192 Report of the Commissioners on the 
character of the vegetation in the ranges, consisting of im- 
mense gum trees, 250 feet high, tree-ferns, thick scrub, and 
other plants, whose growth and luxuriance indicated a great 
amount of moisture, as also a thick vegetable soil, capable of 
holding a large quantity of water; but, as this increased 
vegetation appears to be the effect of the increased moisture, 
and hence, consumes as nutriment a large proportion of it, if 
not all, we are hence not prepared to assert that any portion 
of this additional moisture over Mount Disappointment swells 
the supply already estimated at thirty-one inches over the 
whole basin, which depth of rainfall we therefore adopt. 
Having, therefore, taken the rainfall, we have next to 
estimate what proportion of it will be delivered into the 
Plenty, or that amount which is left and flows over, after 
surface absorption and evaporation. 
This amount will materially depend upon the declivity of 
the surface, combined with the imperviousness of the soil, and 
the number and duration of the rainfalls. In the absence of 
daia on this subject, in this country, we are obliged to fall 
back upon English data, although obtained under different 
conditions. In England, according to G. D. Dempsey’s work 
on Drainage of Districts and Lands,in Wheale’s Series, the 
mean annual amount evaporated from the surface of the 
ground, is 57-6 per cent. of the rainfall, leaving 42-4 per cent. 
as available for collection; assuming therefore that 58°6 is the 
correct per centage of evaporation for England, we propose 
to take such a comparative view of its conditions in England, 
relatively with those in the Plenty basin, as shall enable us to 
form a practical judgment as to the applicability of this per 
centage of evaporation to the Plenty basin. 
This English per centage of loss of 57-6, is in a country 
highly favorable to evaporation, owing to its cultivated surface 
exposing a loose spongy soil, capable of holding a large amount 
of rainwater while being evaporated by the sun, also to the 
slightly undulating character of the country, not involving so 
rapid delivery of its rainfalls into the rivers, and finally from 
the differences of the rainfalls producing milder showers, a 
a greater proportion of which must necessarily be evaporated 
from longer exposure. 
On the other hand, the basin in question is composed mostly 
of steep ranges and hills, presenting only a few square miles 
of flat land, and hence capable of delivering its surplus waters 
with rapidity into the Plenty; it also has, for the most part, 
a close impervious surface, undisturbed by agriculture, and 
only capable of surface absorption, which character of 
