90 BULLETIN 440, U. S. DEPAETMENT OF AGEICULTUEE. 



other reasons it is improbable that any more lumber-carrying flumes 

 will be constructed in California, except in instances where a railroad 

 or incHne is clearly impracticable. 



There are several flumes now in successful operation in California, 

 though the number in use is gradually decreasing. The longest ones 

 ai*e located in the southern Sierras, where longer and more expensive 

 railroads are required to reach merchantable timber than in the 

 northern part of the State. The lengths of the three flumes in the 

 southern Sierras are respectively 42, 56, and 60 miles. On the 

 other hand, one flume located in northern California is only 4J 

 miles in length. 



These flumes consist of a V-shaped box with sides 32 inches wide 

 in the mountains and 48 inches wide where the grade is low and the 

 water sluggish. The angle formed by the sides of the flume is a right 

 angle, and the width across the top is 46 inches where the sides 

 are 32 inches wide. The flume box is supported at distances of 

 either 8 or 16 feet by bents composed of 4 by 6 inch or 6 by 6 inch 

 fir timbers. In the original construction bents were placed at 

 16-foot intervals, but it has been found advisable to place supports 

 every 8 feet for low trestles. Higher trestles are still constructed 

 with 16-foot bents, but heavier timber and sway and stringer braces 

 are used. Two 4 by 6 inch stringers are supported by the bents. 

 Upon the stringers at intervals of 4 feet are placed the braces wliich 

 hold the flume box in an upright position. 



The cost of constructing flumes varies with the difficulty of pre- 

 paring the ground for foundations and the average height of the 

 bents ; with lumber at $12 per 1,000 it ranges from $20 to $25 per 1,000 

 board feet, the higher cost being where the average height of the 

 flume is least. The lowest recorded cost is for two flumes in northern 

 California, approximately $4,000 per mile. In the southern Sierras 

 the natural conditions affecting construction are more difficult, 

 and the average cost of construction is about $5,000 per mile. The 

 most expensive flume in that locaHty is reported to have cost $6,000 

 per mile. The average amount of material is from 225,000 to 275,000 

 feet per mile. Farther north the average is not over 175,000 feet. 



The maximum grade allowable is about 25 per cent for short 

 pitches. Normally the grade is kept down to between 5 and 10 

 per cent, with 12 per cent as a maximum. In the San Joaquin 

 Valley the grade is very low. One flume in which the lumber is 

 shipped in bundles has approximately 13 miles on the lower end 

 with a grade of only 0.13 per cent. Another in which the lumber 

 is shipped loose has a similar length of slack water with a grade of 

 0.26 per cent. The maximum curve used is about 20 degrees. The 

 volume of water required to operate a flume varies from 25 to 35 

 second-feet. 



