The Golden State: Where & How to Live, Secure, Visit, Enjoy and Thrive in California

Sprinkler Irrigation

CROP. Plant roots will vary in depth from less than one foot to five or six feet; the depth to which the plant root will penetrate is the depth to which a plant will feed. It is obviously unnecessary to irrigate beyond the root depth of the plant. It must be remembered that the water, when applied to the soil, does not seep down through the soil until it has reached the saturation point. Then, and only then, will it release water, through the pull of gravity, to the lower levels.

RELATIVE LAND ELEVATION. A knowledge of the difference in elevation between the water source and the land to be irrigated is necessary in order to determine the available head and the size of main pipe and laterals. The main pipe line must be designed to create a minimum loss through friction or a minimum loss of pressure head. The lateral lines should be designed so that there will be not more than a 20% variation in sprinkler nozzle pressure; except in some cases which will be discussed later.

PRESSURE HEAD. The pressure head necessary to operate a sprinkler system is the sum of the pressure in feet required at the sprinkler and the friction loss in the conveyor pipes. To this must be added the lift from the water source to the highest sprinkler, or if the water source is above the highest sprinkler then this difference in elevation will be subtracted from the required pressure. From the result of the above calculation, together with the quantity of water needed, the size of the pumping unit can be obtained by the horse power formula. In some cases the source of water is so much higher than the highest sprinkler that the difference in elevation equals or exceeds the required pressure head. Where this is true the system will operate by gravity and no pump is necessary.

WIND. One of the most important preliminary design factors is to consider the wind. Always run the lateral lines across the wind. This puts the sprinklers closer together and helps to compensate for the wind. If higher than 4 miles per hour winds are encountered it may be necessary to use twice as many sprinklers.