XXX. J. HAYDON CARDEW. 



on the entire drainage area and which had fallen perhaps 

 months previously. 



Of course the author does not wish to infer for a single 

 moment that an analysis of the flow of a river and the yield 

 of rainfall from the catchment is of no value, on the con- 

 trary, such investigations have the greatest value in other 

 directions. The velocity and volume with which water 

 will flow off steep mountainous slopes is one of the latter, 

 and a very important one when a reservoir is to be formed 

 in a valley, the safety of the dam being dependent upon a 

 true perception of the natural laws governing this question; 

 to the lack of this information may be attributed the 

 destruction of many dams on account of the insufficiency 

 of waste weir provision. 



The author was met with this very difficulty when report- 

 ing upon a project for the supply of water to the Lloyd 

 Copper Company Ltd., for their ore reduction works at 

 Burraga ; no authentic information was available as to the 

 efflux from the catchment, but after a careful examination 

 of the physical features and the geological nature of the 

 district, he assumed that 65°/° of the average rainfall (assum- 

 ing the mean annual rainfall of 28*8 inches at Burraga 2\ 

 miles away, as being the average rainfall for the whole 

 catchment) was lost by absorptive and evaporative agencies. 

 Just before the dam was completed an opportunity occurred 

 to the author of actually measuring the amount of rainfall 

 contributed to the reservoir, which proved that 78|°/° of the 

 rainfall was lost on that occasion by evaporation and 

 absorption on the catchment. It may be interesting to 

 describe how this was done. 



Rain commenced to fall 19th September 1901, the ground 

 surface being fairly moistened with the winter rains and 

 snows, but not by any means thoroughly saturated, the 

 rain terminated 26th October, and during that period 4*78 



