200 



Report of the Commissioners on the 



centage of loss from evaporation ; their relative discharges 

 must hence be as their superficial extent^ diminished further 

 by their ascertained loss in the swamps. 



Our measurements of discharge have been obtained by- 

 finding the mean velocities, by the following formula, " dou- 

 ble the square root of surface velocity in inches, deducted 

 from surface velocity, and one added, gives the velocity at 

 bottom, the mean' velocity is half the sum of top and bottom 

 velocities." 



The calculations of loss from the swamps have been taken 

 with such minuteness as circumstances would permit, that 

 for the western swamp has been taken as if for still water, as 

 the water spreads over the surface. The loss on the eastern 

 swamps was truly represented by the excess of the discharge 

 of the eastern arm above the swamps, over that of the Plenty 

 below the swamps on the day of measurement, as at this time 

 the Plenty was only fed by the eastern arm, the western 

 being wholly lost in its swamps. 



We have not attempted to disprove Dr. Wilkie's calcula- 

 tions, by carrying investigations in the same track, as we 

 believe by doing so we could not arrive at a truthful result, 

 inasmuch as he bases his calculations on the summer discharge, 

 which is only derived from storage water in the ranges, which 

 hold the water back and prevent it being delivered more 

 suddenly, hence if there were no ranges there would be no 

 summer discharge, although as much water would pass down. 

 This is the case with the Merri Creek which has 122 square 

 miles of basin, but as it does not rise in ranges, its waters 

 near the source are not stored, but are delivered with rapidity 

 according as they are received, there is therefore no summer 

 discharge, hence measurements of summer flow, unless after 

 rainfall, only indicate the least discharge. 



It only remains therefore for us to state, it was impossible 

 to follow up Dr. Wilkie's paper through the several allegations 

 and deductions contained therein, inasmuch as his calculations 

 are almost wholly based on the fallacy of summer discharge, 

 which we have shown is only due to storage in the ranges, and 

 which therefore only forms the dregs of the actual discharge. 



The amount allowed by him for floods is assumed, and 

 therefore cannot be depended upon, more especially as there 

 is no deflned line between least flow and highest floods, the 

 discharges coming down in variable volumes between these 

 points, hence the inaccuracy of computing ordinary discharges 

 and floods separately, to obtain the total discharge. 



We have therefore adopted a different mode of investigation 



