History of the Water Supply of the World / arranged in a comprehensive form from eminent authorities, containing a description of the various methods of water supply, pollution and purification of waters, and sanitary effects, with analyses of potable waters, also geology and water strata of Hamilton county, Ohio, statistics of the Ohio river, proposed water supply of Cincinnati.

by Thomas J. Bell

“From twenty examples we have 89 as the largest per centage, the lowest 29 per cent., and the average 64 per cent.

“The Eaton Brook water-shed, in Madison County, New York, of 6,800 acres, with steep slope and compact soil, underlaid by hard greywacke rock, elevated 1,350 feet above the sea, availed 66 per cent. of the rain-fall as surface flow.

“A similar water-shed, Madison Brook, gave 50 per cent. Experiments by Wm. McAlpine, for Albany water-works, shows that from a water-shed of 2,600 acres, 41½ per cent. of the rain-fall was carried off by the streams from May till October, inclusive, while from November till April, 77.6 per cent. was so carried off.”

In England the allowance for absorption and evaporation ranges from nine to nineteen inches per annum. In this country it is from 75 to 100 per cent. greater.

We produce from “Fanning’s Water Supply” the following table of experiments on evaporation from surfaces of shallow tanks:

Cambridge—Length of trial,		one year;	evaporation in inches,		56.00
Salem	“	“	“	“	56.00
Syracuse	“	“	“	“	50.20
Ogdensburgh	“	“	“	“	49.37
Dorset, England	“	three years	“	“	25.92
Oxford “	“	five “	“	“	31.04
Bombay	“	five “	“	“	82.28
Croton	average,	six, “	mean evap. equal 81 }		39.21
			per cent. of rain-fall. }
Lea Bridge, London	“	seven “	average rain-fall		27.7
			annual evap. min.		12.067
			“ “ max.		25.141

The following from the same author of the minimum flow of streams in cubic feet per second, per each square mile of water-shed:

From	1 square mile	.083	From	250 square miles	.25
From	10 square miles	.1	From	500 square miles	.40
From	25 square miles	.11	From	1,000 square miles	.35
From	50 square miles	.14	From	1,500 square miles	.38
From	100 square miles	.18	From	2,000 square miles	.41

From the different surfaces, its ratio of the annual rain, including floods and flow of springs, is approximately as follows: