^8 BULLETIN 1026, U. S. DEPARTMENT OF AGEICULTUKE. 



farmer's pocket whether it is in the form of an assessment or a car- 

 riage charge. 



The canal structures of the valley show various designs and types 

 of construction, but in general permanent structures of reinforced 

 concrete are replacing the old timber structures. Diversion dams 

 are rock and brush, timber, or concrete. Eock and brush dams 

 are used by only a few of the small ditches on the lower reaches of 

 the river. The majority of the dams are simple structures consist- 

 ing of piles of rock cribs topped by heavy timber decks on which 

 there are permanent crests or standards for flashboards. Wings 

 may be of masonry, concrete, or timber and seepage underneath is 

 usually cut off by a row of sheet piling. A dam of this type is shown 

 in Plate II, figure 1. The majority of the newer dams are of rein- 

 forced concrete set on piles or rock crib, and having well- designed 

 overflow lips and suitable sluices to scour the channels past the canal 

 intakes. A dam of this type is shown in Plate I, figure 1. The crest 

 of the Larimer County Dam (PL I, fig. 1) was found to be too 

 low for certain stages of the river and was raised 12 inches with 3 

 by 12 planks fastened to iron pins sunk in the crest. In Plate I, 

 figure 2, is shown another type of concrete dam in which the water is 

 held up by flashboards. 



The drift guard at the head of the Larimer and Weld Canal, 

 shown in Plate II, figure 2, is of the same general design as others in 

 the valley. The structure itself and the individual timbers of the 

 grating are placed at such an angle that the drift tends to slide 

 downstream instead of lodging. A few canals depend on booms of 

 logs chained end to end and anchored so that they swing out in front 

 of the gates. 



Headgates are made of timber, concrete, or stone and are fitted 

 with wooden or iron gates raised by some combination of screw 

 and lever, or rack and pinion. A type of gate and lifting device 

 is shown in Plate III, figure 1. Wasteways and sand sluices are of 

 similar design. Some of the canals use an adaptation of the Land 

 sand gate with diagonal ducts to cut out the greater part of the sand 

 near the bottom of the canal. 



In the construction of the canals of the valley flumes are avoided 

 even at great expense as is evidenced by the construction shown in 

 Plate III, figure 2. Some of those which were built are being elimi- 

 nated by the construction of tunnels or inverted syphons, the longest 

 in the valley, a half-mile flume along the side of the canon at the 

 head of the North Poudre Canal, being replaced b}^ a tunnel 1,G00 

 feet in length through solid rock. There still remain a nimiber of 

 timber or concrete flumes for crossings of less than 200 feet, and one 

 of these is shown in Plate IV, figure 1. Bating flumes at the head 

 of canals are usually of concrete or timber, though a few of masonry 



