91 
[Doc. No. 9. 
Report on the General State of the Work 
ON THE 
CROTON AQUEDUCT. 
New York, 12th July, 1842. 
To the Honorable the Board of Water Commissioners of 
the City of New York: 
Gentlemen, 
All the contracts that have been made for the Croton 
Aqueduct have been completed and accepted, with the ex- 
ception of the contracts for extending the Croton Dam, Sec- 
tion 86 (embracing the Harlem River Bridge), Section 96 
(embracing the Receiving Reservoir), Sections 97 and 98 
(which are for grading the 5th avenue for the line of pipes), 
and the Distributing Reservoir. For Sections 90 and 91 the 
accounts are not quite ready for the certificate, but are ex- 
pected to be prepared for final settlement in a few days. 
The work on the Croton Reservoir has been completed, 
and the Turnpike Company have occupied that part of the 
road which has been made as a substitute for so much of 
their road as will be covered by the Reservoir, since Decem- 
ber last. It will be proper to call on the Commissioners, ap- 
pointed under the act authorizing a change of this part of 
the Turnpike, to examine and certify to the construction, as Doc. No. 9.] 
92 
required by said act. There are several small pieces of land 
that lie within the flood line of the Reservoir, which it will 
be necessary to procure. I have directed surveys and maps 
to be made with a view to obtain the title for the same. 
These grounds are not, to much extent, affected by the ordi- 
nary state of water in the Reservoir, but are liable to be co- 
vered by the floods that occasionally occur. 
The work done last fall to protect the unfinished masonry 
of the Croton dam proved to be quite sufficient for the ob- 
ject ; having effectually secured the masonry against injury 
from the winter floods. The length of overfall was 180 feet, 
on which the greatest flood rose 4 feet on the ridge of the 
dam. The overfall was not uniform; this was caused by 
the two sluice trunks that were put down, to carry the water, 
during the prosecution of the work, in November last, and 
which discharged the water at a different point in the pound 
below' the dam. The main apron of the dam appears to 
have sustained the action of the floods without any injury ; 
but the upper tier of plank on the secondary apron was torn 
up for the whole length of the new part of the dam. They 
came up in sections of 20 to 50 feet in length, bringing with 
them one tier of apron timber, showing that the plank were 
more firmly secured to the top timbers, than this timber was 
to the lower work. This damage, I think, was done by the 
powerful re-action of the eddies, that formed next the shores, 
particularly on the side next the old dam. Had the water 
been discharging over the weir of the old dam, this counter 
current would have been destroyed, and probably the work 
would not have sustained any injury ; but the new work be- 
ing so much below the level of the old, the latter was neces- 
sarily left dry; and all the water passing the new work, 
which was also somewhat irregular, from the effect of these 
sluices at the north end, had a direct tendency to produce a 93 
[Doc. No. 9. 
powerful re-action. The lower course of planking on the 
secondary apron does not appear in the least injured. In 
order to increase the security of the secondary apron, I pro- 
pose to sink a pier 12 feet in width, adjoining on the lower 
side ; also to take up some of the timbers in the old part, and 
by tiers, and a new course of planking, to combine the whole 
firmly together. This will make the whole length of the 
secondary apron 30 feet; and this, with the principal apron, 
will make a total length of 65 feet from the toe of the dam. 
I regard the action of the water in passing over the dam as 
by far the most prominent cause that will be liable to injure 
the dam or its appurtenances, and shall endeavor to guard 
with every precaution that appears adapted to resist this ac- 
tion, and give security to the work. 
The water in the Croton continued so high that we were 
not able to resume the masonry on the new part of the dam 
until the 21st day of May ; and at that time the water was 
still so high we were obliged to confine our operations to a 
very limited space, in order to give sufficient passage for it 
to pass offi The contractors had their materials on the ground, 
and have lost no opportunity in carrying forward the work 
in a most energetic manner. On the 21st of June, they had 
so far advanced as to be prepared to take up the last trunk, 
put down last fall, to pass the river. During this day the 
water was stopped and an embankment carried across the 
gap above the head of this trunk; and on the morning of 
the 22d, the water rose in the Reservoir to a sufficient 
height to flow into the Aqueduct, and over the new sluice 
put in to pass off the surplus. A rain fell the next day, and 
caused such a rise in the river as to require vigorous efforts 
to sustain the embankments above the gap, from whence the 
north sluice was removed. This, however, is only one of 
several instances in which we have narrowly escaped serious Doc. No. 9.] 
94 
inconvenience and damage by the sudden rise of the river. 
It is certainly a matter of much gratification, that this diffi- 
cult and important work has so far been carried forward in 
the channel of a river, subject to sudden and violent floods' 
with so little interruption or damage. In looking back to the 
times when danger stood before us, I should not do justice 
to my feelings did I not acknowledge the hand of that Be- 
nign Providence who has so kindly tempered the storm, and 
saved us from material harm. The new sluice, put in this 
season, is at the south end of the new dam, and is 10 feet be- 
low the top. With the exception of the gap at this sluice, 
the masonry of the dam is carried up to within two courses 
of coping on the top. This coping, together with the slope 
pavement, which is to extend from the coping to protect the 
embankment of the dam, will probably be completed in a 
short time. The abutment at the north end is in good pro- 
gress, and the whole of the masonry will probably be com- 
pleted about the middle of August. We are waiting for a 
lower state of water to complete the aprons and secondary 
dam. It will be difficult to do this part of the work, unless 
the water falls considerably lower than we have had it this 
season. It may be expected we shall have less rainy 
weather soon, and be able to complete the whole of this 
work by the 1st September next. 
Since my report of December last, the work at Harlem 
river has progressed slowly. The restriction imposed on 
the contractors has not allowed them to proceed on the 
shafts of three piers, and their work has been confined to 
the foundation, and the masonry in the base courses; conse- 
quently, very little work has been done to advance the ma- 
sonry since that time, on piers Nos. 5, 6, 7, 8 and 9. On No. 
4, several base courses have been laid up. The foundations 
of piers Nos. 2 and 3 have been completed, and on each, se- 95 
[Doc. No. 9. 
veral base courses of the masonry laid up. The foundation 
for pier No. 10 has been completed, and two courses of the 
base masonry laid. The piling for this foundation has ap- 
peared very satisfactory; and I have full confidence in its 
capacity to sustain the pressure of its anticipated load. The 
foundation for three water piers, Nos. 11, 12 and 13 are yet 
to be put down. The coffer dams for all of them are in, and 
they are ready to be emptied of water. The contractors 
are now engaged in putting up a steam engine to perform 
the work on Nos. 11 and 12, both of which are expected 
to require pile foundations. The foundation for temporary 
pipes and other work embraced in this contract, that was 
necessary to be done before the water could be let in the 
Aqueduct, has been so far advanced as to allow the water 
to pass without delay, though it was not in all respects com- 
pleted. The contractors are desirous of excavating the 
foundation of pier No. 14, to enable them to use the stone 
that are required, to form a protection for the temporary 
pipes, and if the restriction should not be generally removed, 
it appears desirable that it should be in this case, as it 
will facilitate work that is indispensable to the protection 
of this pipe. It will require a vigorous prosecution of this 
work to complete it in 2| years, or two full seasons after the 
present, if the contractors were allowed to go on as fast as 
an economical management would permit. There can, how- 
ever, be no doubt the temporary pipe laid at this place, will 
pass as much water as the city will require for use, for seve- 
ral years to come. The Receiving Reservoir was so far 
completed as to allow the water to be introduced from the 
Aqueduct on the 27th ultimo. The walls and embankments 
are now nearly completed. The gate-houses and fixtures 
connected with them, and the railing, require considerable Doc. No. 9.] 
96 
work to complete them. All the unfinished work is now 
progressing very well, and will probably be completed about 
the middle of next month. 
The work of grading the 5th Avenue for the iron mains, 
that connect the two Reservoirs, and the filling in for the 
same, embraced in Sections 97 and 98, is nearly completed 
and may be entirely so in a short time. 
The Distributing Reservoir was so far completed as to ad' 
mit the water on the 4th inst. There is, however, a con- 
siderable amount of work to do to complete this Reservoir. 
The principal items are the west side protection wall, the 
sewer in 40th street, the coping and flagging for the north 
division. It is my impression this work cannot be completed 
before the middle of September next. 
The railing for this Reservoir has not yet been contracted 
for. It is my intention in a few days to submit a plan for 
railing on the inside, and also for railing on the outside 
coping of this work. 
Since my report of December last, it has appeared expedi- 
ent to extend at several places the work that had been done 
to secure the masonry of the Aqueduct, where a partial set- 
tlement had taken place on foundation walls. Although no 
material change had taken place, it appeared proper, as a 
measure of precaution, that the opportunity still remaining 
before the water could be let in, should be improved to give 
the work all the permanency in these cases that the circum- 
stances would permit. Accordingly, several of the founda- 
tion wallshave been grouted, and the bottom and sides of the 
Aqueduct covered with a thorough coat of plastering. Those 
walls that were previously grouted, and which had been the 97 
[Doc. No. 9. 
most troublesome from settling, appear in good order, giving 
much assurance that they will be permanent. The work on 
the outside of the Aqueduct, in clearing the drains, raising 
and in some cases increasing the security of the protection 
walls, and widening the embankments on the top, has been 
steadily carried forward since the commencement of the 
season. 
The work along the steep side hill near the mouth of the 
Croton has ever been a source of much solicitude to me. 
Great care was taken to give it a firm foundation, and thus 
far it promises to be adequate to maintain the Aqueduct. 
The only danger I think may be apprehended, is from a slide 
in the hill that might jeopard the security of our work. I 
cannot perceive much danger from a slide, as the hill is com' 
posed of a pretty dry and firm hard pan, and the foundation 
sunk deep into it. But as the hill is very steep, descending 
directly to the river, it has appeared to me proper to recom- 
mend some precautionary work at two or three places, which 
may be done at no great expense. The exterior improve- 
ment and security to the work has been and continues to 
progress with the small parties of men engaged on it, and 
may be completed in about two months from this time. 
In the year 1839, the Board of Water Commissioners di- 
rected a survey of the Aqueduct line, embracing such a 
breadth of adjoining country as was necessary to give a good 
view of the location, and a map to be made of the same, on 
which the profile of the Aqueduct should be laid down. The 
map and profile have accordingly been made for the 2d and 3d 
Divisions, and that for the 1st Division is nearly finished, 
Some additional surveys are still required for the 4lh Division, Doc. No. 9.] 
98 
which it is intended to have made as soon as other duties will 
allow a party to be formed for that purpose. Thus far the 
work for this map has been prepared with much care, and I 
am desirous of having it completed at the earliest day prac- 
ticable. 
The extra monuments directed last season, to designate 
and preserve more fully the Aqueduct land line, have all been 
procured, and for the 1st and 2d Divisions have nearly all been 
placed, and the work of placing those on the 3d and 4th Di- 
visions will soon be commenced. 
It will be three weeks to-morrow since the water was let 
in the Aqueduct, during which time it has continued to 
flow in the Aqueduct very uniformly at a depth of two 
feet. I have very carefully examined to ascertain whether 
any leakage existed, and have not been able to discover 
any. I have also examined about 25 miles of the interior 
by means of a boat, mostly accompanied by Mr. French, the 
resident Engineer of the 1st and 2d Divisions, to ascertain 
as far as practicable, with the water in the Aqueduct, if 
any change had been produced by the water on the masonry; 
but was not able to perceive that any had occurred. It 
may be advisable in the course of a few weeks to let the water 
out, for the purpose of making a more thorough examination 
of the interior, which may be done without any detriment to 
the supply of the city, as the Reservoir will be very ample for 
the purpose during the short time it will be necessary to shut 
off the water for examination. 
There is now 14 feet depth of water in the northern division, 
and 15 feet in the southern division of the Receiving Reservoir, 
and 18 feet in the Distributing Reservoir. These works thus 
far appear very well, and it is the intention to gradually in- 99 
[Doc. No. 9. 
crease the depth, as fast as it will be prudent to do so, on works 
designed to sustain so great a pressure as is contemplated in 
these Reservoirs. 
Without doubting the great majority of the work would 
fully answer the object of its construction, I have felt great 
anxiety, that in so long a line, occupied by various structures, 
some points would be found on trial to be insufficiently secured; 
and although thus far all appears well, still a few months' trial 
will be necessary before we can have that confidence which is 
necessary for such a work, and such as I hope may be realized. 
While I cannot dismiss my anxiety, I firmly believe there are 
but few points where failure can reasonably be apprehended, 
and that the main work will be proved to have all the perma- 
nence and stability which is necessary to afford the city an 
uninterrupted supply of water. 
It now appears highly probable that all the work required 
to complete the Aqueduct, except the Harlem River Bridge, 
may be accomplished, and the accounts adjusted, by about 
the first of October next. 
Since the water was introduced into the Aqueduct, the ve- 
locity has several times been ascertained, though not in so per- 
fect a manner as I intend to have it done, as soon as other 
duties will allow the time necessary. Sufficient data, however, 
have been obtained to show that the capacity of the Aqueduct 
for delivering water will be at least 15 per cent, greater than 
the calculated flow. I have not been much disappointed in 
finding the flow of water in the Aqueduct to exceed the calcu- 
lation, as all my observations on the currents in canal feeders 
have led me to believe the formula laid down to give rather 
less than the actual result. The flow of water through the 
pipes across Manhattan valley, and also the temporary pipe 
across Harlem River, being attended with circumstances Doc. No. 9.] 
100 
somewhat different, has led some very intelligent persons to 
predict, that our expectations would not be realized in these 
cases; it, therefore, may be proper to observe, the trial has 
proved such prediction to have been not well founded, as the 
flow through the pipes has in a very exact manner corroborated 
the anticipated capacity, as compared with that in the Aque- 
duct. 
The Croton Reservoir (which has received the name of 
Croton Lake), covers about 400 acres of land, and is availa- 
ble as a reservoir for 500,000,000 imperial gallons of water, 
above the level that would allow the Aqueduct to discharge 
35,000,000 gallons per day. 
The flow of the Croton river is about 27,000,000 in 24 
hours, at the lowest stages, which continue, with moderate 
rises by occasional rains, from two to three months in the 
year. This may be considered the minimun capacity of the 
river. When the wants of the city shall require a4 daily 
supply of 35,000,000 gallons, it will be necessary during the 
season of lowest water, to draw daily from this Reservoir 
8,000,000 gallons to make up the deficiency in the natural 
flow of the river. This amount the Reservoir would supply 
for 62 days, without any aid from occasional rains; which 
may safely be relied upon to keep up the required supply 
from the Reservoir, beyond any drought we have ground to 
apprehend. 
The supply of the Croton, from its daily flow, aided by 
this Reservoir, may therefore be taken with great confidence 
at 35 millions of gallons; which will be|very ample for the 
wants of the city for a long time to come; and when the 
day arrives, that it will require a larger quantity, it may 101 
[Doc. No. 9. 
be obtained by constructing other reservoirs farther up 
the stream, where there are abundant facilities for such* 
purpose. 
Respectfully submitted, 
JOHN B. JERVIS, 
Chief Engineer N. Y. W. W.