96 



second admitted tluMe is oidy a net loss of 3 per cent. In a distance 

 of 2 miles there is a j^ain of 5.24 cubic feet per second, derived from 

 the seepage waters of Skalkaho Creek, and in other sections there are 

 large gains derived from waste waters from irrigated farms. 



It is likewise evident from the figures given in the table that the 

 Ward canal has no fixed regime. The net loss arising from seepage 

 seems to depend on the amount of water which percolates from higher 

 ground and which is intercepted by this canal. 



There is less fluctuation in the net flow of the Skalkaho canal, due, 

 doubtless, to the fact that in more than oive-half of its length it flows 

 through a flume which is practically water-tight. 



THE EFFECT OF SEEPAGE AND RETURN WATERS IN AUGMENT- 

 ING THE FLOW OF STREAMS. 



During the summer of 1!M)8 a series of measurements to determine 

 the gain due to seepage was made on the Bitter Root River. 



That part of the Bitter Root River which was included in the inves- 

 tigation extends from Grantsdale highway bridge to the Buckhouse 

 bridge, a distance of 48 miles, and includes the })ulk of the irrigated 

 area of the Bitter Root Valley in a north-and-soutli direction. The 

 arable and irrigable lands in an east-and-west direction average about 

 10 miles in wddth over this same length. 



The first series of measurements was made from June 11 to 1.5, 11)03, 

 and consisted of a measurement of the river at Grantsdale and a meas- 

 urement of each of 39 tributaries, as well' as five diversions through 

 irrigation canals. The results of the first series of measurements, 

 expressed in cul)ic feet per second, are as follows: 



lieturn seepage, Bitter Hoot Hirer, Jnrw 11-15, 190S. 



Discharge of river at Grantsdale, ^lont 9, 111. 3 



Inflow from 39 tributaries 5, 764. 2 



Total inflow 14, 875. 5 



Discharge from river at Buckhouse bridge 12, 660. 6 



Diversions through canals 313. 5 



12,97-11 



Loss in 48 milew 1,901.4 



The second series was made about a montii later, between fluly 9 

 and 14, after the spring floods had subsided. The results of the 

 second series of measurement, expressed in cubic feet per second, are 

 as follows: 



