- - AGRICULTURE CORE CURRICULUM - - (CLF6000) Advanced Core Cluster: ORNAMENTAL HORTICULTURE (CLF6450) Unit Title: IRRIGATION AND DRAINAGE ____________________________________________________________________________ (CLF6454) Topic: DRIP IRRIGATION Time Year(s) SYSTEMS 2 hours 3 / 4 ____________________________________________________________________________ Topic Objectives: Upon completion of this lesson, the student will be able to: Learning Outcome #: (H-4) - Identify the advantages and disadvantages of various systems of irrigation used in ornamental horticulture (e.g., sprinkler, bubbler, drip, and so forth). (H-5) - Describe factors which describe water penetration. Special Materials and Equipment: An assortment of drip irrigation tubing, emitters, fittings, and assembly tools. References: Cotton, Lin. (1985). ALL ABOUT LANDSCAPING. Available from: Ortho Books, P.O. Box 5047, San Ramon, CA 94583. Editors of Sunset Books and Sunset Magazine. (1984). LANDSCAPING ILLUSTRATED. Menlo Park, CA: Lane Publishing Co. Editors of Sunset Books and Sunset Magazine. (1989). WATERWISE GARDENING. Menlo Park, CA: Lane Publishing Co. Editors of Sunset Books and Sunset Magazine. (1988). WESTERN GARDEN BOOK. Menlo Park, CA: Lane Publishing Co. Resources: Urban Farmer Store, 2833 Vicente Street, San Francisco, CA 94116 (415) 661-2204 Drip irrigation supplies and information. Evaluation: Unit Exam TOPIC PRESENTATION: DRIP IRRIGATION SYSTEMS REVIEW: As discussed in (CLF6451) Irrigating Ornamental Plants, landscape plantings are usually irrigated by either sprinkler or drip irrigation. Drip irrigation is a relatively recent innovation and can solve many difficult irrigation problems. Drip irrigation is especially useful as a water conserving method of irrigation. A. Drip irrigation systems enable the slow and precise application of water to the roots of plants, resulting in a minimum loss of water to evaporation, overspray, and runoff. 1. Drip irrigation is a flexible, adaptable irrigation method. There is a wealth of equipment and fixtures to enable the user to irrigate in otherwise difficult situations. a. Drip is used primarily for irrigation of shrubs, trees, and containers such as planter boxes. b. It is particularly helpful in watering hanging baskets out of doors, and is a very good solution to irrigating on slopes where runoff is a problem. Drip is ideal for roof and patio gardens. It can also be used with certain ground covers. c. Drip will not work for watering turf in any but the smallest area. Drip irrigation is not good for the widespread, even application of water. 2. Drip irrigation provides elegant solutions to many of today's difficult irrigation problems, especially where the water supply is strained. There are, however, some situations where there are problems with drip systems: a. Advantages: 1) Drip irrigation enables precise placement of water. There is no overspray and the wind doesn't interfere with most drip watering. 2) Drip irrigation can be used in uneven terrain. Level surfaces are not necessary as with flood and furrow irrigation techniques. 3) Drip is particularly good for irrigating a sloped area. Where sprinkler-applied water would run off, drip irrigation can be applied at the same rate the soil can absorb it, even on a steep slope. 4) Drip is flexible. Because it is not (usually) buried below ground, it is easy to make additions and changes to drip irrigation. It is also easy to access if repairs are needed. 5) Drip systems are easier to design than sprinkler systems. Because drip systems run on low pressure and low flow, designing a drip system is less risky. It is easy to add more outlets without so much risk of running out of water or pressure. 6) DRIP SAVES WATER! Areas which do not require watering are not watered. This means there are fewer weeds to remove moisture from the ground. Also, there is a reduction in evaporative loss and runoff. b. Disadvantages: 1) Drip irrigation cannot deliver large volumes of water if they are needed, such as in large turf areas. 2) Drip systems are not recommended for areas with vehicular or foot traffic because they are more subject to damage. They are usually made of more fragile components than sprinkler systems, and because they are often at or near the surface, can be damaged more easily. (Gophers like to chew through polyethylene drip tubing!) 3) It is difficult to tell when drip irrigation systems are not working. 4) Drip irrigation systems need filters more frequently than sprinkler systems do. B. Importance of Soil Water-Holding Capacity and Infiltration: In order to take full advantage of the capabilities of a drip irrigation system and maximize water savings while meeting plant needs for water, we must have a firm understanding of how water infiltrates (penetrates) the soil, and how it is held once it enters the soil profile. This is critical knowledge in the effective and water-wise application of drip irrigation systems. Please refer to section "B" of the previous lesson, (CLF6453) Sprinkler Irrigation Systems, for a complete discussion on these topics. C. General Principles and Uses of Drip Irrigation 1. Drip systems operate at relatively low pressures (20-25 psi and lower). 2. Drip systems require relatively low flow rates. A water supply which can deliver only four gallons per minute could have, literally, over a hundred drip emitters on one circuit all watering different plants at the same time. 3. Drip systems deliver low precipitation rates. a. This means drip circuits must generally be left on for long periods of time to water plants thoroughly. b. Low precipitation rates also mean lower infiltration rates are permissible in the soil being irrigated. 4. System design is easy to manage with drip irrigation. a. There is usually far more pressure and flow available for a typical residential or small commercial landscape than is required at one time by a drip system. b. Even if mistakes are made in design, elements can be removed or added to a drip system with relatively little trouble. 5. Varying the amount of water delivered with a drip system can be controlled in several ways. For instance, areas requiring more water can have: a. Emitters with higher flow rates installed. b. More emitters added in the same vicinity. c. More time that the drip system is left on (increased run time). d. More frequent irrigations. All of these options result in more TOTAL precipitation. 6. Water is placed only where it is needed through the use of emitters, mini-sprinklers, and soaker tube. D. As suggested above, it is easier to supply most drip systems with water than to supply sprinkler systems, but there are some guidelines: 1. Some drip systems can run on flows as low as one gallon per minute, depending on how much needs to be watered at once. a. Remember, though, that most typical landscapes need sprinklers, in addition to drip, to adequately irrigate the whole landscape. b. It is best to try to provide for good flow if at all possible. This will provide for later expansion if desired. 2. Pressure of about 20 psi is enough for most drip equipment. Some emitters and tubing specify less pressure, so pressure regulators must be added in line. 3. Drip has generally high requirements for water quality. a. The orifices used for drip equipment are narrow and clog easily. b. If water has any sand, silt, or rust coming through at the source, filters must be used or the irrigation system will not function properly. c. Salts can crystalize and accumulate at water outlets. Drip systems using hard water will have to be maintained more carefully. E. The components of a drip irrigation system are much the same as a sprinkler system, with some notable exceptions. The controller, the gate valve, the backflow preventer, the valves, the pipe, and the below- ground fittings are all essentially the same as with sprinklers. (Please refer to (CLF6453) Sprinkler Irrigation Systems for a review of these items.) Below is a description of the components which differ, or are unique to drip irrigation systems. 1. The need for a filter is more acute with a drip system than with most sprinklers. a. A filter will keep debris out of the tiny orifices used in the many emitters. b. Make sure a filter is installed in line and is flushed out regularly. 2. Drip equipment is designed for specific operating ranges, usually low pressures. a. A pressure regulator is almost always needed to bring the regular water supply down to a manageable range. b. Separate pressure regulators are often needed for different parts of a large system; for example, the emitters may take 20 psi, while the drip tubing is designed for a 10 psi supply. 3. Instead of stiff PVC, drip systems rely on flexible, black polyethylene (PE) tubing. a. PE tubing has "memory" which enables it to seal around emitters and other equipment inserted into holes punched in the material; welding of joints is unnecessary. b. PE tubing requires no special equipment for cutting and assembly. A pair of pruning shears works well for cutting the tubing. Teflon tape is sometimes helpful in sealing some joints. c. PE tubing is lightweight, resistant to ultraviolet degradation, relatively inexpensive, and comes in rolls of at least 100 feet. d. The 1/2 inch diameter size is usually installed for most residential and small commercial projects; the low flow rate through most drip tubing allows for a small diameter without significant pressure loss. 4. Because drip fittings are neither glued nor threaded, and because the 1/2 inch format is so widely used, the array of drip fittings is greatly simplified: a. Connecters include TEEs, ELs and couplings, much as with PVC. Both compression fittings (female) and barbed male fittings are available. b. Adapters are available to connect PE to larger sizes of PE tubing, and to connect PE to PVC. c. Some special connecting devices are manufactured to connect the drip lateral line (1/2" PE tubing) to the emitters and spray devices used to water plants. These include: 1) Transfer Barbs: One end is stuck in the line, the other attached to a small line leading to the emitter. 2) "Spaghetti" Tube: 1/8" line, attached to the transfer barb to bring water to the emitter. 3) "Goof Plugs" to fill in holes punched in lateral line which are no longer in use or were made by mistake. 5. Emitters simply drip or spill water out onto the ground slowly, at a prescribed rate. The range of available drip emitters is great. Some basics: a. Flow rates range from about 1/2 gallon per hour to around 5 gallons per hour. b. Pressure-compensating emitters are available to standardize flow. While not necessary in most situations, pressure compensating emitters should be used: 1) Along a line which goes up and down a slope, or emitters higher on the slope will not deliver as much water as the ones lower down. 2) On a long line, (more than 200 feet in length) where emitters farther down the line from the valve will have less pressure and flow than those closer to the source. c. If fertilizers are applied through the irrigation system, or the water source is high in salts, try to use emitters designed to resist clogging. Diaphragm and turbulent flow type emitters are good in this regard. 6. There are a number of other devices besides regular drip emitters available for low-pressure/low-flow irrigation. a. Spray attachments spray water like a sprinkler, only on a much smaller scale. These units generally demand more water (higher flow) than conventional emitters because they are soaking a larger area. 1) Misters have low output and produce the smallest droplets. These are more for humidifying than for watering. 2) Jet sprays have deflectors which spray water in specific patterns such as a quarter- or half-circle. 3) Mini-sprinklers spray larger volumes of water in a full circle and are less affected by the wind. b. Driplines allow water to seep out along a continuous line. Attached to the 1/2" lateral with a transfer barb, they can be used to water a vegetable bed, a hedgerow, or any other dense planting. 1) Driplines come in a variety of sizes and styles. 2) Laser line is drilled at regular intervals (every 6 to 12 inches, or so) with tiny laser-bored holes which allow water to seep out. 3) Bi-walled tubing and porous tubing are other options. F. One of the great advantages of drip irrigation is its flexibility and relative ease of design. While there are a few similarities to sprinkler irrigation, there are some significant differences in design considerations. 1. Like sprinkler systems, drip systems are divided into circuits, but fewer circuits are generally required. a. This is because the low flow requirement of the emitters allows much more plant material to be irrigated on one circuit. b. Often, a landscape will have several sprinkler circuits watering different areas of turf and ground cover and one or two drip circuits will pick up the entire remainder of the landscape. 2. Unlike sprinkler systems, a variety of emitter types can be put on one circuit. If plants need more water, simply changing emitters or adding an extra will solve the problem. 3. Pressure variations have to be accounted for with pressure regulators and pressure compensating devices. a. As with sprinklers, elevation changes in the irrigation system result in a corresponding change in water pressure. b. Pressure loss also occurs through friction with the pipe. However, because of relatively low water velocities, friction loss is only a problem in long runs of tubing. c. (Refer to (CLF 6453) Sprinkler Irrigation Systems for more information on pressure loss.) 4. When using mini-sprinklers, overlap is required if uniform coverage is to be had, just as is the case with regular sprinkler systems. 5. The system can be added to as needs arise, without having to be designed in advance. a. As plants mature and require more water, additional emitters can be added. b. Keep a running tab on the number and ratings of emitters installed, so you know when you are approaching the limit of the available flow on each circuit. G. Installing a drip system is very simple. There is a tinker-toy quality to assembling drip systems which makes them fun to put together. If a mistake is made, a goof plug or a coupling can usually fix the problem. A step-by-step description of installation procedures is beyond the scope of this lesson, but some helpful points to remember are listed below: 1. Lay drip line out near plants to be watered. a. Try to lay line where it will not be seen or walked over. Drip assemblies are subject to damage if tripped over or if emitters are stepped on. b. To make coiled line easier to handle, allow it to lie in the sun before trying to move it into place. c. Drip tubing can be buried a few inches underground, if desired, to keep it out of sight. Trench lightly as necessary. 2. Assemble Tubing and Fittings a. Work from the control valve out, adding tees and elbows as necessary. b. Use a tray to keep all of the tools needed for tube assembly together. The tools and materials you should have are: 1) A pair of pruning shears or equivalent for cutting tubing. 2) A tape for measuring tubing lengths. 3) A supply of teflon tape for threaded fittings. (ALWAYS tape threaded fittings.) Also, teflon tape helps seal some barbed fittings. 4) Polyethylene pipe punches of various sizes, to punch holes for transfer barbs and emitters. 5) An assortment of the fittings needed to complete the job. 6) Optional: A supply of hot water for dipping pipe ends. This makes them softer and easier to fit. c. Some important points on assembling drip fittings: 1) Try to keep fittings and tubing free of dirt and debris. 2) Don't force tubing too far into compression fittings because this interferes with flow. One inch is far enough. 3) When you punch a hole for an emitter, try to punch a clean hole at a right angle. This will prevent a leaky connection. __________________________________________________________ ACTIVITY: 1. Gather an assortment of drip irrigation tubing, emitters, fittings, and assembly tools. Review the names of the various supplies, and have students practice fitting and taking apart the various system components. __________________________________________________________ 3. When assembly is complete except for placement of emitters, flush the system COMPLETELY. This is critical because emitters clog very easily with dirt entering through the water supply. 4. After the system is flushed, install all the emitters and test the system. a. Check for leaks. b. Check for correct emitter function. 5. If desired, the tubing can be mulched over to hide it from sight and to conserve additional moisture. H. Drip system maintenance is simple but critical. Unlike sprinkler irrigation, there is little overlap in a drip system, and if an emitter gets clogged, a plant can go completely without water. Some requirements: 1. On a semi-monthly basis, check the flow from each emitter. This is obviously more critical in hot summer months. 2. Twice a year flush the lines by taking off the end cap and allowing water to run out freely. 3. Clean out the water filter occasionally. Frequency depends on water supply. 4. Salts buildup can be removed from emitters by soaking them in vinegar overnight and scrubbing with a toothbrush. 16/6/91 MH/clh #%&C