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Drip Irrigation Design

 

Drip Irrigation Basics

Many farmers and gardeners have discovered that drip irrigation produces healthier plants, better yields, and it is a great time saver. The use of drip irrigation has decreased the incidence of plant disease that can occur with the use of overhead sprinkler irrigation. Plus, many water-soluble fertilizers can be applied through the drip system, thereby keeping nutrients near the root zone and allowing the plants to get the most value from each fertilizer application.

Most of the drip components were originally derived from Israeli engineers who were the pioneers in this field. Since then many systems have been devised in the United States, being field tested in California, Florida and Hawaii. 

The advantage of a drip system is that you water the plants you want to water, keeping weed growth out of your plantings. And you don’t have to worry about whether you have stood there long enough with the hose (most of us never do!) or whether there will be enough rain to keep the plants going.

If you have ever put something together with Tinker-Toys, you have the basic ability to put together a drip system. It is that simple! Just get the components you need and assemble the system—most home garden systems can be assembled in one afternoon.

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How CLEAN is your water?

The main question you need to answer concerns the  quality of your water. While there are things which can be done to mitigate the effects of bad water, the dirtier the water, the more care must be taken when choosing the components needed to achieve the satisfaction and low maintainence with your drip system.

From most easily clogged to hardest to clog:

1. drip tape such as T-Tape & Chapin Tape

2. small orifice emitters such as 1/2 gph emitters

3. larger orifice emitters such as 1 and 2 gph emitters 

4. minisprayers & sprinklers over 3 gph 

5. in-line emitters such as Netafim & Dripperline 

Within each classification, there are differences in the performance of various products (advantages and disadvantages) so don’t take this as an ironclad rule of thumb.

The worst water is from ponds or lakes that have algae and other suspended particulates. Just above that is water containing iron slime bacteria (these will not filter out, they only come out of solution when they hit the air).  Equally bad is water that contains calcium or magnesium that will precipitate out when it hits air thus leaving deposits. Then comes water that has high levels of sand (many wells pump some sand). Believe it or not, even some municipal water systems have "crud" (a technical term) in their water, although most city water is pretty clean.

 

What Every System Needs

All drip systems should have a filter on them, regardless of water source. It is very cheap insurance so contaminants in the water clog the filter, not the emitters. Some people don’t like how often they have to clean their filter—if that is the case, get the next largest size so you won’t have to do it so often. Some systems require cleaning out the filter every time the system is run and some people only have to do it once a year (depends totally on your water quality).

Most drip systems should have a pressure regulator—especially if you are on city water or have a well set to run between 40 and 60 psi. If you are on a spring box or have a gravity fed tank with not much head above the drip system, you probably won’t need a pressure regulator. Most emitters and minisprinklers are designed to give the rated gallonage at 20 to 25 psi. Most soaker type tubing is designed to run at 10 to 15 psi.

 

Choosing Components

How do you choose which types of emitters, soaker type tubing or minisprinklers you want for your system? It is an individual choice and here are our recommendations on what most people have found to work well for them:

Emitters—Generally, people choose to use emitters when the plants are spaced somewhat far apart as is the case with perennial shrubs, fruit trees and vines and vegetables planted in hills. On flat ground you can use either the Jain Flag, Netafim button or 36” or 48” Dripperline emitters for evenly spaced trees and vines. The Jain Flag emitters can be opened to be cleaned if necessary. The Netafim buttons cannot be opened but they very rarely clog. On hilly ground (greater than 20 ft. vertical change up or down a hill), one should definitely chose from the pressure compensating emitters(which can be either in-line or punched into hose) so that all of your plants get the same amount of water per irrigation. Only the Turbo SC emitters (of all the pressure compensating emitters) can be opened to be cleaned if necessary. All pressure compensating emitters are self-flushing.

Soaker type tubing and tape—these are ideal for watering intensively planted beds of vegetables or flowers, also berries, turf, and other areas where you want to evenly water an entire swath of plants. 

Tape-type tubing (T-Tape or Chapin Tape) is primarily used by vegetable farmers, both large scale and small. Tape-type tubing must be used in straight runs— not around corners or bent (unless you use appropriate fittings) or the flow of water will be restricted.

Dripperline (Soaker Dripline) is often used in ornamental settings and can be gradually curved or bent without affecting its performance.

Tape-type tubing requires 10 psi operating pressure. Soaker Dripline should be used at 15 psi. Dripperline works best at 20 psi. Only Soaker Dripline, 12” Dripperline and 12” RAM Pressure Compensating Dripperline are recommended where heavy iron (i.e. when water stains fixtures) or calcium is present in the water. 

Mini-sprayers and Mini--sprinklers—These are used where people want to water a larger area. They can be utilized more like standard sprinklers in that there are many different patterns available for use, although the gallonage and radius involved is much less. This means more drip mini-sprinklers can be run on one line than would be possible with standard sprinklers. One thing you should be aware of is that the mini-sprayers and mini-sprinklers do not work well in heavy winds—due to the finer droplet size, they will not give you the desired coverage if operated when there is a lot of wind. You can compensate for this by running the system in the evening or early morning when wind is not usually a problem.

 

Drip Irrigation Systems Design

Start by making a sketch or scale drawing of the areas you want to drip. Note the location and size of plants to be irrigated, and whether they are native (and drought tolerant) or introduced (requiring more water), and the location of water sources. Note distances needed for tubing and what fittings will be needed to layout the system (tees, elbows, etc.). Based on the size and type of plant (see watering guide), determine how many and what type of emitters or sprayers will be required.

When designing your drip system make sure to plan for the future. When plants mature, they will require more water. This can be accomplished by watering longer but it is usually more satisfactory to add more emitters as plants grow at different rates. Also, new plants may be added to the landscape so leave about 25% more water capacity available for growth needs.

Garden valves and standard 3/4” sprinkler valves will almost always provide more than enough water for most home landscape/garden needs. To determine how much water the drip system will require simply add up the total number of emitters and their flow rates. (Example: 20- 1 gph emitters = 20 gph; 20-2 gph emitters = 40 gph; 20 + 40 = 60 gph total).

 If in doubt about the capacity of a water source, simply time how long the valve takes to fill a measured container. (Example: If it takes 30 seconds to fill a five-gallon bucket, then the maximum flow available is 600 gallons per hour. The formula is to take the GPM x 60 to get GPH). Should the system require more water than is available, divide the system by using multiple valves or a hose Y connector and run one system at a time.

Because drip irrigation operates at low pressures, effects on pressure caused by changes in elevation should be considered if elevation varies over 20 vertical feet from water source. If elevation changes are a problem, use pressure compensating emitters.

When designing your drip irrigation system keep in mind questions like: Will it get in the way when cultivating, raking or weeding? Should the drip tubing be hidden from view? Is it out of the way of foot-traffic areas? In areas where gophers and other rodents are problems, no drip or spaghetti tubing should be buried or they will chew through it. Mulch can be used to cover tubing.

The following chart is useful in determining what size drip hose should be used as a main line (regardless of whether you are using emitters, soaker type tubing or minisprinklers).

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First, design your system and add up the gallonage required as well as the length the main line tubing will have to run, then look at the chart to see what size drip hose you should use. Most home landscape/garden systems use 1/2” drip hose. Very small systems may be run on 3/8” hose while large systems should use 3/4” hose (or break the system into segments or use more than one faucet hook-up).

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For very large agricultural and commercial landscape drip systems, please contact our Certified Irrigation Designers: Angela Albini, Patty Hamilton, and Chad Griffith.

 

System Head or Manifold Assembly

At the beginning of your drip system, you should install a backflow prevention device or check valve to prevent back siphoning of irrigation water into drinking water systems. Most municipal building codes require the use of these devices. If you are on a well and plan to do fertilizer injection, you should definitely use one.

Depending on what type of filter and pressure regulator will be required for your system, PVC transition fittings may be needed to get from pipe thread to hose thread connections. Use teflon tape on all pipe thread joints (not pipe dope). Hose thread connections will seal with the washer included on them. Do not use a wrench to tighten plastic threads, hand-tighten only!

If you want to automate your drip system be sure to select a controller designed to water at least two hours per station. We feature a number of controllers which are appropriate for drip systems- many older controllers were designed strictly for use on standard sprinklers  and will not run long enough to use with drip systems.

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Installation of Tubing

Allowing the tubing to sit in the sun before installation will make it easier to work with. Lay out tubing as per sketch. When assembling fittings, cut the tubing with pruning shears or a sharp knife and be careful to keep dirt out of tubing and fittings.

Where permanent installation of drip tubing is desired, we recommend using underground PVC pipe and coming up with various riser assemblies utilizing flexible PVC IPS hose to connect to the drip tubing (see accompanying drawings).

Be sure not to bury the ends of tubing. You will need to have access to them for periodic line flushing.

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Emitter Placement

Punch holes in tubing with a punch. Using an ice pick or a nail is not recommended because the hole is not evenly punched and often results in stress cracks and leaks around the hole. Also, you can go all the way through the other side!

Water should be filling the drip hose in warm weather when you punch in emitters. This will help make the tubing firm and easier to punch into as well as make the holes the right size for the emitters (no leaking around barbs).

Insert emitters, etc. carefully. For small plants, emitters are often placed fairly close to the trunk. Do not place emitters, etc. such that they will get the trunk wet. This is especially important with perennial plants such as fruit trees and vines which are susceptible to root rots. A general rule of thumb is to keep emitters 12-18” away from the trunks of plants.

The area wetted by an emitter will vary according to soil types. Sandy soil allows water to percolate down rapidly while water on clay soil moves horizontally much further before it goes down below the root zone. On sandy, coarse soil, a 1 gph emitter will wet an area on the surface about 12-15” in diameter. On clay soils, the emitter may wet an area 24” in diameter. Below the surface, a large onion shaped area is wetted as water percolates down. Emitters should be placed to cover root zones well.

Emitters themselves should never be buried because it is much easier to check and maintain them when you can see them. Also, buried emitters can have problems with clogging due to root intrusion or back-siphoning of dirt.

 

Determine your soil Type

Fill 2/3 of a quart jar with water and add soil until jar is almost full. Attach the lid and shake vigorously, until all the clumps of soil have gone into solution with the water.

Begin taking measurements as the soil particles start settling out. The first to settle are the larger particles. After one to two minutes, mark the sand level on the jar.

Leave the jar undisturbed for several hours. The finer silt particles will settle out on top of the sand. Often, the layers are slightly different colors, indicating various types of particles. Mark the silt layer after a few hours. Leave the jar overnight and measure the settled clay particles. It may take a few days for some soils to settle.

The following drawing shows the proportions of sand. silt and clay for the 3 major soil types. This is useful in determining how far apart emitters and soaker tubing should be placed to water the plants effectively.

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System Startup

Once emitters have been punched in, open all tubing end caps and allow water to flush the lines for several minutes. Close the end caps and check emitter operation. If you have an emitter placed where you don’t want it, remove emitter and insert goof plug in hole. Punch a new hole in the appropriate place and install emitter. 

 

Watering Quantity

Look up the type of plant material you want to water in the chart below to determine the water requirement in gallons per day. Divide the gallons per day required by the gallonage of the emitter delivering the water to each plant to determine hours of watering per day. Determine the days between waterings from the above chart. Multiply the hours of watering per day by the days between waterings to determine how long to run the system. The days between waterings will need to be
seasonally adjusted, to account for rain.

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Maintenance

Inspect emitters and microtubing periodically to ensure no emitters are clogged or that sprayers have moved.

Filter screens should be flushed out at least once a month. We recommend checking the filter screen for debris after each irrigation for the first couple of times to determine how often you will need to clean it. Some people have to clean the filter after every irrigation.

Tubing lines should be flushed periodically, at least once a year. Again, water quality will determine frequency. 

 

Frost Protection

Anytime the temperature goes below freezing, your drip system can be in jeopardy. For most locations, this means winterizing your system or else you will find broken parts come next spring.

The simplest way to winterize either a sprinkler or drip system is to install drain valves which automatically drain the line of water every time your system goes off, so you don’t have to think about it. They are very inexpensive and cheap insurance against broken valves, filters and pipe due to being filled with water when freezing temperatures come. These are installed at the lowest point in the pipe run, with a gravel sump to provide drainage.

Otherwise, leaving part of the drip or sprinkler system open will prevent water from freezing until the temperature gets down into the teens (°F.), where you really need a drain valve or flushing end caps to drain the system.

 

Troubleshooting

Proper filter maintenance will preclude most emitter clogging problems, except in the case of iron slime bacteria, minerals and other contaminants that do not come out of solution with the water until they hit the air. Clogged emitters can often be cleaned by backflushing: While the system is in operation, hold a finger over the emitter outlet for a few seconds. Jain Flag, Turbo-Key and Turbo SC emitters can be manually opened and cleaned if necessary. In a worst case situation, the old emitter can be removed, the hole filled with a goof plug and a new emitter installed in a new hole.

If the problem is more widespread—if many emitters appear clogged or are not putting out as much water as they should—check for a break in the lines. After repairing any breaks, open end-caps and flush lines for several minutes. If there are no line breaks, try turning on and off the system several times. This often helps purge debris from clogged emitters.

If the above tips don’t help, more than likely there is a design problem—not enough pressure and/or water to operate the system properly. In this case, dividing the system will generally solve the problem.