IMPORTANCE OF FEDERAL HYDROGRAPHY. XXXI. 



inches of rain fell, of which 2*65 inches were contributed 

 in one day as recorded at the Burraga rain gauge ; for this 

 rainfall the precipitation on the catchment would represent 

 577 million of gallons. The reservoir was empty when 

 the rain commenced and was full on the 10th December up 

 to the level of the overflow weir, at which date the streams 

 leading thereto had ceased to flow ; during the period of 

 contribution 35 million gallons were run off by the con- 

 tractor, which quantity was measured through the sluice 

 pipe ; 4i million gallons were evaporated from the reservoir 

 calculated on the assumption that the evaporation was the 

 same as Mr. Russell gives for Lake George, viz., 40 inches 

 per annum, the conditions of the two places being apparently 

 similar, and 85 millions of gallons remained in the reservoir, 

 so that in all, the catchment contributed 124f millions of 

 gallons to the reservoir, or about 1 inch out of the total 

 rainfall of 4*78 inches, therefore the proportion of the rain- 

 fall conserved at this period was ] -^ = 21|°/°; it may readily 

 be conceived that after a long drought or in the heat of 

 summer the percentage conserved would be less, as the 

 absorptive and evaporative agencies would be more active, 

 and in the winter when the bulk of the rainfall usually 

 occurs, it might be more ; the results of the test satisfied 

 the author that the length of waste weir he had provided 

 was sufficient to discharge the heaviest rainfall likely to 

 occur, and did not materially disturb the calculations regard- 

 ing the amount of water available for conservation. 



In a country like Australia, having vast areas of what 

 may be termed arid lands with scanty and irregular rain- 

 fall, is of the utmost importance to know not only the 

 amount and distribution of the rainfall, but also what 

 becomes of it, and that at once introduces the consideration 

 of the questions of evaporation, percolation and efflux from 

 river basins ; without a consideration of all these taken 



