196 Report of the Commissioners on the 
obtain the sectional area of the winter discharge, equal to 
forty-one square feet, and having already the fall in two miles 
equal to 8°1 inches, we can obtain by Eytewein’s formula as 
above quoted, the velocity equal to 1:15 feet per second, 
‘which multiplied by the sectional area, forty-one square feet, 
gives 47°15 cubic feet per second as the winter discharge. 
Hence having the summer and winter discharges per second, 
we obtain the mean discharge by taking the half of their sum, 
which is 29°51 cubic feet per second, or 34,467,680 cubic 
yards per annum, and then deducting the loss from the eastern 
swamp already obtained, equal to 2,224,157 cubic yards, we 
have 32,243,523 cubic yards as the effective mean discharge 
of the eastern arm per annum. 
As the western arm has a larger drainage area than the 
eastern arm, and the loss in its swamp not so much, and as 
all its conditions relative to imperviousness, slope, rainfall, 
&c., are precisely similar, it is evident that it must 
have at least as great a mean discharge, if not 
greater; hence the combined mean discharge of both arms 
will be at least double that of the eastern, or 64,487,046 
cubic yards, equal to the effective mean discharge of the 
Plenty above the reservoir, according to-this calculation. 
But the result previously arrived at by the application of 
the English per centage of evaporation of 57°6 of the rainfall, 
was 63,663,297 cubic yards, thus leaving only 823,749 cubic 
yards difference between the two calculations. 
As the calculation of effective discharge for the Plenty, 
previously made upon the assumed correctness of 57°6 per 
centage of loss from evaporation is so amply confirmed by this 
last calculation, we adopt it as correct. 
The whole effective discharge of the Plenty above reser- 
voir, or 63,663,297 cubic yards, is therefore the amount 
available for collection. ‘ 
But as it cannot be supposed that the whole waters of the 
Plenty can be diverted into the reservoir, and thus be ab- 
stracted from the settlers along its banks, we assume that 
at least half of its whole amount will be retained for their 
use, leaving the other half, or 31,831,648 cubic yards, for the 
supply of the reservoir. 
As therefore this amount has to be conveyed by the aque- 
duct before mentioned, leading from the Plenty to the 
reservoir, it is necessary to ascertain the aqueduct’s capacity 
of discharge, especially as some of this supply will come in the 
. form of floods, and also the amount likely to be carried down 
by the Plenty during the greatest ordinary floods. 
