18 BULLETIN" 115, U. S. DEPARTMENT OF AGRICULTURE. 



will carry water 3 feet deep on a grade of 4.2 feet per mile. The 

 gate structure has two openings regulated by steel gates, with a rack- 

 and-pinion lift. The crest of the wings and the curtain wall above 

 the openings are such that the maximum flood known to the stream 

 can pass over the dam without topping the structure. The ditch be- 

 low the gate is separated from the creek by a stepped concrete wall. 

 When the writer saw this structure in May, 1912, there was about 

 1 foot of water passing over the weir, developing sufficient pressure 

 on the openings to induce a velocity of 7 or 8 feet (estimated) per 

 second in the upper reaches of the canal. As only a small amount of 

 water was needed in the canal the gates were opened but a few inches. 

 The high velocity caused scouring of the canal sides for about 100 

 feet below the gate. This condition suggested that the water might 

 be delivered to the canal much more gently by casting some flash- 

 board grooves in the sides of the gate structure downstream from 

 the openings so that boards might be inserted in these grooves and 

 the elevation of the water below the gate kept at such a height that 

 the shutters could be opened wide and the velocity of the entering 

 water correspondingly reduced. The water would fall over the 

 flashboards in a vertical drop and the velocity of the water below the 

 structure cause no damage. If the full capacity of the canal should 

 be desired, the flashboards would be pulled and the elevation of the 

 water in the canal would prevent high velocity at the upper end. 



At the time the photograph shown in Plate V, figure 1, was taken 

 all of the water not entering the canal was passed through the sluice- 

 way in the diversion dam. This not only serves to carry most of the 

 sand down the stream, but also makes it possible to draw off the water 

 below the crest of the dam in order to make repairs. 



HEAD GATE, UINTA COUNTY IRRIGATION CO., WYOMING. 



A good example of modern construction of a river gate for a canal 

 diverting water from a secondary channel of the stream is furnished 

 at the head of the Cottonwood Canal in Uinta County, Wyo. (PL 

 V, fig. 2.) 



Ball Island separates the stream into two branches and the gate is 

 installed on one of these. The amount of water flowing in the 

 branch supplying this gate can be regulated roughly by logs and 

 brush in the channel at the head of the island. This regulation pre- 

 vents the heavy flood flow of the stream from coming with full force 

 against the gate structure and the saving in construction, due to this 

 safe position, is evident from the view shown. It will be noted that 

 the wing walls do not rise far above the natural surface of the bottom 

 land. 



This gate supplies a canal 20 feet wide on the bottom with water 

 3 feet deep. The carrying capacity is 140 second-feet. The gate is 



