LANDSCAPE IRRIGATION SYSTEM DESIGN AND WATER USE EFFICIENCY

by Brian G. Leib and John Buchanan

The University of Tennessee – Biosystems Engineering & Environmental Science Department

Learning Objectives

1. Explain the importance of properly designing and managing landscape irrigation systems. 2. Determine how much water is required for landscape irrigation in conjunction with the

limitations of your water supply. 3. Create and use a scale drawing in landscape irrigation design. 4. Choose the sprinkler and drip irrigation products that are best for your landscape. 5. Place sprinklers and drippers in a landscape to uniformly supply water. 6. Determine the number and type of sprinklers and drippers that should operate at the same

time (zoning) to insure uniform application of water. 7. Locate and size pipe to deliver water to each sprinkler and irrigation zone. 8. Specify additional equipment needed to ensure proper function of the irrigation system. 9. Determine how often and how long to operate each zone in order to meet the water needs

of the landscape plants. Introduction “To irrigate or not to irrigate,” may be your first question. Humid regions like Tennessee receive significant rainfall and a decision to irrigate your landscape requires careful consideration. Historic records show that summer precipitation (June thru August) over the last 20 years has not been sufficient to meet an estimated water use (17 inches) for landscape plants in Tennessee. Small rainfall deficits are not much of a problem because stored soil moisture will supply water to plants and plants will adjust to use less water during dry periods. However, not all rainfall deficits are small. Records also show that in 10 of the last 20 years, rainfall deficits were greater than 6 inches of water which can adversely affect the appearance of landscape plants and, in some cases, plant survival. If you decide to irrigate, you will not be alone. Landscape irrigation is increasing in humid regions such as Tennessee. Irrigation will help you maintain optimum landscape appearance during the entire growing season and will help insure survival of expensive plant material during dry periods. Landscape irrigation is expensive (approximately $2,000 per acre for equipment designed and installed by yourself), but this investment can increase the value of your home. Automated irrigation systems reduce the labor involved in moving garden hoses with sprinklers or in carrying buckets of water. Also, fruit and vegetable gardeners will benefit from an increase in the yield and quality of their produce from irrigating crops. In addition to the capital cost of landscape irrigation, operating costs are high when municipal water supplies are used. In order to apply one inch of water to a one half acre landscape, 13,500 gallons are required. At water costs of $0.25/100 gallons for delivering treated water to your home and $0.36/100 gallons for removing water from your home for sewage treatment, the

combined cost for applying 13,500 gallons is $85.00. If six inches of water are required in a growing season, the yearly cost of irrigation is more than $500.00 for one half acre. In an effort to decrease operating cost, some homeowners pay to install a separate tap and meter for irrigation water and thus avoid the sewer charge. The operating cost from ground and surface water sources is much lower because the water is free and only the energy cost of pumping water is incurred ($1.00 per inch of water applied to a half acre at an electricity rate of $0.07 per kwh). However, surface and ground water supplies will incur additional capital cost for items such as: a pump, new electrical meter or gas engine, construction of a pond or well, longer delivery pipelines, and filtration & chemical injection for drip irrigation. Cost is one factor that should motivate you to pay attention to how much water is applied. Every inch of water wasted is dollars wasted. You should also recognize that wasted water also costs the environment. Over irrigation unnecessarily uses fossil fuels for energy, depletes water resources for wildlife and human beings, and causes pollution when nutrients and plant protection products are transported into surface and ground water via surface run-off and deep percolation of excess irrigation water, respectively. Over irrigation can also harm some plants by reducing oxygen in the root zone and creating an environment that favors disease. Therefore, one goal of this publication is to teach you when to apply water and how much to apply. However, applying the right amount of water at the right time can not be accomplished with an irrigation system that is poorly designed. If an irrigation system applies 0.25 inches in one area and 0.75 inches in another area, the tendencies is to make sure that the dry spots are sufficiently watered leading to an excessive waste of water in the wet areas. Therefore, the primary goal of this publication is to teach you how to design an efficient and uniform landscape irrigation system. Water Requirements and Supply One of the first steps in designing a landscape irrigation system is to make sure that your water source can meet the water use rate of landscape plants. While plants can use over 1.5 inches per week during short periods of peak water use, you should not need to apply this much water because soil moisture can supply a portion of the plants’ water consumption during an extreme dry period and rainfall can then replenish soil moisture at a later date. If you apply 1.0 inches of water per week, temporary soil moisture deficits will occur but plant water stress and deterioration of the landscape appearance will be very unlikely. If you apply 0.7 inch per week, some short periods of water stress may detract from landscape appearance in the worst drought years but plant survival should not be a problem. Remember, you do not have to apply this amount of water each week. Your irrigation system can be turned off during periods of adequate rainfall and/or low water use. Knowing the water use requirements for plants allows you to compare their need with your supply. A requirement of 1.5, 1.0, or 0.7 inch per week can be supplied by a flow rate of 4.5, 3.0, and 2.0 gallons per minute per acre (gpm/ac), respectively if the system is operated 24 hours per day (figure 1). These minimal rates of supply will require that sprinklers are separated into zones that operate independently. For instance, 1.5 gpm would be required to apply one inch of water per week on a half acre (a 3 gpm per acre rate), but only 2 or 3 sprinklers may be operated at one time at this rate, and the large number of zones could make this design very expensive or impractical. In contrast, all the sprinklers could be operated at one time with 40 gpm on a half

acre (an 80 gpm/ac rate). A system supplied at this maximum rate would only have to be operated 1 hr per day to apply 1 inch of water per week, but it will require larger and more expensive components from the meter sizes to the delivery pipe, and the system may still need to be zoned if different types of sprinklers are used. A more reasonable flow rate would be 15 gpm/ac or 3.5 gpm/10,000ft2. At this supply rate, 1.0 inch could be applied per week by

operating less than six hours per day. This intermediate flow rate would: 1) reduce competition for water between landscape irrigation and inside the home water use, 2) reduce conflict between irrigation and outdoor activities, and 3) keep the irrigation equipment cost in a more affordable range. Some homeowners have access to lake and river water and there will not be a limit to the supply rate (figure 2). If a small stream is used, it will be important to verify the flow rate during drought conditions (your stream may be monitored by the USGS, www. ). As a riparian water user on a small stream, you have the right to use water but not the right to harm the right of other riparians to use water. Therefore, don’t assume you can have access to the entire stream of water. If you use a pond that is fed by surface run-off, care must be taken to provide sufficient

Figure 1: How Much Water is Required?

0.7 inches per week 2.0 gpm/ac in 24hr/da1.0 inch per week 3.0 gpm/ac in 24hr/da1.5 inches per week 4.5 gpm/ac in 24hr/da

Irrigate all at one time 80 gpm/ac in 2 hr/day

Allows some flexibility 15 gpm/ac in 7 hr/da

Figure 2: Surface and Ground Water SourcesRivers and Lakes may provide a Non Limiting SupplyCreeks and Ponds; however, may Constrain the Landscape Irrigation System to Supply Limitations

storage for your irrigation needs. The storage required to apply one inch of water on an acre is 3,630 ft3, such that 6 inches of water for a half acre lot would require 11,000 ft3 or 83,000 gallons of storage.

However, for the majority of homeowners, your irrigation source will be a domestic water supply that can limit the design flow rate of an irrigation system. Municipal utilities are connected to most homes with a ¾-inch meter that can often provide a maximum flow of 15 gpm (figure 3). If an increase in flow rate is needed, a 1 inch meter and connection can be added at extra cost to produce a maximum flow rate of 25 gpm. If you are on a residential well, a

normal flow range will be from 5 to 20 gpm. In addition to flow rate, a domestic water supply must provide enough pressure to operate the sprinklers, as well as overcome friction loss in the irrigation equipment and elevation gain. At a minimum, sprinklers that shoot water more than 25 feet will require 35 pounds per square inch (psi) of pressure at the nozzle and the pressure losses in the system will be at least 10 psi, requiring a minimum pressure of 45 psi at the source. Flow rate and pressure can be measured by connecting a pressure gauge and a manual valve to a hose bib or hydrant that is located near the point of connection for the proposed irrigation system (figure 4). As the valve is incrementally opened to one position at a time, the pressure gauge is read and flow is measured by: 1) recording the time required to fill a 5 gallon bucket and then dividing the 5 gallon volume by the number of minutes to calculate gpm,

Figure 3: Municipal Water Sources

Utility Water and Well Water usually constrain the flow available to a Landscape Irrigation System

Figure 4: Measuring Flow and Pressure

Example - Measuring the flow and pressure from a residential hydrant

connection to hydranttee fittingpressure gaugeball valve5 gallon bucket & stop watch or municipal flow meter

or 2) recording the number of revolutions made by the flow meter needle in one minute and equating this value to gpm. You should discover that pressure drops as flow increases (figure 5). The pressure versus flow rate relationship is different for every irrigation system so make sure

that you pick a design flow rate that maintains enough pressure to operate your irrigation equipment. Create a Scale Drawing of Your Landscape A scale drawing of your landscape will help you plan your irrigation system. It will also provide a record of where irrigation equipment is located long after the pipe is in the ground. The scale drawing does not have to be surveyed and the distances you measure don’t have to be perfect. All you will

need to create a scale drawing is graph paper, a pencil, an eraser, and a 100-foot measuring tape (figure 6). A typical scale is one inch (on paper) equals 20 feet (in the landscape). Depending on the size of your lot, you may need to tape several sheets of graph paper together. Then you will need to layout your property, structure, and hardscape boundaries (areas you don’t want irrigated such as driveways). You also should identify the location of different plant material, beds, and gardens. Don’t forget to locate the point of connection (POC) where your irrigation system will hook into the existing supply (figure 7). If you have steep ground, the direction and degree of slope are also important (estimate elevation differences). Note the location of underground utilities on the drawing but be sure to have the utility lines marked directly on your property before you do any installation.

Figure 5: Pressure and Flow Rate

0

20

40

60

80

100

120

0 2 4 6 8 10 12 14

Flowrate (gpm)

Pres

sure

(psi

)

Pressure and Flow Rate are Related(pressure vs. flow rate is different for every system)

Figure 6: Create a Scale Drawing for Your Landscape Irrigation Design

Can you draw a picture of your landscape?

sure you canAll you need is some

graph papera pencila 100-foot measuring tape

Choosing Sprinkler and Drip Irrigation Products for Your Landscape Several types of irrigation equipment are available to best meet the requirements of your landscape: from sprinklers that throw water more than fifty feet to drippers that only wet a small circle of soil. You would not want to use long range sprinklers in a small bed next to your home and you would probably not use drip irrigation in a large open turf area, so selecting the right equipment is an

important part of landscape irrigation. Therefore this section contains a general description of the different products available to homeowners. Sprinklers use water pressure (usually measured in pounds per square inch, psi) to propel water from an orifice (nozzle) through the air to the surrounding area. The development of pop-up sprinklers made this type of irrigation more feasible for landscapes (figure 8). A pop-up sprinkler lays flush with the ground surface when not in use to allow mowing equipment to pass safely overtop without damaging the sprinklers. When in use, the water pressure supplied to the sprinkler will cause the sprinkler to pop out of the ground and operate above the landscape plants. In the case of turf, a four inch pop-up is sufficient to prevent spray blockage. Elsewhere, 18 inch pop-ups will deliver water above low-growing shrubs.

Figure 7: Add Boundaries of Non-Irrigated Areas and Add Your Landscape

Water Source

Figure 8: Pop-Up Sprinklers and Sprayers

Flush with soil surface when not irrigating

water pressure forces heads to “pop-up”less chance of damage from mowing equipment

Rotating sprinklers generally have one orifice that rotates around the sprinkler by means of impact or gears that are driven by water pressure (figure 9). These sprinklers are generally used in large open areas because they can throw water 20 to 60 feet. They require from 30 to 70 psi to operate properly and deliver from 0.5 to 20 gallons per minute depending (gpm) on the orifice size and pressure. Most rotating sprinklers are

considered constant discharge sprinklers because the discharge rate does not automatically change when part-circle sprinklers are used in corners and along boarders and thus the application rate or precipitation rate changes when the same sprinkler is used. In other words, a half-circle sprinkler with the same discharge rate will apply twice as much as a full-circle sprinkler because it is applying the same amount of water to half the area. It should be operated for half the time of a full circle sprinkler. Rotating sprinklers that combine part and full circle sprinklers can produce matched precipitation if different nozzles are used to change the flow rate. In the case of a half circle sprinkler, the nozzle size would need to be reduced to produce half the flow.

Figure 9: Rotating SprinklersA single sprinkler can cover a large area, 20 to 60 foot radiusNeeds a higher flow rate, 0.5 to 20 gpmNeeds higher pressure, 35 to 75 psiSprinklers are “constant discharge” and do not automatically provide “matched precipitation”when part-circles are used

Figure 10: Sprayer Sprinklers

Wets a smaller area, 8 to 16 foot radiusSmaller water flow, 0.25 to 4 gpmLess pressure required, 20 to 40 psiCan wet rectangular areasAutomatic “matched precipitation when part-circles sprinklers are used

Sprayers have different characteristics than rotating sprinklers. They do not turn in a circle because water comes out from all sides at once (figure 10). These sprinklers are used in small open turf areas and in low growing shrub beds because they throw water from 8 to 16 feet. They require from 20 to 40 psi to operate properly and deliver 0.25 to 4 gallons per minute (gpm) depending on the water pressure and the size of the openings around the sprinkler. Sprayer

sprinklers of the same make and model automatically deliver water with matched precipitation rates because a half circle will produce half the flow of a full circle due to the fact that half the opening of a half circle sprayer will be plugged. Bubblers are used to apply water to small areas of a plant bed (figure

11). They are useful for supplying water beneath taller, thicker vegetation that would block a sprinkler’s spray pattern. Bubblers are not considered sprinklers because water is not propelled in the air but rather water gurgles out at low rates (8 gph to 2.5 gpm) and at low pressure (15 to 30 psi). The flow rate from bubblers is often high enough to flood the bed allowing for fairly uniform application of water on level ground. Similarly, drip emitters and dripline can be used in beds where the plants are not well suited for sprinklers (figure 12). However, the flow rates and pressures are even lower than bubblers such that the flow is often designated in gallons per hour (0.5 to 2.0 gph) instead of gpm. At these flow rates, run-off is usually not a problem. Also, pressure regulators

Figure 11: Bubblers

good applications in plant bedswets a small arealow pressure requirement, 15 to 30 psilow flow rate, 8 gph to 2.5 gpm

Figure 12: Drip Emitters and Dripline

Good applications in plant beds and vegetable and fruit gardensvery low flow rate, 0.5 to 2.0 gphvery low pressure, 10 to 25 psi (pressure compensating emitters are designed for a greater pressure range)direct application of water to root zone of individual plantswater must be very clean to prevent clogging of emitters

are used to reduce the water pressure to acceptable levels (10 to 25 psi). Some drip products are pressure compensating which means they will operate uniformly over a greater range of pressures. Drip emitters can be inserted at any location into polyethylene tubing and thus can be arranged to individually water plants within a bed (small spaghetti tubing can be attached to some emitters making it easier to reach all plant material in a bed). This method of irrigation can be very efficient because water is slowly dripped directly to the root zone of desirable plants instead of the weeds in between the plants and because there is less evaporation loss when water is no longer propelled through the air. In contrast to drip emitters, dripline already has the emitters installed inside the drip tubing at a predetermined spacing and thus wets a continuous strip on each side of the tube (not the same as soaker hose that will not be discussed in this article because its hydraulic properties are difficult to define). This product is also very useful in vegetable gardens where the driplines can be laid along side the rows of plants. Because of the small orifice sizes, drip irrigation requires clean water to keep the emitters from plugging. This is not a problem when a domestic water supply is used, but drip irrigation will require filters and possibly chlorination when surface water supplies are used.

Equipment specifications are provided by manufactures to help you chose the right size and type of sprinklers, sprayers, bubblers, and drippers. The manufactures’ specifications will provide information about the flow and wetted radius of a product at different operating pressures (figure 13).

Locating Sprinklers, Bubblers, and Drippers in a Landscape Sprinklers need to be properly located to insure uniform and economic watering of your landscape. If they are placed too close together, you will spend more money than is needed for landscape irrigation. If they are placed too far apart, some areas will be too dry while other areas will become too wet resulting in a less expensive system that does not do a good job of watering your landscape. To better conceptualize the need for proper sprinkler spacing, think of a single sprinkler with cans on both sides of it and then think about how much water will be caught in each can (figure 14). Will the water be even in all cans, or will there be more water in the cans close the sprinklers or the cans further from the sprinkler? Most of us who have watched a

Figure 13: Manufacturer’s Specifications

Rotating sprinklers are selected based on flow rate and on the wetted area around the sprinkler

Sprayers, bubblers, and drip irrigation also have manufacturer’s specifications

Leib & Buchanan Inc. 16" Pop-Up SprinklersModel PU-3 Water

Pressure (psi)

GPM Wetted Diameter

(feet) 25 1.5 66 35 1.7 68 45 2.0 68 55 2.1 70 65 2.3 72

Nozzle Diameter 1/8"

sprinkler operate, would correctly say that more water is going to the outer part of the wetted radius but this does not mean that more water is caught in the outer cans because there is also more area at the outer part of a circle. In fact, a sprinkler that is operating at the correct pressure should result in more water being caught in the cans closest to the sprinkler resulting in a triangular or elliptical pattern with the high point at the sprinkler.

Since sprinklers apply water in an uneven manner, how can we expect to obtain even or uniform irrigation of a landscape? The answer to this problem is that the sprinkler patterns must overlap (figure 15). By placing sprinklers at the edge of the existing sprinkler’s wetting pattern, these sprinklers throw water back toward the original sprinkler and thus create a situation where the water in the cans will be more uniform. A simple rule of thumb is to design sprinklers with head to head coverage. In other words, make sure the wetted radius of each sprinkler reaches the

location of its neighboring sprinklers. This rule can be relaxed somewhat in regions like Tennessee where the wind speed is usually fairly low and irrigation is only supplementing rainfall. In this case, the distance between sprinklers can be 55% of the sprinkler’s wetted diameter instead of 50% or head to head. Remember that these rules only apply to sprinklers operated with in an acceptable pressure range designated by the manufacturer’s

Ideal Pressure and No Wind

How Much Water in the Cans?Even in all cansMore in cans closer to the sprinklerMore in cans further from the sprinkler

Figure 14: Uniformity of Water Caught in Cans around a Single Sprinkler

Figure 15: Sprinkler Overlap For Uniformity

Distance between Sprinklers=

Radius of Throw

Head-to-Head Spacing:1. Good Uniformity2. Good Economics

specifications. If the operating pressure is too high, the water droplets will be too small to travel to the desired wetted radius and the small droplets will also be susceptible to wind drift. If the operating pressure is too low, the water droplets will be too large and most will travel an intermediate distance from the sprinkler. This will leave dry spots both at the desired wetted radius and close to the sprinkler resulting in the classic doughnut pattern often seen around sprinklers. Some landscape areas are square or rectangular making it easy to locate sprinklers with head-to head coverage. However, many landscapes have unique shapes that make sprinkler layout more difficult. The following steps should aid sprinkler layout with both easy and difficult landscape shapes:

1. Pick a sprinkler with a wetted radius that is as large as possible and does not greatly exceed the shortest distance across the area. (It is often wise to break the landscape into several pieces with sprinklers types that match the size of the areas, but overall, limit your self to 2 or 3 sprinklers with different wetted radii).

2. Place part-circle sprinklers at all corners. 3. Place part-circle sprinklers at an even spacing on the edges between corners using head-

to-head spacing as a guide. 4. Place full-circle sprinklers in the interior area using the same head-to-head spacing used

on the edge sprinklers. 5. Perfect head-to-head spacing is impossible in most cases. It is O.K. to stretch and/or

crowd the spacing by 10%. 6. Adjust the sprinklers to evenout the spacing over the entire area and don’t leave a big gap

in one area to make the rest of the area even. Sprinkler lay out is an art as much as a science, so don’t be afraid to play with the design on your scale drawings. Everyone gets better with practice (figure 17). Bubbler and drip layout is very different from sprinklers. For bubblers, the idea is either to flood the entire bed or have enough bubblers for every plant’s roots to reach the wetted area from at least one bubbler. Drip emitters are usually placed on a per plant basis. If all the plants are the same size and have the same water needs, each plant should have the same number of emitters per plant and one emitter per plant is often sufficient. If the shaded area of one plant is say twice that of another plant, it should have twice the number of

Figure 17: Example Landscape Sprinkler Layout

emitters unless it is a drought tolerant plant. Driplines are usually laid out at one line per row of plants but sometimes one dripline in-between two plant rows is sufficient if the rows are close enough together for the dripline to soak into a portion of the roots from each row. Determine which Sprinklers, Bubblers, or Drippers will Operate Together as a Zone. Zones are necessary in most landscape irrigation systems and zoning must be done properly to insure that the system functions with acceptable uniformity. An irrigation zone is a group of sprinklers, bubblers, or drippers that operate together on the same pipe network downstream from a common valve.

Most water supplies for landscape irrigation systems are limited and can not supply water to all irrigation equipment at one time (figure 18). For example, if you can only supply 12 gpm at 45 psi and you attempt to operate 8 sprinklers that require 3 gpm each, you will attempt to pull 24 gpm. Since the system can not meet that demand, the pressure will drop, flow will be inadequate, none of the sprinklers will operate properly, and you will have

wet and dry spots in your landscape. Therefore, you must zone sprinklers so that the flow to a zone does not exceed the supply rate and zones usually can not be operated simultaneously. Even if your supply rate is adequate to irrigate the entire landscape at one time, you may still need zones if different irrigation products or sprinkler spacings are used. Different products such as sprinklers, sprayers, bubblers, and drip usually have very different application rates and if they are operated for the same

Figure 18: Zones Avoid Excess Flow Demand A Zone is a group of sprinklers that operate together on thesame lateral pipe network downstream from a common valve.

Limited Flow Rate of 12 gpm at 45 psi and sprinklers that require 3 gpm

8 sprinklers x 3 gpm/spr = 24 gpm > 12 gpm,a severe pressure drop will occur.

20 psi

20 psi

Figure 19: Zones Allow Equal Application of Water from Different Equipment

Rotating Sprinkler, Full Circle – 0.25 in/hr

Sprayers: Full, ½, & ¼ Circle – 1.5 in/hr

Rotating Sprinkler, Half Circle – 0.5 in/hr

Rotating Sprinkler, Quarter Circle – 1.0 in/hr

Drip – 0.1 in/hr

length of time, they will apply different amounts of water (figure 19). Also, sprinklers with the same discharge rate will be placed at different spacings in order to meet the coverage needs in different parts of a landscape. In this case, the sprinklers with the tighter spacing will have a higher application rate than sprinklers located further apart. Also, full and part-circle sprinkler are needed in most landscapes and rotating sprinklers, as purchased, have a single nozzle that produces the same flow rate (constant discharge). Full- and half-circle rotating sprinklers can be placed in the same zone if the half circle nozzle is reduced to produce half the flow to create matched precipitation. The same is true for half and quarter-circle sprinklers in the same zone, but this practice is not recommended for full and quarter-circle sprinklers renozzled to one-forth the flow rate because the radius of throw is significantly reduced which prevents proper overlap of sprinklers. If necessary, leave the corner sprinklers at half the flow of the full circle sprinklers. In contrast, sprayers of the same model already produce matched precipitation when located at the same spacing and fulls can be mixed with part circles in a zone without modifying the nozzles. Drip irrigation can be treated differently in respect to application rate because emitters can be located on a plant canopy basis instead of a land area basis. For instance, one emitter could be placed to supply water to every 9 square feet of canopy such that bigger plants would have more emitters than smaller plants and all sizes of plant material can be widely scattered within a bed. In conclusion, zones should only contain irrigation equipment that has similar application rates, either on a land area basis for sprinklers or on a plant canopy basis for

drip. Zoning is also useful in managing different landscape materials (figure 20). Some plants need more water than others and these areas could be zoned separately to apply the desired amount of water. Zoning decisions can also improve irrigation uniformity on steep slopes by creating zones that follow contours instead of traversing up and down a slope. Because water is heavy, every 2.31 feet of elevation change create a

pressure change of 1 psi (1 psi of pressure is gained going down a slope or lost going up a slope in a pipeline (figure 21)). Finally, zones should consist of sprinklers or drippers that are near to each other because long pipe runs in a zone can caused high friction loss that interferes with the uniform operation of irrigation equipment.

Figure 20: Zoning Allows Different Plant Material to be Watered Separately.

Water Source

Water Loving Treesversus

Drought Tolerant Trees

Sizing Pipe As noted earlier, pressure is lost in an irrigation system due to the friction of water moving along the pipe walls and passing through each piece of irrigation equipment. Friction losses require that pipe size correspond to the flow rate in each segment of pipe. Pipe that is too

small will create excessive pressure drop and water will not be applied uniformly or some equipment may fail to operate at extremely low pressures. On the other hand, pipe that is too large will unnecessarily add to the cost of the irrigation system. The higher the velocity of water, the higher the friction loss and pressure drop in a pipeline (figure 22). If 20 gpm is carried by a 1.5 inch PVC pipe (class 160), the velocity is 2.65 feet per second (ft/sec) and the pressure drop will be 0.71 psi/100 feet of pipe, while the same 20 gpm flow in a 1 inch pipe would cause the velocity to be 5.71 ft/sec and the pressure drop to be 4.59 psi per 100 feet of pipe. As shown by these friction loss estimates, long pipe lengths will also increase pressure loss in an irrigation system.

Figure 21: Zones can Minimize Pressure Variations in Pipelines

45 psi

30 psi

45 psi

60 psi

Zone on a contour instead of up and down a slope, and minimize pipe length.

– 1 psi for every 2.31 feet up a slope+ 1 psi for every 2.31 feet down a slope

Figure 22: Sizing Pipe with a Velocity Method

Flow is Q = 20 gpm

1.5” pipe 1” pipe

Proper pipe sizing will reduce friction loss, improve uniformity, save material costs, lower pumping costs and control waterhammer.

Velocity Method

• Locate pipe network for irrigation system.

• Determine the flow in each section of pipe.

• Determine the smallest size pipe that keeps flowvelocity below 5 feet per sec (fps)

Pipe charts are available in most Irrigation Supply Catalogs

V = 2.65 ft/sec

FL = 0.71 psi/100’

V = 5.71 ft/sec

FL = 4.59 psi/100’

A simple three step method has been devised to keep pressure loss due to friction at acceptable levels. First, route the mainline pipe from the water source to the zones and also route pipe to

sprinklers within the zone (consider how a trencher will operate and the efficient use of pipe). Second add up the flow in gpm for each pipe section based on the expected flow rate per sprinkler, and third, choose the smallest pipe that will keep the flow velocity below 5 feet/sec in each section. Manufactures provide pipe charts that show the friction loss and water velocity for different pipe types, pipe sizes, and flow rates. Using the manufacturer’s literature and the 5 ft/sec rule, a

simplified pipe chart can be created that shows the pipe size that correlates with a flow range (figure 23). Remember that different pipes have different hydraulic characteristics and a chart should be made for each pipe type because the material roughness and the inside diameters differ. Using the simplified pipe chart, assign a pipe size to each pipe section based on flow (figure 24). Many homeowners will discover that their water supply is often limited to less than 15 gpm and therefore they can simply use 1” PVC pipe for their entire system.

Figure 23: Simplified Pipe Chart based on 5 ft/sec Rule

Size in Inches Flow (gpm)1 1 – 15

1 ¼ 16 – 281 ½ 29 – 37

2 38 – 592 ½ 60 – 85

3 86 – 1304 131 – 2005 201 – 3256 326 – 450

S MSource

1. Corp.Valve

2. GateValve

3. WaterMeter

4. BackflowPreventor

5. 2” PVCMainline

200’

6. 1.5’Diaphragm

Valve7. 1.25”20 gpm

8. 1”

9. 1”

10. 1”

40 gpm

15 gpm

10 gpm

5 gpm

11. ¾” or ½”Swing Joint

POC

Figure 24: Pipe Size in a Zone & Mainline Based on 5 gpm per Sprinkler

Additional Irrigation Equipment used in Landscape Irrigation Thus far we have mostly talked about water application equipment such as sprinklers, sprayers, bubblers, and drip along with pipe needed to deliver water. However, other equipment is needed to provide safety, maintenance, and ease of management in landscape irrigation systems.

Control of when zones operate is accomplished by means of valves (figure 25). Valves can be either manual of automated. Automation will save you time in turning water on and off, allow irrigation while the you are away, and makes it easy for the you to change watering times. Manual valves are less expensive and help to insure that

the landscape will only be watered when needed i.e. why would you go through the trouble of turning valves on and off unless it is necessary. On the other hand, automation should make it easier to manage water but there is a tendency to forget to adjust irrigation times because the system operates on its own without any need for attention. The ability to automate irrigation shut downs due to rainfall and lower plant-water requirements will be given more attention in the next section. Automation is accomplished by means of

Figure 25: Valves for Irrigation Zones (sets)

Valves off of the mainline control individual sets

can be manual valves or electric valveselectric valves are needed when using timers

Figure 26: 24 V-AC Solenoid Valves

Magnetic coil is used to open a spring-loaded valve

very common applicationeasy to rebuild or replaceallows for manual operation

electronic solenoid values and a controller (timer). Solenoid valves are placed at the head of every zone and each valve requires a common wire and power (actuation) wire that connects to a central controller (figure 26). Most solenoid valves have manual override that allows operation of the zone when power is not available (solenoid valves are normally closed), and many

solenoid valves have a valves stem that can be turned down into the flow path allowing for a limited degree of pressure regulation. An 18 AWG (American Wire Gauge) wire size is usually sufficient for landscape irrigation on a homeowner scale, but if the wire run between the controller and solenoid vales is long (greater than 500’), a smaller, heavier gauge wire may be required. Once the valves and controller are properly wired (the controller stations should

equal or exceed the number of solenoid valves), the controller program can be set-up. The Controller program has three main settings: the length of time to operate each valve, the start time to initiate the valve sequence, and the days on which the valve sequence will operate (figure 27). Controllers come in all makes and models but fall into three basic categories: electromechanical, solid state electronic, and hybrids. Electromechanical controllers were the first type of controllers with settings made on rotating dials with trip pins. Later, solid state controllers were introduced with all settings entered on a keypad within a program loop. Presently, hybrid controllers are the most popular because a limited number of dials help the user enter the settings without having to enter a long programming loop. Even with

Figure 27: Controller (timer)

Normal ProgramDays of the week to water –MTWThFSaSuStart time during the day to initiate the valve sequenceValve run time of each zone (set)

Special Features Available:Rain DelaysRaingauge shutdownSoil sensor shutdown

Figure 28: Backflow Prevention

If you use utility wateryou must have backflow prevention installedprevents water from flowing backwards into the supply line in case of pressure-loss from within the system

industrial-sizedbackflow prevention

automation, a manual valve should be installed at the beginning of the irrigation system so that all components can be maintained with the water turned off. Choosing manual or automatic operation depends on your preference but backflow prevention may be required. Backflow prevention is necessary on many landscape irrigation systems to keep stagnant or contaminated water out of the water supply (figure 28). It is especially important for protecting drinking water but can also be important in other situations. Backflow can occur when a pump is turned off (intentionally or by loss of power), there is major pipe break, or there is a large demand for water for another use such as a fire truck pumping from a municipal water system. There are many backflow prevention devices that range from a simple check valve (like a foot valve used in pumping from a pond or stream) to a Reduced Pressure Backflow Device (RPBD). A RPBD provides the most protection, has the highest cost, causes the greatest loss in pressure, and is required for hook up to domestic water by many municipalities. The RPBD can be used in most situations, but it can not be located where it will be submerged. A pump will be required if your intended water supply is a stream, a pond, a well or a domestic supply that does not provide enough pressure to operate the irrigation system (booster pump). In order to select a pump, you must determine the flow it will deliver, the pressure or head (feet of water, 2.31 feet of water / psi) that will be added to the water, and the height of the pump above the water supply (figure 29). Pump flow can be determined from the zone with the highest flow

and the pump type (centrifugal, vertical turbine, or submersible: electrical or engine driven) will be determined from the location and type of water supply along with the height of the pump above the water supply. The required pressure or head is a summation of pipe friction to the most distant location, friction loss through all equipment (valves, backflow prevention device, etc.), elevation gain from the water source to the highest water emission point, and

the pressure needed to operate highest pressure sprinkler, sprayer, bubbler, or dripper in the system. It is advisable to seek the aid of an irrigation professional in making the calculations needed to size a pump. Even if you are using a pressurized source, such as municipal drinking water, it is important to subtract the friction losses and elevation gain from the existing pressure to make sure there is enough pressure to operate the sprinklers, bubblers, and/or drippers.

Figure 29: Pump Specifications

Elevation difference from water source to pump location.Largest expected flow.Pressure (psi) or head (feet) required to operate the system.

Pressure to overcome friction losses at the most distant point.Pressure to overcome the elevation gain to the highest point.Pressure to operate the sprinklers at the designated level.

Air flow in a pipeline needs to be controlled in addition to water. Air release/vacuum relief valves allow air to evacuate when filling the pipe and also allow air to enter the line when the pipe is drained. A continuous acting air relief valve allows air to be purged from high points in the pipeline once the system is under pressure. In many instances, sprinklers allow for proper air management and the devices described above are often not needed for small landscape systems.

Excess pressure can also damage your irrigation system. A pressure regulator will reduce the pressure to acceptable levels while your irrigation system is operating and a pressure relief valve will release water when a high pressure threshold is reached. In many situations, this type of equipment will not be needed because municipal systems usually provide water pressure at acceptable levels for irrigation, and if you pump water, you can

often design the system to operate at acceptable pressures. Class 160 PVC pipe is rated to withstand 160 psi and is commonly used in landscape irrigation. Normal operating pressures should not be close to 160 psi because this pipe must also be able to withstand pressure spikes caused by waterhammer. Some equipment is specific to the irrigation products. For sprinklers, a swing joint is a flexible connection between a sprinkler and the lateral pipe that allows easy adjustment of the sprinkler height and protects the sprinkler and lateral from mower damage (figure 30). For drip irrigation, filtration is needed to keep the emitters from plugging (figure 31). Municipal and well water are often clean enough to use without filtration, but a screen filter is still recommended to protect the emitter from debris caused by pipe breaks and the sand that is sometimes carried in well water. A disc filter is a

Figure 30: Swing Joints for Sprayers and Sprinklers

Use a flexible connector-piping from lateral to sprinkler

allows the sprinkler to be set at the correct depth and to be moved deeper if the soil settlesallows sprinkler to move it run-over by tractor tirereduces damage to lateral

Figure 31: Drip Irrigation Equipment

Water must be cleaned with 120 to 200 mesh filters depending on the drip product.

Screen filters are recommended for well and utility water.Disc filters are better for surface water irrigating a small area.Sand media filters are best suited for surface water and large drip projects.

Water pressure must be within the appropriate range.

Pressure regulators protect the drippers and insure operation at a designated flow.Pressure compensating emitters operate under a greater range of pressures.

better choice if surface water is used on a small drip area. If an extensive area is drip irrigated with surface water, a sand filter will be a better choice than a disc filter. Filters for drip irrigation will be in the 120 to 160 mesh range, but you should check the manufacturer’s literature for the actual requirement. When sprinkler and drip are used in the same landscape, small pressure regulators will help reduce the pressure for use in the drip irrigated zones. Equipment like solenoid valves, backflow prevention devices, pressure regulators and filters are usually sized to correspond with the pipe diameter or at one size smaller than the pipe diameter. Check the manufacturer’s literature to make sure the pressure drop will not be excessive at the flow and size you choose. Determining Irrigation Timing in Your Landscape Once you have designed and installed an irrigation system that can uniformly apply water within each zone, it is important to know how to operate the system so your landscape always looks its best, yet you don’t waste water and money by over-irrigating. The first step in determining how long to operate the zones in your irrigation system is to calculate how fast water is being applied to each zone. An application rate is calculated by dividing the flow in gpm by the area irrigated in square feet and multiplying by the conversion factor, 96.3 to determine the inches of water applied in one hour. For sprinklers, the flow rate

can be for a single sprinkler divided by the area of the individual sprinkler spacing or it can be the flow into an entire zone divide by the area of that zone (figure 32). For drip irrigation, the flow for one emitter can be divided by the plant canopy area for each emitter (remember to divide gallons per hour by 60 to obtain gallons per minute). For dripline, the flow per 100’ is divided by the area between driplines (100 feet multiplied by the line spacing). Some of you may prefer to place

raingauges or vertical-sided baking pans in a zone, run the zone for an hour (two hours may work better), and measure the depth of water caught in inches in order to determine the inches applied in an hour. However, this method will not work very well for bubblers and drip. Once you have obtained the application rate for each zone, the operation time is calculated by dividing the irrigation amount by the application rate. For instance, during peak water-use periods, you may want to apply 0.5 inches of water two times per week if there is no rainfall. If

Ar = 96.3 Q = Application rate in inches per hourA

Q = Flow or discharge in gallons per minuteA = Area into which flow is applied in feet^2

Example: A full-circle sprinkler discharges 2.4 gpm and the sprinkler spacing is 30 by 30 feet.

Ar = (96.3 x 2.4) / (30 x 30)= 0.25 inches per hour

Figure 32: Application Rate – Flow into an Area

a zone’s application rate is 1.0 inch per hour, the zone would need to be operated for one half hour or 30 minutes (0.5 inches / 1.0 in/hr = 0.5 hours). Once, you have calculated the peak operation times for each zone (figure 33), you can program the valves on the controller to operate for the desired time (often referred to as valve run time). You will also program which days of the week on which the zones or valves will operate along with the start time which initiates the sequential operation of all vales on a program. You will find that zones of full-circle

rotating sprinklers, part-circle rotating sprinklers, sprayers, bubblers, and drippers have very different operation times for applying the same amount of water per area. There will be times that you will not need to operate your zones for the full length of time. Peak water use generally occurs in June, July, and August when solar radiation and temperature are high. Even during potentially peak water-use times, plants will not be using water at a

peak rate when the weather conditions are cool, cloudy, humid, and/or still (little wind). Also, during the spring and fall, landscapes will not be using as much water and operation time should be reduced by shortening the valve run times or skipping days on which the program is scheduled to operate. In addition to periods of lower water use, rainfall can meet your landscape water requirements and the controller should be turned off during periods when rainfall exceeds water use rates. Some controllers have a rain delay feature that allows you to turn of a controller for a specified time period before resuming normal operation. For instance, after a 1 inch rainfall event, you can set a rain delay of 7 days in which normal operation of the controller will be suspended for the specified time period. Some controllers are equipped with raingauges that automatically suspend controller operation for different lengths of time depending on the rainfall amount. Finally, some controllers are equipped with soil-moisture sensors that will not allow the controller to operate until the soil dries to a specified soil moisture. This type of control will respond both to rainfall and a change in the landscape water-use rate. Although automation and sensors can help you manage water more efficiently, it always pays to observe what is going on in your landscape. A zone on an exposed south facing slope will dry out faster than a shaded area on a north slope causing you to increase the valve run time on the former while decreasing the time on the later. You may observe run-off on sloping ground or on heavy more clayed soil. To prevent this loss of water leading to dry soil conditions, shorten the runtime and operate more often. Sandy soils will show signs of stress sooner than a silt or clay soil. Since sands hold less water you may need to irrigate more often than once or twice per

Z 1 1.0 in/hr

Z 2 0.5 in/hr

Z 3 1.0 in/hr

PrecipitationRate

PrecipitationRate

2.0 in/hr Z 4

Set Controller to apply 0.5 inches 2 days per week = 1 inch per weekTime for zone 1 = 0.5in / 1.0 in/hr = 0.5 hours or 30 min.

M Th

Valve Tz On Off1 30 min 10:00 10:302 60 min 10:30 11:303 30 min 11:30 12:004 15 min 12:00 12:15

Figure 33: Irrigation Scheduling and the Controller Settings

week but at the same time reduce the run time because long irrigations on sandy soils are liable to percolate water through the root zone where the plant can not access this water. Authors’ Note Our desire was to help you design, install, and operate a cost efficient and water-saving landscape irrigation system with as few words as possible. There are other resources available that provide greater detail of information on landscape irrigation systems (figures 34 to 37).

Figure 34: Landscape Irrigation Books

Garden and landscape drip irrigationWell-written and illustratedISBN

0-9615848-2-3Metamorphic Press

Figure 35: A Simplified Textbook

Landscape Irrigation DesignEugene W. RochesterASAE Publication #80-929355-61-X

Figure 36: A Good Source of Information

A good do-it-yourself book

can be found at home centersMeredith Books IncISBN 0-89721-413-7

Figure 37: Another Excellent Book

More comprehensive than the Ortho-Book

John Wiley & Sons, Inc.ISBN 0-471-28622-22