The Northern Daily Times.
Liverpool, Merseyside, England, 1857-03-03 00:00:00

POLYTECHNIC SOCIETY.

The monthly meeting of this society was held last night
in the Royal Institution Colquitt street. It was more than
usually interesting, owing to the fact that Mr. George
Rennie, C.E., F.R.S.. attended, on the special invitation
of the society, to explain his project of a breakwater at
the mouth of the Mersey. There was a numerous
attendance of members and strangers The chair was
taken at eight o'clock by Mr. Joseph Boult. In opening
the meeting, he read a letter from Charles Turner, Esq.,
chairman of the Dock Committee, stating that he would
have had much pleasure in attending the meeting, to
hear Mr. Rennie's explanation, were it not that he was
prevented by a previous engagement.
Mr. Rennie then proceeded to explain his project,
illustrating his plans by reference to maps. He e,bserved
that he was no stranger to Liverpool, he having been
engaged nearly thirty years since in an important sur-
vey of the river, and he, therefore, did not come to
the consideration of the important subject which he
was about to lay before them ignorant, or
with an imperfect knowledge of the cirenmstances
connected with it. The subject of his discou-se was the
formation of a breakwater trom the Black Rock to near
the Lighthousf, for about three miles in a north-easterly
direction, the effect of which would be to guide the stream
of she river in certain courses, and eaase the currents to
pass more directly through them. Another effect would
he to protect the northern shore from the strong winds
that now blew on it. On of the evils of the p )rt was
the various channels and sand banks with which it was
filled, and to keep up these channels the greatest precau-
tion wos necessary, so much so, in fact, that in his judg-,
ment it was a wonder how the immonse trade of the port
was so successfully and safely carried on. If these
channels could be combined into one, the navigation of
the river would be rendered more easy than at present,
while the expense of maintaining it in a stee of
efficiency would be less than at present, and the loss from
shipwreck also less. The only way to effect it would be
to throw a bre,kwatet in the direction-lie-Bad Mentioned.
The Victoria Channel was well sheltered when the wind
blew from the south and south-west, and in consequence
it was frequently used, as many as 15,000 vessels basing
passed through it in 1856. Consequently he would make
a small pier or jetty from the Black Rock, and allow a
gap of half a mile open, through which the channel
might continue to flow. Mr. Rennie then referred to
the gradual increase of the Great Burbo bank, and the
changes in the other banks and channels of the river, and
from these argued the necessity of such a work as that
projected by him. _

The Chairman exhibited surveys of the Mersey,
taken in 1689, 1756, 1813, and 1847, which showed
that the north shore, from Bootle to Formby, had
advanced between the interval of the first and last date
1,000 yards, and that the harbour, which, in the time of
Col'ins' survey (1689), existed at Hoylske, I•iad been
completely filled up. He also exhibited Lieut. Parke's
surveys of the river of 1852, '54, and '56, and from the
frequent changes of the position of the Bell buoy, as
shown in these surveys, argued the n 'cessity of some
steps being taken to preserve the safe navigation of the
river.

Captain Conk, superintendent of pilots, asked to what
cause Mr. Boult attributed the changes ?
Mr. Book said, they were to be attributed chiefly to
freshes, draughts, winds, and reductions of tidal area,
and the remedial measures should be especially addressed
to those causes. Mr. Boult stated, that lie found, by
experiment that the clay washed away at Egremont,
consisted of upwards of .50 p-r cent. of gravel and
sand. The banks in the river consisted for a great part
of clay and gravel, and lie had no doubt that a great part
of the formation of banks in the river was thus derived
from the shores.

Captain Cook stated that within his knowledge the
channel was never in a worse condition than at present,
and he thought it a miracle how their pilots ever got
vessels into port.

Mr. Heath remarked that in the Roman charts, and
even in the charts of the time of the Conquest, there
appeared no mention of the estuary of the Mersey at
all. The conclusion seemed almost certain that the
formation of the harbour of Liverpool was of a compara-
tively recent date. Then the question arose, what was the
law which had rendered perhaps a narrow and shallow
stream—forming an outlet into a kind of sea lake—into a
deep water channel to so noble a port ? He thcugbt it
impossible to avoid coming to the conclusion that
the 'interior part of the harbour of the Mersey was
something in the shape of a sea lake, communioating
with the sea by means of a shallow stream, and
the probability was, that the sea entrance was
where Wallasey pool now was. He therefore thought it
would not be safe to adopt any such plan as that of Mr.
Rennie, with the comparatively limited and partial infor-
mation which they had at present. The course he suggested
that wou suutaa accumulate and generalise
the facts which came out piecemeal, adding thereto their
own conclusions, drawn from historical and geological
sources, so that the public might be able to ascertain a
far as possible what the law affecting the changes was,
whether the tendencywas to increase the sand banks, whether
the Bootle shore was advancing or going back, and the
other points connected with the question.
Mr. Towson said all large rivers passing into the sea had
a tendency to form deltas at the mouth. He thought it a
question to be considered, whether there was not some
natural law which rendered it necessary in some way that
those hanks, islands, or deltas should be formed.
Mr. Brown remarked that the greatest changes appeared
to have taken place since the formation of the docks, when
very great interruptnn must have taken place to the
stream. He expressed an oninion that when the dock
works ceased upon this side, a deep channel would be formed
where the water had an inclination, which it should be th,z,
duty of those who had the charge of the river to waaalt and
encourage. He therefore urged that there was not the
ground for apprehension which some parsons seemed to
think eaista

A conversation followed .ipon the details and probable
effect of the projoct, in which Mr. Abrahams, Mr. Hall,
Mr. Alderman liennett, Mr. J. R. Jeffery, and other
gentlemen took part.
Captain Cook observed that he considered it essential to
the navigation of the river to preserve the Rock channel,
and as Mr. Rennie's project would have the effect of
silting up that channel, he would, as one practically
couversant with the navigation of the river, be opposed to
it. He a'so doubted the safety and practicability of
making the breakwater with secure foundation in the place
mentioned.

In answer to Mr. Heath and Mr. Jeffery, Mr. Hall and
other gentlemen, Mr. Rennie stated, that he would leave
the breakwater as high as the highest water on the bank,
and that its tendency unquestionably would bo to silt up
the rook channel, but that while doing so, it would compen-
sate by general improvement to the channel. He declared
that the river was becoming more inaccessible, not from
any decrease in the depth of water, but from its changes.
The effect of the breakwater upon the banks outside
the river would probably be to remove them gradually or
drive them further from the mouth. He would not have
the breakwater made all at once, but by degrees, so that
its effect could be judged of. He maintained that the
construction of the breakwater was perfectly sa►e and
practicable, supporting his argument by instances of similar
works elsewhere.

Mr. Boult at some length supported Mr. Rennie,
remarking, among other points, in reply to Mr. Brown, that
the tendency of the river was much more to form many
channels than to run into one. He claimed for the project
a full and fair hearing, and expressed regret that for more
than two years back no move had been made upon the
whole subject by any of the public or corporate bodies of
Liverpool.
The proceedings closed with a vote of thanks to Mr,
Rennie.