THE ENTRANCES TO OUR RIVERS. 27 
heavy wave action to throw up the material to form a bar.” The 
same remarks are equally true in the case of the Hawkesbury 
no bar. The contrary effect is seen in the case of the Richmond 
River, where the entrance is dnt to the wave action ; con- 
sequently a bar obstructs the entrance. 
ely deduce alge this that, in order to cope perman 
ently and saison Wi the sand, it is necessary to ex tend 
sa 
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 a ways terminates in about 3} fathoms, 
and in his works he goes pon the broad principle of passing 
beyond the line of disturbance.!' This demonstrates the advisa- 
“the effect of wave action is at least a hundredfold greater than 
that of the tidal action.” And if this be so, it clearly proves the 
necessity of breaking the — of the waves before they have an 
opportunity of throwing u 
‘Mr. Walter Raleigh Brown M.A., M. Inst. C. E., speaking 
opinion, was to concentrate all efforts upon one point, in order to 
p a clear and deep channel at that pla ernon 
Harcourt, C = : in reply to the discussion 
be formed with solid a 0 starting from the shore at some distance 
apart, and converging at their extremities, which should be carried 
into as deep water as pn 2S cable.’ 
on our cic in other parts of the world—that is, bar harbours 
situated on rapidly shelving coasts. 
The entrance to the Tyne (plate No. 1) has many points of resem- 
blance to our rivers. Upon an examination of the chart of the Tyne 
in 1813, it will be seen that at that date it was in almost exactly the 
inutes, Inst. C.E., 
¢ Minton Tusk OE, sax 
ssn Inst. C.E., ea Kies, 
