Wesley Porter, Extension Irrigation Specialist, revised the article.
Kerry Harrison, Extension Agricultural Engineer, wrote the original text.
- Planning the Irrigation System
- Sprinkler Irrigation
- Drip Irrigation
- The Distribution System
- The Water Source
- Backflow Prevention
- Irrigation Scheduling App for Turf
Georgia receives roughly 50 inches of rain per year, which is more than enough to meet most plants’ entire water needs. However, this rain does not always fall in adequate amounts during the time of year when the plants want it the most. During peak water demand seasons, supplementary water in the form of irrigation is often required to maintain a beautiful green lawn and fruitful garden.
Sprinkler irrigation and drip (or trickling) irrigation are the two most common methods of irrigation for the residential landscaping. There are several varieties of sprinklers available that, when appropriately chosen, may be tailored to cover practically any area. For grass areas, sprinklers are typically the best option. Drip irrigation has grown in popularity in recent years, and it is particularly appropriate for watering individual plants such as shrubs and trees, but it may also be used in decorative or vegetable gardens. Some drip irrigation systems also work well with garden row crops.
An irrigation system may be as basic as a sprinkler attached to a water hose or as complex as an underground pipeline system with various circuits and sophisticated controls. This paper focuses on more sophisticated systems, although the majority of the material may be applied to any lawn or garden irrigation system.
A step-by-step design method is not always straightforward. A variety of things are at play. Sprinkler systems, in particular, require that the kinds and quantity of sprinklers fit the pressure and volume capacity of the water supply. In addition, the application rates from sprinklers and drip emitters should be low enough to avoid excessive runoff from the soil surface while being high enough to fulfill the crops’ water needs. Choosing the optimum sprinklers, emitters, and spacing for a specific system might be a trial and error procedure. Before designing an irrigation system, many variables must be considered:
- irrigation needs of a certain crop or plant
- shape of the area;
- Soil type (soil water holding capacity/intake capacity);
- water source;
- operational necessities (hours per day, automatic or manual controls, etc.).
When there is an existing water supply, the system must be constructed with pressure and volume constraints in mind. In other cases, the irrigation design will establish the water source needs, and the water supply will be placed appropriately. In any case, while designing an efficient irrigation system, you must take into account all of the previous aspects.
This article includes the fundamentals for planning most lawn and garden irrigation systems, as well as choosing the appropriate kind of system for a specific circumstance. The order in which certain topics are described in this article does not always correspond to the order in which they should be handled when creating a system. The design method will differ depending on the conditions.
This article cannot address every question about lawn and garden watering that may occur. Water needs for certain crops and plants, for example, have been purposefully removed. This information may be obtained from a variety of sources, including Extension publications and your county Extension agent. If you have any more questions, contact your county Extension agent or a local irrigation dealer for assistance.
Types of Sprinklers
The most popular kinds of sprinklers used in lawns and gardens are rotary sprinklers and spray heads. Both kinds have distinct operating characteristics and are intended for certain purposes.
Rotary sprinklers (Figure 1) often run at high pressures (30 to 80 psi) and cover enormous regions. (a 30- to 50-foot radius). They typically have an application rate of 0.2 to 0.5 inch per hour. Rotary sprinklers are often the most cost-effective option for big gardens and open grass areas. Rotary sprinklers may be permanently installed on risers or utilized with fast coupling valves to travel from one position to another. There are also rotary pop-up heads available. When water pressure is applied, they are implanted flush with the soil surface and rise above ground level. They are especially beneficial in grass areas since they keep lawn mowers and other vehicles out of the path.
Figure 1. Rotary sprinklers.
You may want to keep water away from nearby locations such as walkways or building sides. Part-circle rotary sprinklers are available for this sort of application. These are normally adjustable, with the arc of throw ranging from 20 to 360 degrees.
Spray heads are intended to work at lower pressures than rotary sprinklers (Figure 2). (usually 15 to 35 psi). They spray 1 to 2 inches per hour and cover a smaller area than rotary sprinklers (10 to 20-foot radius). This property may restrict their usage and duration of application in thick soils or places with steep slopes. Spray heads are most often employed in tiny or narrow grass areas, as well as regions with uneven shapes.
Figure 2. Spray heads.
Spray heads, like rotating sprinklers, may be fixed on permanent risers or are available as pop-up kinds for usage in grass areas. Spray heads are available in a variety of forms, allowing them to be tailored to practically any shaped area. Full circles, half circles, quarter circles, and even square and rectangular designs are available. As a general rule, all lawn and garden sprinklers should be positioned on a swing joint or a flexible riser. This is particularly true with popup sprinklers. The swing joint enables the sprinkler to be adjusted so that it is flush with the ground. It also protects the sprinkler and subterranean pipe from harm if they are driven over by large machinery.
Sprinklers must be correctly spaced to produce a consistent application of water across the watered area. Most sprinklers apply more water in the middle of the pattern than at the margins when run at the right pressure. (Figure 3). They must overlap in order to provide a consistent distribution. (Figure 4). The amount of overlap is determined by the sprinkler spacing pattern and the normal wind conditions at the time of usage.
Figure 3. Single sprinkler.
Figure 4. Distribution with overlap.
The two most prevalent sprinkler spacing designs are square spacing (Figure 5) and triangular spacing. (Figure 6). In certain cases, a rectangular design may be employed.
When the distance between sprinklers (S) equals the distance between rows, a square pattern is formed. (L). The square pattern is often utilized in square or rectangular spaces where part-circle sprinklers are required along the borders and in the corners. The appropriate square pattern spacing for different wind conditions is shown in Table 1. These suggested spacings are based on a proportion of the sprinklers’ wetted diameter as specified by the manufacturer.
Figure 5. Square spacing pattern.
Figure 6. Equilateral triangle spacing pattern.
|Table 1. Average square spacing ranges.|
|For a Wind Velocity of:||Use a Maximum Spacing of:|
|0 to 3 mph||55% of Diameter D|
|4 to 7 mph||50% of Diameter D|
|8 to 12 mph||45% of Diameter D|
All sprinklers in an equilateral triangle arrangement are the same distance (S) apart. With this arrangement, the distance between sprinkler rows (L) is.86 times the distance between sprinklers (R). (S). A triangle design is often employed in regions with uneven borders or when part-circle sprinklers along boundaries are not required. The required spacings for the triangle design are shown in Table 2.
|Table 2. Average equilateral triangle spacing ranges.|
|For a Wind Velocity of:||Use a Maximum Spacing of:|
|0 to 3 mph||60% of Diameter D|
|4 to 7 mph||55% of Diameter D|
|8 to 12 mph||50% of Diameter D|
Because of unusually shaped places or impediments, you may need to make changes to the previous rules. To prevent an obstruction, the square and triangular designs, for example, might be blended in the same space. Adjustments are permitted as long as the required spacing between sprinklers is maintained. This is known as “sliding spacing.”
Determining Application Rates
Sprinklers are chosen based on their output volume, measured in gallons per minute (gpm), and wetted diameter. (feet). A sprinkler’s output volume is largely determined by nozzle size and pressure. Wetted diameter is largely influenced by the kind of sprinkler, even if it is also controlled by nozzle size and pressure.
The output volume and wetted diameter for various nozzle diameters and operating pressures are typically specified in the manufacturer’s specifications. If this data is not accessible, the output volume of a certain sprinkler may be calculated in two methods. Table 3 may be utilized for most sprinklers since output volume is dependent on nozzle size and pressure. The third option is to apply the necessary pressure to the sprinkler and collect the water for one minute in a bucket. This volume of water is then measured in gallons to get the flow rate in gallons per minute.
|Table 3. At 100% efficiency, the nozzle discharges in gallons per minute.|
|Nozzle Diameter in Inches|
Setting up a single sprinkler at the correct height, applying water pressure, and measuring the distance of water throw is the best technique to establish the wetted diameter. The kind and size of sprinkler used are determined by the available water supply (volume and pressure) and the area to be covered.
The application rate is another element to consider while selecting sprinklers. The application rate of a sprinkler is the rate (typically expressed in inches per hour) at which it sprays water to the soil. If the application rate exceeds the soil’s intake capacity for a lengthy period of time, unwanted puddling and runoff ensue. Soil intake capacity is affected by a number of elements, including soil type (sand, loam, clay), plant cover, and slope. Table 4 estimates intake capacity for various soil types. When there is vegetative cover, these predictions will be somewhat higher.
|Table 4. Soil intake rates.|
|Surface Texture of Soil||Intake Rate (inches/hour)|
|sandy; loamy sand||2.0 – 3.5|
|sandy loam; loam||1.5 – 2.5|
|silt loam; clay loam||0.5 – 1.5|
|sandy clay; clay||0.2 – 0.5|
To calculate the application rate for a particular sprinkler and spacing pattern, use the following equation:
AR = (96.3 x Q) / (S x L)
AR = application rate (in/hr)
Q = the number of gallons per minute applied by a complete circle sprinkler.
S = spacing between sprinklers (ft)
L = spacing between rows of sprinklers (ft)
If the estimated application rate is much greater than the soil intake rate, use a lower nozzle size. Use a sprinkler with a greater wetted diameter and adjust the sprinkler spacing appropriately.
When part-circle and full-circle sprinklers are controlled by the same valve, lower the nozzle diameters on the part circles so that the sprinkler output rates are proportionate to the area covered. A half-circle sprinkler, for example, should emit half as much water as a full-circle sprinkler; a quarter-circle sprinkler should emit one-fourth as much as a full-circle sprinkler.
Drip irrigation is the repeated, gradual delivery of water to soil using mechanical emitters. Emitters are incorporated inside or connected to little plastic water delivery pipes that provide water to each irrigated plant. This application technique avoids most water losses and ensures a somewhat uniform distribution. It also enables you to keep a careful eye on the quantity of water used. Drip irrigation consumes less water because it gives for more control over the distribution and quantity of water delivered and lowers evaporation losses. Growing vegetables, ornamental and fruit trees, bushes, vines, and outside container plants may all benefit from drip watering. It is unsuitable for dense plantings of shallow-rooted plants like grass and certain ground coverings.
Emitters, lateral lines, main lines, and a control station comprise a drip irrigation system. Emitters, which regulate water flow from lateral lines into soil, are classified as either porous-wall (line source) or individual (point source). (Figure 7). Emitters reduce the pressure from the inside to the outside of the lateral, allowing water droplets to exit. Small orifices, bigger orifices in sequence, lengthy passages, vortex chambers, flexible discs, or other mechanical techniques may be used to achieve this. Some emitters maintain a constant flow at varying pressures by varying the length or cross section of the tunnel. These are referred to as pressure compensating emitters. Flow rates for point source emitters are typically set at 1/2 to 2 gallons per hour (gph); 1 gph is the most frequent rate.
Figure 7. Typical drip emitters.
Line source emitters are often made of porous wall tubing or twin chamber-type tubing with tiny orifices spaced at preset intervals. This tubing is ideal for row crops and closely spaced ornamentals in the garden. The output is typically expressed in gallons per minute per 100 feet of length.
Emitters are frequently attached to or a part of the lateral lines, which are small diameter black polyethylene tubing (3/8 to 3/4 inch).
Water is transported from the control station to the lateral lines through main lines, which are typically underground plastic pipe. The size of the main line is determined by the number of laterals and the flow of water to them.
Water is filtered or screened at the control station (Figure 8) and pressure and application time are controlled. To avoid emitter clogging, drip irrigation water should be as pure as drinking water. (either initially or after filtration). To purify the water, many kinds of sand filters, cartridge filters, disk filters, or screens with mesh sizes ranging from 100 to 200 mesh may be employed. For landscape and garden applications, a modest screen filter designed for the specified flow is generally adequate, especially if the water source is the same as that used for the home. If the water comes from a different source, such as a pond or stream, a larger filter will be required.
Figure 8. The pressure gauge is optional, and the control valve may be either electronic or manual.
Most systems need some pressure control, which is normally accomplished using an in-line pre-set pressure regulator. Pressure requirements for various emitters range from 2 to 3 psi to 30 to 40 psi. Most point source emitters are intended to operate at pressures ranging from 15 to 20 psi.
Applications may be controlled manually using gate valves or automatically using an electric time clock and electrically powered valves. Water applications may often be changed between 15 minutes and 24 hours per day using a time clock. You may purchase time clocks that will regulate one or more valves on varied schedules.
Though more companies are custom designing and installing residential drip irrigation systems, you may be able to design and install your own. Check local codes for suitable backflow device placements and regulations if you opt to self-install.
Water is often applied on a daily or alternate day basis using drip irrigation throughout the growth season. Plants consume water more quickly due to the tiny root volume wetted. Drip irrigation is also meant to avoid plant stress by maintaining an optimal moisture level in the soil. This need regular water treatments to keep the soil from drying out.
The application duration should be the amount of time required to apply the water used since the last irrigation. It should not be continuous and should last between one and sixteen hours. Increase the number of emitters if the system must function longer than 16 hours per day on a regular basis. Duration should not exceed the period when ponding or runoff begins; this may be prevented by shutting off and resuming the water later.
To ensure that your drip system works effectively, clean filters and screens on a regular basis by hand or with built-in backflushing. Flushing may be necessary weekly, twice weekly, or twice a month, depending on the water quality and filter size. Open the termination of each lateral line once a year to drain away accumulated silt.
To familiarize yourself with a new drip system, turn it on for a brief period of time each day and then assess the soil moisture state before irrigating again. Soil moisture may be measured with a soil coring device or auger, or by installing a soil moisture measurement apparatus. (Make your measurement 8 to 12 inches from an emitter beneath the leafy portion of the plant.) The feel and look of a soil sample may be used to determine its wetness.
Pipe size is a critical factor when building any form of irrigation system, whether sprinkler or drip. Water pressure reduces when it passes through a pipe owing to friction between the water and the pipe walls. This pressure loss rises with increasing water flow and pipe length, necessitating bigger pipe diameters for greater flow rates, particularly in systems with lengthy sections of pipe.
Pressure is defined as a force acting on a certain area and is often expressed in pounds per square inch or feet of water. A 1 foot of water head equals 0.43 psi. This value is calculated from the weight of a 12-inch-high column of water with a 1 inch by 1 inch base. The pressure on the bottom is 0.43 psi since the area of the base is 1 square inch.
The pressure demand of a lawn irrigation system is determined by three components: (1) the pressure necessary to run the sprinkler or emitter, (2) the pressure loss due to friction in the pipe and fittings, and (3) the pressure loss or gain owing to elevation changes. Pumping water uphill requires more pressure. As a result, 0.43 psi is added to the pressure requirement for each foot of elevation change. When water travels downhill, 0.43 psi is obtained for every foot of elevation change. Most lawns, on the other hand, are flat enough that the elevation factor may be overlooked. Because elevation is typically neglected and the pressure needed on the sprinkler or emitter is already known, the only pressure component left to calculate is the friction loss in the pipes and fittings.
Pipe size selection is critical to ensuring appropriate pressure for all sprinklers or emitters and keeping pressure variances on a circuit within acceptable limits. To ensure excellent water application uniformity, the pressure fluctuation on a circuit should be no more than 20% for sprinklers and non-pressure compensating emitters. Greater pressure discrepancies may be permitted with pressure compensating emitters as long as the pressure remains within the range of the emitter.
Choose pipe diameters such that the water velocity in the pipes does not exceed 5 feet per second, and then calculate the pressure differential between the circuit’s first and final sprinklers. If the difference is higher than 20%, you may try bigger pipe diameters until the pressure differential is acceptable. Pressure losses are often expressed in psi per 100 feet, as shown in Table 5. (which also gives the velocity for a given flow rate for each pipe size). The velocity of any pipe size may be calculated using the following equation:
V = Q / (2.45 x D2)
V = velocity (ft/sec.)
Q = flow rate (gal/min.)
D = inside diameter of pipe (in)
Using Table 5, the pipe size for each segment may be chosen such that the velocity is less than 5 feet per second. (Figure 9).
Assume that each sprinkler produces 5 gallons of water per minute and that the target pressure at the final sprinkler is 40 psi. The next step is to sum up the pressure losses between the circuit’s first and last sprinklers:
Loss (B to E) = Loss (B to C) + Loss (C to D) + Loss (D to E) = 1.34 psi + 2.145 psi + 2.07 psi = 5.55 psi
As a result, if the pressure at the final sprinkler is 40 psi, the pressure at point B is 45.55 psi.
Pressure at B = 40 psi + 5.55 psi = 45.55 psi
The percent pressure differential between the circuit’s first and last sprinkler may be calculated as follows:
% Difference = [(45.55 – 40.00) / 40.00] x 100 = [(45.55 – 40.00) / 40.00] x 100 = 13.87%.
Because the difference is less than 20%, the pipe diameters chosen are adequate.
The same method may be used to size tubing for a drip system. The only difference is that the pipe line outputs are drip tubes rather than sprinklers.
(Scroll right for more)
|Table 5. PVC plastic irrigation pipe pressure loss (125 and 160 psi rated) [PSI per 100 feet of pipe, C = 150]|
| Note: Values below colored cells have velocities more than 5 feet per second and should be chosen with care.
V – Velocity ft/sec
P – Pressure drop psi
Figure 9. Typical sprinkler lateral.
Select a maximum velocity of 5 feet per second for the main lines that feed the various circuits. If the lines are too lengthy, or if the available pressure at the supply is low, you may wish to use bigger pipes than recommended by this recommendation. The entire system pressure requirement may be calculated by taking the pressure at the system’s final sprinkler and adding pressure losses all the way back to the water source. Include pressure losses caused by check valves, control valves, and so on. The valve maker will normally publicize these pressure losses.
Water for lawn and garden irrigation systems is often supplied by house wells or municipal water mains. In these cases, you must calculate the amount of accessible water as well as the pressure at which it may be provided.
To evaluate an existing well’s capacity, first confirm that there is an operational pressure gauge at the well discharge or on the pressure tank. Open enough taps so that the well pump starts and remains on. Allow the pressure to stabilize before taking the reading. The pressure should then be adjusted to fit the sprinkler system’s pressure requirements. (usually 40 to 60 psi). By progressively shutting one of the faucets, you may gradually raise the pressure at the well. Reduce the pressure by turning on another faucet. Once the pressure has settled at the optimum operating pressure (this may take several minutes), use a 5-gallon bucket and a timer to measure the flow rate from each faucet in gallons per minute. The total flow from all of the taps equals the well’s pumping capacity at the required operating pressure.
The amount of water accessible from a municipal water system is determined mostly by the size of the water meter that supplies the water. The static water pressure in a municipal main may range from 30 to well over 100 psi; thus, measuring the pressure yourself is a smart idea. As shown in Figure 10, attach a pressure gauge to any outdoor faucet. Close all other outlets before completely opening this faucet. The gauge pressure represents the available static pressure in the city main. To ascertain the minimal pressure, this pressure should be monitored multiple times during the day.
Figure 10. Pressure gauge on outside faucet.
The pressure loss via the meter should not exceed 10% of the available static pressure. Table 6 shows the pressure losses via municipal water meters at different flow rates. If your static pressure is 60 psi, the pressure loss through the meter should be no more than 6 psi. (take 10 percent of 60). Assume you have a 5/8-inch meter and follow that column until you reach 6. Because the closest value is 6.1 at 13 gallons per minute, you must reduce the supply to 12 gallons per minute for a 5/8-inch meter at 60 pressure.
Flows more than 75% of the maximum safe flow for the meter should never be utilized for design purposes. (For a 5/8-inch meter, take 75% of 20 gpm = 15 gpm, according to Table 6.)
An existing water meter’s size is normally cast or stamped onto the meter casing next to the meter dial. The dial should also show the nominal size. After determining the meter size, the available water supply may be calculated using the previous principles. Check the capacity of the supply tap from the water main to the meter as well.
If the present meter is insufficiently big, or if sewage rates are dependent on water use, you may wish to install a separate irrigation meter. For a charge, most municipal water systems will install a second meter. Divide the area into zones based on the amount of water available and the output of each individual sprinkler, so that all sprinklers in each zone may be run at the same time. For example, if the water capacity is 12 gallons per minute and each sprinkler has a 2.5 gallons per minute output, each zone may have a maximum of four sprinklers.
|Table 6. Pressure Loss through City Water Meters (psi).|
|Meter Size (inches)|
|Note: The highest flow listed for each meter represents the meter’s maximum safe flow capacity.|
Wherever a permanent irrigation system is linked to a public water supply, most city and state plumbing rules mandate the installation of some form of backflow protection device. This device is intended to prevent tainted irrigation water from entering the main water supply.
Most regulations demand the installation of a double-check valve device at the point of connection. Depending on the style and size, these gadgets might cost anywhere from $30 to several hundred dollars.
When there is a significant level of risk, such as when fertilizer or chemicals are pumped into irrigation water, some rules require a more complex device known as a reduced pressure backflow preventer. These devices may be quite costly, but since nutrients are not injected, they are typically not necessary for residential irrigation systems.
Always verify local and state rules before building an irrigation system with a municipal water source to ensure compliance.
Much of this paper focuses on basic scheduling techniques and measures to avoid over- and under-watering your crop. The length of time the crop is watered is usually determined by the soil type in which your lawn or garden is placed. There is, however, an irrigation scheduling tool available that may help in more accurately anticipating lawn water requirements. The Smart Irrigation Turf Scheduling App is presently available for Apple devices through the iOS App Store and for Android devices via Google Play.
Using a simplified method for automated irrigation systems, the scheduling software will give users with an estimate of the irrigation run time required (in minutes) to fulfill the current grass turf water demand. The FAWN and GAEMN meteorological data are used by the urban lawn model to generate a basic, real-time weekly water balance. The model has a variety of irrigation heads, including fixed spray, gear-driven rotary, and impact. These irrigation kinds are user-selectable depending on the irrigation system of each unique user. Temperatures are checked to see whether they are higher than the minimum necessary for crop development. Irrigation should be curtailed or cancelled if temperatures fall below the minimum.
It is recommended that the user install a rain gage near the area being scheduled to record actual rainfall values at the area to ensure the app is recommending the most accurate irrigation rate possible by using the most accurate data available. The app will also provide the user with an estimate of water saved in gallons over the original timer schedule provided by the user. There is also a citrus, cotton and strawberry irrigation scheduling app that could be relevant to users of the turf app. Additional information on all four apps is available at http://smartirrigationapps.org.
Status and Revision History
Published on Jul 01, 1997
Published with Minor Revisions on Sep 07, 2006
Published with Minor Revisions on Feb 23, 2009
Published on May 14, 2009
Published with Minor Revisions on Mar 12, 2014
Published with Minor Revisions on Apr 30, 2017