6 
iasy to sunmse oerorenana. az certain positions in tiienvei n^uiu, 
)v bringing in a current of salt water, possibly increase the surface saltness ; at these 
lositions the saltness would be greater at high tide and less at low tide. But at other 
on 
the alternate tides. As to which tide would produce the greater saltness it was not 
easy to surmise beforehand. At certain positions in the river the incoming tide would, 
b\ 
posit i a 
portions of the river — probably, indeed, throughout its greater tidal length the effect 
of the incoming tide would lie to retard the outflowing current, thus damming back 
the fresh water on the surface of the river, and hence lessening the surface saltness. 
An inspection of the results given in Tables 1 . — V. will show that this latter was the 
case ; with readily explainable exceptions, the water at the surface was less salt at 
high tides than at low. These exceptions, however, were not of such a kind that they 
could easily be foreseen ; therefore, no simple rule for taking water only at high tide 
could be given. The average of a long period is, however, in favour of high tides. 
Thus, at the Richmond Boot Sheds, on the surface of the left bank (Table IV., 
I) 1 surface) an average of fourteen days observations gave the following results : — 
High tide ... ... ... ... 75*5 parts of chlorine per 100,000 
Low tide ... ... ... ... 94*1 „ „ „ 
Difference between Night and Day . — It was not found possible, without 
considerably extra labour, to investigate this point. 
Difference between Midstream and Sides . — This point has been already referred 
to under the head of u Vertical Distribution the observations made in the early 
stages of the investigation were fully confirmed by all the subsequent observations; 
and it was found that at all the stations, right up to the Twickenham Ferry, the water 
was fresher, often considerably so, in the middle of the river than near the banks. 
In fluence of Falls of Rain . — At the top of Tables I. and IV. are notes showing, 
various days, the falls of rain at the Melbourne Observatory. These, of course, 
are not a direct indication of the rainfall over the whole basin of the \arra; probably, 
whenever rain occurs at Melbourne, much heavier rain occurs on the mountains, in 
which are the chief sources of the Yarra. 
The influence of heavy rain in the early part of the season is evinced very 
clearly by the observations taken on the 24th December, and already reverted to. A 
fall of 1*16 indies at Melbourne on the 21st to 23rd December was accompanied by a 
flooding and cleansing of the river throughout. By the 2nd January, however, the 
river at the pumping station was getting increasingly salt. But a very small shower 
of rain at Melbourne was accompanied bv a considerable diminution in the saltness on 
the 9th ; and the influence of heavy rain on the nth was decidedly noticeable in the 
observations up to the 1 8th January. Again, about the 15th February ( vide 'Tables 
I., IV., and V.), falls of 20 cents on the 14th and 17th were accompanied by a rapid 
drop in the saltuess of the water. For instance, in the well, the chlorine dropped 
from about 150 on the 14th to 30 on the 17th; and, at Richmond Boat Sheds, it 
dropped from over 70 at high tide in mid-stream on the 14th to only 7 on the 17th. 
Falls of 20 cents and 15 cents on the 7t.l1 and 1 ith March were not accompanied by 
such marked diminution of the saltness ; but whether this fact was clue to the rainfall 
011 the mountains at this time not having been so great, or to the increasing dryness 
and consequent, absorptiveness of the soil in the Yarra basin after the hot weather — 
either of which causes would result in less fresh water flowing into the river — or 
whether it was due to the accumulation of salt at this time and its extension up the 
river, the observations taken do not enable us to decide. It is very likely, however, 
that the latter cause was a considerably operative one. 
Gradual Extension of Salt up the River. — The observations up to 1 8tli January 
did not give any decided indication that it would not be possible to get sufficiently 
fresh water from near the present pumping house. There was nothing to positively 
indicate the impracticability of obtaining good water by judiciously selecting for pump- 
ing only times of low saltness, and by the use of a floating rose, either near the left 
batik or in mid-stream at the Botanic Gardens footbridge (site No. 3). But on the 
20th January the river began to get sal ter, and on the 24th January at the Botanic 
Gardens footbridge in mid-stream the chlorine at the surface was already 99. O11 the 
22ud, therefore, observations were commenced at a new site — No. 4 on the accom- 
panying sketch map. With the exception of two or three days, from 25th to 30th 
January, this did not seem an unpromising site; but for eleven days, from 5th to 15th 
February, the observations gave quite forbidding results. Consequently two new sites 
— Nos. 5 and 6 on the map — were taken up on 6th February. For two or three 
days these appeared promising; but on the 10th February it was found necessary to 
