11 Items To Better Understand A Turf Irrigation System
We have a simple goal of keeping the turf and plants healthy!
Item 1. Water Source
– Irrigation systems are designed around the water source. Most residential irrigation systems have a city water source and are therefore designed based on the gallon per minute safely run through the pipe going from the connection at the street to the water meter located in the basement. For example, if the piping going from the street to the house is 100’ long we can safely use 12 gallon per minute or less. Exceeding the 12 gallons per minute goes beyond what the manufacture recommends as a safe amount of water flowing through the piping in feet per second.
Item 2. Design
– The design is critical, there are two types of irrigation systems, effective or effective and efficient. An effective system will keep the grass green. An effective and efficient system will keep the grass green and do it using the least amount of water possible to maintain a healthy landscape.
Item 3. Product
– There are many different types of irrigation products (heads, controllers, piping, fittings, and wiring). Every product manufacturer has its strengths and weaknesses so we encourage all homeowners to do homework and find the product that will best fit their application.
Item 4. Contractor
– This is the most crucial step in irrigation installation. The contractor that you select will in many cases be the one you have service your system year after year so ask many questions from the contractors you get quotes from.
Item 5. Zones
– Zones or sections are different areas that run at different times around the property. Zones are generally based on the water source given by the property. For example, if you have a water source that provides 12 gallons per minute you generally will have 4-5 rotor heads per zone or as many as 10 spray heads per zone.
Item 6. Vacuum breaker (back flow device)
– commonly called the back flow preventer is an anti-siphon device that prevents dirty water within the irrigation system from going back into the drinking water supply. The vacuum breaker is required on all irrigation systems. The two most common types are PVB or pressure vacuum breaker or RPZ reduced pressure assembly. Both types are required to be installed by a licensed plumber. The PVB is required to be set 12” above the highest sprinkler head were the RPZ is allowed to be set below grade for instance in a basement.
Item 7. Best time to water
– With any irrigation system the best time to water is early morning. We always recommend having the irrigation system done watering by 10am. For example if you have a system with 7 zones with a total run time of 4 hours it is best to have the system start at 6 am.
Item 8. Zone run time
– The total amount of time needed on each zone changes by the day. Soil type, plant type, shade, slope, and weather determines the amount needed. However, for a regular time based controller we generally recommend 8-10 minutes on spray zones and 25-35 minutes on rotor zones every day. Once you have your base than adjust the amount of days to water or the seasonal adjust option on the controller to set the exact amount of water needed per day.
Item 9. Weather Based Controllers
– Most irrigation systems have a time based irrigation controller were the owner set the start time and the amount of run time per zone. However, in the last 5 years manufactures have come out with Weather Based Controllers that take into account some or all of the 5 factors of weather (solar radiation, wind speed, temperature, humidity, rainfall) and allow the controller to adjust duration and frequency automatically saving on the water usage and maintain a healthy lawn.
Item 10. Cost of water
– After an irrigation system is installed in most cases you will pay for the amount of water you use. The cost depends on the municipality were you get your water from. For example an average irrigation system with a 5/8” water meter, and 10,000 square feet of turf, depending on the weather and how the controller is set. An average year will cost the homeowner $300.00-400.00 per year in water costs to maintain a healthy landscape.
Item 11. Pump/Well or City Water
– In terms of a water source with a property that has the option of city water or a pump utilizing a lake or pond, or install a dedicated well for the irrigation system, we generally use the determinant of 30,000 square feet. If the yard is above 30,000 square feet we generally recommend looking at the option for a well/pump. However, factors including cost of city water, well depth, water contaminants, and water quality affect the decision to use a well/pump.
Glossary Of Terms
Rotor head
– A rotor head is generally a larger sprinkler that covers an area from 25-35’. Rotor heads generally have an application rate around .45 inches per hour.
Spray head
– A spray head is generally a smaller sprinkler head with a consistent spray covering an area 8-15’. Spray heads generally have an application rate around 1.4 inches per hour.
Controller
– The controller or timer is the device that controls when the irrigation will turn on, run times on the individual zones, and days that the irrigation system will run. Most irrigation controllers are considered time based.
Irrigation Control Valves
– The irrigation control valves are typically located throughout the yard and covered by valve boxes. The irrigation control valves receive 24 volts from the controller to the solenoid located on the top of the valve releasing the atmospheric pressure allowing water to flow through the valve to the zone.
Vacuum breaker
– The vacuum breaker or back flow preventer is an anti-siphon device that prevents dirty water within the irrigation system from coming back into the drinking water supply. The vacuum breaker is required on all irrigation systems.
Pressure
– Pressure is typically determined by the municipality in which you receive your water however elevation in an irrigation system will either add or remove psi based on the following rules; One foot of elevation equals .433 psi or a column of water 2.31 feet tall equals 1 psi
- Static pressure – The water pressure when the water is at rest.
- Dynamic pressure – The water pressure while the water is in motion,for example, flowing through an irrigation system.
Velocity
– The speed of water flowing through piping measured in feet per second. Most irrigation piping manufactures recommend not exceeding 5 feet per second.
- If the pipe diameter is cut in half, the velocity of the same flow is increased 4 times
Base
– The amount of time needed on each zone and the number of days the controller is set to run to keep the plants healthy during the average part of the year.
Field capacity
– Soil is thoroughly wet and drainage rate is small.
Permanent wilting point
– No moisture left in the soil.
Evapotranspiration (ET)
– It is the sum of evaporation and plant transpiration from the Earth’s land to the atmosphere. Evaporation accounts for the movement of water to the air from sources such as the soil, canopy interception, and waterbodies. Transpiration accounts for the movement of water within a plant and the subsequent loss of water as vapor through stomata in its leaves.
Effective Irrigation System
– An irrigation system that mechanically works, all of the components are in proper working order.
Efficient Irrigation System
– An irrigation system that is not only effective, but also utilizes design techniques to use the least amount of water possible to accomplish the goal of maintaining a healthy lawn and landscape.
Quick Facts
1 acre = 43,560 sq. ft.
1 acre 1 inch deep = 27,154 gallons of water
Weight of water = 8.34 lb per gallon
Volume of water = 7.48 gallons equals 1 cubic foot
A column of water 1 foot high = 1 foot of head =.433 psi
- 1 psi = 2.31 foot of head
SDR – Standard Dimension Ratio – The ratio of pipe diameter to wall thickness. SDR = D (pipe outside diameter)/ S (pipe wall thickness)
Measuring Lawn Sprinkling Efficiency
Coefficient of Uniformity
– This is a measure that is more widely accepted in use for agricultural irrigation. The measure deals with the average deviation and the average amount of water in each catch device. Perfect is 100%, but good is 75% to 85%. However, this measure is limited due to its failure to distinguish between areas that are either too wet or too dry. For example, if the Coefficient of Uniformity is 75% and the turf requires 2 inches of water per week than 2/.75= 2.67 inches per week.
Distribution Uniformity
– This is a measure that deals with spacing, distribution, and sprinkler type. It is measured using catch devices. Distribution Uniformity is an improvement over Coefficient of Uniformity because it treats under-watering as a more significant problem than over-watering. Distribution Uniformity in short is the rating for how well water is applied over an irrigation area. The measure takes into account the average water applied in the 25% of the area receiving the least amount of water, divided by the average water applied throughout the area being irrigated. A properly designed and professionally installed irrigation system will have a Distribution Uniformity between 55% -75%. For example, if the Distribution Uniformity is 73% and the turf requires 2 inches of water per week than 2/.73 = 2.74 inches per week.
Scheduling Coefficient
– This is a measure that takes into account the average precipitation rate over the area being irrigated and divides it by the lowest precipitation rate in that same area. The precipitation rate is acquired using catch devices. The Scheduling Coefficient is a measure that gives us the amount of additional water needed to sufficiently water the area with the lowest precipitation rate (driest spot). The measure is a number that is multiplied by your inches per week to give you your inches per week needed to water the driest spot within the irrigated area. For example, if you have a Scheduling Coefficient of 1.4 and the turf requires 2 inches of water per week than 2 x 1.4 = 2.8 inches per week.
3 Rules For Determining Gallon Per Minute For Your City Water Source
Rule 1
-Pressure loss through the water meter can not exceed 10% of the available psi from the municipality.
Rule 2
-Volume through a meter can not exceed 75% of maximum flow of the meter.
Rule 3
-Feet per second through the feed from the street to the water meter. Based on the distance from the water main along the edge of the street to the water meter in the basement. Rigid piping is 7 feet per second, plastic piping is 5 feet per second.
After the Gallon Per Minute for the 3 rules is determined, use the lowest number and that will give you the available Gallon Per Minute allowed for irrigation in a residential application.
Learn More About Vacuum Breakers (Back flow Devices or Cross Connection Control Devices)
2 Items We Need To Prevent
Back pressure
– where the pressure in the irrigation system is higher than the water supply pressure from the municipality.
Back siphonage
– where the pressure in the water supply is reduced below the pressure in the irrigation system.
4 Types Of Vacuum Breakers
1 – Pressure Vacuum Breaker, PVB
-Typically used in most residential irrigation systems and controls backsiphonage only. The PVB must be mounted 12” above highest head, and must be installed by a master plumber.
2 – Reduced Pressure Zone Assembly, RPZ
– Typically used in commercial irrigation systems and some residential irrigation systems. The device controls back pressure and backsiphonage, may be used with an injection system, for example, fertilizer injection into the irrigation system. The device must be mounted 12’ above the flood plain, above grade (it may be mounted in the basement of a property), and installed by a master plumber. This type of device requires the use of a drain.
3 – Double Check Valve Assembly
– Typically not used for an irrigation system. This type of vacuum breaker can not be used with an injection system. The device controls back pressure and backsiphonage. This type of device does not require the use of a drain.
4 – Atmospheric Vacuum Breaker
– Typically no longer aloud by municipalities for use on an irrigation system. Controls backsiphonage only. The device must be mounted 12” above flood plain, and 6” above the highest sprinkler head. Every zone of an irrigation system would require this type of back flow device.
