Welcome This session discusses some of the technical aspects of providing supplemental water to residential landscapes. We are not going to get too technical, but rather introduce you to some of the concepts that are used to design a good irrigation system. The true purpose of this session is to make you a savvy consumer of irrigation products and to get the most bang for your buck when you invest in irrigation. Some folks have natural technical skills and will be able to take this information and install an irrigation system in their landscape. For the rest of us in this class, this session will provide information that will be useful when making arrangements with an irrigation contractor to have a system installed.
So, What is your water source? Do you live next to a river or a creek? Do you have a pond and is the pond big enough? When the water supply is much bigger than the water demand, you have greater flexibility in the design of your system.
Or, Are you going to use the same system that your drinking water comes from? When using your drinking water supply, most likely your water supply will limit your irrigation system design
Measuring flow and pressure The first piece of equipment needed is a pressure gauge. You will probably need a gauge that can read between zero psi and 100 psi. If you are out in rural part of the water utility, you may only have 50 or 60 psi. The following example shows how to make these measurements from the outside hydrant. If you plan to connect your irrigation system to the mainline going to your house, and if you are not confident in your plumbing skills - now is the time to call a professional plumber or irrigation contractor. Having said that, usable information can still be gained from making these measurements from the hydrant. These measurements will be conservative compared to the measurements made at the mainline. However, for a small-acreage system - they will be sufficient. Downstream of the pressure gauge you need a valve to restrict the flow. A PVC ball valve is easy to use. You can purchase all the fitting from a hardware store. Remember that a garden hose fitting is not the same as a 3/4-inch pipe fitting. You can purchase a garden hose by 3/4-inch pipe adapter.
Oh my, another graph. So, the total pressure and the flow rate are related. If we have more pressure to force the water through the pipeline, then we will get more flow. On the other hand, if we do not have much pressure, then we cannot force much water through the pipe. As you can see by this graph, as flow rate increases, the pressure required to achieve this flow also increases.
We could use sprinklers Sprinklers can cover a large area with a single head. Generally speaking sprinklers have higher flow rates per head and require higher pressures in order to spray water over a larger area.
We could use sprayers Sprayers wet a smaller area, have a smaller flow rate, and require less pressure. Sprayers can wet round areas and rectangular areas. Fundamentally there is not any difference between sprinklers and sprayers. It is generally accepted in the irrigation industry that: sprinklers apply water in a narrow, rotating band of water sprayers spray the whole area at the same time
We could use bubblers Bubblers allow water to spill out of the top of the nozzle. This allows for water to be applied to a small area. This a good way to apply a large volume of water to a plant bed. They do not require much pressure because the water is not sprayed far from the head. It might take several heads to cover a large plant bed.
We could use drippers. This slide shows two drippers that are being fed by a multi-outlet emitter. A device like this can supply eight drippers from one tap off of the water supply. Drippers have very low flow rate. Often they are measured in gallons per hour. The water is directed straight to the root zone. Drippers are part of a family of products called microirrigation or drip irrigation. Some of the advantages of drip irrigation include not wetting the foliage, reduced soil-surface wetting (reduced evaporation), and reduced runoff. The major disadvantage of drip irrigation is that the water must be very very clean. Drip irrigation works because the water is forced through very small channels (called emitters). Any sand or algae in the water will plug the emitters and prevent water from being discharged.
Remember, if you must protect your water supply from backflow. Backflow occurs when all the pipes are full of water, and the pressure drops upstream. This causes the water in the pipe to change direction and flow backwards. This can cause a vacuum to occur in the pipes and draw soil (and possibly nutrients and pesticides) into the water source. All water utilities will insist that you install backflow preventors if you are irrigating with their water. Similar to ones shown on the slide, these are not cheap. The ones shown in the slide are industrial sized. Any activity, whether industrial, commercial, or residential must have backflow prevention if there is any possibility that contaminated water could pulled back into the water supply.
When installing pop-up sprinklers and sprayer, do not use rigid pipe to connect the head to the lateral. The advantage of pop-up heads is that mowers and trimmers will pass over the top. However, if a wheel presses on the head, then a flexible hose will allow the head to move without breaking the rigid pipe connection. Note: A lateral is a pipe that supplies the sprinklers and sprayers.
Irrigation Sets or Irrigation Zones Irrigation sets are controlled by valves. The valves can be manually operated (ball valves or gate valves) or they can be electric (solenoid valves). If you want an automatic system, then you will have electric valves. As shown in this slide, valves can be placed subsurface and accessed through a meter box. The arrangement shown is called a manifold. The main water supply is connected to all three valves, and the valves control the flow to the individual laterals.
Most electric valves use 24 volts AC. A 24-V system is relatively safe for use in the landscape. However, no electric system is completely safe and these valves must be handled with good electrician practices. These valves can be opened both automatically and manually. They are easy to rebuild and replace. As shown in the slide, they operate by raising or lowering a plunger (shown in yellow).
Agricultural Extension Service
The University of Tennessee
*Design and Management Factors
1. Water Supply Requirements and Limitations
2. Scale Drawing of the Site
3. Sprinkler/Drip products that Match the
4. Spacing of Sprinklers
5. Sprinkler Zones
6. Pipe Sizing
7. Irrigation System Equipment
8. 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
Creeks and Ponds;
however, may Constrain
the Landscape Irrigation
System to Supply
*Municipal Water Sources
Utility Water and Well
Water usually constrain
the flow available to a
Measuring Flow and Pressure
Example - Measuring
the flow and pressure
from a residential
connection to hydrant
5 gallon bucket & stop
watch or municipal flow
Pressure and Flow Rate
0 2 4 6 8 10 12 14
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
when part-circles are
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
precipitation when part-
circles sprinklers are
good applications in plant
wets a small area
low pressure requirement,
15 to 30 psi
low flow rate, 8 gph to 2.5
*Drip Emitters and Dripline
Good applications in plant
beds and vegetable and
very low flow rate, 0.5 to 2.0
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
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
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?
*Zones Avoid Excess Flow Demand
A Zone is a group of sprinklers that operate together on the
same 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.
*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
Proper pipe sizing will reduce friction loss, improve uniformity, save material
costs, lower pumping costs and control waterhammer.
• 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 Rule
Class 160 PVC Pipe
Size in Inches Flow (gpm)
1 1 – 15
1 ¼ 16 – 28
1 ½ 29 – 37
2 38 – 59
2 ½ 60 – 85
3 86 – 130
4 131 – 200
5 201 – 325
6 326 – 450
5. 2” PVC
11. ¾” or ½”
Pipe Size in a Zone & Mainline Based on 5
gpm per Sprinkler
If you use utility water
you must have backflow
prevents water from
flowing backwards into
the supply line in case of
pressure-loss from within
*Swing Joints for Sprayers and Sprinklers
Use a flexible
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
*Valves for Irrigation Zones (sets)
Valves off of the
can be manual valves or
electric valves are
needed when using
24 V-AC Solenoid Valves
Magnetic coil is used to
open a spring-loaded
very common application
easy to rebuild or replace
allows for manual
Days of the week to water –
Start time during the day to
initiate the valve sequence
Valve run time of each zone
Special Features Available:
Soil sensor shutdown
Ar = 96.3 Q = Application rate in inches per hour
Q = Flow or discharge in gallons per minute
A = 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
2.0 in/hr Z 4
Set Controller to apply 0.5 inches 2 days per week = 1 inch per week
Time for zone 1 = 0.5in / 1.0 in/hr = 0.5 hours or 30 min.
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
Uniformity Impact on Operating Cost
Six 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
85% 6.0 $ 510.00
80% 6.2 $ 525.30
75% 7.2 $ 612.00
65% 10.8 $ 918.00
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-
Drip Irrigation for Every Landscape and All
Climates by Robert Kourik, Metamorphic Press,