THE IRRIGATION AGE. 



261 



that are too steep for other methods. Fields having a 

 firm soil and a fall of 25 feet to 100 feet have been flooded 

 successfully. From this extreme the slope may diminish 

 to less than 0.1 foot in 100 feet. Its cheapness is another 



Fig. 10. Leveler Used in Gallatin Valley, Montana 



feature which recommends, it to the farmer of limited 

 means. Ordinary raw land can be prepared for flooding 

 at an expense of $2 to $5 per acre. Again, it is adapted to 

 the use of small water supplies. In the mountain States 

 the irrigation systems have been planned and built to 

 deliver water in comparatively small streams for use in 

 flooding or in furrows, and water users should be certain 

 that the larger volumes required for 

 checks and borders can be secured before 

 going to the expense of preparing their 

 fields for either of those systems. 



In grading the land for this par- 

 ticular method it is not customary to 

 make many changes in the natural sur- 

 face. Only the smaller knolls are re- 

 moved and deposited in the low places. 

 An effort is made always, however, to 

 make the farm laterals fit into the natural 

 slope and configuration of the tract to 

 be watered so as to bring the water to 

 the high places. On steep slopes the 

 laterals may be less than SO feet apart; 

 on flatter slopes they may be 200 feet or 

 more apart. Whatever the spacing it is 

 always desirable to have the slope be- 

 tween them as nearly uniform as possi- 

 ble. When the land in its natural state is uneven, the 

 grading can be done best by a grader of the kind shown 

 in attached figure 7, or a scraper of the kind shown in 

 figure 9. When these are used, it is often advantageous 



to make use of some such implement as the grader shown 

 in figure 10 for the final smoothing and grading. If the 

 field in its natural state is comparatively smooth and level 

 a homemade drag or leveler, as shown in figure 11, serves 

 the purpose fairly well. 



The distribution of the ditches on 

 the field varies too widely to admit 

 of presenting a standard plan, but fig- 

 ure 12 shows an arrangement of field 

 laterals common to the mountain 

 States. A supply ditch, AB, is built on 

 one side and laterals, CB and FF, 

 branch out from it on a grade of 0.5 to 

 0.75 inch to the rod. These laterals are 

 spaced 75 to 100 feet apart and are 

 made with double moldboard plows, 

 either walking or sulky. Figures 13 

 and 14 illustrate other common arrange- 

 ments in use in northern Colorado. 



In the vicinity of Fort Collins, 

 Colo., the main lateral is built to the 

 highest corner of the field to be ir- 

 rigated and the smaller laterals extend 

 out from it, spaced 75 to 225 feet apart, 

 the spacing depending on the slope of 

 the ground and the coarseness of the 

 soil. The size of the laterals is gov- 

 erned by the head which may be had, 

 but on steep slopes and on soil that 

 erodes readily, small heads are best. 

 Around Berthoud, Colo., the land is 

 naturally of uniform, even slope, and 

 little grading has been necessary. 

 Heavy timber or iron drags are used to 

 smooth the surface after plowing so 

 that the water will spread evenly. 

 These are built in various ways and 

 out of whatever material happens to be 

 available on the farm. Worn-out steel 

 rails, such as have been removed from 

 a railway, are often used, two rails 

 being fastened together about 30 inches 

 apart. A team is hitched to each end 

 and the driver rides on the drag. Once 

 over a field with a drag of this kind 

 is usually sufficient to make the surface 

 quite uniform and smooth. The proper 

 location for field laterals is usually evi- 

 dent to the irrigator without the use 

 of surveying instruments, though in 

 fields where the fall is slight it is often 

 necessary to have a topographical sur- 

 vey made and the laterals located by 

 an engineer. Field laterals are always 

 so located that they cover the highest 

 parts of the field and their distance apart in alfalfa varies 

 from 10 to 20 rods. 



The head required for flooding from field laterals in 

 northern Colorado varies from 2 to 3 cubic feet per second 

 and is divided between two or three laterals. Canvas or 

 coarse manure dams are used to check the water in the 

 laterals and to force it out over the banks and down 



Fig. 11. Homemade Drag or Leveler. 



the slopes of the fields. In less than three hours the 

 upper foot of soil is usually thoroughly moistened. To 

 apply one watering in this way costs from 15 to 30 cents 

 an acre. 



