. Water Supply and Irrigation Papers of the United States Geological Survey . umed to be 20 feet thick and 50 miles wide, with a slope of 10feet to the mile, is barely 10 cubic feet per minute. If the effectivesize be assumed to be mm., the underflow would be about 36cubic feet per minute. A sand as coarse as 1 mm. would, under thesame conditions, furnish an underflow of 3,600 cubic feet per minute. RETURN WATERS FROM IRRIGATION. Some remarkable instances of changes from the condition of dimin-ishing rivers of arid valleys to the condition of growing rivers ofhumid valleys have been noted
. Water Supply and Irrigation Papers of the United States Geological Survey . umed to be 20 feet thick and 50 miles wide, with a slope of 10feet to the mile, is barely 10 cubic feet per minute. If the effectivesize be assumed to be mm., the underflow would be about 36cubic feet per minute. A sand as coarse as 1 mm. would, under thesame conditions, furnish an underflow of 3,600 cubic feet per minute. RETURN WATERS FROM IRRIGATION. Some remarkable instances of changes from the condition of dimin-ishing rivers of arid valleys to the condition of growing rivers ofhumid valleys have been noted in various parts of the West, thesebeing the results of the irrigation of considerable portions of riverlands. Data relating to these changes have been given in various «The underground waters of the Arkansas Valley, by G. K. Gilbert: Seventeenth Ann. S. Geol. Survey, Pt. II. 1890, p. 557. 44 MOTIONS OF UNDERGROUND WATERS. [NO. 6? annual reports of the United States Geological Survey, in connectionwith the results of river measurements, notably on the Gila, Boise,. Fig. 16.—Diagram showing growth of Cache la Poudre River. The horizontal distances orabscissae give the distances in miles from the first weir at the canyon to the point of measure-ment. The vertical distances or ordinates represent the amount of return waters in cubic feetper second. The distances were measured not along the curves of the river but on the map,taking generally a straight course across the bottoms, because it was thought that the amountof inflow will not be increased by the curves of the river, but, instead, will depend upon thestraight course of the stream, other things being equal. It is evident that there is a generalagreement between the various lines, notwithstanding certain irregularities, such as the smallinflow in the first section in March and August, 1894, and actual losses recorded in the fifth oradjacent sections in 1891, 1893, and 1894. Platte, and other rivers. One of the most
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