WATER SUPPLY AND IRRIGATION. 155 
result shows that the river has averaged throughout the year 6’ 8” 
above the summer level. The width of the river at Bourke is 180 
prove that } of an inch of rain over the watershed, or 35 part 0 
of the rainfall, represents all the water that passed Bourke during 
the whole year. When full allowance is made for the power of 
evaporation in a dry year, and for all other circumstances which 
might prevent the rain-waters reaching the rivers, it is certain 
t a very much greater proportion than 35 becomes running 
water. In such country as that under discussion common exper- 
lence would give } of the rainfall as the available water, but for 
e of being on the safe side, we will assume that only 
is Of the rainfall becomes running water, and it still represents a 
quantity sufficient to supply eight rivers like the Darling for the 
whole year. 
d. 
ing 70 
“In his report for 1881 Mr. Russell further states :—“ The evi- 
Well worth our serious consideration. : 
The rainfall over the Darling basin above Bourke having been 
determined with more or less accuracy during 1879, 80 and 81, 
and the mean level of the river at Bourke having been also ascer- 
ed for the same years, we are enabled to make a rough com- 
Parison of the fall and discharge. 
1879.—Mean rainfall... 33°24 inches. Mean river level ... 29°08 feet. 
> : 20°47 ” 6°66 
1881, me a 18-88 me ss im 0°75 
- The proportional difference between the rainfall and the river 
discharge for these years is so great that it necessary to try and 
: : n, 
es ® connection this may have with the general questi —that the 
“normous proportion of the rainfall, mentioned a. 
“Pears underground and feeds our waterbearing 
