Planning an irrigation system

PLANNING

Measure & draw property lines

The first step to planning your irrigation system is to examine your property carefully and to make a map. Once this step is finished, planning the types of sprinkler heads and locating the pipe lines will be much easier. Having a plan in hand also helps when talking to store representatives who can help you complete the planning process.

• Note all measurements, trees, shrubs, driveway, walkways, tool shed, patio, or any other obstacle you need to consider.
• Make a scale drawing on graph paper so you have a top down view of the entire property.
• Label the different areas of the yard, such as the rose bushes, lawn, flower beds, potted plants, trees, shrubs, and vegetable garden. Each area will represent a different watering zone and require different types of sprinkler heads.
• Make sure you mark the scale, e.g.  one square equals one foot, or 1" = 1'.

Designate watering zones

An effective irrigation system operates on the basis of one type of sprinkler head per watering zone. For example, the lawn will need large sprinkler heads whereas the flower beds will need sets of small sprinkler heads. Analyze the watering needs for each area of the front, back, and side yards at the beginning of the irrigation planning phase.

• Designate watering zones based on soil conditions, the plants to be watered, and the quantity of water needed. Shaded areas of the property will have different needs than full sun areas, just as certain plants require more water than others.
• Each watering zone will have its own valve to serve a group of sprinklers.
• Each zone will use the same type of sprinkler heads.
• Determine the maximum water flow capacity for each watering zone to make sure the number of sprinkler heads per zone does not exceed this maximum. Manufacturers provide planning guides to help  determine maximum water flow and the maximum number of  sprinkler heads per zone.
• Each zone may use a different-sized pipe to carry water to the sprinkler heads.
• Label each watering zone on the plan with the maximum number of sprinkler heads allowable per valve. Include the suggested sprinkler head size (small, medium, large) on the plan.
• Assign numbers to each watering zone for easy reference.

IRRIGATION PIPES

Measure the water source

Knowledge of water GPM and PSI is critical to designing an irrigation system to suit your property; you need to know what the water pressure is and the flow rate, since the pipe sizes you choose will depend on these measurements.  s. If each zone has the appropriate number of sprinkler heads, you can know exactly how much water will be emitted from each sprinkler.

• By determining the available water flow for the entire system, you will be able to establish how many sprinkler heads can run at the same time.
• Water flow is measured in GPM (gallons per minute).
• You can measure GPM by placing a one-gallon container under an outdoor faucet and time how long it takes to fill the container, then dividing this time into 60 to determine your GPM (for example, if it takes 20 seconds to fill a one-gallon container, and 60 divided by 20 equals 3, your water flow rate is 3 gallons per minute. You can also determine GPM using your PSI calculations and the size of your main water service line. .

Follow these steps and use the charts below:

• To determine water pressure, hook up a water pressure gauge to an outside faucet, and record the reading on the gauge. This will be your PSI (pounds per square inch) measurement.
• Measure the main water service line by wrapping a piece of string around the pipe, then measure the string.
• You can now determine the flow-pressure relationship. Use your PSI measurements and the water supply line dimensions in the chart below to determine exactly how much GPM your system will deliver.

Pipe sizes
The length of the irrigation system pipes, the number of sprinkler heads the pipe serves, and the available water flow (or GPM) for each pipe will determine its size within the overall system’s design. Keep the following recommendations in mind when designing your piping system.

• The main sprinkler line for the irrigation system will need to be one size larger than the home’s water main supply line.
• If the main sprinkler line is ½", limit its total length to accommodate between 150 and 200 gallons per hour.
• Make sure that all header lines are sized larger than 1".
• Make sure that all lateral lines are sized larger than ¾".
• For any pipes sized at ½", limit their length in each zone to a maximum of 200'.
• For any pipes sized at ¼", limit the GPM to no greater than 30 GPM.

Pipe layout
Make sure you know the approximate or actual pipe sizes for the entire irrigation system. Then, you need to plan and draw the layout for your main sprinkler line and lines for each zone and to each sprinkler head. The irrigation system will consist of: the main sprinkler line, header lines to carry water out into the yard, and lateral lines connected to the header lines that feed water directly to the sprinkler heads.

Follow the steps below for the pipe layout design:

1. Use a direct route to draw the main sprinkler line from the main shut-off valve (or main water supply) to the front and back yard manifolds.
2. There will likely be two branch lines extending from the main shut-off to the front yard manifold and to the backyard manifold.  The manifold attaches the main sprinkler lines to the header lines.
3. Draw a header line directly from the manifold to each zone. Header lines will be intersected with lateral lines. Remember that sprinkler heads should not be installed on header lines.
4. Draw lateral lines that connect the header line to sprinkler heads. These lines should be branching out to each sprinkler head, and not circular.

SPRINKLER HEADS

Each watering zone will need its own selected sprinkler head. Determine the sprinkler size for each zone. Make sure  your design conforms to the maximum number of sprinkler heads per watering zone.

Head Sizes
The type of sprinkler head you choose should cover the area adequately; a large head will emit more water, and a smaller head will limit the amount of water emitted. There are two basic types of sprinklers: rotor heads, which spray a rotating stream of water (up to 360˚), and fixed spray heads, which disperse water in a fixed pattern. Sprinkler heads with a narrow spray zone are suitable for small level areas, such as strips of lawn or narrow flower beds, and rotating sprinkler heads are more suitable for slopes. Each sprinkler head is labeled with a description of the type of watering zone for which it is designed. Always refer to the manufacturer’s recommendations for spacing sprinkler heads.

Large area sprinkler heads

Large area sprinkler heads are generally designed for areas larger than 25' x 25'. For example: the satellite sprinkler can reach up to 80' in diameter and is therefore ideal for watering the lawn.

Large sprinkler heads are appropriate for backyards and play areas and are typically spaced 15' to 45' apart.

Medium area sprinkler heads

• Medium area sprinkler heads are generally designed for areas smaller than 25' x 25'. Medium-sized sprinkler heads may be spring-loaded pop-up, or with adjustable spray radii and patterns.
• Medium sprinkler heads are appropriate for the front and side yards and are typically spaced 10' to 15' apart.

Small area sprinkler heads

• Small area sprinkler heads are generally designed for flowers, shrubs, spot watering of trees, and ground cover. One example is the mushroom bubbler that produces a gentle stream, ideal for delicate plants.
• Small sprinkler heads are appropriate for watering areas that have low-lying vegetation and are typically spaced 3' to 5' apart.

Tips for designing your system

• On your irrigation plan, place a sprinkler head in each corner of your drawing. Then use a compass to draw the spraying pattern around each sprinkler head.
• Add sprinklers along the sides or in the centre to increase coverage. Adjust spacing.
• Space the heads evenly, and overlap the diameters of the spray patterns (by 50%) to ensure good coverage.
• There should be no dry patches remaining.
• For narrow watering strips, use spray heads with strip nozzles. These nozzles typically water areas up to four feet wide.

VALVES & TIMER

Valve placement
After designing the layout of the irrigation water lines and sprinkler heads, the valves are the third major component of the entire irrigation system.

Follow these recommendations:

• When the layout of the sprinkler heads and water lines has been established, determine a logical place for the system’s main shut-off valve. This valve will shut off water to the entire sprinkler system. Mark its location on the irrigation design plan.
• The next step is to connect the main shut-off valve to the sprinkler valve manifolds. It is common practice to put one manifold in the front yard and one in the back yard. Locate each manifold in an accessible area, away from heavy foot traffic. If possible, locate it on elevated ground to avoid water pooling around it.
• The irrigation system will also need a backflow prevention device valve. Backflow prevention devices are used to stop contaminant materials from back flowing into the main water supply. Types of backflow preventers include: double check valves, dual check valves, a pressure vacuum breaker, and an automatic anti-siphon valve. Local building codes typically determine the type of backflow preventer that should be installed, along with the recommended location. Make sure the backflow preventer is indicated on the drawing.

Timer location

A timer for your irrigation system is more an indispensable component than a luxury item. It can enable you to use your irrigation system when there will be e minimal loss due to water evaporation, but when it is least convenient for you to turn it on manually. Timers can also be programmed to turn the system off to prevent over-saturation, i.e. when it is raining.

• Select a location for the timer that is near an available power source and easily accessible. It is also recommended to mount the timer within a weather-resistant box for protection.
• Electrical wires will be needed to connect the timer to each manifold valve.
• Mark the timer on the irrigation design plan. Draw lines from the timer to the front and back yard manifolds as well as any additional manifolds required for an extended irrigation plan.

Additional installation notes

• Local water districts have requirements for irrigation systems, so you should become familiar with existing regulations before beginning the design process. You may need a permit or a specific type of backflow preventer and your system may need to conform to particular pipe requirements. You may also be required to contact a licensed plumber.
• Make sure you are aware of any underground utility lines. Call local utility companies for specific locations and be sure to mark them on your plan.

Water conservation tips
The main benefit of an irrigation system is water conservation. There are geographical areas with low water tables where irrigation systems are mandatory. Furthermore, conserving water can be translated into lower utility rates. Follow the tips below and you can conserve even more water.

• Select the smallest sized sprinkler head possible for each watering zone.
• Drip irrigation systems minimize water use by as much as 70% compared to watering with a hose.
• When locating your sprinkler heads, make sure you’re only watering the gardens and lawn and not the street and sidewalks.
• The more efficiently the timer is used, the better. Take the time to read the instructions carefully and to experiment with different options.
• Your water utility company may have specific suggestions regarding your geographical area.
• Set up the irrigation system to water in short bursts rather than for long, extended periods of time. Long periods of watering tend to cause excessive water runoff. Excessive water runoff can also cause unwanted soil erosion.
• Green lawns do not need daily watering. When lawns are watered, make sure the water is on for a long enough time to ensure deep penetration. A good rule of thumb: lawns usually require one inch of watering per week during the growing season.
• Turn on the irrigation system so that it waters during the night and early morning to avoid evaporation.
• In addition to setting a time for the entire irrigation system, install a rain sensor so that the system will not turn on after a rainfall. Again, this feature saves both water and money. Set up a regular maintenance schedule and check regularly for leaking water lines and clogged sprinkler heads.

Winterizing the system
If you live in a more northern climate, you may need to design an irrigation system with winterizing strategies in mind.

• There are basically two different strategies: either install auto-drain manifold valves or use an air compressor.
• The air compressor is used yearly at the end of the watering season to blow all water out from the entire system.
• Always refer to the manufacturer’s instructions for winterizing each specific irrigation system.

FURTHERTIPS

• Ultra-sustainable systems make use of rainwater or gray water for irrigation applications. . Additional equipment and planning will be necessary, but the results could contribute to a zero-waste residence.
• Look for extra water-saving sprinkler head options; many are available through special orders.
• For homeowners designing their own irrigation system, consider starting on a smaller scale and adding to the system later.
• Some homeowners prefer to design an irrigation system that not only emits water, but also liquid plant food. Look for these special technologies when designing and purchasing an irrigation system.