7 
proceed to site No. 7, still further up the river; and on the 13 th it was necessary to go 
again still higher {vide Tables IV. and V.). The site now fixed upon, namely No. 10, 
or “Toorak Bend,” seemed perfectly safe; for from the 15th to the 26th February, 
although lower down the river the water was and had for some time been excessively 
salt, it was here no salter at the surface than it had, on the 10th, been found to be 
above and below Bight’s Falls. This site then seemed absolutely safe. But on the 
4th March the salt had crept up even to this place, and a new site still further on — 
No. 11, a little below Twickenham Ferry — was taken up. The water here was still 
considerably less salt than at Toorak Bend. 
The heavy rains commenced at Melbourne on the 25th March, and on the 28th 
observations at all stations were stopped. They had for the sake of comparison been 
continued up to this date at the present pumping station (No. 1), at the Richmond 
boat sheds (No. 4), and at the South Yarra railway bridge (No. 6). 
General Conclusions. 
(a) The Seaso?i Just Past . — During the season just past, by omitting to take 
water on two or three days of excessive saltness, an abundant supply of fresh water 
suitable for irrigating the Botanic Gardens could have been obtained during the dry 
weather by fixing the intake at the site named in our map the u Toorak Bend such 
a supply could not have been obtained at any point lower down the river. By taking 
the water at the Twickenham Ferry, it is very probable (though the observations there 
do not extend far enough to make an absolute statement possible) that such a supply 
of water could have been obtained by pumping on all days and in all tides without 
exception. 
( b ) Past and Previous Seasons . — A general impression in regard to the season 
just past is, that it was as trying a one as is ever likely to occur; so that it the water 
has remained fresh at Twickenham this year, it is likely to do so in all years. We 
have, however (through the courtesy of Mr. Ellery, the Government Astronomer), 
been able to examine the rainfall records of all the past recorded years; the results 
are given in Tables VI. and VII. From Table VI. it will be seen that there have 
been several years of more prolonged drought than has occurred during the season 
just past; these periods are underlined in the Table. We would refer especially to 
the periods November, 1864, to April, 1865; February and March, 1870; and January 
to March, 1882. 
It is not so much the action of the tides that must be considered as causing the 
salt to ascend the river, but the slow diffusion of the salt into the fresh water. I his 
diffusion takes place mainly along the bed of the river and along the banks, and in a 
season of little rainfall the salt gradually creeps up the river for two or three miles 
above Prince’s Bridge. The more copious the fresh water down-flow, the longer will it 
take for the salt to creep up. But if, owing to prolonged dry weather, the down cur- 
rent becomes contracted to a surface stream of shallow depth in the middle of the river, 
then the conditions are favorable to a rapid diffusion of the salt up the bed of the 
river. Hence in a period, for instance, like that of 1882, it is quite likely that the 
surface of the river at Twickenham Ferry would, towards the end of the season, 
exceed the safe limit. It is to be noted in Table VII., giving the daily rainfalls, that 
even in the previous year, 1889, tl iere was from 8th February to 18th March, a longer 
period of light rainfall than we had this year between nth January and 14th 
February. 
There is also to be considered the possibility of the gradually saturation of the 
river bed with salt. Whether this will take place or not, and what, in case it should, 
would be the effect on the saltness of the water at the surface, we can do no more than 
surmise and not decide. But this is a contingency which should not be disregarded. 
Final Conclusion . — Considering all these things, we are of opinion that some 
stage higher up than the Twickenham Ferry would be necessary in order to be within 
the limits of safety. Above this point there is an acute bend in the river, which 
results in a point more than 1J> miles higher up, measuring along the course of the 
stream, to be approximated to the point of the ferry, so as overland to be little more 
than quarter of a mile distant. We refer to the point crossed by the Hawthorn rail- 
way bridge. We feel confident in recommending this bridge as a perfectly safe place 
from which to draw the water by constant pumping for irrigating the Botanic 
Gardens. 
