Landscape Irrigation

Agricultural Extension ServiceThe University of Tennessee

*Design and Management Factors

1. Water Supply Requirements and Limitations2. Scale Drawing of the Site3. Sprinkler/Drip products that Match the

Landscape 4. Spacing of Sprinklers5. Sprinkler Zones6. Pipe Sizing7. Irrigation System Equipment8. Programming an Irrigation Controller

How Much Water is Required?

0.7 inches per week 2.0 gpm/ac in 24hr/da 1.0 inch per week 3.0 gpm/ac in 24hr/da 1.5 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

*Surface and Ground Water Sources Rivers and Lakes may

provide a Non Limiting Supply

Creeks and Ponds; however, may Constrain the Landscape Irrigation System to Supply Limitations

*Municipal Water Sources

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

Measuring Flow and Pressure Example - Measuring

the flow and pressure from a residential hydrant connection to hydrant tee fitting pressure gauge ball valve 5 gallon bucket & stop

watch or municipal flow meter

Pressure and Flow Rate

0

20

40

60

80

100

120

0 2 4 6 8 10 12 14

Flowrate (gpm)

Pre

ss

ure

(p

si)

Pressure and Flow Rate are Related

(pressure vs. flow rate is different for every system)

*Proper Equipment: Rotating Sprinklers A single sprinkler can

cover a large area, 20 to 60 foot radius

Needs a higher flow rate, 0.5 to 20 gpm

Needs higher pressure, 35 to 75 psi

Sprinklers are “constant discharge” and do not automatically provide “matched precipitation” when part-circles are used

*Sprayer Sprinklers Wets a smaller area, 8 to

16 foot radius Smaller water flow, 0.25

to 4 gpm Less pressure required,

20 to 40 psi Can wet rectangular

areas Automatic “matched

precipitation when part-circles sprinklers are used

*Bubblers

good applications in plant beds

wets a small area low pressure requirement,

15 to 30 psi low flow rate, 8 gph to 2.5

gpm

*Drip Emitters and Dripline

Good applications in plant beds and vegetable and fruit gardens

very low flow rate, 0.5 to 2.0 gph

very 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 plants

water must be very clean to prevent clogging of emitters

Ideal Pressure and No Wind

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

*Uniformity of Water Caught in Cans around a Single Sprinkler

*Sprinkler Overlap For Uniformity

Distance between Sprinklers=

Radius of Throw

Head-to-Head Spacing: 1. Good Uniformity 2. Good Economics

*Rules for Spacing Sprinklers.

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.

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 even out the spacing over the entire area and don’t leave a big gap in one area to make the rest of the area even.

Are most landscape areas simple squares and rectangles?

Example Landscape Sprinkler Layout

*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

*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

Sizing Pipe with a Velocity Method

Flow is Q = 20 gpm

1.5” pipe1” 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 flow velocity 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’

Simplified Pipe Chart based on 5 ft/sec RuleClass 160 PVC PipeSize in Inches Flow (gpm)

1 1 – 151 ¼ 16 – 281 ½ 29 – 37 2 38 – 592 ½ 60 – 85 3 86 – 130 4 131 – 200 5 201 – 325 6 326 – 450

S M

Source

1. Corp.Valve

2. GateValve

3. WaterMeter

4. BackflowPreventor

5. 2” PVCMainline

200’

6. 1.5’ Diaphragm

Valve

7. 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

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

Backflow Prevention

If you use utility water you must have backflow

prevention installed prevents water from

flowing backwards into the supply line in case of pressure-loss from within the system

industrial-sized backflow prevention

*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 settles

allows sprinkler to move it run-over by tractor tire

reduces damage to lateral

*Valves for Irrigation Zones (sets) Valves off of the

mainline control individual sets can be manual valves or

electric valves electric valves are

needed when using timers

24 V-AC Solenoid Valves

Magnetic coil is used to open a spring-loaded valve very common application easy to rebuild or replace allows for manual

operation

*Controller (timer)

Normal Program Days of the week to water –

MTWThFSaSu Start time during the day to

initiate the valve sequence Valve run time of each zone

(set)

Special Features Available: Rain Delays Raingauge shutdown Soil sensor shutdown

Ar = 96.3 Q = Application rate in inches per hour AQ = 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

Application Rate – Flow into an Area

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 Off 1 30 min 10:00 10:30 2 60 min 10:30 11:30 3 30 min 11:30 12:00 4 15 min 12:00 12:15

*Controller Settings and Irrigation Scheduling

Uniformity Impact on Operating CostSix inches of water required on a half acre lot

Municipal Water Cost of $0.61/100gal

Driest 10% receives 66% of requirement

Uniformity Water Applied Irrigation Cost

inches

85% 6.0 $ 510.00

80% 6.2 $ 525.30

75% 7.2 $ 612.00

65% 10.8 $ 918.00

Resources

Landscape Irrigation Design by Eugene W. Rochester, ASAE Publication #8, 0-929355-61-X

Simplified Irrigation Design by Pete Melby, John Wiley & Sons, Inc., ISBN 0-471-28622-22

Ortho’s All About Sprinklers and Drip Systems, Meredith Books Inc, ISBN 0-89721-413-7

Drip Irrigation for Every Landscape and All Climates by Robert Kourik, Metamorphic Press, ISBN 0-9615848-2-3