IMPORTANCE OF FEDERAL HYDROGRAPHY. XXXIII. 



investigation of a great number of other rainfall returns 

 shows from -§- to -Mh of the mean annual rainfall as being 

 the greatest rainfall in 24 hours, but there is nothing to 

 shew what proportion of these heavy falls occurred in a 

 period less than 24 hours, and yet for the determination of 

 the capacity of spill ways to reservoirs with limited catch- 

 ments, or for culverts on roads and railways it is absolutely 

 essential to have such data. The author has observed in 

 many settled districts of New South Wales away from the 

 coast, that the maximum rainfall for 1 hour fairly approxi- 

 mates to \ of the maximum daily rainfall, and that for a 

 period of 8 hours the maximum rainfall is double of that 

 for one hour, and he has constructed works upon that 

 general assumption, but it must be admitted that the treat- 

 ment of the question in this manner is not always conducive 

 to good practice. 



The determination of the efflux or "run off" from a 

 catchment is a very important one to the engineer when 

 designing water ways for railways or roads, but it is so 

 intimately bound up with the question of rainfall, the slope, 

 and permeability or impermeability of the strata, the 

 amount of vegetation, and the effects of evaporation that 

 it is peculiarly one for the determination of the hydro- 

 grapher, and if such information had been available before 

 our railways had been built, one would have no hesitation 

 in saying that a vast amount of public money would have 

 been saved, both in the curtailment of unnecessarily 

 extensive works or by the provision of more ample means 

 for the passage of water ; the same thing may be said of 

 all works carried out by our municipalities, which have 

 lost large sums of money by actions at law consequent on 

 the neglect of the study of hydrology. 



Again the systematic gauging of the rainfall, the regular 

 daily observations of our rivers, the measurement of evapor- 



3— June 18, 1902. 



