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 make up 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 Systems
In 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 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, there is not enough rain to produce most crops naturally, and additional water must be applied for cultivation. In Utah, be water was originally developed for agricultural irrigation, this practice consumes a significant amount of the developed water supply – almost 80%!
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 area is slightly sloped and level enough for the water to distribute evenly over the surface. The more level the ground, the more efficient the flooding will be. Efficiency in irrigation is measured by how much of the water seeps 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%. (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 inefficiency, and some high-tech, laser-leveled fields may achieve up to 99% efficiency!
Furrow flooding is another form of flood irrigation. Gated pipes, canals, and ditches are used to supply water to small trenches formed between rows of crops. This method can 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, another efficiency-improving technique is surge irrigation. 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 release allows the water to move 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 irrigation systems are usually more efficient than flood irrigation systems. On average, agricultural sprinkler systems in Utah are about 60% 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 spray the entire field evenly. Center pivot systems are anchored in the middle of a circular area 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 to a new location. Wheel line (or side-roll) sprinkler systems are motorized, but require somebody to adjust the position of the sprinkler line manually. 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 the 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, plants may be more easily watered throughout the season.
A conveyance system allows water to be moved from a water source to the fields. This system can be canals, ditches, and pipes. 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 creation is called an irrigation company. There are roughly 1,500 irrigation companies located throughout Utah.
Why are dams built?
There are several reasons for building dams. Dams are made to create reservoirs that capture water from streams and store the water in reservoirs. This excess water from the snowmelt and floodwaters is used throughout the year and during drought years. Dams also provide irrigation water, drinking water, hydropower, and flood control. Many reservoirs provide recreational activities like fishing, boating, and other water sports
What are dams made of?
There are several different kinds of dams. Some dams are called embankment dams. Embankment dams are called either earthen dams or rockfill dams, depending on what material is used most in the dam. Earthen dams are made mostly of soil or earth. Rockfill dams are made mostly of rocks. Embankment dams are the most common type of dam in the United States. Other dams are made of concrete. Concrete dams can be either gravity dams or concrete arch dams, depending on how they are built.
How is an embankment dam built?
Before a dam can be built, there are several things that have to be done. First, the location of the dam has to be chosen. Builders look for a place that is close to where the water will be used. They need to find a valley that will be able to hold the amount of water they want to store. The valley needs to be big enough and have soils and rock that will not let all the water seep into the ground.
Geologists determine what kind of soils and rock there are by drilling holes deep into the ground and pulling out the soil. Then they test the soils to see if it will be a good place for a dam and reservoir.
Once a good location is found, engineers design the dam. They have to look at where the dam will be built to figure out how big the dam will be and what kind of dam will work best. When the design is complete, construction begins. If a dam is being built where there is already a river or stream, workers have to divert the water away from the construction site or build a small dam called a cofferdam to hold back the water while they build the dam.
Workers start building an embankment dam by digging a large trench into the existing ground that runs the length of the dam. They fill this trench with dam material to form a cutoff trench. This helps keep the water in the reservoir. Then the dam is built above the ground. Engineers use different materials in different areas, or zones, so the dam will work properly. A central zone within the dam is made of clay soil that holds the water and allows very little water to get through. Other downstream zones are made of soil or rock that give strength to the dam. During the construction of these different zones, workers must also build other parts of the dam, like outlets and spillways.
Outlets are used to control the amount of water that is let out of a reservoir at any time. The outlets have gates that can be opened and closed when the water users need them. Spillways allow water to flow out of the reservoir when it gets full so that water does not flow over the top of the dam.
When the construction of the dam is complete, water is allowed to fill the reservoir so water will be available when it is needed.
Drinking water is one of the easiest things in the world to take for granted. We turn the tap and out comes clean and fresh life-sustaining water. Most people don’t realize just how much planning, design, and work goes into delivering water to their homes. Providing an adequate water supply for a community includes three things: 1) finding and developing an adequate water source; 2) treating the water to ensure that it is clean enough to drink; and 3) delivering the water to every residential, commercial, and industrial building within the service area.
Finding and Developing a Water Source
In Utah, as with most parts of the world, there are two types of water sources: groundwater and surface water. In some parts of the world, other water sources have been developed. Rainwater can be collected where precipitation rates are high enough. In extremely arid regions bordering the ocean, desalination (salt removal) of seawater is an expensive alternative that is becoming more common. In Utah, however, drinking water supplies come from either surface or groundwater sources. Of course, both of these sources are fed by precipitation. It is primarily the snow in our mountains during the winter months that recharge the groundwater aquifers and fill up our streams, rivers, lakes, and reservoirs.
Groundwater is extracted from an aquifer by the use of wells. While groundwater taken from different locations can have vastly different water quality characteristics, generally, groundwater is much cleaner than surface water. Surface water tends to pick up natural and man-made pollutants. As water moves through the ground, many of these pollutants are filtered out. Consequently, groundwater usually requires less treatment and is cheaper to process to drinking water standards.
Surface water sources include rivers, streams, lakes, reservoirs, and even springs. A Spring is a location where groundwater comes to the surface. Consequently, the classification of a Spring as surface water or groundwater depends upon the definition. For a long time, springs were considered to be groundwater sources and treated as such. The proximity with the ground surface, however, makes a spring very susceptible to the same pollutants that can contaminate surface water sources. Consequently, springs are now considered surface water sources by governmental regulatory agencies, and the treatment of spring water is held to the same strict standard as other surface water sources.
Water that is taken from a surface or groundwater source is referred to as “raw” water to distinguish it from treated or “finished” water. Raw water is treated not just to remove disease-causing organisms but also to remove silt, grit, and humus material (suspended solids), which can have a detrimental effect upon pipes, meters, and other components of the water distribution system. Treating raw water also improves the taste and eliminates objectionable odors or color
The cleaner and better the quality of the raw water, the easier and cheaper it is to treat. Consequently, federal, state, and local government agencies have developed plans and laws that protect and preserve the quality of drinking water sources. Many surface water streams along the Wasatch front are important sources of drinking water, but also double as recreation areas. Since we camp and picnic in the watersheds and boat, fish and water-ski on the very water we drink, it is important that we are responsible about litter control, use of public restrooms and safeguarding against fires to minimize the impact upon a critical drinking water source
The water treatment process can range from a simple filter or chlorination to a complex treatment plant. A small rural community drinking water system, with a high-quality groundwater source, may need very little if any, treatment. For much larger public water systems, particularly when the water source is subjected to repeated human contact such as heavy recreational use, the treatment process is much more complicated and will likely include a combination of the following processes:
Initial Filtration – Often the initial step is to filter the water through some course screens to remove any fish, bugs, leaves, twigs, and debris.
Coagulation & Sedimentation – Alum and lime are added to the water. These chemicals then bond with suspended sediments, bacteria, and fine particles present in the water to form a sticky floc, which looks like white foam or suds on the water. Over time and as the water is stirred slightly all the fine particulate matter is bonded to the floc, which eventually becomes heavy and sinks to the bottom of the tank.
Disinfection – This is the controlled addition of some germ-killing chemical, usually chlorine, to the water. This treatment step can take place early, late, or even repeatedly in the water treatment process. Often it is a final step.
Aeration – Taste, and odor problems are often a result of the presence of dissolved gas such as naturally occurring hydrogen sulfide, or living organic material such as algae, or decaying organic material, industrial waste, or even residual chlorine. Forcing tiny bubbles of air through the water facilitates the release of these gases from the solution reducing unpleasant odors and taste.
Water Delivery and Distribution
Once the water has been treated, it is ready for distribution to homes and businesses. There is, however, a logistics problem between treatment and delivery. While treatment plants are designed to treat water at a constant rate, people don’t use water at a constant rate. Traditionally there is less water use during the late-night and early morning hours than during the day. Daily water use tends to peak in the morning as people prepare for their day, and then again in the evening as people return home to prepare dinner. In the summertime, lawn watering can also dramatically impact the peaking nature of water use. Consequently, it is important to have enough storage capacity within the distribution system to meet the days peaking requirements without running out of water. Pipes that deliver the water from the storage tank to the individual homes and businesses also have to be sized large enough to convey water during the times of peak usage. Fire-fighting imposes even greater demands upon the system, requiring that pipes and storage reservoirs be sized large enough to battle a blaze during periods of peak water use without losing water pressure or depleting
Ensuring adequate water pressure throughout the system is yet another problem for water system designers. Smaller pipes cost less to purchase and install than large pipes. But to deliver the same amount of water through a smaller pipe means that the water must travel faster. Since there is an interdependent relationship between the velocity of the water and the pressure in the pipe, the designer must size pipes large enough to accommodate the required flow without increasing the project cost by over-sizing pipes.
INDUSTRIAL WATER USE
Every manufactured product, whether it be steel, paper, lumber, chemicals, gasoline, or oil must use water in some capacity during its creation. Even though industrial water use only comprises five percent of Utah’s total public use, it is vital to the many businesses that utilize it. This five percent equals 28 million gallons per day of fresh, culinary water that Utah’s public systems deliver to various industries. Nationally, industrial water use encompasses about twelve percent of all public water supply deliveries or 4,750 million gallons per day!
Industrial water is not only supplied by public entities. Most of the industrial water used in Utah – 92 percent or 320 million gallons per day – is self-supplied, meaning the industry has a well or another water source. If an industry is self-supplied, the water may be from fresh or saline (saltwater) sources. In Utah, about half the industrial self-supplied water use is saline, which makes sense when considering the largest lake west of the Mississippi River, the Great Salt Lake, is in our backyard! The industries that use Great Salt Lake water are salt and mineral producers. Water is diverted from the lake to evaporation ponds, where salt and other minerals, such as magnesium, are extracted.
In Utah, power generation is another important industrial water use. Unlike the salt and mineral producers, this water is not consumptively used. To generate power, Lake Powell water is released and flows through the massive turbines at Glen Canyon Power Plant. This water is not consumptively used because it simply passes through on its journey to the Gulf of California. The minimum amount of water that must be run through the turbines is 7.3 billion gallons per day. On average though, more water runs through the plant, generating roughly 16.5 GigaWatt-hours of power per day!