Department of Biological and Agricultural Engineering i NC STATE UNIVERSITY
The project designed an irrigation system for a small blueberry field in Pender County, North Carolina. The 0.25 hectare blueberry field is used for a small pick-your-own blueberry operation and currently has no irrigation system in place. An irrigation system is desired to increase crop yield and to provide frost protection to the crop. The irrigation system needed to provide irrigation for the field, provide frost protection, and not have any pipes that disturb established plants. A solid set system made of Schedule 40 PVC was chosen with a buried main and above ground laterals. The main will run across the rows and the laterals will run along the rows with risers lifting the sprinkler heads above the crop. RainBird 29JH sprinkler heads were chosen and 8 laterals were used with 3 sprinklers per lateral with the main running across the middle of the field. A pump house already in place cuts into the field so the northwestern most lateral only has one sprinkler head. For frost protection RainBird 14VH heads were selected. The system design required a flow of about 6 L/s at 42m of head so a Goulds 5CLC 3-stage submersible pump was chosen. With design, labor and materials the cost as specified was $12,805.
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Table of Contents
Executive Summary ............................................................................................................................................ i Table of Contents .............................................................................................................................................. ii Problem Statement ............................................................................................................................................ 1
Department of Biological and Agricultural Engineering 1 NC STATE UNIVERSITY
Location The site of interest is a 0.25 hectare blueberry field on a non-commercial family farm in the Coastal Region of Pender County, North Carolina (34° 25' 59.0016" N, 78° 04' 41.9622" W). The primary crops of the farm are blueberries and corn. Figure 1, shown below, shows the size and shape of the blueberry field and the relative location of a nearby pump house. The soil is classified as Leon (Web Soil Survey). Leon is a very deep, poorly to very poorly drained sandy soil with a Bh horizon within a depth of 30 inches (Soil Profile Gallery). The slope of the site is practically zero due to its location near the coast.
Figure 1: Layout of 0.6 acre blueberry field and pump house.
Site Problem This particular field is open to individuals who want to pick their own blueberries and there is currently no irrigation practice in place. Because of this, plants suffer from lack of water and frost damage. A large well and a pump exist in a pump house at the corner of the field, as pictured above.
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Objectives & Constraints
Objectives An irrigation system needs to be designed to replenish depleted plant available water during the growing season. The system should also be designed to prevent frost damage to blueberry blossoms, which occurs in spring. The system will most likely be manually operated, as an automatic control system will be cost prohibitive. If possible, the system should use the existing pump, but this is not required if system performance will be hindered because of it. Constraints
• Replenish plant available water during growing season. • Prevent frost damage to plants. • Design needs to minimize the disruption of established plants.
As noted in the previous section the goal of this irrigation system is to replenish plant available water during the growing season as well as provide frost protection during the winter months. Because frost protection must be provided with the design, techniques such as microirrigation or subsurface drip irrigation are not appropriate. Also, due to the small size and irregular shape of the field a center-pivot system would not be feasible. Possible design solutions are listed below. Possible Solutions
1. Install a travelling gun system supplied by an appropriate pump.
2. Develop a hand move solid set system to irrigate the field.
3. Design a permanent solid set system with laterals along perimeter of the field.
4. Design a permanent solid set system with a main going through the middle of the field and
laterals branching to each side.
A travelling gun approach is simple when compared to other irrigation methods and is adaptive to fit any field shape. However, initial costs are too high and the intense manual labor is more than desired. In addition, losses due to wind and evaporation are much higher when compared to other systems. A hand move system could be designed to fit the irregular field size, although more than desired manual labor would be required like the traveling gun system. A permanent solid system would be the most efficient in distributing water. The price of the permanent solid system will be more expensive to install, but little manual labor would be required after installation.
Two designs were considered for a solid set system. The first layout planned to avoid disturbing the mature plants located in the field by placing two laterals on each side of the field. While ideal, additional sprinkler heads would be required to provide frost protection. Also, the large sprinkler heads required for irrigation would create large droplet sizes which could cause damage to the plants. The second design was a more traditional approach, with a main buried underground through the center of the field. Laterals for this design would be placed above ground and along the
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plant rows. Smaller sprinkler heads could be used to achieve both objectives of the project, irrigation and frost protection. Therefore the fourth approach was selected for design.
Analysis and Design Specifications
The blueberry field measures 74 meters by 34 meters and has 14 rows of blueberries running the length of the field. With the established, mature blueberries already in place the design needed to limit the disturbance to the field. To limit the impact on the blueberries the lines were designed to run above the ground along the blueberry rows as much as possible. Because machinery needs to travel along the rows any pipe running across rows would need to be buried which would impact the established blueberries. By running only one main line across row to the center of the field the impact is limited. The laterals were then laid out along the rows; because there was an even number of rows the lateral spacing could not be symmetrical which will reduce the uniformity.
Figure 2: Sprinkler Spacing
As shown in Figure 2, the northwest corner of the field has a pump house that cuts into the field so that lateral only has 1 sprinkler. The spacing of the sprinklers was based on the specifications for the sprinkler chosen. A RainBird 29JH sprinkler with a 3.97 mm nozzle was selected which has a 12.8 m effective radius at 250kPa and a flow of 0.27 L/s. With the sprinkler spacing along the lateral of 13m and spacing along the main of 10.4m and discharge of 0.27 L/s the average application rate was found to be 7.19mm/h. This value was much lower than the maximum application rate of 38.1mm/h published in Chapter 15, Section 11 of the National Engineering Handbook. The irrigation requirement for blueberries was found to be approximately 30.2 L/plant/day; with the average application rate this gives a daily run time for the irrigation system to be 1.34 hours per day. Selecting 1.5” Schedule 40 PVC pipe the head loss in the lateral was found to be 0.49 m so the average pressure head in the lateral was 25.6 m, or 250.7 kPa. This pressure variation was well below the 20% recommended limit. The sprinkler flow was then recalculated with this value through an iterative process. From the average pressure and friction losses the sprinkler pressure at the inlet was computed, the slope along the lateral was nearly 0% so there was no slope effect. The total flow for each quadrant was found to be 1.622 L/s. This process was the same for the northeast, southeast,
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and southwest quadrants but because the northwest quadrant had non-uniform laterals it was addressed independently. For the northwest quadrant each lateral was looked at independently. The northern most lateral was found to have a flow of 0.27 L/s and the southernmost lateral in the quadrant was found to have a flow of 0.81 L/s giving a total flow that the main would have to supply of 5.95 L/s. To irrigate the field the sprinklers needed to be elevated above the blueberries, this riser height was taken into account when determining the head required at the junction of the main and the lateral. To keep velocities under 1.5 m/s 3” Schedule 40 PVC was chosen for the main. The length of the main from the pump house was 61.8m, with the fittings the equivalent length was 82.3m giving a friction loss in the main of 1.55 m. With the friction losses in the main, the head required at the junction of the lateral and the elevation difference between the pump and the water supply after drawdown the total head was found to be 42.1m. For the system a pump needs to be found that can supply 5.95 L/s at 42.1 m of head. Because the water source is a well, a submersible or line pump was needed to lift the water. Looking at curves for available pumps, a Goulds 5CLC 3-stage submersible pump was selected. The pump has a 71.8% efficiency and will operate at 3.5kW. For frost protection the field needs to be sprayed continuously but only a small amount of water needs to be sprayed; smaller RainBird 14VH heads with 1.59mm nozzles will be used which have a much lower flow rate so the field is not over irrigated.
Figure 3: Pump Curve for Goulds 5CLC 3 stage pump
The well supplying the irrigation is also used by the client as a fresh water source so to ensure that there is no contamination of the well the water will be pumped through an RPZ
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backflow prevention device as well as a check valve. The pipes will be chemically welded with PVC solvent and to connect the mains and laterals 3” x 1.5” slip T fittings will be used and then a 1.5” x 1.5” slip T fitting will direct the lateral in each direction. The risers will stand off of the laterals with slip T fittings and the heads will be attached at the top of the risers. To provide added stability to the risers, 4” x “4” x 8’ pieces of lumber should be driven into the ground and secured to the riser.
The cost statement can be seen in Table 1 below.
Table 1: Cost Statement
Operation and Maintenance Instructions
Operation To operate the irrigation system safely and properly it is important to follow the following guidelines for safe practice. Before turning on the irrigation pump check the position of all control valves and make sure they are in the proper position. With all valves in the proper position, turn on the pump to activate the irrigation system. When starting there may be some water spray out of the RPZ backflow device, a small amount of spray when starting and stopping the pump is normal and ok. While the pump is running if any valves need to be moved they should be moved slowly to prevent the inertia of the flowing water from blowing apart any pipes or fittings. The pump should not be started and stopped rapidly; doing so can pull a large load on the starter and blow fuses or pull down breakers. Allow the pump to run for the required amount of time for the daily cycle and then shut down the system. For freeze protection operate the system continuously.
Item Quantity Unit Cost Sales Tax (7.75%) Extended Cost
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Maintenance Periodic maintenance is important for the continued efficient operation of the irrigation system. A monthly inspection of the pipes and sprinkler heads should be performed to check for damage. If any sprinkler heads are damaged they should be removed and repaired or replaced. RainBird has common wear parts available for replacement. To minimize the impact on the existing blueberries most piping was laid above ground leaving it vulnerable to damage by machinery. Care should be taken while operating machinery in close proximity to the irrigation lines; if any lines are damaged the damaged section should be cut out and replaced with new pipe. All lines are standard Schedule 40 sizes and replacement pipe and fittings are available at any hardware or plumbing supply store. If replacing any damaged section of pipe it is important to use Schedule 40 pipe; foam core and drain-waste-vent pipe is also available in the same sizes but is not pressure rated and should not be used in this application. During normal operation mineral and sediment deposits can build up inside the pipes, especially at fittings. To flush the system the system can be run with some of the sprinkler heads removed to clean out any sediment. If severe mineral deposits are suspected inspect the inside of one of the exposed section of pipes and look for scaling or rough deposits on the inside surface of the pipe. Some deposits such as calcium can be hard to see but are apparent by a rough, rippled texture on the inside of the pipe. Winterization Freezing temperatures can damage the irrigation system when not being used for frost protection if steps are not taken to winterize the system. When temperatures drop below freezing any water in the exposed pipe or sprinkler heads can freeze and cause damage. If the irrigation system is not being used during periods of below freezing temperatures the system will need to be winterized. Winterizing the system involves opening the system to allow all of the water to drain out of the pipes. With the system off all sprinkler heads should be removed and stored. The RPZ backflow device should also be removed and stored in a climate controlled location if possible; water trapped in the device can freeze. All valves should be opened completely to allow water to drain and after they have drained close each valve a few degrees so they are not left in the fully open position. Opening the system and letting it drain should be adequate for most seasons however in abnormally cold seasons the lines can also be blown out with an air compressor to ensure that no water is trapped in the system. With the air compressor attached at one end of the system move along and open each valve slowly allowing the air pressure to push the water out of the system to the furthest point. When using an air compressor take care not to over pressurize the pipes as this could cause fittings or pipes to blow apart.
The blueberry farm currently has no irrigation system and has a low yield, an irrigation system is needed to increase the yield and make the field more profitable. One of the first steps when designing the irrigation system involved determining the irrigation requirement of the field. A good deal of time was spent trying to determine the irrigation requirement for the field to ensure that the system provided adequate seasonal irrigation. The seasonal evapotranspiration rate was found from weather data for the area, effective rainfall and leaching requirement were calculated for the field and application efficiency was assumed to determine the seasonal irrigation requirement. Based on research the required peak irrigation amount for mature blueberries was much higher than the seasonal irrigation requirement so this ended up a small factor for the time spent.
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With the design the intention was to layout a system with as high uniformity as possible, the established, mature blueberries made this hard as they could not be disturbed. This limited lateral placement to along the rows so that equipment could travel between the rows and no plants were disturbed. As there was an even number of rows unequal lateral spacing along the main was needed to appropriately cover the field. This will result in slightly lower uniformity but was the trade off required to minimize the disturbance of the blueberries. The field is currently a low-profit operation, irrigation should increase yield but costs were wanted to be kept to a minimum. Because of the number of fittings required the price started to creep up. A drip irrigation system may have been less expensive alternative, but the requirement of frost protection limited the design to sprinkler irrigation. The frost protection issue was solved by throttling back the pump and using smaller sprinkler heads for times when frost protection was needed. This was the most practical solution for the scope of the project; another solution that was considered was using a variable frequency drive pump so that the operation would run as efficient as possible in both irrigation and frost protection modes. Ideally more time would have been spent investigating this option.
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Wilk, P. et al "Irrigation and Moisture Monitoring in Blueberries." Primefact 827 (2009): 1-10. Web. 15 Apr. 2010. <http://www.dpi.nsw.gov.au/__data/assets/pdf_file/0016/303325/Irrigation-and-moisture-monitoring-in-blueberries.pdf>.
David, Himelrick & Curtis M. Larry. ACES: Commercial Blueberries. Alabama Ag Irrigation Info