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Irrigation System Selection

Sprinkler, drip, and surface are three basic irrigation system types that can be used in horticulture applications. Each system type has many variations adapted for specific conditions.

Sprinklers

Sprinkler systems are commonly used for turf applications. Selection of sprinkler type depends on size and shape of area being irrigated, and the flow rate and pressure of the water supply.

Rotating Sprinklers

Full and part circle rotating sprinklers are used to irrigate large areas. These sprinklers can have single or multiple nozzles, gears, cam or impact driven, spacing from 35 to 115 ft, operating pressures from 40 to 100 psi, and flow rates from 6 to 65 gpm. Some rotating sprinklers have built-in valves (valve in head) and/or pressure regulators. Depending on nozzle size, pressure and sprinkler spacing, average application rates vary between 0.25 and 1.0 inch/hour. The application uniformity of rotating sprinklers depends on sprinkler geometry, angle of trajectory, wind, nozzle size, pressure and sprinkler spacing. Each sprinkler has a specific application, design and operating requirement. Consult an irrigation contractor or supplier for specific information on the design of irrigation systems. Improper design and installation of a sprinkler system will result in poor uniformity and water waste. Water pressures higher than recommended tend to make small water drop size which are subject to evaporation and drift in wind conditions. Low water pressures decrease the radius of throw and do not break up the water stream properly, causing poor uniformity of application. Sprinkler spacings too close or too far apart decreases application uniformity.

Rotating heads are usually used for large turf areas such as golf courses, parks, commercial or large residential landscapes. Their precision usually results in high uniformities (up to 90 percent uniformity of application) when designed and installed properly. Low precipitation heads can be used on slopes or other problem areas with less chance of runoff.

Fixed Spray Sprinklers

Small turf areas are often watered by pop-up or fixed spray heads. Spray heads can have full, part circle or rectangular patterns, with radiuses from 4 to 22 feet, several angles of spray trajectory, application rates ranging from less than 1 to over 2 inches per hour. The application uniformity of sprays are very dependent upon spacing, nozzles pressures, sprinkler orientation and nozzles size. Generally spray heads should be operated at low pressures 15 to 50 psi. Higher pressures cause excessive drift, evaporation and poor application uniformity. Many residential landscapes are irrigated with spray nozzles without a pressure regulator resulting in poor uniformities. The high application rates of spray nozzels needs to be considered in irrigation scheduling and application to prevent runoff.

Pop-up spray irrigation systems typically have the poorest uniformities, possibly reaching a maximum of 70 percent uniformity of application. Their high precipitation rates make them a problem on many landscapes with slopes, mounds, compaction or heavy soils. Pop-ups vary from 2-inch heights for warm-season grasses and others mowed at 1-1/2 inch or lower, up to 18-inch for shrub or planter areas.

Drip and Micro-Sprinklers

Micro sprinklers are a cross between spray nozzles and drip irrigation. These sprinklers have low flow rates, low application rates, small radiuses and operate with low pressures. Sprinkler flow rates range from 0.1 to .07 gpm, average application rates from 0.2 to 0.4 inches per hour, wetted radiuses from 4 to 12 ft and operating pressures from 10 to 25 psi. They are very well suited for small ornamental plantings and single trees or shrubs. Micro sprinklers require filtered and pressure regulated water.

Drip

Drip or micro irrigation applies water to the soil at point locations at low controlled flow rates. Drip emitters discharge from .5 to 2 gallons per hour. Many emitters are pressure compensating, applying a nearly constant application rate over a wide range of pressures. Emitters are installed by individual plants or grouping of plants. All drip irrigation systems should include a filter and pressure regulator.

Drip Tubing

Drip tubing is another form of drip irrigation in which water is emitted at equally spaced points (6 to 60 inches) along a tube. There are semi-rigid tubing with emitters built in the tubing. These emitters can be pressure compensating. The tubing is similar to polyethylene irrigation tubing. Bi-Wall drip irrigation tubing has a main chamber (tube) to supply water to an outside secondary distribution chamber with drip holes regularly spaced. Bi-Wall tubing is thin walled and is less expensive and durable than the semi-rigid drip irrigation tubing. Irrigation tubing discharge is expressed in gpm per 100 ft of tubing or in gallon per hour per emitter. There is also porous drip irrigation tubing that allows water to seep out along the entire length of the tube. Depending on the drip irrigation tubing type, operating pressures are from 5 to 20 psi. Drip irrigation tubing can either be laid on top of the soil or buried in the soil. Buried drip tubing is being sold to irrigate turf.

Bubblers

Bubblers are similar to drip emitters except that they have a much higher flow rate. The flow rate of bubblers is adjustable from 2 to 6 gpm, resulting in application rates much higher than soil intake rates. Bubblers essentially flood a small area and the water continues to infiltrate into the soil after the bubbler has been shutoff. Bubblers are only applicable in areas where small basins can be constructed to contain the water and where the soil is surface is level.

Surface or Flood Irrigation

Surface or flood irrigation systems can be used in a few horticulture situations. Surface irrigation generally applies deeper irrigation and requires higher flow rates for a shorter period of time than sprinkler or trickle. Leveled and diked turf areas can be irrigated by flooding if the soil infiltration rate is slow enough to allow the water to flow over the entire area. Landscapes and gardens are sometimes irrigated with furrow or diked irrigation. In surface irrigation the soil is the distributing and infiltration system and requires careful design for efficient irrigation. Surface irrigation is limited by the slope of the area.

All types of Irrigation methods and systems have both advantages and disadvantages that need to be considered in each specific application and design.


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