“Relation between Rainfall, Flow off the Ground, Size and Actual Yield of Reservoirs.”

THE INSTITUTION OF CIVIL ENGINEERS.

ENGINEERING CONFERENCE.

Section VI.—WATERWORKS, SEWERAGE AND GASWORKS.

26 May, 1897.

(No. 6.)

In deciding the size of storage reservoirs, unless they are calculated to store the rain falling in wet years to equalise the flow with dry years, the usual practice of taking as a basis the rainfall from January to January in each year is open to doubt. More accurate results would be obtained by commencing the yearly record from the same time that the drought ceases, and the reservoir is most likely to be emptied, and when the yield of the gathering ground is at its lowest, say from the 1st October instead of from the 1st January, for it is obvious that rain falling in October, November and December of any particular year can have no beneficial effect in supplying the reservoir in the previous months of that year. This suggestion does not, however, affect the result to the same extent when the calculation is made on an average of two or three dry years.