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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