Report on the lands of the arid region of the United States, with a more detailed account of the lands of Utah

by John Wesley Powell; Willis Drummond; Clarence E. Dutton; Grove Karl Gilbert; A. H. Thompson

THE UNIT OF WATER USED IN IRRIGATION.

The unit of water employed in mining as well as manufacturing enterprises in the west is usually the inch, meaning thereby the amount of water which will flow through an orifice one inch square. But in practice this quantity is very indefinite, due to the “head” or amount of pressure from above. In some districts this latter is taken at six inches. Another source of uncertainty exists in the fact that increase in the size of the orifice and increase in the amount of flow do not progress in the same ratio. An orifice of one square inch will not admit of a discharge one-tenth as great as an orifice of ten square inches. An inch of water, therefore, is variable with the size of the stream as well as with the head or pressure. For these reasons it seemed better to take a more definite quantity of water, and for this purpose the second-foot has been adopted. By its use the volume of a stream will be given by stating the number of cubic feet which the stream will deliver per second.