14-4: IRRIGATION OF LAND. 



parts) the rise or fall between the feet of the instrument, which 

 should be eight feet three inches (half a rod) apart. With the aid 

 of this instrument nearly all the elevations and depressions on the 

 line of a contemplated ditch may be passed without making deep 

 cuttings or high embankments, and the ditch will olso have a regu- 

 lar grade when properly excavated, and the distance ascertained by 

 counting the steps made by the instrument for summer watering 

 when the crop is growing. The surface should in all cases have a 

 sufficient inclination or slope to cause the water io floiv consianlly 

 over it, allowing no water to stand on any portion of the watered 

 field, and this rule must be strictly adhered to, for sia<^)iant water 

 will destroy vegetation. A perfect level for the main canal and 

 laterals may be resorted to, when it is desired to reach a given 

 point, or to embrace as much land as possible. ^Vherever the incli- 

 nation of the field to be watered is sufficient to admit of the outlets 

 to convey the water on to the surface being a little lower than the 

 surface of the water in the main or lateral, this will cause a cur- 

 rent in the canal though it be on a level. Yet it is always desira- 

 ble to have a fall in both main and laterals — whenit can be obtained, 

 which should be by true grade the entire length, but sufficiently 

 gradual to prevent the water from washing away the sides and bot- 

 tom of the ditches. It is said that a furrow or channel four inches 

 deep by six inches wide with perpendicular sidea, and one inch fall 

 to the rod, will discharge about sixty gallons of water per minute, 

 but it is difficult to ascertain in advance the quantity of water re- 

 quired to irrigate a given space of ground, without regard, however, 

 to the quantity which is constantly soaking into the soil. It is said 

 that a sheet of water one inch deep, flowing over the entire surface, 

 should be the medium aimed at. The earth taken from the ditches 

 and furrows, especially on meadows, should be spread evenly over 

 the surface or otherwise disposed of, as the mowing machine, horse 

 rake, &,c., will then pass them with less difficulty. In taking the 

 water from large streams, the main canal should extend from the 

 stream at a right angle for a few rods when practicable, and to effect 

 this it is better to resort to an entire level for this distance, even 

 where the declivity of surface does not require a level, and the 

 canal may here be made proportionally wide or deep, to turn off the 

 water when necessary; and to guard against injury from freshets, a 



