Van Yean Reservoir* 



183 



burn^ was sufficiently extensive to maintain the permanent 

 discharge of the streams in question in the following manner: 

 the rain percolates through the very permeable soil on the 

 top of the range, and lodges in extensive interior cavities 

 and fissures in the granite ; and from these subterranean 

 reservoirs the water is gradually exuded at lower levels, 

 through the spongy masses of decomposed vegetation which 

 fill up the external interstices of the granite, and constitute 

 the soil from which spring up, in such rank luxuriance, the 

 gigantic mountain Eucalyptus, and dense undergrowth of 

 tree-ferns and creepers that choke up the ravines of Mount 

 Disappointment. 



This opinion of the probable cause of the very permanent 

 and regular flow during the summer months of the mountain 

 streams, was briefly enunciated in one of my reports in 1852, 

 and has been since corroborated by Messrs. Acheson and 

 Christie. 



During the four hottest months of the year, the enormous 

 quantity of water lost from the effects of evaporation and 

 absorption in the river swamps between Mount Disappoint- 

 ment and Whittlesea (equivalent to a discharge per minute 

 gf about 2500 gallons) would render it necessary that, for 

 these months, a quantity of water, equivalent to a discharge 

 of at least 3000 gallons per minute, should be deducted from 

 the total yield of the mountain streams, in order to maintain 

 a sufficiency of water in the Lower Plenty for the adequate 

 supply of the setttlers and stock thereon. During the other 

 eight months of the year, a quantity equivalent to a dis- 

 charge of 2000 gallons per minute would suffice to effect this. 



The guagings of the Plenty made from time to time by 

 Mi\ Blackburn, Mr. Jackson, your Committee, and myself, 

 are from their want of connexion in a regular series, of little 

 value in affording data for determining the total annual dis- 

 charge of the Plenty. The information afforded by the 

 settlers on that river relative to its winter discharge, floods, 

 &c., is also exceedingly contradictory, I therefore considered 

 it safer, as explained in some of my foregoing remarks, to 

 endeavour to arrive at some estimate of the supply on 

 general principles* 



I submit with much diffidence the following very rough 

 approximation to the probable amount of population that the 

 Yan Yean scheme would prove adequate to furnish with a 

 sufficient supply of water. Since my lecture of this paper I 

 have however arrived at the conclusion, that sufficient ex- 

 periments on dew have not been made in this colony to 



