154 



Failure of the Van Yean Reservoir, 



and a half Inches: so that, deducting two feet five inches, 

 there will only remain nine feet one and a half inch, or just 

 sufficient to cover the evaporation from the surface. 



In the meantime, therefore, until such means are adopted, 

 it may safely be asserted, that there will be no water for the 

 city at all : and it is rather a singular circumstance, that if 

 we are to get any supply for the city, it must be by saving 

 tlie two feet five mches that are at present lost by evaporation, 

 and very probably also by absorption in the swamps, and if 

 this can be done, there will be a supply for 71,500, at forty 

 gallons per head per day. 



To bring both arms of the Plenty to Yan Yean, clear of 

 all loss from the sw^amps, would be a very difficult undertaking. 

 The swamps are only to be likened to large sponges, and 

 simply to cut a watercourse through them, and lower their 

 level, would have very little effisct in withdrawing the stream 

 from their influence. 



The evaporation would continue nearly the same, and would 

 be fed from the current. The eastern swamps are about three 

 miles in length, the western five miles; and I am strongly of 

 opinion, that the loss from evaporation and absorption, could 

 be saved in no other way than by conveying both branches in 

 iron pipes. 



Mr. Christy has kindly favored me with an estimate of the 

 cost of laying suitable pipes for this purpose, which w^ould 

 amount to £14,000 per mile, or to £42,000 for the eastern 

 branch, and £74,000 for the western. So that, after all, it 

 may become a grave question, whether it be really worth 

 while to go to any expense at all to save either branch from 

 the evaporation of the swamps. 



I have also taken for granted that we shall have sixty hours 

 of floods each year at Yan Yean, while it is not unusual to 

 have no floods at all; and I have allowed an increase in the' 

 Plenty of two-thirds, during the three winter months, for 

 rain ; although Ave sometimes, as last year, have very little 

 rain in winter, and I have allowed a rainfall of thirty- 

 six inches for the reservoir, although it is very doubtful 

 whether there really is that average at Yan Yean. And, I 

 may Avell ask, what became of the thirty-six inches of rainfall 

 in 1851? I have no doubt that there is a larger and more 

 constant rainfall at the Dandenong Eanges ; but they are 

 much nearer the Bay than Mount Disappointment, and there- 

 fore attract and intercept the rain-clouds, and it is well known 

 that there is n, greater rainfall near the coast than further in- 



