184 JOURNAL OF SCIENCE. 
bar. The contrary effect is seen in the case of the Richmond 
River, where the entrance is exposed to the wave action; conse. 
quently a bar obstructs the entrance. We may safely deduce from 
this that in order to cope permanently and successtully with the 
sand, it is necessary to extend artificially the entrance to a point 
where the depth of the water is such that the waves are unable to 
heap up the sand, to make the entrance of such form that the force 
of the waves will be expended before they advance into shallow 
water, and at the same time directing and concentrating the action 
of the ebb tide and upland waters, so that their force may be used 
to the best advantage in combating the mischievous action of the 
waves. Sir John Coode’s observations show that the movement 
of the sand from the beach seaward always terminates in about 34 
fathoms, and in his works he goes upon the broad principle of 
passing beyond the line of disturbance. (Minutes Inst. C.E., Vol. 
LXX., p. 45.) This demonstrates the advisability, where practic- 
able, of carrying the works out to at least that depth. On dealing 
with the action of waves he says that ‘ the effect of wave action is 
at lease a hundredfold greater than that of the tidal action.” And 
if this be so it clearly proves the necessity of breaking the force of 
the waves before they have an opportunity of throwing up. sand. 
Mr. Walter Raleigh Brown, M.A., M. Inst. C.E., speaking upon 
the subject, says (Minutes Inst. C.E., Vol. LXX., p. 35):—‘‘ In all 
cases ot sand pushing across the mouth of a harbour, the principle 
to be kept in mind, in his opinion, was to concentrate all efforts 
upon one point, in order to keep a clear and deep channel at that 
place.” Mr. Vernon Harcourt, M.1.C.E., in-reply to the discus- 
sion on his paper on ‘‘ Harbours and Estuaries” (Minutes Inst. 
C.E., Vol. LXX., p. 53), considered that ‘‘a. harbour should. be 
formed with solid piers, starting from the shore at some distance 
apart, and converging at their extremities, which should be carried 
into as deep water as practicable.”’ It may be well at this point to 
examine what has been done in dealing with bar harbours situated 
in similar positions to those on our coasts in other parts of the 
world—that is, bar harbours situated on rapidly shelving coasts. 
The entrance to the Tyne has many points of resemblance to our 
rivers. Upon an examination ot the chart of the Tyne in 1873 it 
will be seen that at that date it was in almost exactly the same 
state as our principal rivers are at present, namely, nearly blocked 
by a shifting-sand bar, with deep water on either side. A refer- 
ence to a recent chart of the same river shows what a great trans- 
formation has been made in this entrance by the carrying out of. 
judiciously planned works. By the construction of the two break- 
waters, starting from the shore at a considerable distance apart, 
approaching each other as they extend seaward into deep water, 
the sand bar has ceased to exist, having been removed by the com- 
bined action of the induced scour and dredging ; the breakwaters 
extending into deep water thus prevent the waves from lifting 
fresh sand, the waves losing their force after they enter on account 
of the widening out of the works, and at the same time the tidal 
scour has been greatly improved by reason of the large area en- 
closed by the breakwaters. The toreshore has only slightly 
advanced, and from the rapidly increasing depth seaward there is 
little danger of any serious trouble from this cause. The entrance 
to the Tees has undergone a somewhat different treatment, the 
