AGRICULTURAL IRRIGATION SYSTEMS

What is an irrigation system?

Plants need water to survive and in arid regions, an irrigation system is the conveyance mechanism to provide water. An irrigation system may be composed of many parts. Storage reservoirs, pipes, sprinklers, ditches, and canals are just a few of the components that might constitute the entire system. Any of these components can be arranged together to form a whole and beneficial system

Why do we need irrigation systems?

Early Irrigation SystemsIn July of 1847, Utah's pioneers arrived in the arid west from their rainy roots in the east. One of their initial tasks was to divert water from the Salt Lake valley streams for irrigation use. They realized that irrigation systems were the key to cultivating crops and surviving in this new desert land. As additional people arrived in the harsh climate, scouts were sent out to survey undeveloped land and identify potential water sources before new areas could be settled. Once it was determined that there was water for irrigation, people established self-sufficient agricultural communities.

In the mid-western and eastern areas of the United States, rainfall supplies the needed water for crop growth and most crops can be raised without supplemental irrigation. In Utah however, there is not enough rain to produce most crops naturally, and additional water must be applied for cultivation. In Utah, since water was originally developed for agricultural irrigation, this practice consumes a significant amount of the developed water supply - 85 percent!

Irrigation System Types and Applications

There are two basic types of agricultural irrigation systems: flood and sprinkler.
Surface Flood (or flooded border) irrigation consists of releasing water over the surface of the land to flood the fields. Flood irrigation is the oldest form of irrigation, and can be used for any crop. Ideally, the land is slightly sloped, and level enough for the water to distribute evenly over the surface. The more level the land, the more efficient the flooding will be. Efficiency in irrigation is measured by how much of the water spreads to the roots of the plant. If too much water is applied, the water can soak below the roots and be wasted. Conversely, if not enough water reaches the roots, the plant's health can be diminished. On average, flood irrigation systems in Utah have efficiencies of roughly 35 to 55 percent. (These efficiencies take into account the reservoirs, canals, and ditches which transport the water to the field, and not just the time when the water is soaking into the plant roots. Most of the inefficiencies in the flood irrigation systems come from evaporation loss and water soaking into the soil in canals and ditches). Of course, there is a wide range in efficiencies, and some high-tech, laser-leveled fields may achieve up to 99 percent efficiency!


Another form of flood irrigation is called furrow flooding. Gated pipes, canals, and ditches can all be used to supply water to small ditches formed in-between rows of crops where the water is channeled. This method may be used if the field is not level in all directions. It allows the water to flow more evenly instead of forming puddles in uneven areas.

In both furrow flooding and surface flooding an efficiency-improving technique is surge irrigation. Furrow Flooding This involves quickly releasing large amounts of water at timed intervals, thus allowing the first surge of water to soak in before the second surge is released. When the second surge of water is released, it will travel over the already saturated ground instead of soaking in. This allows the water to travel further along the length of the field in less time.

Sprinkler irrigation systems utilize pipes and sprinkler heads to distribute water to the plants. Three common types of sprinkler systems are solid set, continuous move, and periodic move. Sprinkler irrigations systems are usually more efficient that flood irrigation systems. On average, agricultural sprinkler systems in Utah are about 60 percent efficient. Of course, they are more susceptible to wind than flood systems are, and can have much lower efficiencies in windy conditions.

Solid set sprinklers are permanently set in the ground and cannot be moved around the field. Typically the agricultural applications include orchards, vineyards, and other perennial plans that are not plowed.

The two most commonly used types of solid set systems in agricultural practices are impact sprinklers and drip or micro irrigation. Impact sprinkler heads are similar to residential or commercial sprinkler systems seen in homes or building grounds. Micro irrigation systems are newer, and because of their cost, are typically used only for high valued crops such as vineyards or nuts. They utilize rubber tubing and micro-sprayers or emitters to water efficiently - one emitter at each plant.

Continuous move sprinkler systems include center pivot systems and linear systems. Just as the name implies, these systems are motorized and continuously move to evenly irrigate the entire field. Center pivot systems are anchored in the middle of a circular field and rotate on wheels around that center. They are becoming increasingly popular due to ease of use and low labor costs.

Linear systems work in the same manner as center pivot systems except they move in a straight line instead of a circle. Again, these are popular with farmers because they are much less labor-intensive than periodic move systems

Periodic move sprinkler systems are not continuous in their movement, and must be manually moved a new location. Wheel line (or side-roll) sprinkler systems are motorized, but require somebody to manually adjust the position of the sprinkler line. Farmers will water one area until it is fully saturated, then move the line to the next area. A hand line does not have wheels and is not motorized. Each part of this sprinkler system must be disassembled and moved by hand to water the next section of field.

Additional Irrigation System Components

An irrigation system must include a water source, a conveyance system, and some way to distribute the water to the crops. Distribution systems - flood and sprinkle - have already been discussed. The source of water may be a reservoir, pond, well, stream or river. A reservoir or pond is a more reliable source of water because it can be managed to retain a desired amount of water. Rivers and streams are more susceptible to fluctuations in weather patterns. In the western United States, there is usually plenty of water running in streams and rivers during the spring, but not nearly enough for crops in the summer and fall. If an irrigation system has some storage capacity, such as a reservoir, crops may be more easily watered throughout the season.

A conveyance system allows water to be transferred from a water source to the fields. This can be achieved with canals, ditches, and pipes, or any combination of these. Ditches and canals are open to the air and are more susceptible to seepage and evaporation than pipes.

A ditch or canal can be lined or unlined. Unlined means that a trench has been dug for the water to run through. Lined canals and ditches can have concrete, clay, or impermeable membrane linings on their bottom and sides. Lined canals are much more efficient than unlined canals because they prevent water from seeping into the earth.

Irrigation systems are an integral element for agricultural viability in Utah and the rest of the arid western United States. They are built, operated and maintained by individual users as well as groups where all the members benefit. It is common for farmers to join together and create an irrigation system, such as a canal that runs along the top of all their fields, because it saves them the cost, energy, and time of doing it themselves. This is usually called an irrigation company. There are roughly 1,500 irrigation companies located throughout Utah.