270 



THE IRRIGATION AGE. 



about 160 feet long, are located eleven sluice gates, each 

 five feet in diameter, to control the entrance of water 

 to the main canal. Each of these gates is set in a 

 separate recess, the entire front of the wall being pro- 

 tected by 12 by 12 timber ice-guards, spaced two feet 

 center to center. 



MAIN CANAL AND LATERALS. 



On account of the slight fall of the river, which 

 averages only about two and a fifth feet per mile from 

 the point of diversion to its confluence with the Mis- 

 souri, it has been necessary to run the canal on the light 

 grade of one in 10,000, or about six inches to the mile. 

 This grade is maintained for nearly forty-six miles, and 

 is then gradually increased as the canal becomes smaller. 

 Two important points are indicated here, necessity for 

 accurate level-work, and use of a comparatively deep 

 canal section to insure sufficient velocity. 



Starting from the headgates. the canal is located 

 in thorough-cut for four miles. The excess material has 

 been used as a dike on the side adjacent to the river, to 



Partly finished lateral, with new town of Sidney, Mont., in 

 the distance. 



protect the canal in event of ice gorges. Lighter work 

 then follows to the ninth mile where there is about 

 three-quarters of a mile of side-hill work. Burns creek, 

 one of the largest tributaries to the Yellowstone in the 

 length of the project, is crossed in the tenth mile, follow- 

 ing which is a short stretch of thorough-cut, then a loca- 

 tion at the foot of steep bluffs to the thirteenth mile. 

 Continuing for about twelve miles from this point, there 

 is a gradual climb of the side-hill, with some interrup- 

 tions. A comparatively small acreage of irrigable land 

 is covered by the canal in this length, although there 

 are occasional areas which are easily watered. One of 

 the largest of these is reached in the twentieth mile by 

 a lateral which will be dropped through turbines gen- 

 erating sufficient power to pump water to about 2,500 

 acres of fine bench land lying above the canal. From 

 the twenty-sixth mile there is about eight miles of loca- 

 tion in fairly flat country. In the thirty-fourth mile 

 the canal approaches Fox creek, the largest creek in the 

 project, and encounters two miles of heavy side-hill 

 work. Beyond this creek the canal is located almost 

 entirely on level bench lands, with large irrigable areas 

 bordering it. As seventy per cent of the total irrigable 

 acreage lies below Fox creek, the canal rapidly decreases 

 in size until at the sixty-seventh mile it becomes a lat- 

 eral, watering a part of the Missouri bottoms. 



In addition to the main canal, 205 miles of laterals 

 are required to distribute the water to the farms. By 

 reason of the comparative narrowness of the irrigable 

 area these laterals have been kept down to moderate 

 sizes, and have been located along section-lines as far as 

 topographic conditions will allow, to avoid cutting up 

 the farms inconveniently. 



CANAL-LINE STRUCTURES. 



All structures on the main canal have been con- 

 structed of reinforced concrete. Creek crossings have 

 been accomplished in four ways: (1) by carrying the 

 canal under the creek in a conduit on grade; (2) by 

 carrying the creek under the canal in culvert; (3) by 

 carrying the canal in an inverted siphon under pressure, 

 entirely below the bed of the creek, and (4) by carrying 

 the creek over the canal in a superpassage or flume. 



(1) Conduits. This type of crossing has been 

 used for three larger creeks with somewhat irregular 

 flow, where sufficient head can not be spared to use a 

 siphon. It consists typically of a box-shaped concrete 



Side hill work just before crossing Fox Creek. 



passage designed to carry the canal at about double its 

 ordinary velocity, joined to the regular canal section by 

 wing walls, and long enough to accommodate the maxi- 

 mum discharge of the creek flowing over it. To prevent 

 the creek from cutting back under the conduit, a riprap 

 apron edged by sheet piling is provided on the down- 

 stream side, and to prevent the storm-water from wash- 

 ing into the canal, dikes are built on the upstream sides 

 of the creek. 



(2) Culverts. Culverts are used for all small 

 drainage areas, where the storm-flow may be estimated 

 somewhat definitely. On account of the low head room 

 which usually exists between the bottom of canal and 

 bed of rock, a flat box-shaped section has commonly been 

 found advantageous. The outer slopes of canal bank 

 have been protected by flaring wing walls. Vitrified 

 pipe has been used instead of concrete for small water 

 courses, the minimum size being twenty-four inches 

 diameter. A total of over sixty culverts will be required 

 in the entire length of canal, ten of which might be 

 classed as major structures. 



(3) Siphons. Viewed from the engineering 

 standpoint, these structures present the most interesting 

 features of the project; and are used for seven creek 

 crossings on the lower half of the work where the canal 

 has reached a level above the general surface of country. 



