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 caleulations 
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 defined 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 
