186 JOURNAL OF SCIENCE. 
force of the waves is dispersed as soon as they pass the entrance, 
on account of the widening out of the works. The third is that 
whilst the flood-tide approaches from all directions, and any 
material it may bring in is deposited near the entrance, as soon as 
it arrives in comparatively still water the ebb-tide and the up-land 
waters having their forces directed and concentrated in a certain 
fixed direction, are therefore able to remove, and carry well out to 
sea, any deposit that may have been left by the flood-tide, and at 
the same time maintaining a straight channel out to sea. Having 
so far endeavoured to bring forward general principles, it is now 
proposed to see how they can be applied in dealing with our rivers, 
and in doing so it must be remembered (to quote the words of Sir 
John Hawkshaw) “that there is nothing more certain than that 
each one must be dealt with according to its own special regime.” 
At the entrance to the Hunter River, Newcastle, there is a remark- 
able instance of a natural breakwater, illustrating the advantage 
of protection works (natural or artificial) extending into deep water. 
By referring to the plan of the river taken in 1816 we see a chan- 
nel of three fathoms marked under the lee of areef extending from 
the mainland to Nobby’s Head. But as this reef only afforded 
partial shelter, we find the waves struggling with the tidal current, 
and reducing the width of the channel to very narrow limits by the 
formation of the dangerous “ oyster bank.” The improvement of 
the reef by the construction of the southern breakwater somewhat 
reduced the ‘“‘oyster bank,” and now the breakwater has been 
extended beyond Nobby’s Head. The entrance being thus more 
perfectly protected from the waves, we see a most satisfactory im- 
provement by the widening of the channel and the almost entire 
removal of the ‘‘ oyster bank,” brought about by the comparatively 
undisturbed action of the tidal and upland water scour. At the 
present time the entrance is so far protected by the breakwater on 
the south, and the bay-like line of the coast on the north, that the 
tidal and upland waters have decidedly the best of the situation, 
and thus we see a progressive state of improvement. Although 
this harbour possesses great natural advantages by the position of 
the reef upon which the south breakwater has been built, and by 
the deep water and absence of sand to the south of the entrance, 
it labours under a serious disadvantage on account of the great 
curvature of the river at the harbour, the effect of which, as is 
well-known, is to cause the current to scour out deep holes at cer- 
tains points, and to throw up banks at others, and there 1s no doubt 
that this action will necessitate a large amount of dredging to keep 
the harbour of uniform depth. In investigating how far the general 
principles set forth above, and illustrated bythe works at the Tyne, 
Tees, and Liftey may be applied in dealing with our rivers, it may 
be well to take the Richmond and Clarence Rivers as examples, 
and in dealing with these cases to show how, with modifications to 
suit local circumstances, they may be generally applied to the other 
rivers along our coast. The Richmond River flows through one 
of the most fertile districts of the colony, and is navigable for ves- 
sels of moderate size for some distance from the entrance; but, as 
is unfortunately the case with most of our rivers, it is blocked by 
a very dangerous shifting bar. The width across the entrance is 
about 3000 feet. The North Creek joins the main river at nearly 
right angles, opposite the centre of the entrance, thus forming a 
