Ask the Scholar
Document scope · 1 page
Scholar
Ask about this object, its catalog metadata, its source description, or the page inventory.
For page-specific OCR and visual context, open one of the page chats.
Scholar Source Context
Document identity
localId
203745170
label
Opinion on a Project for Removing Obstructions to a Ship Navigation to Georgetown, Columbia, by B.H. Latrobe, 1812
core
doc
dtoType
document
citationUrl
pageCount
1
Source metadata
id
203745170
contentType
document
title
Opinion on a Project for Removing Obstructions to a Ship Navigation to Georgetown, Columbia, by B.H. Latrobe, 1812
citationUrl
collections
Dr. Robert Kapsch Collection
Senior Scholar Records
largeImageUrl
imageCount
1
hasImages
yes
source
import
hasTranscription
no
Source extras
naId
203745170
levelOfDescription
item
recordType
description
ocrSource
nara-archive
Single page context
seq
1
pageIndex
0
type
document
mediaId
1a2b98f29041bf58
ocrText
Google
This is a digital copy of a book that was preserved for generations on library shelves before it was carefully scanned by Google as part of a project
to make the world's books discoverable online.
It has survived long enough for the copyright to expire and the book to enter the public domain. A public domain book is one that was never subject
to copyright or whose legal copyright term has expired. Whether a book is in the public domain may vary country to country. Public domain books
are our gateways to the past, representing a wealth of history, culture and knowledge that's often difficult to discover.
Marks, notations and other marginalia present in the original volume will appear in this file - a reminder of this book's long journey from the
publisher to a library and finally to you.
Usage guidelines
Google is proud to partner with libraries to digitize public domain materials and make them widely accessible. Public domain books belong to the
public and we are merely their custodians. Nevertheless, this work is expensive, so in order to keep providing this resource, we have taken steps to
prevent abuse by commercial parties, including placing technical restrictions on automated querying.
We also ask that you:
+ Make non-commercial use of the files We designed Google Book Search for use by individuals, and we request that you use these files for
personal, non-commercial purposes.
+ Refrain from automated querying Do not send automated queries of any sort to Google's system: If you are conducting research on machine
translation, optical character recognition or other areas where access to a large amount of text is helpful, please contact us. We encourage the
use of public domain materials for these purposes and may be able to help.
+ Maintain attribution The Google "watermark" you see on each file is essential for informing people about this project and helping them find
additional materials through Google Book Search. Please do not remove it.
+ Keep it legal Whatever your use, remember that you are responsible for ensuring that what you are doing is legal. Do not assume that just
because we believe a book is in the public domain for users in the United States, that the work is also in the public domain for users in other
countries. Whether a book is still in copyright varies from country to country, and we can't offer guidance on whether any specific use of
any specific book is allowed. Please do not assume that a book's appearance in Google Book Search means it can be used in any manner
anywhere in the world. Copyright infringement liability can be quite severe.
About Google Book Search
Google's mission is to organize the world's information and to make it universally accessible and useful. Google Book Search helps readers
discover the world's books while helping authors and publishers reach new audiences. You can search through the full text of this book on the web
athttp://books.google.com/
A 761,167
DUPL
Digitized by Google
Digitized by Google
1
Digitized by Google
Digitized by Google
6406
Thettonble Wm Cranch
OPINION
cre
ON A
PROJECT
FOR
REMOVING THE OBSTRUCTIONS
TO A
SHIP NAVIGATION
TO
GEORGETOWN, COL
BY B. H LATROBE, ENGINEER.
WASHINGTON:
W. Cooper, Printer.
1812.
Digitized by Google
Transportation
Library
P9
L3
7w.
Digitized by Google
PREFACE.
THE deposition which is contained in the following
sheets and to which are now added, the answers I gave
to the questions put to me by the Committee of the House
of Representatives, to whom was referred the bill from the
Senate respecting a ship navigation to Georgetown, toge-
ther with some further remarks and authorities relates to
a subject of the utmost importance, not only to this dis-
trict, but to our country at large. It has already been
published by Mr. T. Moore in the newspaper called the
Spirit of 76, and in a detached pamphlet, together with his
comments upon it, and parts of a private correspondence
between Mr. Moore and myself. Both these publications
are in many places so inaccurate as to be unintelligible.
Had I foreseen them, I should have endeavored to have
rendered the deposition more worthy of a public appear-
ance, and my private letters would never have been writ-
ten. My inducement to lay the whole of my view of the
subject before the public, is, principally, that it may be cor-
rectly and fully before them, unaccompanied by any thing
that relates to me personally. It is, in fact, of no conse-
quence that the public should know in what manner the
interests or the tempers of individuals have operated in the
discussion of the practical effects of adopting one or other
of two modes of effecting a public benefit. The old adage,
that, in every dispute, he that is first angry is wrong, should
be remembered, in all such discussions, by professional
men, on whose reputation depend their means of exist-
ence. The public are always more amused by personality
than by argument: but the power to amuse is not that
which ensures respect.
On these considerations, I have avoided any remarks on
the personality of Mr. Moore's comments, excepting in
cases in which my personal defence involved my argument.
Digitized by Google
iv
PREFACE.
I shall here only add, that the insinuations which so plain-
ly attribute to me the vanity of believing that I possess,
exclusively, all the science necessary to the investigation of
the subject under consideration, are very gratuitously
made. That I have endeavored to acquire a sound theory,
that I have been well instructed, and that I have some ex-
perience, is not denied; and it is all that I claim. There
may be some vanity in the belief that I should know less
had I studied less; that without instruction, I might have
invented over again, methods which have been long ago
condemned; and that without a stock of experience of my
own, the public must have paid for the acquirement of it ;
but this vanity is excusable: for no man is so humble as
to believe that the labor of his life has been thrown away.
But further I have not gone, either in conversation or in
private correspondence; and no one is so well convinced
as I am, how very inferior are my acquirements to those
of a Smeaton, a Perronet, a Fabre, or a Proni. Indeed I
should blush to range their names in the same line with
my own.
To those gentlemen of the corporation of Georgetown,
to whose wishes I have been forced to oppose my unbought
opinion, whatever may be its value, I do not in fact owe
an apology; for they never expected that I should sacrifice
the integrity of a professional conviction to sentiments of
personal attachment and respect; nor should I have thought
it necessary, to say any thing now on this subject, had it
not been insinuated in their presence that my opinion was
not disinterested. I therefore now appeal to the very re-
spectable petitioners against the bill, for the truth of this
fact, that I refused the professional compensation offered to
me on their side, on consideration that much personal ir-
ritation existed; that the pecuniary interests of Mr. Moore
were involved, and must be sacrificed, if my opinion should
be against his project, and should prevail; and that I might
lose personal friends if I engaged in the discussion. I was
then summoned as a witness in court, and although I think
that a professional man may, and ought to be allowed to
object to give his opinion in court às a witness without a
fee, my objection was not admitted by a lawyer of great
eminence in this district.
Digitized by Google
PREFACE.
V
I have been obliged to say more of myself, by the cha-
racter of the comments on my deposition, which are now
a document in the hands of the Committee of the House
of Representatives of the United States, than on any other
plea, could be justified. I have done.
Digitized by Google
NAVIGATION OF THE POTOMAC
THE following information respecting the navigation
of the river Potomac up to Georgetown, was taken from
the mouth of the late Mr. Robert Peter, one of the earliest
Scotch factors and merchants settled at that place, and father
of the numerous and highly respectable family of that name.
The expressions are nearly those which he used in giving
it, and it coincides with the testimony of many other living
witnesses.
Prior to the residence of Mr. R. Peter at Georgetown,
it does not appear that the channel of the Potomac from
Bellhaven (Alexandria) had been examined as high up as
Georgetown: for the people at that place were entirely ig-
norant of the existence of water navigable for ships above
the former port. After submitting for several years to very
great inconvenience, Mr. Robert Peter caused the river to
be sounded, and, to his astonishment, discovered a good ship
channel, having at least 25 feet of water, up to the town.
From that time to the year 1784, the navigation to Geòrge-
town admitted ships of the largest size, and the merchants
carried on all their business from their own wharves, instead
of loading their vessels by means of lighters at Bellhaven, or
a little above, as they had done before.
The channel here spoken of, passed at its upper end, be-
tween Mason's Island and the city shore. Below the island
it passed to the Virginia shore, parallel to which it continu-
ed, until it reached the channel leading from Alexandria to
the Eastern Branch. In March 1784, however, a very im-
portant change took place. The passage between Mason's
Island and the Virginia shore had been till then not only
shallow, but much obstructed by detached rocks, so that it
is not known that any vessel, even of the smallest kind, had
sailed through it; it being considered practicable only for
row boats. The winter of 1783....4, had been so severe that
the river was entirely and thickly frozen, both above and be-
low Mason's Island. In March, 2 sudden and rapid thaw
Digitized by
Google
vii
occasioned the ice to break up above, and it came down in
large flakes, but with a very moderate swell of the river.
The immense fields of unbroken ice below the islard, im-
peded its progress it was driven in extensive masses upon,
and under them, so as to form large bodies and islands of
ice at the sister rocks, about a mile above Georgetown,
where the river is from 80 to 100 feet deep. Opposite to
the town, the ice was piled up so high that the ferry road
was in some places obliged to be cut through it. In this
situation, a sudden renewal of severe weather put a stop to
the thaw and to the fresh, and held the river frozen. The
number of days during which it remained in this state is not
remembered; but another very sudden change of weather
soon succeeded, attended with a warm rain in the mountains,
which rapidly thawing the snow accumulated there, sent
down such a tremendous flood, as to raise up from the bot-
tom the accumulated masses of ice, and to roll them forward
(as Mr. Peter expressed himself) in a vast body into the
narrow channel east of Mason's Island, in which, reaching
the bottom, they soon formed a dam of ice across, complete-
ly preventing the further progress of the flood by that course.
A stronger current then necessarily took place round the
other side of the island, by the Virginia channel, and another
dam was formed there. This latter, however, being either
composed of lesser masses of ice, or of such as had been
compressed by a less heavy current, yielded first, and soon
after its formation. The other dam, thus relieved, stood
while the whole torrent, raised by this time to a great
height, rushed through the opening, and not only carried
before it the softer materials of its bottom, but (as Mr. Peter
said, using a very strong expression) rocks of enormous bulk.
The dam on the east side, afterwards, also yielded, but not
until after the weather had become warm. The torrent
raised above all the wharves, had carried with it all the
warehouses and dwellings within its reach, " as if they had
been so many cornstalks." Many of the masses of ice, which
had formed the dam, remained unmelted till the month of
June.
After the fresh subsided, it was found, that it had scoured
out a channel 25 feet deep between the island and the Vir-
ginia shore, extending as far as the old channel on the Vir-
ginia side. This event was by many considered as extreme-
ly fortunate for the harbor of Georgetown, and the new
channel remained the principal one for many years. In
Digitized by Google
viii
1793, a French ship, drawing at least 18 feet of water, and
having on board 720 hogsheads of tobacco, sailed through
that channel, and went to sea at once without again casting
anchor.
It was however after that period, observed, that a bar be.
gan to be formed at the junction of the two channels below
the island, which annually increased. Whether such obser-
vation had been made prior to the year 1794 or not, I cannot
ascertain. This bar was found to rise more rapidly at the
new than at the old channel, and, in 1803, the new channel
was so much reduced in. depth, that the old one became
again the only one in use. From that time the evil increas-
ing considerably, induced the corporation to expend consi-
derable sums in an endeavor to remove it, by a ballast ma-
chine. The purpose was not however answered, and the
project of Mr. Thomas Moore, who had successfully carried
a mole or causeway across the Virginia channel, was formed.
Before the corporation of Georgetown attempted its execu-
tion, application was made by them to the then city councils
for their sanction of the work, and an assent, though not ex-
pressed in the form of an ordinance, was obtained. The
work was then commenced The project however, gave
alarm to the bridge company, and to the proprietors in the
city, who were interested in the navigation of the Eastern
Branch, and an injunction out of the district court was pray-
ed, and granted, to stop its further progress. This legal
proceeding gave rise to the deposition which is contained in
the following sheets. The injunction was afterwards made
perpetual, and the work ceased, to the great disappointment
of the corporation and inhabitants of Georgetown, and, I be-
lieve, to the individual disadvantage of the projector, who
had contracted to complete the work for a stipulated sum,
and for a further compensation, should he be successful.
Application was then made to Congress by the corpora-
tion of Georgetown for relief; and a bill has passed the
Senate, authorizing such works in the bed of the river, as
may be sanctioned by three commissioners, to be appointed
by the President of the United States. This bill, on its ar-
rival in the House of Representatives, was committed to the
committee of the district of Columbia, at whose desire the
further evidence in the case has been taken, which these
sheets contain.
Washington, April 28, 1812.
Digitized by Google
DEPOSITION
OF
B. H. LATROBE.
Benjamin Henry Latrobe, civil engineer, and surveyor
of the public buildings of the United States, being duly
sworn, deposeth and saith, that he understands the oath ad-
ministered to him binds him to the perfect integrity and im-
partiality of that opinion, which he shall give as to the proba-
ble effects of certain works, &c. proposed to be erected in
the bed of the river Potomac agreeably to the report and
project of Mr. Thomas Moore, and as laid down in a map or
chart of the river in the office of the court: but that all the
facts in the case, to wit, the various soundings laid down in
the several maps of the river Potomac, which have been
filed in court, as well as the forms and dimensions of the
shores, channels and shoals, and the facts (independently of
the opinions) stated in the deposition of Nicholas King, esq.
also filed, not being within his personal knowledge, are mu-
tually conceded by the said parties. The deponent there-
fore, on these facts, as well as on his own observations on the
river Potomac and its waters within the District of Colum-
bia, and on other information which he shall use in the
course of his deposition, proceeds to state the opinion re-
quired: for the clear understanding of which, he begs leave
to give it in the form of answers to the following interroga-
tories, which comprehend, in his opinion, all the points rele-
vant to the decision solicited of the court.
1. Will the wing dams proposed to be constructed in the
river Potomac by Mr. Moore, as laid down upon the map
filed in the office, have the effect of deepening the channel
called the middle channel, from the foot of Mason's Island
through the bar or shoal, so as to produce an uninterrupted
ship channel seaward from Georgetown?
B
Digitized by Google
2
2. If these wing dams produce the proposed effect, will
any effect injurious to the Washington bridge, or to the
harbors of the city on the Potomac, or in the Eastern Branch,
be also produced.
In considering these questions and forming upon them
an opinion, I have confined myself to the great principles of
the case; and although 1 have carefully examined the
several charts and inaps, and observed the changes which
from time to time have taken place in the soundings and
width of the channels, I shall avoid entering into any discus-
sion which did not strongly bear upon the ultimate decision
of my mind on the subject. I shall also say little on the sub-
ject of freshets. They are a powerful operation of nature,
either to create 'to destroy a channel, but they are uncer-
tain, irregular and unmanageable in their effects, and what
one fresh creates may be-destroyed by the next, without its
being possible to account for the operation of either.
To the first interrogatory, I answer If the wing dams
are so constructed as to have the effect which is stated to be
expected from them, they will, in the first place, obstruct the
passage of the body of the current towards the Virginia
shore: and in the second, deflect the current towards the
city shore. But I must here observe that the first wing
dam, as laid down in the map, does not cross the Virginia
channel therefore it will have no effect in obstructing the
natural course of the current, such as it is, more or less
strong, down that channel. That there must be a strong
tendency of the current to take that course, is to be con-
cluded, with much certainty, from the form of the shore
above, from which the current must inevitably be deflected
towards the Virginia shore. This deflection and tendency
will exist in the greatest degree when the current is weakest;
that is, when it is opposed by the flood tide, and when there
is no fresh in the river.* But when there is a heavy fresh
That this tendency of the current towards the Virginia shore cx-
ists, and in a stronger degree than before the causeway, shutting up
the western channel, existed, is evident from its effects on the shore of
Alexander's Island at the south end of the bridge. When the passage
on the west side of Mason's Island was open, the water of that passage
gave to the united channel below Mason's Island a direction parallel to
the Virginia shore. There is now nothing to resist or bend the current
deflected from Peter's point, into a direction parallel to the Virginia
shore; and the shore near the bridge is so rapidly wasting as, in my
opinion, to endanger the abutment of the bridge. In the late fresh it
was so strong as to undermine the mud-selle of the first or second pier,
Digitized by
Google
3
in the river, the volume of descending water, after being
confined between the roeky point of the island at the Ferry
and the opposite city shore, suddenly finds vent and expan-
sion; and striking both the shore of the island and of the
city, recoils upon itself, and a great mass of the water
takes a mean direction down the middle channel for some
distance. This effect may be observed in all similar situa-
tions in the world. From the same cause arise all middle
channels that are found in broad flats which are thoro-fares,
or are stopped up at the lower end and to the same origin
may be referred all horse shoe shoals, numerous in every
river which is liable to unequal currents. The object, how-
ever, of the first wing dam, appearing to be to prevent the
tendency of the current towards the Virginia shore, there
can be no doubt of the ability of the worthy and ingenious
projector, so to construct it as to make it answer that end. I
will therefore proceed in the first instance, as if this point
were effected. The whole current of the Potomac being
thus confined to the eastern side of the range of the wing
dams laid down in the map as far as the bridge, and for some
distance below the same, I have not the smallest doubt but
that in a short time, there will be a channel worn by the
same from Mason's Island as far as the foot of these works
at the least, and as much further as the current shall main-
tain itself in a body without much spreading. This channel
will probably be from 20 to 30 feet deep, i. e. equal to that
between the island and city shore. But if the wing dams
cease immediately below the bridge, and no other works
are erected, then the current striking the city shore be-
tween the squares 473 and 506 will be deflected irresistibly
towards the Virginia shore, and a total change will take
place in all the channels and shoals, from that point down-
wards. 1 beg leave here to refer to the engraved plans of
the city and of the district. On reference to these, it will
be seen, that if the entrance of the current into the Virginia
channel below Mason's Island be obstructed, and the ob-
structions be continued as low down as the dam laid down
below the bridge in Mr. Moore's plan, then will the effect be
exactly the same as if Mason's Island were removed to the
situation of the lowest wing dam. The relative position of
.the city shore to the current, and the angle under which the
current will strike the shore, will be exactly the same as it
and to cause them to settle; as may be seen by any passenger who will
notice it.
Digitized by Google
HOW is at the foot of the island, and of course, the same ef-
fect being produced by the same cause, the current will be
deflected towards the Virginia shore, as it now is below
Mason's Island. On this point there cannot be a difference
of opinion, unless an instance can be produced of a current
striking a shore and not being deflected to the opposite side:
But, as the filed report of Mr. Moore shows it to be his
opinion that no very considerable portion of the current of
the Potomac is deflected towards the Virginia shore, at the
foot of Mason's Island, so as to keep open the present. Vir-
ginia channel, and as the facts adduced by bim prove this
channel to be both narrower and shorter than formerly,
therefore I ought not to presume that he would obstruct
that channel; yet, as it is my opinion that a considerable
current will always take that course if not obstructed, it is
therefore also my opinion that if that channel be left open,
the current through the middle channel, which will be
strengthened only by the addition of the water which finds
its way southward across the flats, will not be sufficiently
strong to make any very sensible change in the depth of that
channel below the wing dams. In respect to the wing dams
themselves, I have the following remarks to make that the
edge of the current will strike the first of them nearly in an
angle of 45 degrees. Currents would be reflected on the
principles ofthe reflection of all other elastic bodies impelled
against geometrical planes, were they not always surround-
ed and confined by eddies, by water moving with less. velo-
city, or by stagnant water; that is, the angle would be equal
to that of reflection. But all these circumstances operating,
the motion of a deflected current in a river, is irregular, but
is always a curve, tending towards the true line of reflection.
It is therefore my opinion that the wing dams placed as they
are laid down, would operate to throw the current, and of
course the channel; towards the city shore, much to the east
of its present situation. This would not in itself be injuri-
ous, otherwise than as rendering the ultimate place of the
channel uncertain. But, should the Virginia channel be
entirely obstructed, the new channel would then, I am of
opinion, be thrown entirely on to the city shore. Thus far
I have considered the subject without any reference to the
operation of the flood tide, or of the deposit of alluvium.
I will now proceed to examine the probable effect of the
flood tide upon the channel or channels effected by the pro-
posed works, or remaining after their erection. The channel
Digitized by Google
5
of the Potomac, below Greenleaf's point, lies in a nearly
direct line-from the wharves of Alexandria to the point.
Over this channel both the tide of ebb and the tide of flood
pass. The tide of ebb and the land-current coming down
the Virginia channel strikes the shore at the south point of
the Eastern Branch, and is deflected towards Alexandria.
The current and tide of ebb coming down along the city
shore proceeds straight forward in this direction, into
which the tide out of the Eastern Branch is also borne by
the powerful current of the Potomac. The tide of flood
coming up from Digges's point, strikes the shore at Alexan-
dria, and is deflected into the same channel, reaching the
Maryland shore at the mouth of the Eastern Branch. Here
the flood is met and opposed by the land current of the Poto-
mac on the left, and by the weaker current of the Eastern
Branch* on the.right: consequently it makes its way with
most force where it finds the least resistance, that is, into
the Eastern Branch, in which the flood runs with the same
rapidity as the ebb, keeping open a deep channel, which ac-
cording to the information of Mr. Thomas Carberry, former-
ly a pilot of the Potomac, now inspector of lumber in the
Navy Yard, has not decreased in depth for the last thirty
years. The tide of flood which proceeds up the Potomac,
finds the greatest resistance from the main stream which
comes down the Virginia channel, and the least along the
city shore it therefore makes its way first and strongest
along the city shore and I cannot but believe the present
city channel to be principally the work of the flood tide, and
also that the middle channel owes its existence in a great
degree, to the flood tide deflected at the bend of the shore
between the squares 473 and 391. The remainder of the
tide goes more slowly up the Virginia ehannel, and finds its
way over the middle flats, till at Georgetown it rather accu-
mulates, by holding back the land water, than runs.t
I think the Eastern Branch takes off one third the water of the flood.
Its deep channel is the work of the flood, not of the trifling stream that
feeds it.
To obviate lengthy reasonings on this subject in the body of my
deposition, I will beg leave to state in this note a theory as to the flood
tide, which if true, (and to me it appears both mathematically and ex-
perimentally so) is of immense importance, in prognosticating the effects
of works proposed to be created in tide water. By whatever cause the
water of the ocean is raised and depressed twice in 24 hours, the fact
itself is not disputed. The motion of this mass in shore is the effect, in
Digitized by Google
6
From these facts the following conclusions appear to me
irresistibly to follow : That as the current of the river will
be thrown towards the Virginia shore opposite to the city
square 473, or thereabout, it will make for itself a channel
along that shore towards Alexandria, and that the flood tide
being deflected at or about Alexandria towards the Maryland
shore, and its course thence not depending on any thing
above until it reaches the mouth of the Eastern Branch, the
flood tide and the ebb will not go over the same ground, and
of course that both channels will become shallower, gradual-
ly, to a degree which it is not in my power or the power of
any other to predict.
There remains now the consideration of what will proba-
bly be the effect of the proposed works on the deposit of
alluvium in the channel thus effected, or changed.
It is not necessary to enter at large into the discussion of
the theoretic part of this consideration: so much has already
been said and written thereon, that every body interested is
familiar with the theory, and its truth is conceded on all
hands.
It is simply this ; that of the alluvium brought down by a
current, the heaviest particles will be first deposited as the
rapidity of the current decreases that those that are lighter.
will, in succession, sink to the bottom, with the further de-
crease of its rapidity ; until stagnant water at last will clear
the first instance, of gravitation: the water falls into the lowest place.
The momentum of falling bodies is known to increase as the square of.
the descent. Therefore, pursuing the motion of a single portion of this
mass, the flood tide going up the Chesapeak, for instance, it is endued
with a power to go forward, equal to the momentum which it has re-
ceived in falling from the height to which it had been raised in the ocean,
above the water in the rivers at low water. If from this momentum of
the flood be deducted the momentum of the land water, and the power
of its own gravitation, (or the root of which the momentum is the pro-
duct) you have the power with which the flood will run upbill, until it
is exhausted by the same law reversed, which created it. Thus the tide
rises at the bottom of the bay of Fundy 60 feet, and at its mouth, as I
am informed, only 20. On this principle is the water raised in Montgol-
fier's hydraulic ram, nor am I prepared to deny, if it were asserted, that
the level of high water in the Potomac at Georgetown is 100 feet or
more, higher than at the capes. In the North River it is high water at,
Albany at the same time at which it is high water. at the narrows, and
low water at the highlands, as I have been informed. The flood tide,
let it be ever so rapid, is easily resisted by works, because its force de.
creases in the ratio of the square of the height to which resistance
forces it, while a downward current acquires force as the square of the
height to which resistance raises it.
Digitized by Google
7
itself of all particles held in solution, that are heavier than
water.
In like manner if the rapidity of a current be increased, it
will take up all bodies capable of solution or admixture with
itself, and carry them along in a proportion of their weight
increasing with its increased velocity.
On this very principle the works have been projected, and
are expected to answer the intended purpose. The velocity
of the river Potomac has brought down with its waters cer-
tain particles of sand, clay, and other matter soluble or ad-
miscible in water. It has carried them to a certain point, at
which the current becoming weaker by its expansion over a
larger space, it has deposited, first the heavier, then, by de-
grees, the lighter particles. This point has hitherto been at
the lower end of Mason's Island, where the shores receding
so as to give to the water at least four times as much space
in width for its discharge as it had above the island, has
enabled the same quantity of water to pass off with much
less depth, or, which amounts to the same thing, to pass off
less rapidly. Experience has taught, that above and along
the island where the current of the river is always confined,
there has never been shoal water and, availing themselves
of this experience, the corporation of Georgetown, have
projected the erection of works which shall continue the ef-
fect which is produced naturally above, artificially down-
wards, as far as beyond the bridge. These works will as-
suredly answer their expectations as far as they go. They
will force the current to take up the alluvium which obstructs
its increased velocity, and to Garry it down the stream; and
they will enable the water of freshets, loaded with new al-
luvium, to carry it forward to the very extent of the increas-
ed velocity of the current. But wherever the works cease,
and the expansion of the water begins, there will be a point,
which, in all its circumstances, of the direction of the current,
of the angle formed by the shores with that direction, of
their distance from each other, and the consequent expansion
of the stream and of the quantity of water to be discharged,
will be, as nearly as possible, similar and equal to the present
situation of the river below Mason's Island. If in the course
of twelve or fifteen years there has been so much alluvium
deposited at the foot of Mason's Island as to destroy the navi-
gation for ships up to Georgetown, then, under exactly the
same circumstances, the annual quantity of alluvium being
rather increased than diminished by the annual extension of
Digitized by Google
8
our agriculture, there will be, in twelve or fifteen years, an
equal quantity of alluvium deposited in the new channels,
situated in all respects as the former were. And as the in-
creased current will afford stronger resistance to the flood tide,
which now passes over the ground expected to be occupied
by the new channel, the equilibrium of the force of each, that
is, slack water, will be carried lower down, and the deposit
take place lower down. But the navigation for ships to
Georgetown will be equally obstructed, with only this differ-
ence, that ships will not be able to approach as near to the
town as they now do.
In respect to the injury likely to be done to the Washing-
ton bridge to the harbor of the city on the Potomac, and
in the Eastern Branch, if the said works should be erected, I
answer
The injury-which may be done to the Washington bridge,
will consist in deepening the river, in the new channel, in
such a manner, as that the piles on which the bridge is
built, may not be sufficiently deep in the mud to be held up-
right against the weight of any fresh, or logs, or ice, brought
down by the current; the mud itself being washed away
by the increased rapidity of the current in a place where no
such current ran or had been expected in the erecting of the
bridge. The amount of this injury would be actually equal
to the expense of erecting such piers or bridge wharves, as
would be sufficiently strong to uphold the bridge across the
channel thus made. But it is my opinion that the channel
would be thrown in the first instance into the city shore near
the mouth of the Tiber, that it would be afterwards deflected
towards the wing dams, which being so constructed as not
to let the current pass, would again deflect it towards the
shore, and that at the bridge. it would probably pass under
the present draw. I am however wholly uncertain as to
this point, presuming no more than to say, that it would
pass nearer to'the city shore than the middle channel, and
probably as close to the shore as the shore eddy would per-
mit.
In respect to injury to the harbor of the city on the Poto-
mac, it is my opinion, that there would be deeper water
from Peter's point downwards to the extent of the wing
dams than there is at present, probably from 20 to 30 feet.
In Ellicott's map of the city channel at the bridge, it is
marked to be nine feet deep; below the bridge, from 12 to 20.
The channel appears hitherto to have been the work of the
Digitized by Google
9
flood tide, as I have stated above, and it would probably re-
main open to that depth, excepting on a bar which might be
formed at the eddy between the flood tide and the current
deflected below the wing dams to the Virginia shore. 1 am
not therefore of opinion that the harbor of the city on the
Potomac will be injured by the shoaling of the water along
its shore, but that the water will rather be deepened.
In respect to the harbor in the Eastern Branch, I am of
opinion that it will not be injured, because, it is my opinion,
that the effect of the current produced by the wing dams,
will cease above the mouth of the Eastern Branch, and that
the current itself will be deflected to the Virginia shore, so
that the deposit of alluvium will take place above Greenleaf's
point, and the flood tide enter the branch as at present ; and
should no wing dam be placed below the last, laid down in
Mr. Moore's map, I am of opinion that the space below the
bridge above the point, and between the two shores, will be
sufficiently ample, and the water in this expanse sufficiently
sluggish in its current to receive and contain the alluvial
deposit of a great number of years, without injury to the
channel, which the flood tide would keep open from Alex-
andria into and in the Eastern Branch. But as the opinion
of Mr. Moore, differs in this respect from mine, in as far as
he believes that the current of the Potomac, as guided by
the wing dams, would be sufficiently strong to keep open á
good channel below the mouth of the Eastern Branch, I
must add, that if his opinion be correct, then the harbor of
the Eastern Branch would be filled up by degrees in conse-
quence of the resistance given by the Potomac current, at
its mouth, to the entrance of the flood tide by the alluvium
of the Potomac, brought so low down by the increased cur-
rent of the Potomac, which alluvium is now deposited
above and that, even if the water in the Eastern Branch
harbor were to remain of the same depth, it would become
inaccessible to large ships, because, wherever the contracted
current expands, there will be deposited in the course of
from 10 to 20 years, a shoal or bar across the whole river,
on which there will be not more than from 9 to 10 or 11 feet
of water in the deepest part of the channels which may
cross it.
Having taken the liberty to quote Mr. Moore's opinion as
stated in his 'filed report, I hope I shall not be considered
as encroaching on the respect due to the talents and opinions
of that gentleman, if I point out a circumstance in his
C
Digitized by Google
10
report, which appeared to me worthy of particular considera-
tion and remark. In all the facts which-he states, and in all
the deductions he draws from them, he seems to consider
the Potomac as if it were not a tide river; that is, as if the
flood tide had no operation whatever, and the current were
constantly downwards. Now it is a fact, that although at
Georgetown, excepting in very dry weather, or in strong
easterly winds, the tide has little perceptible current up-
wards, its effect is very strongly perceptible in the Tiber
creek, as I well know, from my own experience. All that
Mr. Moore advances would be undoubtedly strictly true, so
long as it were assumed that there is no such thing as an
operative flood tide in the river, operative to the deposition
of alluvium, even when it only diminishes, by opposing, the
velocity of a heavy fresh, without being at all able to turn its
current. In reasoning however, on the probable effect of a
work which is to change the present state of the river, the
operation of the flood tide is of as much importance to a cor-
rect conclusion as that of the current and ebb. The flood
never brings with it any alluvjum of its own, but it returns
to the land water back that which it sent to the tide, and, as it
were, forces it to deposit the greatest part of it on the ground
where they meet at the foot of Mason's Island; or if obstruc-
tions, acting as Mason's Island now acts, are continued down-
wards, removing the operation of the flood tide downwards
to the foot of those obstructions.
I might quote every river in Europe and in America in
proof of this fact, that the deposit of alluvium will be where
the tide meets the land water. But as this point is, con-
ceded, it remains to be considered, whether, considering the
volume of water discharged by the freshes of the Potomac,
such for instance as we have lately seen, there would be a
sufficient vent for them over a shoal of 10 feet in depth, and
about one mile wide. On this head a single fact satisfies
my mind, and forbids me to take up time with calculations.
The James river, in Virginia, discharges more water by one
third at least, than the Potomac, calculating their relative size
by the extent of country they respectively drain. Formerly,
that is 100 years ago, ships loaded with tobacco, at the mouth
of Shockoe creek, at the foot of the falls: now, the heaviest
fresh is discharged over a shoal near Rocket's below Rich-
mond, not a mile wide, and having only 10 feet water in the
channel. I might indeed have quoted the Potomac itself:
but as the immense quantity of timber which came down
Digitized by Google
11
with the late fresh, and touched the ground on the flats, ob-
structed the passage of the water, and forced it into the
channel, the example is not so conclusive.
Having had but a short time allowed me to put my opinion
on paper, I am aware that I have not been as full, as me+
thodical, and as clear as I could have wished. In the prins
ciples that govern the merits of the case, there is no mystery.
Independently of my oath, I could wish that the conclusive-
ness of my reasonings were evidence of my impartiality. It
is of infinite importance to this whole establishment, that
Georgetown should not lose its shipping harbor, or that,
having lost it, it should regain it. The advantage of every
part, is the success of the whole. But it is not my opinion
that the means proposed will do more for Georgetown, than
to create deep water for a greater distance below the town
than there is at present, and that the obstruction will be only
removed lower. There is indeed a means of bringing up to
Georgetown ships of the largest dimensions, and only one
means. But our present state of population and wealth, so
little warrants the undertaking, that to propose it, would be
to expose one's self to ridicule; and yet I believe it will be
undertaken and executed by our posterity. I will conclude
by recapitulating the substance of what I have said.
1. It is my opinion, that the works proposed by Mr.
Moore, especially if the Virginia channel be closed, will be
successful in making a deep channel, suppose of 20 feet at
least in depth, near the city shore, to the extent of the works,
probably to some distance below them.
2. That at the foot of the works the channel will be de-
flected towards the Virginia shore, and will not fall into the
channel leading from Alexandria to Greenleaf's point, until
it arrives near Alexandria.
S. That the increased velocity of the current will deepen
the new channel under the bridge, and that the bridge may
run the risk of being undermined and partially carried away,
unless supported by additional piers or wharves.
4. That the harbor of the city on the Potomac will not
lose its depth of water.
5. That the harbor in the Eastern Branch will probably
not be injured.
6. That there will be a deposit of alluvium, or bar at the
foot of the works above Greenleaf's point, across the whole
river, through which there will be two or more channels
but that it is not probable that there will be more depth of
Digitized by Google
12
water in any of these channels than there is at present on
the bars below Mason's Island.
7. That if the works and the velocity of the current be
carried lower down, the bar will be pushed lower down, and
may be carried below the mouth of the Eastern Branch, se
as to destroy. all shipping navigation above Alexandria.
8. And I will further add, that as a marsh has formed it-
self below the rock on Mason's Island, in its eddy, SQ it is
my opinion, that marshes will be formed in the eddy of the
wing dams; a circumstance which would be very injurious
to the health of Georgetown and of the city.
From all which, it results, that though the projected works
may not injure either of the two harbors' of the city, and al-
though the injury to the bridges which is reparable, scarcely
deserves consideration, compared to the importance of pro-
curing a shipping harbor to Georgetown, and although ad-
ditional depth of water will assuredly. be obtained, as far as
the works. extend, yet the object of these works will fail
because the causes, constant, powerful, and increasing,
which have destroyed the shipping harbor of Georgetown,
will still continue to exist, and will only be made to operate
in a different place. They will, therefore, produce in that
different place, the same certain effect.
Questions by the defendants to B. H. Latrobe.
1. Have you not been consulted on the proper means to
remove certain, obstructions to the navigation of the Dela-
ware near the mouth of the Schuylkill?
Answer. Yes.
2. Explain the method you have. proposed for that pur-
pose, and its principles
A. The shoal above fort Mifflin in the Delaware, is created
by a deposit of alluvium from the Schuylkill, in the passage
between two islands, or rather between a pier and the island
on which the fort is built. This passage or opening, is in
the eddy between the flood tide and the ebb tide. The tides,
that is, the flood tide going up and the ebb going down, do
not pass over the same ground. In the line of their eddy is
a range of islands daily increasing in size, while in all those
parts of the channel in which, above and below the islands,
the tides pass over the same ground, there. remains the
Digitized by Google
13
same depth of water which has existed the memory of
man.
The works I have recommended, have for their object to
stop up the present course of the ebb tide so as to force it
over. the passage between the fort and the pier, and also to
obstruct the present course of the flood so as to make it alse
take its course through the same passage. The Delaware
is so wide in this part, that the alluvium has ample space for
its deposit, which experience has proved never to take place
in any part over which both tides pass.
3. What is the kind of work you have recommended?
A. Loaded cassoons, or piers sunk at certain distances
from each other, and connected by ranges of piles driven
into the mud so as-to prevent the passage of water between
them. I have suggested this kind of work as the cheapest
which can be made to answer the purpose.
4. Do you understand the project of Mr. Moore, and the
nature of his works, sufficiently to compare them to those
proposed by yourself in the Delaware; and without disputing
about terms, may not both be called wing dams?
A. A wing dam is a term used to designate a work placed
in a stream in order to divert the course of the water in a
desired direction. It may be defined an artificial obstacle to
the natural course of a stream, which is not intended to ob-
struct entirely, but only to divert its course, and which, there-
fore, does not ever cross the stream from shore to shore.
The object of the works proposed by me in the Delaware,
and by Mr. Moore in the Potomac, being the same, they may
be called by the same name.
5. Is there not danger that the shoal you propose to re-
move in the Delaware, will, if removed, be deposited else-
where, and if'not, why is there no danger?
A. The fact being ascertained and admitted that no shoal
can exist in a place over which both the tide of flood and
tide of ebb. pass, the shoal removed will not be deposited in
such a place. But that it will be deposited elsewhere is cer-
tain ; it will be deposited out of the channel, unless in any
part of the present channel there should be an eddy. But
the whole of my principle goes to this point, that there shall
not be left any such place.*
Mr. Moore, in his comments, lays great stress on my having in the
Delaware recommended. works which he thinks similar to his own, for
the purpose of removing a bar, while I have denied their efficiency when
proposed by/Inm to be erected in: the. Potomac. And. he. has concluded
Digitized by Google
14
6. Supposing the wing dams proposed by Mr. Moore, to
be carried so low down, as to prevent any deflection of the
current towards the Virginia shore, but to throw it into the
line of the channel now existing between the Eastern Branch
and Alexandria; would not that obviate the evils you appre-
hend from the change of the channel of the current from
above?
his comment on this part of the subject with the following passage
" All these conclusions are plainly deducible from the deponent's own
" words, and from these conclusions one general result is also deducible,
" which is, if the projector of the Potomac works had projected those of
" the Delaware, they would, by removing one obstruction, have produced
" two more; and if the projector of the Delaware works had projected
" those of the Potomac, no alluvium could be deposited in the channel
" between the mouth of the Eastern Branch and Digges's point." The
passage is so obscure, that I cannot help believing that it became so in
the struggle between the desire to destroy the credibility of an opinion
given on oath,' and the reluctance to charge an honest man with perjury.
For the paragraph, if it means any thing, can only mean this That
whichever of my opinions was sincere, the other is in direct opposition
to it; and that, from some motive which is unexplained, I should at all
events have given an opinion opposite to that of Mr. Moore, and have
sworn to its integrity, whether it had been really my opinion or not.
For my opinion, given by desire of the Chamber of Commerce of
Philadelphia, I charged and received 150 dollars. There were no local
interests concerned, to bias either myself or those who consulted me; and
therefore, there is every probability in supposing, that my opinion, being
unbiassed, was honest.
In the case of the Potomac, I have not had even the temptation of a
fee; and I believe my interests coincided quite as much with those of
Georgetown as with those of the Eastern Branch.
In the difference of the two cases, however, is to be found the differ-
ence between my two opinions. Above the bar in the Delaware the
tide runs up to Trenton, a distance by the river of about 45 miles. The
tide rises 7 feet, and runs at an average rate of 2 miles to 3 miles an
hour. Such a tide 18 capable of removing the alluvium from the chan-
nel if the ebb and flood both pass over it. The only place in which
alluvium is deposited, is that over which, partly by the interference of an
ill placed pier, the ebb and flood do not pass. All above and below this
bar is kept open by the joint effect of the ebb and flood.
In the Potomac, on the contrary, the effect of the flood as a current
ceases at the bar, and this very circumstance alone, has caused the bar
to be deposited where it is now lodged.
Could the flood be made to run up to Georgetown, over the same
ground over which the ebb or land water now passes, with the same
force with which it now runs in the Eastern Branch, it would keep
open a channel as it does in the Delaware.
The difference of the two cases therefore, sufficiently accounts for
the difference of my two opinions, without the necessity of supposing
me to have been dishonest or perjured in the delivery of either of them.
Digitized by Google
15
A. If the wing dams were carried down as low as stated
in the question, and so as to effect the object implied by it, I
am of opinion that, then the situation of the river in all re-
spects at the foot of the works, would be the same as it now
is at the foot of Mason's Island. If I may be permitted to
put a very strong case by way of expressing strongly my con-
viction, I would say, that if the river were confined by works
from Mason's Island downwards, as low as Digges's point,
that there would be created a deep channel as low down as,
that point; and that the flood tide would scarcely be per-
ceptible a mile above that point; but that below the foot of
the works, there would, in time, be formed a bar exactly
similar to that now below Masons's Island; which would
rise until it had increased the current of the water from
above through its channels, so much as to prevent further
deposit in those channels. The alluvium would then be de-
posited lower down and make the bar wider. I would go
with my case to the mouth of the Potomac, if several power-
ful streams, as the Occoquan, which creates the Matawoman
shoal, did not fall in below Digges's point; above Digges's
point, I believe there would not be less nor much more than
9 feet water on such supposed bar, because no powerful
land stream enters the river above that point, so as material-
ly to change the circumstances which exist above at Mason's
Island.
7. By your answer, and from your deposition it appears,
that you conceive the bar across the Potomac, wherever it
may be, to be created by an irresistible operation of nature,
which art cannot control; to wit, by the deposition of alluvium
at the point where the flood tide slackens, or abates the cur-
rent of the land water. I ask you whether this operation
will take place at the point at which there is slack water at
the time of a fresh, or at the usual place of slack water when
there is no fresh ?
A. The operation of the flood producing an abatement of
the velocity of the land current, a deposition will take place
far above the place of slack water. Its place will begin at
the point at which the current decreases, and will extend
downwards to the place ordivision line of slack water. Now,
as the heavier particles will be first deposited at the first
abatement of the current, and as from the first abatement of
the current downwards, its motion becomes regularly and
gradually slower, it follows, that the alluvium will be de-
posited all the way from the first abatement of the current
Digitized by Google
16
until it entirely ceases, the quarity remaining to be deposit-
ed decreasing with the increased tendency to deposition.
But, independently of the decreased current arising from the
resistance of the tide, the expansion of the water from a con-
tracted state, causes great part of the relaxation of. the cur-
rents. In a great fresh the first abatement will-be certainly
lower down than when there is not any fresh in the river.
8. You have said that you know by experience that there
.is a strong flood tide in the Tiber; does that circumstance
argue that there is a flood tide or current upwards in the Po-
tomac opposite the mouth of the Tiber? or is it not suffi-
ciently accounted for by the swell of the Potomac?
A. The tide rises and falls in the Tiber 3 feet 4 inches at
an average, and runs strongly. This proves that there is a
swell at least in the Potomac, which acts to diminish the 've-
docity of the current, and of course promotes its tendency to
deposit its alluvium, with a force capable of raising the water
in the Tiber to that height. On this point depended the
remark made on the importance of the effect produced by
the flood tide, which I know, and have stated to produce no
great current at Georgetown.
9. Do you believe that there will not be a difficulty in pre-
serving ship navigation to any port of the district of Colum-
bia, for any considerable number of years?
A. Not being able to, see any cause for the decrease of the
annual descent of alluvium from the upper country into our
tide waters, it is my opinion that in the course 'of time our
bars will spread so as to confine the extent of this navigation
to places more and more distant from the falls of our rivers.
But it is not in my power to say when the bar commencing
below Mason's Island will be so extended downwards, as to
block up ship navigation below the line of the District.
10. Do you think that, without artificial aid, our ship navi-
gation into the district will remain open for 100 years?
A. The term artificial aid renders it difficult to answer the
question precisely. But without saying what kind of artifi-
cial aid would be effectual, I have no hesitation in saying
that I think that in 100 years, more or less, artificial aid will
be necessary throughout the district.
Digitized by Google
17
Question by the complainants.
Q. Have you been consulted on similar works in Ameri-
ca or Europe, and concerned in their construction? If you
have, state your experience?
A. I have, and having, after my arrival in England, in
1785, and during 9 years residence in that country, had the
benefit of the instruction of Mr. Smeaton, and of his experi-
ence, and also of my own, especially at Maldon and Rye; I
will answer by generally asserting, that it is the universal
opinion of all experienced engineers, founded upon the
uniform miscarriage of all works constructed to form chan-
nels by scouring, as it is termed, that such works, far from
answering their object, increase the evil, by creating a hole
at their mouth, and for some distance below, and heaving up
a bar beyond it. This has exactly been the operation of the
freshes since the confinement of the water to the east side
of Mason's Island. The same cause and effect may be seen
at all fords, across which the bottom, being disturbed, is
deepened, and a bar formed below.
Answers to the Queries proposed by the-committee of the dis-
trict of Columbia, respecting the improvement of the Navi-
gation of the Potomac.
WASHINGTON, April 23d, 1812.
SIR,
I HAVE had the honor to receive your letter, pro-
posing certain questions respecting the improvement of the
ship navigation of the Potomac up to Georgetown; and sub-
mit the following answers.
Question. 1. Will it be practicable to improve the ship
navigation from Mason's Island, to the Eastern Branch, by
any works placed in the bed of the river; and if practicable,
what is the best method of effecting it ? and what will be the
effect of such works on the navigation of the Eastern Branch,
and of the Potomac below the Eastern Branch?
Answer. The question relates only to the improvement of
the navigation in the distance between Mason's Island and
the Eastern Branch. This part of the navigation is at pre-
sent obstructed by a bar deposited within the last 20 to 25
years below Mason's Island, about the point at which the
D
Digitized by Google
18
expansion of the river in breadth, diminishes the rapidity of
the current of the river from above: being in the place, and
under the circumstances, which occasion bars to be invariably
deposited, in all the rivers of the known world. The di-
minution of velocity in the current at the foot of Mason's
Island being the cause of the deposit, any works, that by
compressing the current, and thereby maintaining its veloci-
ty as far down as the Eastern Branch, will remove the bar
from its present situation, and prevent any deposition in the
same place. The best works that could be erected to effect
this particular object, if desirable, would be those, that are
most permanent in their form, construction, and materials.
The effect of such works on the navigation of the Eastern
Branch, and of the Potomac below the Eastern Branch, will
be as follows If the works bè so constructed as to increase
the rapidity of the current to a degree sufficient to remove
the bar, and to keep the channel clear, as low down as the
mouth of the Eastern Branch, and if the works be not con-
tinued beyond that point, then the abatement in the rapidity
of the current, about the mouth, or below the mouth of the
Eastern Branch, will cause the alluvium which has been
brought down thus far, to be deposited gradually from the
point at which the current abates its velocity, to that at which
the flood tide holds it in equilibrium, or to the point at which
there will be slack water at the time of flood. For the situa-
tion of the river both above and below the termination of the
works, will be precisely the same, as it is now above and be-
low the foot of Mason's Island. To believe, therefore, that
no bar will be formed by the deposit of alluvium in the first
place in which the current becomes languid by its expansion,
and in which it twice in 24 hours ceases by the opposition of
the flood tide, is to believe, either, that there will be no new
alluvium brought down from the upper country, or that the
laws of nature which have hitherto operated in the Potomac
to create the bars below. Mason's Island, and which have
operated in all out rivers, will cease to operate, after the
erection of the proposed works.
And from this it results, that if there be a bar formed
below the Eastern Branch at the foot. of the works, the navi-
gation of the Eastern Branch will be: obstructed, nor will the
current of the Eastern Branch force a. passage through the
bar; in as much as the water of Rock creek, which is as
copious as that of the Eastern. Branch, is unable to force a
passage through the present bar which is below. the mouth
Digitized by Google
19
of Rock creek. And although the flood tide, which is oh-
structed in its passage up the Potomac by the weight of the
descending water*of that powerful stream on the east side of
Mason's Island, finds its way-with rapidity into the expanded
bays of the Eastern Branch, where it meets with little oppo-
sition, and now runs with equal velocity at the flood and ebb
tide, yet, if the current of the Potomac should be maintained
in its rapidity by the proposed works as far as the Eastern
Branch, then the flood tide meeting at that point the same
opposition which it now encounters at Mason's Island, will
not enter the Eastern Branch as it now does, and a bar across
its mouth, will be formed on the margin of the land current,
which will rise until it leaves a passage only sufficient to dis-
charge the average quantity of water supplied by the streams
which fall into the Eastern Branch.
The effect on the Potomac below the Eastern Branch,
will be to obstruct the navigation, by a bar at such a distance
below the termination of the proposed works, as shall be
sufficient to abate the rapidity of the current by its expan-
sion.
It may be proper to add, that the period at which the bars,
of which I have spoken, will be removed and formed, will
depend on the frequency, violenoe, and muddiness of freshes;
and on their coincidenoe with strong gales from the east.
For it is ta be noted, that a strong easterly wind always raises
the flood tide, sometimes, as much as 2 feet 6 inches above
its common level, and lengthens its duration, so as, some-
times, to prevent its falling more than one foot; that is, to
keep it at the time of ebb, sometimes 1 foot 6 inches above
high water mark. The common rise and fall at the point,
is above 3 feet. In a strong south easterly gale, if there is a
muddy fresh in the river, the deposition is more rapid, and
higher up the river, than at any other time.
Q.2. Will the navigation to the Tiber be injured by the
proposed plan, and in what manner?
A. To answer this question decidedly, the manner, in
which the Washington canal is ultimately to be completed,
should be known, as that canal occupies the bed of the Tiber.
But under the best consideration that I have the means of
bestowing on this part of the subject, I answer, that I do not
believe that any injury will be done to the navigation of the
Tiber by the proposed plan, if the canal be properly com-
pleted, and in the manner in which it is most for the intereat
of the canal company that it. should be. If, however, the
Digitized by Google
20
Tiber remain in its natural state, as the proposed works will
diminish the fall of the ebb, the bed of the Tiber will rise in
the same proportion; and the water will Be shoaler at flood
tide.
Q.3. Will the proposed plan so change the current or
channel, as to endanger the safety of the Washington bridge,
or render it necessary to make an additional draw ?
A. If. by. the proposed plan, that is meant which has been
filed in court, and laid on the table of the committee, in
which oblique dams are laid down on the middle ground
I
answer, that it is my opinion, that the current will, in conse-
quence of the oblique dams, be thrown still more decidedly
into the city shore at the bridge, than it is at present, and,
that the channel will probably pass through the present
draw.
If this opinion be correct, then the bridge will receive no
material damage. But if the opinion on which these wing
dams have been projected be correct, and their object be ob-
tained, which is to force a channel through the centre of the
horse shoe shoal, or middle ground, then it will be necessary
of course, to open a draw in that channel, and to alter, and
strengthen the construction of the bridge in that place. If
the proposèd channel should be effected, and this be not
done, then it is my opinion, that the bridge would be too
weak in that place to resist the force of current, ice and logs
which would be brought against it, after losing the support
which the piles at present derive from being driven through
mud from 16 to 27 feet deep.
Q. 4. Will the effect of the proposed works be to fill up
the main channel near Alexander's Island, by diverting its
course towards the opposite shore, or in what manner will
the proprietors of that island be injured?
A. If the works to be constructed, are made efficient to
divert from its present course the channel or main current,
into the middle of the river, it will of course desert the
channel now runningmear Alexander's Island. The conse-
quence will be a bar across that channel at its upper termina-
tion, and near the edge of the new channel and current,
where it diverges from the old one. But the channel itself,
although rendered by this means useless, will continue deep
for a length of time, because the alluvium carried down by
the current, will take a different direction, part being de-
posited along the edges of the new channel, part being car-
ried forward to form new bars and shoals in the expanded
Digitized by Google
21
water below the works. As far, therefore, as it is advan-
tageous to the proprietors of the island to have a practicable
channel along their shore, they will be injured. What effect
the destruction of the channel will have on their fisheries, I
am unable to determine, from want of correct knowledge
and experience on that part of the subject.
Upon the whole, I beg leave to answer as follows.
The main question appears to me to be this Is it possi-
ble to improve the natural bed of any river, which is subject
to freshes that bring down alluvium from the upper coun-
try, so as to prevent the deposition of that alluvium in the
form of bars, at the place at which the rapidity of the current
is repelled, slackened, or annihilated, by the flood tides, or by
its expansion?
If this question be answered, that it is impossible, then the
works proposed in the natural bed of the Potomac will be
useless at least, and may be destructive of the navigation
where it now does, and for many years to come may, subsist.
In answering the question thus positively, I need only ap-
peal to the fact, that, although great works have been from
time immemorial constructed, either through ignorance, or
as temporary expedients, at the mouths of tide rivers and of
rivers discharging themselves into seas in which there is no
tide, as into the Mediterranean, and the Baltic, they have
never succeeded in one single instance to effect a perma-
nent channel through a natural bar, but have always done
permanent injury, where they have even effected a tempora-
ry good. In this opinion, I am supported by the testimony
of the ablest engineers who have treated on the subject,
especially by Fabre, whose work on the theory of rivers,
streams, and torrents, is invaluable, and in which the system
laid down, is not less ably proved by mathematical demon-
stration, than by the facts which he exhibits from his own
experience, and that of others, in works actually erected for
the last 2,000 years. The essential points in proof of what
I have advanced from this work, I have had the honor to
read to the committee.
In consequence of the opinion I have stated being so
general as to cover all the details, I think it unnecessary to
enquire minutely into the effect of the works proposed
on the deflection or reflection of the current, on the waste of
shores, on the change of the channel, or into the particular
form, height, and position of the works. If they are partial,
inefficacious, and not permanent, then their effects will be
Digitized
by
Google
22
partial, useless, and evanescent. If they are extensive, ef-
ficient, and strong, then the effect will be decided, rapid, and
lasting. But in all cases, they will be useless to the object
proposed, which is to prevent the formation of a bar below
the termination of the current downwards; for while allu-
vium is brought down into water languid in its current, and
which is sometimes stagnant, so long will bars be formed in
that water.
B. HENRY LATROBE.
To the Honorable Joseph Lewis,
Chairman of the Committee
of the District of Columbia.
Additional Remarks and Authorities.
IT is very evident, from the whole drift of the-opinion
which I have given in my deposition, and the answers re-
turned to the questions put to me by the committee of the
House of Representatives of the United States, that 1 consi-
der every attempt to recover the ancient ship channels in
the beds of our great Atlantic rivers, which formerly led up
to the very foot of their falls, as wholly nugatory.
A question was put to me in the committee to this effect
How does. it happen, that formerly, under all the circum-
stances, of freshets and opposing tides, which now exist, and
under which, you state, that bars must necessarily be formed,
the navigation of the Potomac remained for so many years
deep and practicable, up to the foot of the falls?
The answer is this: It is not 100 years since the whole
of the country above the falls was covered with wood, and the
soil was bound together by the roots of vegetables, so as to
secure it from being washed. At that time, also, the heavy
rains of the spring and summer, were filtered and let down
gently upon the ground through the branches and leaves of
the trees. The case is how wholly altered. The plough not
only loosens, but bares the soil; and the increase of shoals in
our rivers has kept exactly pace with the extension of our
agriculture. The Potemac is not, in this respect, more un-
fortunate than any other river in the United States. Below
Albany, a bar is formed, highly prejudicial to the navígation
of that city, The Delaware, the Susquehannah, opposite to
Digitized by Google
23
Havre de Grace, the Quantico, the Rappahanoc, the James
river, the Appomattox, the Roanoke and its neighboring
streams, are all in the same situation with the Potomac.
Large ships formerly loaded at Albany, at Dumfries, at
Fredericksburg, at Richmond, and at Petersburg, as well as
at Georgetown; now, the depth of water admits only small
craft. 1 mention these situations particularly, because I
have seen them, and enquired into the facts myself.
If it were the question in the case of Georgetown, whether
it is beyond the power of art to produce a ship navigation to
the wharves, I should certainly not answer in the negative.
But the enquiry is at present only into the possibility of ef-
fecting this object, by means of works in the bed of the river,
intended to operate on the channel, by means of the natural
current. Such works will assuredly be not only useless, but
prejudicial. The expense will be thrown away, and the
navigation rendered much worse than at present.
After what I have said, it might appear invidious to find
fault with the form and manner of the projected piers or
wing dams; especially as the bill passed in the Senate speci-
fies no particular kind of works. Knowing myself, however,
to be wholly unprejudiced in the case, either by interest, or
affection; as it is not denied, that the plan of wing dams is
that in contemplation; and all delicacy having been re-:
moved by the manner of Mr. Moore's comments, I will offer
a few words on this subject.
1. Oblique piers were formerly, that is, not later than a
hundred years ago, used in Europe for similar purposes as
those intended to be accomplished here. They were found
not only useless to the attainment of their object, but preju-
dicial, where the current ran decidedly and always, in the
same direction. Here they would be. still more injurious,
where there is a draft of the flood upwards. This draft,
current, or eddy, would be increased at the back of the piers,
and also receive a new direction from them, the pressure of
the land water being held off by their upper sides.
2. The provision, contained in the bill as solicited origin-
ally on behalf of Georgetown, that the wing dams shall not
rise above high water mark, is a most extraordinary one.
Such a dam in time of a fresh, would create an enormous
hole behind it, and throw up a bar, which would, perhaps,
amount to an island when the water had subsided. Let any
one drop a stone into water running over 2. soft bottom, so
Digitized by Google
24
that the top of it shall be a little below the surface of the
water,and the effect will be instantaneously evident.
3. If the works, however, were to succeed perfectly as to
the channel, the chance, I had almost said the certainty, of the
creation of marshes, ought to be well considered. George-
town would suffer severely from such a circumstance.
I annex a few authorities translated from Fabre on this
subject, and recommend his work entitled Essai sur la
Théorie des Torrens et Rivières, to the study of all those who
attempt to meddle with so difficult and important a subject,
as the navigation of natural streams. There is none in
which works that do not succeed in doing good, are more
certain of doing injury .injury, which repentant art cannot
afterwards repair.
§ 270. " We have seen above, that rivers carry down to
" the sea (to the tide) the earth which the rains wash into
" them ; that this alluvium being pushed forward by the
" land water and repelled by the ocean, will stop where there
" is an equilibrium between these two powers, and will there
" form bars, or islands according to the local circumstances.
" This general remark may be here made, that on the ocean
" (where there is tide,) bars will be formed, and islands in
" the Mediterranean," (where there is none.) (see p. 115.
Paris ed. 1797.)
The subsequent discussion in this chapter is of great im-
portance, but too long to find room here.
P. 204. § 270 He observes, that these accumulations are
less injurious where there is a tide, because the flux and re-
flux spreads the bars and keeps them down; and because, at
the time of high water, a vessel may pass them; whereas,
where there is no tide, the accumulation produces islands.
At the head of our tides, the state of our rivers is inter-
mediate between the two cases. We have not sufficient
flood to spread and keep down our bars, nor have we the ad-
vantage of a high tide to lift the vessels across them.
§ 450. p. 205, He proceeds, " From what we have said
" above, § 447, it is evident, that it is impossible to secure
" the navigation of rivers falling into the Mediterranean. In
" order to prevent the alluvial deposits, the formation of
" islands, or the division into many channels, you may con-
" tract, if you please, the current, by piers, and push them
" as far the sea. You do not, however, by this means, anni-
" hilate the mud brought down by the river. It will con-
" tinue to come down, and be carried to the spot, at which
Digitized by Google
25
" the land water and the sea water are in equilibrium: that
" is, in the neighborhood of your new embouchure, (or at
" the foot of your works.) Thus the difficulty will not be
" conquered, but only displaced."
§ 453. " The difficulties explained § 450, oppose them-
" selves, and for the same reasons, to the removal of bars
" formed on the ocean (at the tide.) All the piers which
" can be erected in order to contract and contain the current,
" and to give to it more force, serve only to remove them,
" in order to reproduce them further off," &c.
He then gives numerous instances of the truth of these
remarks in practice.
On the subject of wing dams, see his chapter on piers.
(digues.)
§ 319. He examines theoretically the defects of wing
dams, and proceeds thus: " All these inconveniences are
" most amply proved by experience. The piers constructed
" on this principle on the river Durance, furnish examples
" of them without number."
§ 320. " It is seen by this enumeration (of defects) that
" piers, (or dams) placed obliquely to the current, are vicious
" in every point of view that they never produce the effect
" intended : that they always produce one contrary to that
" which ought to have been had in view and that, conse-
" quently, they ought always to be proscribed, when the
" question is about the protection of the shore, or a part of
" the river against the current." (by diverting the same.)
In § 321, he points out the only use to be made of wing
damis, namely, to throw the current of the river ashore, into
the head of a canal, diverging from the stream, &c.
I could have accumulated authorities from other authors
equally respectable, but more are not necessary, in a case,
perhaps, too fully treated already.
E
THE END.
Digitized by Google
Digitized by Google
Digitized by Google
Digitized by Google
Digitized by Google
R
Digitized by Google
Digitized by Google
Digitized by Google
Digitized by Google
Digitized by Google
Digitized by Google
Digitized by Google
Digitized by Google
Digitized by Google
Digitized by Google
R
Digitized by Google
Digitized by Google
Digitized by Google
Digitized by Google
Digitized by Google
Digitized by Google
Digitized by Google
Digitized by Google
Digitized by Google
Digitized by Google
Digitized by Google
Digitized by Google
Digitized by Google
Digitized by Google
Digitized by Google
Digitized by Google
Digitized by Google
Digitized by Google
Digitized by Google
Digitized by Google
Digitized by Google
Digitized by Google
Digitized by Google
Digitized by Google
Digitized by Google
Digitized by Google
Digitized by Google
Digitized by Google
Digitized by Google
III E ur MICHIGAN LIBRARIES
Digitized by Google
Digitized by Google
Digitized
Digitized by Google
or LIBRARIES
Digitized by Google
Digitized by Google
Digitized by Google
Digitized by Google
Digitized by Google
Digitized by Google
MICHIGAN
1
Digitized by Google
Digitized by Google
Digitized by Google
Digitized by Google
Digitized by Google
LIBRARIES
Digitized by Google
Digitized by Google
Digitized by Google
Digitized by Google
Digitized by Google
1
Digitized by Google
Digitized by Google
Digitized by Google
Digitized by Google
Digitized by Google
Digitized by Google
Digitized by Google
Digitized by Google
Digitized by Google
Digitized by Google
Digitized by Google
Digitized by Google
Digitized by Google
Digitized by Google
Digitized by Google
Digitized by Google
Digitized by Google
Digitized by Google
Digitized by Google
Digitized by Google
Digitized by Google
Digitized by Google
Digitized by Google
Digitized by Google
Digitized by Google
Digitized by Google
Digitized by Google
Digitized by Google
Digitized by Google
Digitized by Google
Digitized by Google
Digitized by Google
Digitized by Google
Digitized by Google
Digitized by Google
Digitized by Google
Digitized by Google
Digitized by Google
Digitized by Google
Digitized by Google
Digitized by Google
Digitized by Google
Digitized by Google
Digitized by Google
Digitized by Google
Digitized by Google
Digitized by Google
Digitized by Google
Digitized by Google
Digitized by Google
Digitized by Google
Digitized by Google
Digitized by Google
Digitized by Google
Digitized by Google
Digitized by Google
/
C
Digitized by Google
Digitized by Google
Digitized by Google
Digitized by Google
Digitized by Google
Digitized by Google
Digitized by Google