MEETINGS OF SOCIETIES. 185 
river having been taken through the estuary between half-tidal 
groining walls, but these not having proved as successful as the 
Tyne works, it was decided to construct two breakwaters in some 
respects similar to those on the Tyne, one of which has been con- 
structed and the other is in progress, the result so tar being most 
satisfactory, for since the completion of the south breakwater, a 
considerable improvement has already taken place, the bar having 
been lowered several feet. The entrance to the Liffey, near Dub- 
lin, is one of the most interesting and instructive examples of the 
successful treatment of a difficult bar. The improvement works 
were commenced in the last century by the construction of the 
great south wall, extending seaward in almost a straight line with 
the river, crossing the low foreshore known as the South Bull 
Sand. The effect of this wall was to fix the direction of the chan- 
nel. Several plans were suggested early inthe present century for 
further improving the entrance, and if possible for the removal of 
the bar. Eventually it was decided to construct the great north 
wall, starting some distance up the coast and converging towards 
the end of the great south wall, thus enclosing a great tidal area 
for scouring purposes, at the same time torming, with the south 
wall, a sort of nozzle, directing and concentrating the action of the 
tide on the bar, and likewise protecting the inside harbour from 
the waves. Although these works are placed at great disadvan- 
tage, on account of the shallowness of the sea for some distance 
from the entrance, they have been designed so as to make the best 
possible use of the available scouring power, and their success is 
established by the fact that the bar has been lewered to the extent 
of 1ofeet. The following figures give a progressive account of the 
effect of these works since their completion :—1822—minimum 
depth on bar at low water, 6 feet 3 inches; depth on bar at stan- 
dard high water, 19 feet 3 inches. 1828—minimum depth on bar 
at low water, g feet 6 inches ; interval 6 years; rate of increase of 
minimum depth per year, 6°50inches; increase of minimum depth, 
3 feet 3 inches; depth on bar at standard high water, 22 feet 6 
inches. 1833—minimum depth on bar at low water, 10 feet 6 
inches; interval, 5 years; rate of increase of minimum depth per 
year, 2.40 inches; increase of minimum depth, 1 foot; depth on 
bar at standard high water, 23 teet 6 inches. 1856—minimum 
depth on bar at low water, 13 feet; interval, 23 years; rate of in- 
crease of minimum depth per year, 1°82 inches; increase of mini- 
mum depth, 3 feet 6 inches; depth on bar at standard high water, 
26 feet. 1873—minimum depth on bar at low water, 16 feet; in- 
terval, 17 years; rate of increase of minimum depth per year, 2°11 
inches ; increase of minimum depth, 3 feet; depth on bar at stan- 
dard high water, 29 feet. An interesting history of the Dublin 
works will be found in Mr. J. J. Mann’s paper on ‘‘ The Removal of 
River Bars by Induced Tidal Scour,” published in ‘‘ Engineering,” 
Vol. XXVI, from which paper the above table has been taken. 
Another history will be found in the ‘“ Minutes ot the Institution 
of Civil Engineers,” Vol. LVIIL, in a paper by Max.-J; P. Griffith, 
M. Inst. C. E. From these cases it will be noticed that there are 
‘certain fixed principles involved ineach and all of them. The first 
is that the entrance is fixed at a point in a direct line with the 
direction of the river, and in as deep water as circumstances will 
allow. The second is that the works are so constructed that the 
