Army manual of hygiene and sanitation, 1934 / [War Office].

Date:
1941
Catalogue details

Licence: Public Domain Mark

Credit: Army manual of hygiene and sanitation, 1934 / [War Office]. Source: Wellcome Collection.

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    streams or rivers and collects in hollows to form ponds and lakes. Artificial lakes or reservoirs may be made by damming a stream or blocking the end of a valley down which it flows, the area draining into such a reservoir being called a ‘‘ catch- ment area.’’ Water obtained from natural lakes in moorland districts or from reservoirs is known as “ upland surface water.”’ Some of the water from the surface of the earth soaks into SS @ CLouos ) cp ae Ae | ca DERGROUND | 4a \\\ \ \ pense \ WELLE . “ \\\ AN XN MOMMY - baa] See Fic. 5.—Sources of Water. the ground to form underground water, and the depth to which it soaks will depend upon the formation of the earth below. The earth below the surface soil is composed of geo- logical layers, or strata, of which some are composed of impermeable clay or rock, which will not allow water to pass through them, while others consist of chalk, sand or other permeable material, through which water soaks. Such strata usually run in slopes or may form folds with the result that