This image comes from the 13th edition of the Encyclopædia Britannica or earlier. The copyrights for that book have expired in the United States because the book was first published in the US with the publication occurring before January 1, 1929. As such, this image is in the public domain in the United States.
English: Note:
The figures in the right-hand column at the ends of the
curved lines are inches of mean annual rainfall over a period of
50 years.
The co-ordinates to any point upon any curved line give respectively
the required reservoir capacity and daily yield in gallons per
acre of drainage area, corresponding with the mean annual rainfall
represented by that curved line.
The curves have been drawn for a mean annual evaporation of
14 in. For any increased rate of evaporation 1¼ in. are to be
subtracted from the rainfall for each inch of evaporation above 14 in.
For any decreased rate of evaporation 1¼ in. are to be added to the
rainfall for each inch of evaporation below 14 in.
Any excess of evaporation from the water surface and allowance
for bottom water are to be added to the storage so found.
The period over which the reservoir equalizes the flow is shown
by the number of years marked on the straight radial lines.
Where the absolute minimum stream flow is known to be greater
than the minimum of 1⁄5 cubic foot per second per 1000 acres (108 gallons
per acre per day) assumed in the diagram, the capacity of the reservoir
as taken from the diagram may be reduced by the amount corresponding
to that minimum flow for the particular rainfall and evaporation.
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{{Information |description = {{en|1=Diagram of Reservoir Capacity and Yield. See note below.}} |date = 1911 |source = “Water Supply,” ''Encyclopædia Britannica'' (11th ed.), v. 28, 1911, p. 391, fig. 4. |author = George Frederick Deacon |permission = {{PD-Britannica}} }} {{en|Note:}} The figures in the right-hand column at the ends of the curved lines are inches of mean annual rainfall over a period of 50 years. The co-ordinates to any point upon any curved line give respe...