the storage 
capacity, to justify the procedure with the 39 
work. When the execution of the project 
has been determined upon, it will be advis- 
able to make a more accurate survey of the 
bed of the valley, and this can best be done 
by covering the whole plan with a series of 
contour lines at a vertical distance from 
each other of about 5 ft. This kind of 
survey will be of lasting value to the engi- 
neer, for it will enable him to calculate 
what quantity of water the reservoir will 
contain at each foot of depth ; and, conse- 
quently, he will know, from a mere inspec- 
tion of the gauge in the reservoir, how 
much water he has at his disposal for 
service. 
It has been assumed that the gathering 
grounds are sufficient to maintain the re- 
quisite supply in the reservoir ; but it may 
be well to pause and inquire what extent of 
water-shed will be sufficient to furnish a 
given supply, and what method may be 
adopted for supplementing an insufficient 
drainage area. It has before been remark- 
ed that the only reliable information, when 
there is any question as to the sufficiency 
of the rainfall or the area of the catchment 40 
basin, can be derived from careful gaugings 
of the stream or streams that may be depend- 
ed upon to contribute to the supply. If the 
catchment area is very large as compared to 
the capacity of the reservoir, a mere inspec- 
tion of the map and an exploration of the 
ground will generally be conclusive as to 
the sufficiency of the supply for storage. 
Should there not be such conclusive evi- 
dence on this point, it must be determined 
by measuring the quantity of water that 
absolutely flows off the ground, at the same 
time gauging the rainfall. This latter pre- 
caution would appear unnecessary, but in 
truth it is of great value, for it will furnish, 
by comparison with the rainfall registers 
that have been kept through the same year, 
and a series of previous years, evidence as 
to the amount of available rainfall that may 
be expected during terms of comparative 
drought. If the supply of a town with 
water be the desideratum, the rule to be 
rigidly observed is that of making a mini- 
mum supply meet the maximum demand, 
and therefore it is of the highest impor- 
tance to determine beyond any doubt, what 41 
the minimum yield of a catchment basin 
will be. 
As a mode of supplementing an insuffi- 
ciently large drainage area, catchment drains 
or feeders have frequently rendered good 
service. These are cuts that are carried 
outside the water-shed line to arrest the 
surface drainage and catch the contribu- 
tions of small streams, and conduct the 
water into the reservoir. The greater the 
area enclosed between catchment drains 
and the water-shed line, the more valuable 
will they be as aids to the supply of the 
reservoir. They of course virtually extend 
the area of the catchment, adding so many 
square miles or acres to the rainfall. 
Knowing the exact requirement of a 
given population, or rather having fixed, 
after every consideration, the daily con- 
sumption of every individual that it is pro- 
posed to supply, there will be no difficulty 
whatever in proportioning the reservoir to 
the demand upon it. It is sometimes ne- 
cessary, however, to provide reservoirs for 
DESIGNING OF WOKKS. 42 
the purpose of preventing damage to the 
country by floods, and in this way the in- 
convenience and injury naturally conse- 
quent upon very sudden and excessive falls 
of rain may be to a great extent obviated. 
The duty of the reservoir will be to arrest 
all water in excess of what the stream can 
carry within its banks, and to dispose of this 
excess water, so to speak, in detail, after the 
excessive rainfall has become moderated. 
A comparison of a stream’s discharge, taken 
at highest floods, with the quantity that it 
can carry without overflowing its banks will 
show the excess that has to be retained by 
the reservoir ; and these data can only be 
arrived at through a carefully kept record 
«of the extent of the floods and of their du- 
ration. The maximum flood in this con- 
sideration will not be that which rises to 
the greatest height for a short time, but 
will be the product of the excess above 
what the river can discharge by the length 
of time the flood lasts; which will, in fact, 
be the necessary capacity of the reser- 
voir. 
The Table given on a preceding page will 43 
afford an interesting study when compared 
with the following Table, extracted in part 
from the same work. The first gives a 
comparative view of the volume of water 
gauged and stored in small hill districts, 
the last column indicating the proportion of 
the total available rainfall to the amount 
actually intercepted for storage. The fol- 
lowing Table shows the ordinary summer 
discharge of various rivers, streams, and 
springs, as unaffected by immediate rain. 
(See Table B.) 
Where the reservoir is designed to check 
the injurious effects of floods, the propor- 
tion of*the storage to the rainfall will, in 
most cases, be much smaller than what 
would be necessary to provide for the 
better part of a whole year’s fall of rain, 
for it is not probable that the maximum 
known flood can ever exceed the amount 
that it would be necessary to store for 
economic purposes. 
PROPORTION'S OP BANK. 
The proper proportion to be given to an 
embankment for the support of water is a 44 
Table B. 
Rivers. 
Height 
above Sea. 
Thames at Staines, chalk, greensand, 
Oxford clay, oolites, etc 
Severn at Stonebench, Silurian 
Loddon (February, 1850), greensand. 
Nenc, at Peterborough, oolites, 
Oxford clay and lias 
Mimram, at Panshanger, chalk.... 
Lee, at Lee Bridge, chalk (Rennie, 
April, 1796) .. 
Wan die, below Carshalton, chalk. .. 
Medway, dryest seasons (Rennie, 
Valley Hill, 
ft. ft. 
40 to 700 
400 to 2600 
110 to 700 
10 to 600 
200 to 500 
30 to 600 
70 to 350 
Ditto, ordinary summer run(Rennie, 
1787) 
Verulam, at Bushey Hall, chalk.... 
Gade, at H unton Bridge, chalk 
Plym, at Sheepstor, granite 
Woodhead Tunnel, millstone, grit.. 
Glencorse Bum 
150 to 500 
150 to 500 
800 to 1500 
1000 
750 to 1600 45 
Table B. — Continued. 
C5 
© 
mL. 
3086 
3900 
221.8 
620.0 
50.0 
570 0 
41.0 
481.5 
481.5 
120.8 
69 5 
7.6 
Drainage Area. 
oo a> n 
to j-*jo jo jw ooj3> *-i P 
m t-1 'to "oo oo to'o om o h hk 
03 05000W O O 00 OO OM© Sr? 
O © O O O O CO OO OO g*# 
Total Discharge. 
21 6 
c. ft. 
per min. 
12.98 
8.49 
13.53 
8.45 
2.4 
15.58 
43.9 
4 59 
5 23 
14.9 
36.2 
71.4 
Discharge per Sq. Mile. 
CO 
in. 
2.93 
1.98 
3.01 
1.88 
5.5 
3 53 
9.93 
1.04 
2.19 
3 37 
8 19 
15.10 
Representing Rainfall 
per Annum. 
Co • • • . to- toto to • tO B* 
© O* • • • • 003 P 
• • • © • C5H* • Ox 
Total average Rainfall 
per Annum. 46 
question that appears to admit of a good 
deal of difference of opinion, some designers 
taking one view, some another, of the pro- 
per theory that is to determine the dimen- 
sions of a bank. Some few, with whom 
the author cannot agree on this point, 
maiutain that a bank ought to be designed 
with strict reference to its theoretical power 
of resisting hydrostatic pressure, or the 
effort of the water to displace it. Regarding 
the question in its abstract form, it will be 
evident that any structure intended to sus- 
tain the pressure of water may be supposed 
to fail in one of two ways—either, in the 
first place, by yielding to the horizontal 
pressure of the water and overturning, or 
by progressive motion, i. e. sliding on its 
base. In considering the first theory, that 
of resistance to overturning, the easiest 
method of examining the question will be 
to take a simple example of a vertical 
rectangular wall, and ascertain what power 
it exercises to resist the pressure of water. 
The pressure of water upon any plane 
surface immersed is known to be equal to 
the area of that surface, multiplied by the 47 
depth of its centre of gravity below the 
level of the water and by the weight of a 
unit of water. Generally speaking, the 
unit adopted in calculations is a foot; and 
the unit of water being taken at a cubic 
foot, weighing 62.5 lbs., the resulting pro- 
duct from the multiplication of the three 
quantities will give the pressure in pounds 
on the surface immersed. Let it be sup- 
Fig. 5. 
posed, for simplicity, that water to the 
depth of 10 ft. has to be sustained by a 
vertical rectangular wall, as in Fig. 5. It 
is usual to take but 1 ft. length of the 48 
wall for the calculation, though it will not 
affect the result whether 1 ft. or 100 ft. 
he the length assumed. We then have 
the surface under pressure = 10 sq. ft., the 
depth of the centre of gravity = 5 ft., and 
the weight of a cubic foot = 62.5 lbs., the 
product of which quantities gives us 3,125 
lbs. pressure on 1 ft. length of the wall. But 
this pressure is not the whole of the force 
that the wall has to resist; the leverage 
that it exerts must also be taken into 
account. In the example under consider- 
ation—viz. that of a vertical plane with one 
of its sides coinciding with the surface of 
the water, as in Fig. 5—the whole of the 
pressure is so distributed as to be equal to 
a single force acting at a point one-third of 
the depth from the bottom. Thus, the 
total force to be resisted by the wall is 
3125 X 3.33 = 10,406, which is the moment 
tending to overturn the wall. 
It is evident that a certain weight of the 
wall must be opposed to this overturning 
force; and as the height of the wall and 
the length are determined quantities, the 
thickness alone remains for adjustment. 49 
But as a rectangular wall in upsetting is 
considered to turn upon a single point, F, 
in the Figure—viz. the outer line of the 
wall—there will be a certain amount of 
leverage to assist the wall in resisting 
the pressure of the water. This leverage 
is the horizontal distance of the centre of 
gravity of the wall from the turning point, 
F, and when the structure is rectangular 
and vertical, it is equal to half the thick- 
ness. The amount of the wall’s resistance 
will then be equal to the number of cubic 
feet in one foot of its length multiplied by 
the weight of a single cube foot of masonry 
and by half the thickness of the wall. 
Taking w — weight of a cubic foot of water 
= 62.5 lbs., w 1= weight of a cubic foot 
of brickwork, say 112 lbs., x — thickness 
of the wall, and h — the height, the con- 
ditions of simple stability will be fulfilled 
when 
wlX7iX*x| — w X h X | (1) 
w'hx2 wh3 
2 ~6~ ’ 
and solving for x, we get 50 
[whl 0 
* = V SF <*> 
the thickness of the wall — 4 ft. 4 in. 
A simple example has been selected for 
illustration; but of course a rectangular 
section of wall would not be found gene- 
rally applicable in practice, nor would it be 
convenient to limit the dimensions of a 
retaining wall of whatever kind to the 
minimum that would sustain the pressure. 
If this principle of calculation be applied to 
ascertain the stability of a bank of earth 
with long slopes of 2 £ or 3 to 1, it can 
easily be shown that in every case the 
resistance of the bank to overturning is 
greatly in excess of the horizontal leverage 
exercised by the water sustained. 
The only theory, then, in any degree 
tenable, is that assuming a bank in yield- 
ing to the pressure of water to slide on its 
base. In order to conceive how this can 
apply, it is necessary to assume the em- 
bankment to be a rigid body resting, for a 
given length of its section, on a horizontal 
plane ; and without any adhesion, or a very 
small fraction, existing between the sur- 51 
faces pressed. The amount of the friction, 
however, is just the point upon which the 
whole matter hinges, and until it has been 
ascertained that the surfaces of earth that 
are carefully incorporated with one another 
have any such thing as a co-efficient of 
friction, it is idle to to pursue the investiga- 
tion by a mathematical mode of reasoning. 
The conditions of stability will be satisfied 
when the horizontal component of the 
water’s pressure against the bank will 
equal the weight of the bank, plus the 
vertical pressure exercised by the water to 
hold it down and multiplied by the co- 
efficient of friction; but nothing is known 
of this co-efficient, and consequently the 
equation remains incapable of solution. 
As a matter of fact, embankments do not 
slide bodily forward on their base when 
they fail, but give way from other causes 
than mathematical reasoning can supply. 
Landslips, it is true, to some extent support 
the principle that maintains the sliding of 
embankments ; but, here, the circumstances 
are widely different. Landslips either take 
place when a mass of earth rests upon an 52 
inclined surface of rock, with an ample 
supply of water to lubricate the surfaces in 
contact, or else they are the result of cutting 
or embanking earth to a higher slope than 
the material will stand at; the infiltration 
of water also in this case is the chief agent 
in producing the effect, acting as a lubricant, 
and causing the earth to assume its natural 
slope. In each case the surface of separa- 
tion is an inclined plane, an element that 
does not enter into the question of the 
stability of embankments, by either of the 
modes of reasoning above referred to. The 
principles that direct the design of embank- 
ments to retain water are not those that 
apply to the calculation of the forces to be 
resisted or the means to overcome them, 
any more than breakwaters and harbor 
walls can be designed on mathematical 
principles. The whole question naturally 
turns on what slope the material composing 
the bank will stand at. If earth could be 
got to remain at a slope of 1 to 1, even 
though the embankment had no thickness 
whatever at top, it would be amply sufficient 
in weight to uphold the water in a reser- 53 
voir. This, however, cannot be accomplished 
without the assistance of retaining walls, 
which would be found in most cases much 
more expensive than the additional earth 
required to increase the slope to the angle 
of stability; and therefore the section is 
so disposed that the earth shall stand both 
inside and outside the reservoir at such a 
slope as will be under all circumstances 
permanent. These slopes have been deter- 
mined by long practice and by success and 
failure in pre-existing instances—that is to 
say, the limits have been laid down, for it 
is not to be assumed that all descriptions of 
earth will fall to exactly the same slope 
when exposed to the constant action of water 
or weather. Earth when subjected to the 
contact of water almost invariably loses a 
certain amount of its stability, and there- 
fore it is usual to give the inner side of an 
embankment a longer slope than the out- 
side. In most of the best existing examples 
the inside slope of the bank is either 3 to 1 
or 2i- to 1, and it is rare to meet any de- 
parture from this rule. The outside slope 
may be designed at from 2 to 1 to 3 to 1, 54 
depending upon the character of the material, 
its power of withstanding the erosive action 
of the air, and the means used to protect 
the surface from being washed off or from 
crumbling away. In designing embank- 
ments, the impermeability of the earth is a 
matter that cannot be relied upon. There 
are, it is true, innumerable embankments 
now standing that have never allowed the 
escape of a drop of water from the 
reservoir, although no special precaution 
was taken to make them water-tight. Of 
these India abounds with examples, the 
introduction of a puddle wall being in the 
older embankments of very exceptional 
occurrence. The earth was merely dug out 
close at hand, and carried by the work- 
people in baskets on their heads to where 
it was deposited, without any regard to the 
mode of disposing the material. The 
author has had occasion to construct a 
considerable length of levee, or embank- 
ment, on this simple plan for the protection 
of the country from the flooding of a river; 
and although, so far as he is aware, no 
flood has yet taken place to test the work, 55 
he has, from the study of existing examples, 
entire confidence in the result. The earth, 
so far as practicable, was disposed in layers, 
and before each was completed it was 
thoroughly consolidated by the tread of 
the workmen. It is not suggested that the 
puddle wall should be dispensed with in 
designing embankments, for the additional 
degree of safety, in most instances, will 
more than compensate for the extra expense 
it entails; but, in low embankments made 
of good retentive clay, the precaution of 
puddling is by no means a necessity. 
In most of the best examples of embank- 
ments in England, the practice adopted has 
been to carry up the earthwork in layers of 
2 or 3 ft. in thickness, disposed in the man- 
ner shown in Figs. 6 and 7, and at the 
same time to construct in the centre of the 
bank a wall of well-puddled clay, the foun- 
dation of which is carried down for what- 
ever depth may be necessary in order to 
reach an impermeable bed of earth or rock. 
It is not in all situations possible to pro- 
cure earth exactly suitable and in sufficient 
quantity for the construction of an embank- 56 
Fig. G.—No. 1. 57 
RESERVOIR EMBANKMENT. 
No. 2. 58 
ment, and consequently it is usual and ad- 
visable to dispose the best part of the ma- 
terial—that is, the most retentive of water 
—in juxtaposition to the puddle wall, as 
indicated in Fig. 6. In this example, the 
selected material is disposed equally at ei- 
ther side of the puddle; but, as its func- 
tion is to withstand the admission of water, 
it would probably be more consistent, though 
less in accordance with practice, to place all 
the selected material on the inner side. 
The practice of excavating the earth for an 
embankment from the inside of the reser- 
voir is one that should not be followed 
without caution. Removing so large a 
mass of material would, no doubt, give a 
considerable increase of storage room; but 
sometimes the bed of a reservoir is covered 
by a layer of impervious clay that is of im- 
mense value, and if this be cut through 
or removed, it is quite possible that a bed 
of porous material may be met with suffi- 
cient to allow the escape of water when it 
comes to be admitted. In specifying for 
the dimensions of the puddle wall, a sound 
rule for adoption is, that it shall have a 59 
SECTION OF EMBANKMENT—BIDDEFORD WATER-WORKS. 
Fig. 7. 60 
thickness of 10 ft. at the top water-line and 
increase in thickness to the surface of the 
ground at the rate of 1 in. on each side for 
every foot of height. Before any excava- 
tion is commenced, it will be essential to 
make a sufficient number of borings to as- 
certain the nature of the soil beneath the 
surface. 
It may here be mentioned that profes- 
sional men are not apparently agreed as to 
the principles to be kept in view in con- 
structing reservoir embankments ; and this 
want of concurrence never was more appa- 
rent than in the discussion that followed 
the destruction of the Dale Dyke reservoir, 
near Sheffield. Fig. 8 shows a plan of the 
embankment site after the catastrophe. 
The bank was 95 ft. high, with slopes of 2| 
to 1, and a top width of 12 ft. The puddle 
wall was 16 ft. in width at the ground-line, 
and tapered to 4 ft. at the top of the bank. 
This embankment, with the exception of 
the puddle wall, was composed of rubble 
stone and shale; an additional price hav- 
ing been given by the engineers to insure 
the use of the former material; which 61 
SHEFFIELD RESERVOIR. 
Fig. 8. 62 
proves, at any rate, that this mode of con- 
struction was adopted on principle and not 
through ignorance or mistake. From the 
evidence given by the engineers of the com- 
pany, it appears that it was, in their opin- 
ion, desirable that the inner part of the 
embankment should be permeable to water, 
because earth was much more likely to sub- 
side and slip than an open and less yielding 
material like stone. This mode of construc- 
tion implies that the puddle shall be fully 
sufficient of itself to resist the passage of 
water, and, that there is no necessity to re- 
lieve it of any part of the pressure against 
it. Of course, if a bank be composed of 
open work, every point in the face of the 
puddle is exposed to the full and direct hy- 
drostatic pressure ; and if at any point there 
is the smallest fissure or imperfection, the 
water has full power against it, and will, to 
a certainty, take advantage of such point to 
breach the dam. The assumptipn, then, of 
the constructors of this and the Agden res- 
ervoir evidently was that a puddle wall of 
some 25,000 sq. ft. of area was to be con- 
structed without an imperfection of any kind, 63 
or a single weak point in the whole sur- 
face. 
The obvious reason for employing pud- 
dle at all, in embankments, is to thorough- 
ly close up any imperfection that may occur 
in the earthwork; it is in fact merely an 
accessory, and cannot be relied upon of it- 
self to secure the embankment against de- 
struction. If an embankment be construct- 
ed of good sound earthwork, properly exe- 
cuted, it is highly probable that the water 
may never penetrate half way through to 
the puddle wall, and probably, in the ma- 
jority of examples, has not done so. Earth- 
work, however, is not always executed 
without imperfection; some decomposable 
material may be introduced, which, in 
course of time, dissolves, leaving a fissure 
one part may be at first less consolidated 
than another, and, subsiding, lead to imper- 
fection ; or an embankment, be it ever so 
well constructed, may be burrowed through 
by moles, rats, and other vermin. It is to 
meet the first two of these sources of imper- 
fection that puddle is used; and if, by such 
fissures as may occur in ordinary earth- 64 
work, water is admitted as far as the pud- 
dle wall, it can only exercise pressure 
against it at a few points, the puddle and 
earth being, in good work, so bonded and 
incorporated with each other that there is 
no space left for the water to occupy and 
press against the surface. Most who have 
read the account of the disaster that occur- 
red in March, 1864, at Sheffield, will recol- 
lect how singularly conflicting the profes- 
sional evidence on that occasion was. Some 
of our first engineers were ranged against 
each other in order to satisfy the public as 
to whether the failure of the embankment 
was attributable to bad engineering or to a 
landslip; and although the impression 
finally remained on the public mind that 
“ there was not that engineering skill and 
attention to the construction of the works 
that their magnitude and importance de- 
manded,” the engineers were fairly divided 
in opinion as to the cause of the disaster. 
One section pronounced, without qualifica- 
tion, that the embankment gave way in 
consequence of a landslip, and entirely 
ignored the fact of the embankment being 65 
defectively constructed; whist the other 
gentlemen gave their verdict dead against 
the company, and their mode of construct- 
ing water-tight banks. The two diagrams, 
Nos. 6 and 7, may he taken as indicating 
the system of constructing embankments 
most generally approved of. The puddle, 
as will be observed, is carried up to the 
natural surface of the ground without any 
batter, and from that point slopes on each 
side to the top of the bank ; on either side 
of the puddle is disposed, in concave layers, 
the most sound aud retentive part of the 
material, and outside of all comes the ordi- 
nary earthwork. 
As a security against the eroding action 
of the water, and also against the inroads 
of vermin, the most desirable, as well as the 
most usual practice, is to pitch the whole of 
the inner face of an embankment with 
stone, carefully laid by hand. Neglect of 
this precaution has led to the destruction of 
many embankments in other respects se- 
curely constructed, and even when ample 
height of bank above the surface of highest 
water was provided. In all ordinarily in- 66 
clement weather the disturbance of the 
surface of a reservoir amounts to no more 
than a mere ripple; but when the surface 
is of large extent, and a severe storm blow- 
ing, the waves produced are such as to 
cause reasonable apprehension, and, in fact, 
have, before now, overtopped the bank and 
cut it down, till the water flowed over and 
caused the destruction of the work. In 
most cases, it will be necessary to leave 
about 5 ft. between the level of the highest 
water and the top of the embankment, and 
never less than 3 ft. 
A mode of construction not very gener- 
ally used, but apparently consistent with 
reason, is that shown in Fig. 7, the em- 
bankment for the Bideford Waterworks. 
It consists in covering the whole of the 
inner face with a layer of puddle, with some- 
times a layer of peat outside it. On some 
occasions it has been thought desirable to 
mix with the puddle a quantity of small 
stones or furnace cinders, by way of ob- 
struction to vermin—a precaution that is by 
no means unnecessary. As an instance in 
point, the author is reminded of a masonry 67 
dam in India that had to be pointed every 
year regularly, because the fresh-water 
crabs in the reservoir found it convenient 
and promotive of their development of shell 
to appropriate the mortar to their personal 
use. The joints were cleaned out as effec- 
tually at the end of each monsoon as if the 
work had been done to order. 
The preparation of the foundation for an 
embankment is a matter requiring some 
care. The soil, consisting of grass, roots, 
etc., and other matters of a decomposable 
nature, should be carefully removed over 
the whole surface to be covered by the 
bank, and if any porous material, such as 
sand or gravel, be present, it must be re- 
moved, until a compact and water-tight bed 
is arrived at. The bank must, in fact, be 
in contact with some sound and reliable 
material that will not admit the passage of 
water. 
Under this heading may he considered: 
The whole apparatus for allowing the 
water to escape, including the pipes, the 
valve tower, and the culvert. 
APPENDAGES OF RESERVOIRS. 68 
The waste sluices. 
The waste weir or by-wash. 
The most economical mode of discharging 
water from a reservoir is through a single 
pipe passing either through the embank- 
ment or immediately under it; but this 
plan cannot, under any circumstances, be 
recommended, though it is some times found 
in existing examples. It is open to several 
grave objections, the principal of which, 
perhaps, is that the failure of a joint under 
the embankment pressure, or 
from whatever cause, will probably produce 
the destruction of the embankment, or at 
any rate, entail a serious interruption to the 
supply, by the reservoir having to be 
emptied in order to repair the pipe. Buried 
in or under an embankment, a pipe is com- 
pletely out of reach and out of view, and 
may be in a very defective state without its 
being possible to detect the imperfection. 
In order to secure the satisfactory work- 
ing of a reservoir as a source of constant 
supply, it is essential that the outlet pipes, 
valves, and all other appendages for con- 
trolling and regulating the escape of the 69 
•water, should be accessible for inspection 
and repair. The usual mode of accom- 
plishing this is to carry the pipes out 
through a culvert of brick or masonry of 
sufficient dimensions to admit a man. This 
culvert communicates with the valve tower, 
as shown in Figs. 6 and 7, so that there is 
a complete communication between the out- 
side of the reservoir and the inside. When 
unavoidable, the culvert is carried straight 
under the embankment in the natural 
ground ; but the safest and most generally 
approved mode of construction is to bring 
the culvert round the end of the embank- 
ment, where it will be out of reach of in- 
jury from unequal settlement ; a source of 
no small apprehension when either culvert 
or pipes alone are carried under the bank. 
Where possible, it is an excellent plan to 
run a heading through the solid ground, 
lining it with brickwork and puddling it, 
forming a tunnel entirely independent of 
the embankment. The principal objection 
to carrying either the culvert or* pipes 
through or under the bank is their liability 
to fracture from the unequal settlement of 70 
the earthwork. It would appear that their 
liability to damage cannot with certainty be 
insured by any reasonable depth of excava- 
tion, and is, therefore, generally disapproved 
of by the best authorities. 
In the best constructions the culvert is 
situated half way or two-thirds up the em- 
bankment, and in such case the outlet pipes 
for drawing off the water in the reservoir 
act as syphons when the water surface has 
fallen below the culvert. Fig. 6 shows a 
p’an, as well as a cross section, of a reser- 
voir dam designed for general application 
by Mr. Rawlinson. Here the bottom of the 
culvert is about 25 ft. above where the in- 
ner slope of the embankment intersects the 
ground at the lowest point. The syphon 
pipe is also shown passing through the 
culvert; the horizontal culvert is connected 
with a shaft inside the embankment, in 
which are placed the valves for leading off 
the supply from the reservoir. The valves 
are made to be closed on the inside by 
valve spindles and screws, and the inlet 
pipes are closed on the outside by plugs 
which can be applied from the top of the 71 
valve-tower. Thus the engineer has full 
command of the whole of the outlet works ; 
all the pipes and valves are easily accessible 
and under perfect control, so that the supply 
can at any time be arrested for the repair 
of any derangement that may occur, even 
to the removal and replacement of all the 
pipes. The inlet pipes are shown in this 
example, as well as in Fig. 7, fixed at 
different heights in the valve-tower, the 
object of which is to draw the supply from 
the reservoir from points near the surface. 
The outlet pipe, passing through or under 
the embankment, may be connected on the 
inside of the reservoir by a flexible joint 
with another pipe of the same diameter, to 
the upper end of which is attached a. float. 
This pipe is movable in a vertical plane, 
being controlled from lateral motion by the 
guide-posts. Such an arrangement admits 
of the water being drawn off from the sur- 
face, where it is least liable to be contami- 
nated with impurities. AVhatever arrange- 
ment be selected for drawing the supply 
off from a reservoir, the system of carrying 
the pipes, either with or without a culvert, 72 
through, or under the embankment, cannot 
be sufficiently deprecated; they are, in 
such a position, beyond the reach of inspec- 
tion, and, moreover, are very likely to induce 
leakage from the reservoir. It is usual to 
puddle carefully the culvert or pipes when 
carried under or through the bank, but, even 
with such a precaution, the water has under 
a considerable head a tendency to creep 
along the pipe, and, by soaking into the 
earthwork, may cause any one of the many 
evils that imperil and destroy embank- 
ments. 
When embankments are not of great 
height, an exceedingly cheap and simple 
mode might be adopted for drawing off the 
water. This would be by laying a syphon 
over the embankment, as was done in the 
case of the middle-level drainage in Cam- 
bridgeshire, which syphon would at the 
inner side have a flexible connection with 
another tube having a float attached, as 
above described. Such an arrangement 
would apply in principle to heights not ex- 
ceeding 30 ft., as the pressure of the atmos- 
phere would maintain no greater height. In 73 
practice, however, the syphons cannot be 
worked with success at much above 20 ft., 
for it is found that after a short time, the 
flow becomes arrested by the collection of 
air in the upper part of the syphon, and it 
becomes necessary to pump the air out con- 
stantly, to prevent it from interfering with 
the flow, as it would do if not removed. It 
would appear a simple matter, where it is 
desirable to adopt a syphon, to utilize the 
power of the water flowing out for the pur- 
pose of getting rid of the air; it might 
easily be applied, through a small wheel 
and suitable gearing, to work an air-pump 
fixed at the highest point of the syphon, 
making the whole arrangement self-acting. 
The arrangement could be successfully ap- 
plied to irrigation tanks in India, where the 
embankments are frequently less than 30 
ft. Each leg of the syphon should be pro- 
vided with a valve to retain the water, and 
when the supply was intermittent it would 
be essential to have an opening at the= 
highest point of the syphon, and some ap- 
pliance, perhaps an air-pump, for filling ik 
with water in case of leakage. 74 
To insure a constant discharge from a 
reservoir with a constantly varying head, 
several methods have been adopted; of these, 
one of the most ingenious is that used at 
the Gorbals Waterworks, near Glasgow. 
Fig. 9 represents a transverse section 
through the regulator-house, showing the 
arrangement by which the discharge is 
equalized. To the orifice of the outlet pipe, 0, 
is fitted a square-hinged flap valve of wood, 
against which presses, by a friction roller, 
a lever, B, the arms of which are bent. To 
the upper arm is attached a chain that pass- 
es over a pulley, and is connected with a 
cast-iron cylinder or float, D, that stands in 
the reservoir, E, of slightly larger diameter. 
At the side of the entrance-door of the 
building is placed another cisterfi, G, of 
cast-iron, closed at top, and communicating 
by a pipe, R R, with the vertical pipe, H, 
which is in connection with the outlet pipe, 
and passes up the slope of the embank, 
ment, to carry away any air that may ac- 
cumulate in the main. The cistern, G, is 
connected with the reservoir, E, by a pipe, 
K, which supplies water to float the cyl- 75 
Jig. 9. 76 
inder, D. Now, it is evident tliat the dis- 
charge from the reservoir will be regulated 
by the position of the lever, B, and this 
again will be controlled by the height of 
the float, D. To regulate this height the 
supply from the cistern, G, must be self- 
adjusting, or be regulated by the amount 
of water flowing away. The float, N, has 
attached to it a spindle, on which are fixed 
two double-beat valves that work in the 
vertical part of the pipe, K, one of which 
admits water from the cistern, G, into the 
cylinder, E, and the other allows the water 
to escape from the reservoir, E. Now, if 
the surface of the water upon which the 
float, N, rest8 should rise above the proper 
level, the float forces up the spindle, closing 
the supply valve from the cistern, and at 
the same time opening the lower valve. 
Thus the supply is cut off and the escape 
opened, enabling the float, D, to fall. The 
subsidence of the float closes more or less 
the flap valve, and checks the discharge, in 
consequence of which the surface of the 
water falls, and with it the float, N, which 
consequently opens the supply valve, and 77 
again admits water into the cistern, E. 
Thus an almost perfect equality between 
the consumption and the supply of water is 
preserved. It would appear that the same 
effect could be produced by connecting the 
lever directly with a float on the surface of 
the water, but such an arrangement would 
only apply when the pressure against the 
flap is trifling. 
It is essential that every reservoir should 
be provided with some means of getting rid 
of the excess of water that flows into it, and 
whether this provision be made by a waste 
weir, sluices, or waste pit, it is one that 
should not be omitted. The most advan- 
tageous position for a waste weir will 
generally be at some point remote from, 
and entirely unconnected with, the em- 
bankment, and occasionally a natural de- 
pression in the ground, as shown in Fig. 4, 
will afford remarkable facilities for the 
construction of an escape. The level of the 
crest of the waste weir with reference to 
the top of the dam will require to be care- 
fully adjusted, the minimum difference of 
level being 3 ft., and the maximum about 78 
10 ft., depending on varying circumstances. 
The height of the waste weir will, of course, 
regulate the top water level in the reservoir; 
and this must be fixed with regard to the 
probability of the embankment being over- 
topped by waves. The circumstances in- 
fluencing the height of the waves in a 
reservoir are the extent of the water surface, 
the depth, and the amount of exposure to 
nr shelter from wind, all of which will vary 
with each particualar case. Under ordinary 
circumstances, the height of the top of the 
embankment above the crest of the waste 
weir should be for 
an embankment 25 ft. deep, 4 ft. 
“ 50 ft. “ 5 ft. 
“ 75 ft. “ 6 ft. 
and for greater height of embankment the 
difference of level may be proportionately 
increased. 
When the configuration of the ground 
does not afford any facilities for the con- 
struction of a waste weir after the manner 
described, sufficient provision for the escape 
of the overflow is made through a waste 
pit. This waste pit, or tower, is generally 79 
a circular structure built over the outlet 
culvert inside the reservoir, and serves 
equally for access to the valves and for the 
escape of the flood water. With regard to 
the capacity of the waste weir or waste pit, 
whichever be adopted, it will be necessary 
to make ample provision for the discharge 
of the sudden accessions of flood water that 
reservoirs are subject to, and which so 
seriously imperil their safety. To provide 
for this there is an empirical rule amongst 
engineers that is supposed to suffice for the 
most urgent contingencies. It states that 
there shall not be less than 3 ft. of length 
of overfall for every hundred acres of 
gathering ground, but it is obvious that to 
proportion the length of the waste weir to a 
given area of country in all cases would be 
unreasonable. 
The discharge over the weir will not 
depend only upon the quantity of rain fall- 
ing on a certain area of ground, but also on 
the extent of the reservoir as compared to 
the gathering ground, and on the flat or 
precipitous character of the basin. The only 
safe mode, then, of proportioning the length 80 
of the escape will be to ascertain with 
exactness what the discharge of the stream 
or streams flowing out of the reservoir was 
during the greatest known flood, and then 
fixing upon an arbitrary depth for the 
water to flow over the weir, say 2 ft. or 3 
ft., to calculate what length of overfall will 
suffice for the discharge of the excess 
water. In India, where large waste-weir 
accomodation is essentially necessary, while 
it is equally a necessity to save every 
gallon of water that is possible, it is a 
common practice to form a temporary dam, 
of earth and sods, on the top of the waste 
weir; this serves to pond up some 3 ft. or 
4 ft. of water over the whole surface of the 
reservoir, and does not imperil the security 
of the works. In times of heavy floods the 
water rises and overtops the temporary dam, 
and no sooner does so, than the whole is 
carried away, and the water in the reservoir 
quickly subsides. 
In works designed for the supply of 
towns, it is sometimes necessary to make 
provision to arrest the entrance of flood- 
■water into the reservoir, as the streams may 81 
come down charged with large quantities of 
matter in suspension that would injure the 
purity of the water for domestic consump- 
tion. These streams may be diverted and 
carried round the margin of the tank past 
the dam, and can be admitted into the 
channel of the stream, or be utilized for 
mill power. On the Manchester Water- 
works are constructed across the mountain 
streams weirs of an ingenious design, for 
the purpose of separating the flood-waters 
from the ordinary flow. The dimensions 
are adjusted from observations of each par- 
ticular stream, so that the discharge up to 
a certain amount will take place into the 
channel for the supply of the town; but 
when the discharge increases, and the water 
becomes turbid, it has sufficient velocity to 
carry it over the opening, as shown in the 
diagram, and flows down to the compen- 
sation reservoir for the supply of mill 
power. 
In determining the dimensions of a weir 
■of this kind it is first to be ascertained 
what the mean velocity of the water flow- 
ing over will be for a given depth of water, 82 
h, above the crest. The mean velocity, v, 
will be 
v = | X 8 0241/h = 5.35 -iA. 
If the vertical height of the crest of the 
weir above the point to be overleaped by 
the cascade be called x, the distance across 
will be 
2v\/x 4 .—r 
’’=7W=*V 
Before concluding, it will be well to give 
a brief consideration to ihe causes tending 
to the failure of embankments. The fore- 
going remarks will, in suggesting the best 
mode of construction, have anticipated much 
that might be said on the subject of failures; 
but there are a few points, the recapitula- 
tion of which the importance of the subject 
demands. 
There are unfortunately on record, acci- 
dents, if they can be so called, from the 
bursting of embankments, that if estimated 
by the loss of life attending them, are as 
appalling as anything within the memory of 
man. Thousands of human lives have been 
sacrificed to ignorance and false economy, 83 
as well as in some instances to natural de- 
fects that it would have been difficult to 
foresee. 
The existence of springs on the site of an 
embankment is an undoubted cause for ap- 
prehension, and considerable care should be 
taken to carry all water from this source 
away, that it may not, as it certainly will if 
not checked, force its way between the sur- 
face of the ground and the seat of the em- 
bankment. In doing so there is every prob- 
ability that the earth of the embankment 
will be washed out by constant trickling till 
a fissure is formed of sufficient dimensions 
to render the destruction of the bank a cer- 
tainty, if the water from the reservoir 
should ever penetrate so far. As a provis- 
ion against this source of injury, all springs 
found on the site of an embankment should 
be taken up and carried away in proper 
drains sufficiently and securely puddled. 
Thus the water is confined to a single chan- 
nel, and has no tendency to soak into the 
earthwork and blow it up in endeavoring to 
escape. In embankments of all kinds the 
presence of water is a most serious evil, and 84 
one by which may be accounted for, some of 
the most extensive land slips that are on 
record. It is erroneous to assume that 
when water is the active element in pro- 
ducing disruption in an embankment or 
mass of earth of any kind, that it only acts 
as a lubricant between the surfaces in con- 
tact. The truth is, the bulk of earth is sen- 
sibly affected by the amount of moisture in 
it, as is seen in the subsidence of newly- 
formed railway banks when exposed to rain. 
If, then, a sufficient quantity of water find its 
way into the centre of a bank that has been 
put together in a comparatively dry state, it 
will rise and soak into the earth until at 
length what was a solid mass becomes 
semi-fluid, settles into a smaller space than 
it before occupied, and, as a consequence, 
will leave a vacuity above it. The inevita- 
ble result is the subsidence of the superin- 
cumbent earth; but instead of resting, as 
at first, on a resisting material, it floats, so 
to speak, on the semi-fluid mass underneath, 
and having little or no friction to overcome, 
slips away to a lower angle than it before 
stood at. Natural springs, therefore, when- 85 
ever they occur, must be dealt with care- 
fully and completely. Exactly similar 
effects to those produced by natural springs 
may result from the defective practice of 
carrying outlet pipes through or immedi- 
ately under embankments. Be the pipes 
ever so well puddled, there will be a ten- 
dency to trickling along the line of their 
direction, and assuredly if this trickle makes 
its way to the centre of the bank it will 
carry mischief with it. It is true that 
springs are occasionally found issuing from 
the foot of an embankment, without after 
several years causing any appearances 
to justify apprehension. The Doe-park 
reservoir is an example in point, and though 
at one time fears for its safety were enter- 
tained, the embankment is still standing,, 
and, so far as the author is aware, the 
spring is still trickling away. An engineer 
of eminence was called upon to report upon 
the state of the works, and gave his opinion 
that, as the spring came away without any 
earth in suspension, there was no mischief 
taking place, and that the work was in a 
safe condition. There is no doubt that em- 86 
bankments in tliis condition require to be 
narrowly watched, although the presump- 
tion may be that, having lasted for several 
years, they will continue in safety. 
The empirical and unscientific mode of 
proportioning the length of waste weirs has 
proved before now a source of danger and 
destruction to embankments, from the space 
afforded not being sufficient to discharge 
the excess water without the surface rising 
to such a height as to top the embankment. 
To avoid risk, the stream must be gauged 
with great care, and the discharge calculat- 
ed for the greatest known flood; and if 
with a given head the length of the weir be 
adjusted to discharge this amount, or a 
little in excess, there will be no risk to the 
embankment. 
Regarding finally the whole subject, the 
danger that may result from careless or 
unscientific construction, the large outlay 
entailed in the establishment of storage 
works, and the benefit that may accrue 
from them whatever their purpose may be, 
the subject cannot be undertaken on merely 
rational grounds. Its successful applica- 87 
tion will rest alone on the study of the 
question in its scientific details, and an 
ample practical experience. 
DISCUSSION. 
Mr. H. P. Stephenson said he entirely 
agreed with the author as to the impro- 
priety of carrying a pipe through the em- 
bankment of a reservoir. He would extend 
his objection to the passing of a culvert 
through the embankment. If the culvert 
were laid on the natural ground, they 
would avoid the risks pointed out by the 
author, either of the settlement from the 
joints of the pipe, or of the water creeping 
along between the material and the pipe. 
He believed that the true principle of con- 
struction for reservoirs was the placing of 
a good puddle dam in the centre, and on 
each side of this dam layers of earth well 
punned in. One reason why he should 
prefer the puddle wall in the centre was 
that there was less tendency in the puddle 
to slip in such a position than when laid on 
the slope. 
Mr. Albert Latham agreed with Mr. 88 
Stephenson in his remarks as to the pipes 
and culverts; but he thought it was an 
open question whether the puddle wall 
should be in the centre of the dam. He 
had a strong opinion that it should be on 
the face of the dam. 
Mr. Cargill said that he believed that the 
reason the puddle wall was not required in 
Indian embankments, referred to by the 
author of the paper, was that the earth 
seemed to have been thoroughly consolidat- 
ed by the continual trample of people upon 
it. That thorough consolidation was the 
great point in all puddling, and it was on 
that account that specifications were gener- 
ally so stringent as to the thickness of the 
layers of the puddle. As to the position of 
the puddle wall, he could not see the parti- 
cular value of having it in the middle of the 
dam, and he thought that a far better place 
for it would be the face, because the object 
of the puddle wall was to prevent the infil- 
tration or the escape of the water. This 
could be effected by puddling the whole 
slope right down to the permanent strata. 
The puddle wall was not required to 89 
promote the stability of the dam. The 
question of putting pipes or culverts under 
the dam required more consideration. 
It was alleged that the putting of a naked 
pipe through the dam of the Bradfield re- 
servoir was one of the causes of its bursting. 
In some very large waterworks now being 
constructed in Dublin there were two dis- 
tinct sets of main pipes, and they were laid 
in two large culverts at the bottom of the 
dam. The culverts were large enough for 
a man to walk upright in them. If the 
foundation were well looked after, there 
would be no fear of the arch or dome of the 
culvert giving way in consequence of any 
inequality of pressure above it, as, if pro- 
perly constructed, an arch would stand any 
amount of pressure short of what would 
crush the material. 
Mr. Baldwin Latham said he could not 
agree with Mr. Jacob that a dam could not 
be constructed from theoretical deductions; 
for unless regard was paid to theoretical 
considerations there might result either a 
deficiency of strength or a waste of material 
and labor. In the dam shown in the draw- 90 
ings, and designed by himself, the pipe did 
not run through, but on the outside of the 
dam, on the solid ground. It was a well 
received opinion among engineers that if 
you had a pipe or culvert running through 
an embankment, that pipe or culvert would 
be unsafe. He believed that well made 
and properly tested pipes were quite as safe 
as culverts when in the solid ground. A pipe 
was simply a small culvert made of iron 
instead of brickwork. In cases in which 
there was a tendency fur the water to creep 
along the outside of the pipe, that might be 
stopped by having projecting flanges on the 
pipe. The same creeping of water might 
take place along a culvert as along a pipe. 
With regard to the slope of a dam, the in- 
side slope should be greater than the out- 
side slope, because the greater would be 
the stability of the dam, and the water 
would have less destructive effect on the 
dam ; he had effectually prevented leakage 
by the use of socket-pipes. The square 
projection of the sockets was alway present- 
ed to the reservoir, and the pipes were laid 
in the virgin ground. It was very bad 91 
practice to lay the pipes in made ground, 
and especially through a dam. Pipes laid 
under a dam should be tested under pressure 
after being laid and before being covered 
up, so that any defective joint might be 
discovered. In cases in which he had laid 
pipes through dams, they had been so 
tested, which resulted in good and effective 
work ; but he was bound to say that, if the 
pipes had not been tested in situ the result 
would not have been satisfactory. 
Mr. Schonheyder said that Mr. Jacob had 
said that wherever springs occurred they 
should be well carried away. He (Mr. 
Schonheyder) wished lo know how a spring 
was to be prevented from diffusing through 
the earth. 
Mr. Hendry said that he had seen pipes 
which were laid through embankments, 
but had never seen one that was perfectly 
tight. It was almost impracticable to make 
it so, owing to the continuity of the puddle 
being disturbed at the point where the pipe 
passes through. 
The Chairman asked what was the 
largest diameter of pipe Mr. Hendry had 
seen used. 92 
Mr. Hendry replied that the largest was 
18 in. He had heard of several methods 
being tried, but he did not think it was 
possible to prevent leaking, more or less, 
from the reservoir along the outside of the 
pipe. He should like to be informed how 
it was possible to connect the puddle with, 
the pipe ; if the pipes be laid in the natural 
ground below the foundation of the em- 
bankment, then there is no fear of leak- 
age, provided the pipes are properly 
laid. 
Mr. Jacob, in replying to the discussion, 
said, that in the opinions that had been 
expressed there were but few points of 
disagreement with those that he himself 
held. He could not agree with Mr. Latham 
in his belief that embankments could be 
calculated on mathematical principles. In 
order to deal with embankments theoret- 
ically, they must be regarded as rigid 
masses, and be assumed to rest upon a 
horizontal plane. It could be shown math- 
ematically that a rigid body of the same 
specific gravity as ordinary earth need not 
present the same section as is usually given 93 
to embankments, in order adequately to 
resist the pressure of water. A right angle 
prism with the hypothenuse resting upon 
the plane would be quite sufficient to resist the 
pressure of water, even supposing the sur- 
face of the water to coincide with the upper 
edge of the prism. The reason of giving 
long slopes to an embankment is discover- 
able from the fact that banks, when exposed 
to the action of water, are found to waste and 
slip away to such an angle as will withstand 
the action of the water. The chief reason of 
the failure of embankments is the infiltration 
or soaking of the water from the inner side, 
which renders the material semi-fluid and 
causes it to subside into a smaller space than 
it originally occupied. The superincumbent 
mass then sinks and allows the water to 
overtop the embankment. The earth used 
for making embankments in the Deccan 
and in parts of the Madras Presidency in 
India is of a most suitable quality for the 
purpose. It is what is called “black soil,” 
being very dark in color, and of a highly 
argillaceous character. The color is, no 
doubt, due to the presence of carbon. The 94 
clay makes most excellent puddle; but, no 
doubt, the consolidation produced, by the 
tread of the work-people is the real secret of 
the earth resisting the pressure of water so 
successfully as it does. In North America, 
the levees for protecting the country from 
flooding by the Mississippi are sometimes 
constructed simply of sand ; and are found, 
for the most part, sufficient for their pur- 
pose. As regards carrying away springs 
from the seat of an embankment, there is 
no difficulty in ascertaining where they 
exist when the ground is laid bare, as they 
are generally well defined streams. Before 
the earthwork is commenced it is necessary 
to construct drains of masonry, or brickwork, 
or to lay iron piping to carry away the 
water clear of the work. 
The Chairman said that the paper of Mr. 
Jacob was a very interesting one, and the 
subject was one which, during the last 
year or two, or, he might say, within the 
last week or two, had commanded the at- 
tention of the whole body of engineers. 
Last session a special Act of Parliament 
was passed that all reservoirs and embank- 95 
ments should be constructed to the approval 
of the Board of Trade. The subject of 
irrigation in India, which was alluded to 
in the paper, was one of vital importance. 
There was no question that the only means 
we had of irrigating that country in an 
efficient manner was by the construction of 
reservoirs.