120 Failure of the Van Yean Reservoir, 



situation where it could not fail to be considerably augmented 

 by the rainfall of fifteen hours. The measurement of the 

 eastern arm, which was obtained the following day, could not 

 give any certain result, as it was taken above the junction of 

 three small tributaries. In one point of view, however, it is 

 very important, as the object of the measvuxment was to 

 illustrate the constancy of the supply. 'AH the other tribu- 

 taries of the Plenty have been known to fail on several 

 occasions. 



The measurement of the main eastern branch, therefore, 

 shows an approximation to the amount of water supply 

 that would be available above the swamps in a severe 

 drought, but it is only an approximation, as it too may 

 also fail ; there is certainly no guarantee in the height of 

 Mount Disappointment, which is only 1,500 feet, to warrant 

 a more favourable opinion. 



All the tributaries of the Plenty equally depend on the 

 rainfall of the mountain ranges, and it is simply because the 

 main eastern branch rises from the highest point, where 

 there is most rain and least evaporation, that it holds out the 

 longest when the ordinary supply of rain is cut off. 



f come now to mention the measurements which were made 

 by the Committee who were appointed to investigate this 

 subject at the last meeting of the society. 



The river, at its junction with the aqueduct, with a velo- 

 city of half a mile an hour, gave a discharge of 2,537 gal- 

 lons per minute, or an equivalent to three feet four inches 

 in the reservoir. The eastern arm above the swamps 

 yielded 4,450 gallons per minute, or an equivalent to five 

 feet eleven inches. If we take Mr. Hodgkinson's measure- 

 ment of the western arm, where it issues from the rocks, 

 namely, 1,180 gallons per minute, and add to it the Com- 

 mittee's measurement of the eastern arm, we shall have 

 5 630 gallons as the discharge of all the streams above the 

 swamps ; and if we take into consideration that one week 

 before their visit to Yan Yean there Avere nearly three days 

 of heavy rain, which is an unprecedented occurrence m 

 January, the 630 gallons may be regarded as due to this 

 source, and the balance of 5,000 gallons per mmute will 

 exactly correspond with Mr. Blackburn's estimate. 



From these measurements, it would also appear that the 

 eastern arm bears the proportion to the western arm of 4,4o0 

 to 1 180 or very nearly four to one. By this estimate we 

 shall find that the discharge of the western arm was 1,340 



