Irrigation 101

Your complete guide to understanding Landscape Irrigation

Landscape Irrigation is a system comprised of piping, an electronic timer, control valves, and water delivery heads that provide automatic supplemental watering of your plants and turf grass areas.

True need for irrigation is determined by an on site “ET” (evapo-transpiration rate). “Evapo” evaporation is the loss of moisture caused by wind, temperature sunlight etc. “Transpiration” is the loss of moisture that is utilized in the photosynthesis process of a plants or grasses natural feeding cycle.

ET rates vary by month and are measured in inches of replenishment. In Roanoke, Virginia, April and May have low ET rates-normally an inch or less. June, July and August may exceed 7 inches of replacement. Notice most people’s yards and plants look great in May and start to brown out in late June or early July depending on the rainfall amounts.

Experts have determined that for best plant and grass health we should irrigate when the soil moisture level has been depleted down to the 50% level then replenished to 100%. Think of a kitchen sponge that is 100% saturated to the point where it just stops dripping, and then you squeeze out 50 % of the water. Then fill again to 100%. This watering should be done in the early morning hours when winds are light and water pressure is at its highest.

Notice we speak about plants and turf grass separately. This is because, on average, plants require only 1/3 the amount of water as do grasses. It is imperative that, when economically feasible, system designs separate all planted beds from turf grass areas! Do not let an installer tell you differently! If so you will end up with brown grass and happy plants or green grass and root rotted plants.

With the above in mind, let us not forget water is only one part of a three part equation.

Part two: A “Weed and Feed” program is a must!

Part three: Mother Nature

Irrigation System Components:

Water Source:
We have systems that employ wells, creeks, lakes and even cisterns; however the majority of our water comes from the public water source. In most cases, your water purveyor is a reliable and “fairly” economical source who provides uninterrupted service at a pressure we need to make your system function properly. Where applicable, we install sewer subtraction meters so you do not pay sewer charges on water used for irrigation.

Back flow Prevention:
If your potable (drinking) water and irrigation water are derived from the same source then we must ensure the two never mix! We assure this by installing a Reduced Pressure Zone (RPZ) Back flow Prevention Valve. This mechanical unit monitors pressure and reacts by venting if it detects Back flow or Back siphonage. In most cases it is required by Virginia Plumbing Code. And because it can vent at any time it must be installed above ground 12” from the bottom of the vent to ground level.

While some mechanically inclined people think this bronze beauty is worthy of being a museum piece, we prefer it to be placed out of site. This unit also requires a yearly inspection by a state licensed tradesman. We are licensed and will check the unit each spring during the turn on to keep you in compliance with Virginia Plumbing code.

Pipe:
Pipe must be correctly sized for your system! Far too many installers do not observe basic physics pipe design principles. They choose to use the smallest cheapest pipe they think they can get away with. However, this is a recipe for future disaster! PVC pipe, commonly used in irrigation systems, allows for a maximum flow rate of 5.5 feet/second. Using pipe that is undersized will cause this max flow rate to be exceeded. Then, scrubbing occurs and your pipe and fitting are eaten away by water from the inside out. And!!! Future additions are out of the question. What appears to be a bargain is probably not! If your potential installer can not quote by heart the 5.5ft/second rule send them packing!

Pumps:
A pump is needed if existing water pressure, or if you have a well, is inadequate to run an irrigation system. Generally, we need a minimum of 65psi at the point of connection (P.O.C). If not, we will have a licensed electrician install a 240v circuit (115v inadequate) and we will size and plumb a pump that is right for your system. One size does not fit all. Too large a pump will cavitate and destroy itself. Too small a pump is like not having a pump at all. Pumps are sized by knowing the input in gallons /minute GPM and the desired output pressure. These variables are plugged into a Pump Curve Chart and the proper size is derived from this info.

Controllers, ET Controllers and Rain Sensors:
A Controller is the electronic timer that provides a signal to a control valve. When commanded by the controller the valve opens and water starts flowing to a Zone (a like group of heads). Standard Controllers are usually programmed based on educated guesses as to how much and when to water.

ET Controllers get daily satellite updates and water based on true “ET” rates. These calculated ET rates are accurate to one kilometer. These are a real money saver and provide for a very healthy overall landscape.

Rain Sensors measure precipitation and preclude watering following periods of rainfall.

Electronic Control Valves:
Valves act as an on/off switch. On the inlet side of the valve “Mainline water is ever present and waiting for the valve to open. When called for by the controller the valve opens and water begins to flow to the respective zone.

Water Delivery Heads:
1. Rotor Heads: These units are used to cover large open spaces. Mounted at grade, as water begins to flow they pop up and the water flow turns a series of gears which rotates the top of the head where the nozzle is located. These heads can cover distances as close as 21 feet up to 90 feet. They can be adjusted from 40 degrees to 360 degrees of rotation.

2. Spray Heads: These units are designed to cover smaller more geometrically challenging areas such as planted beds or small strips of grass. Also installed at grade, they accept nozzles from 4 to 18 feet and have radius adjustments from 1 degree to 360 degrees. Pressure regulated and non-pressure regulated units range in heights from 2 inches to 12 inches. However, a 2 or 4 inch head is of no value- insist on a 6 inch minimum height spray head.

Spray Heads are designed to operate a 30 psi. However, rotor heads require a minimum of 60 psi. A non-pressure regulated spray head operating above 30 psi.waste water! Instead of disseminating the correct size droplet, water is atomized and sent off into the atmosphere. Even though pressure regulated heads cost 25% more they will pay for themselves the first year. Rain Maker only installs pressure regulated spray heads!!!

Zone:
(A like group of heads) System design usually calls for multiple zones. You may for example, have a zone that waters the front grass, another that waters a front bed, another that waters a vegetable garden, and one that will fill a pool or water feature.

Fertigation:
Technology from the agriculture industry found a way for us to fertilize every time we water. Results are outstanding. Just fill an in ground tank every few month and the system will take care of the rest

How much does an irrigation system installation cost?
A properly installed quality turn-key system will average, depending on how much hand excavation is involved, $135-$150 per head. At a minimum this system should include: Installation Permit, Sewer Exemption Meter, 1” Main Line Piping, 1” Reduced Pressure Zone Backflow Prevention Valve, A (non builder grade) Controller and Rain Sensor installed by a Professional Electrician, Minimum of 16ga Direct Burial Irrigation Wire, Head to Head coverage with Pressure regulated Spray Heads.

How much water does a system use?
On average each irrigation rotor head uses 2.5 gallons per minute (gpm) Each spray head averages 1.8-2.2gpm. A typical rotor zone has between 6 and 8 heads per zone and a spray zone has between 8 and 12 heads per zone.

We conservatively program each rotor (Grass Zone) to operate for: 1 hour two times per week and each Bed (Spray Zone) to operate: 20 minutes two times per week. So, on average a Rotor Zone will consume 2(7x2.5x45) 1,575 gallons per week. 6,300 gallons/month and a Spray Zone will consume 2(10x2.0x20) 800 gallons per week.

Our average residential system is comprised of 4 Rotor zones 25,200 gallons (grass) and 2 Spray zones 3,200 gallons (beds). This system uses 28,400 per month. This is what we need to deliver the recommended 1” per week of water. Now you really understand the importance of the Rain Sensor and Sewer Subtraction Meter.

How much does water cost?
Each water purveyor (provider) has its own convoluted system in order to try and keep us confused. For the most part they have done a good job but if we take a closer look it is not an insurmountable task to figure it out. Remember Water and Sewer Charges in most all cases are calculated separately - again the importance of the sewer exemption meter!

Annual Maintenance Costs:

Spring Turn on Service
We perform this service in late April/early May. We program/re-program the controller based on winter moisture levels and forecast rainfall. We check the system zone by zone for leaks, overall head condition and alignment. We check the Back Flow Valve and for Roanoke city and Salem residents we acquire permit and certify the unit.
$125.00 up to 6 zones. $12.50 each additional zone
$135.00 Backflow Permit and Certification (Roanoke City and Salem)

Fall Winterization Service (system blowout)
We perform this service in late October/early November. To preclude freeze damage we employ a specially outfitted air compressor that incorporates filtered high volume low pressure air to force the water from the system.
1-3 Zones $85.00
4 to 6 zones $105.00
Next 6 Zones up to 12 $12.50/Zone
More than 12 Zones $10.00 per Zone

Warranty
We will warranty labor and pipe related products for the period of one year provided that we accomplish the spring and fall services. Controllers, heads and other parts have varying warranties depending on the manufacturer. We will provide liaison services however; service call charges will be incurred

I hope you will find this information useful! You can see all these products on our web site go to sales@rainmakerirrigationinc.com.