Moved-Lateral, Gun, and Traveler Sprinkler Systems

Dean E. Eisenhauer; Derrel L. Martin; Derek M. Heeren; Glenn J. Hoffman

doi:10.13031/ism.2021.12

Article Request Page ASABE Journal Article
Moved-Lateral, Gun, and Traveler Sprinkler Systems
Dean E. Eisenhauer, Derrel L. Martin, Derek M. Heeren, Glenn J. Hoffman
Pages 233-275 (doi: 10.13031/ISM.2021.12) in Irrigation Systems Management. ,
Abstract. A PDF of the entire textbook and a spreadsheet to use with this chapter is at https://www.asabe.org/ISM.
Keywords. Periodically Moved Laterals, Solid-Set Systems, Guns, Travelers, Irrigation, Textbook
12.1 Introduction
Sprinkler devices were invented at the end of the nineteenth century with over seventeen patents issued before 1890 (Morgan, 1993). Since then, sprinkler irrigation has become widespread. It is used around the world on many types of crops and soils. Water is delivered through pipes under pressure directly to the application location, thereby minimizing field conveyance losses while supplying crops on undulating terrain and/or highly permeable soils. Sprinkler systems can be efficient when properly designed and managed. Success depends on understanding characteristics and capabilities while operating within resource and management limitations. What questions should be asked to determine operator goals and restrictions? How should the irrigation system be configured to efficiently meet crop needs while satisfying constraints? What management plan would be most effective? How should you monitor the system to evaluate performance? Concepts presented in this chapter will allow you to address these issues.
Table 12.1. Data on sprinkler irrigation from USDA (2019).
Type ofSprinkler System Number
of Farms Total Area(acres) Acres
per Farm Percent ofSprinkler Area
Center Pivot 49,923 26,800,613 537 85%
Side Roll 16,130 1,788,443 109 6%
Solid Set 18,216 1,206,860 66 4%
Traveler 7,518 596,059 79 2%
Linear Move 3,669 469,408 122 1%
Other 8,673 401,318 46 1%
Hand Move 22,266 394,194 17 1%
Total 126,395 31,656,895 100%
The USDA-NASS (2018) lists the seven types of sprinkler irrigation systems shown in Table 12.1. Survey results show that center-pivot irrigation systems represent approximately 85% of the sprinkler irrigated land in the U.S. in 2017. Linear-move irrigation systems are mechanized systems with characteristics much like center pivots, yet only represent approximately 1% of the irrigated land. The remaining five types of irrigation systems constitute approximately 14% of the sprinkler irrigated land in the United States. While that area is much smaller than for center pivots, it still is significant. The USDA-NASS database includes the number of farms that employed the types of systems. The acres irrigated per farm for center pivots is much larger than other types of sprinkler irrigation. The extent of periodically moved systems for the ten states with the most area is listed in Table 12.2. Most of the area for side-roll and hand-move systems is in the states in or west of the Rocky Mountains. Solid-set systems are used in some states east of the Rocky Mountains, yet California, Washington and Oregon dominate. Big-gun systems are more uniformly distributed across the country.
These data represent irrigation development in the United States. Periodically moved systems are significant internationally, especially in areas with small landholdings or developing areas that lack financial resources needed for drip or mechanized systems. The characteristics and management practices for systems except center pivots and linear-move systems are examined in this chapter. Center pivots and linear-move systems are considered in Chapter 13. Detailed design of moved-lateral, solid-set and gun-based systems involves matching all components and ensuring that hydraulic principles are satisfied—see Keller and Bliesner (1990) and/or Stetson and Mecham (2011) for design procedures. Most management situations depend on systems already in place, so design considerations are only discussed to help evaluate alternatives when system changes are needed or when monitoring system performance.
Table 12.2. Rank of top ten states for each type of periodically moved system (data from USDA, 2019).
Rank Side Roll Hand Move Solid Set Big Gun
State Acres State Acres State Acres State Acres
1
Idaho
406,429
Oregon
115,405
California
454,924 Oregon 112,182
2
Utah
258,816
Idaho
73,733
Washington
253,939 Michigan 61,636
3
Montana
198,603
California
50,262
Oregon
88,463 Washington 48,632
4
Oregon
196,155
Washington
44,429
Arizona
58,051 Georgia 43,631
5
Texas
86,163
Montana
33,825
Idaho
46,463 Texas 36,217
6
California
83,396
Utah
13,745
Florida
42,564 Florida 31,256
7
Washington
82,373
Colorado
6,973
Texas
38,368 Missouri 24,766
8
Colorado
79,972
Texas
6,714
Wisconsin
34,903 California 24,433
9
Illinois
42,338
Wyoming
6,548
Georgia
29,471 New Jersey 22,336
10
Wyoming
36,645
New Jersey
5,106
Michigan
18,995 N. Carolina 21,305
12.2 Periodically Moved Laterals
Figure 12.1. Typical layout for a moved-lateral sprinkler system for two successive sets.
The layout and design of sprinkler laterals in general were presented in Chapter 11. The typical layout of moved-lateral systems is illustrated in Figure 12.1. Water is supplied from a pump into the mainline which conveys water to the lateral. The mainline may be lengths of aluminum pipe aboveground. If multiple laterals operate simultaneously, valves may be placed along the mainline to adjust the pressure into a lateral and to shutoff a lateral for moving without shutting down the pumping plant. Buried PVC pipe may also be used for mainlines with riser pipes and valves to connect to laterals. Hand-move and tow-line systems often require sprinkler risers several feet tall to position the sprinkler above the crop so that the canopy does not interfere with the water jet. Moved-lateral systems use impact or rotating sprinklers that provide a large diameter of coverage allowing for wider spacings and fewer sets. Effective operation depends on selecting the proper sprinkler and nozzle for the chosen spacing of sprinklers along the lateral and the width between sets as discussed in Chapter 11. Laterals should be large enough to limit pressure variations along the lateral to less than 20% of the average operating pressure. Pressure regulators and flow control nozzles may be necessary in some instances to meet uniformity goals. Ultimately, the system should be designed to provide the water requirements of the crop while maintaining efficiency by minimizing deep percolation, evaporation, and runoff. Operator preferences must be incorporated into the management plan.
12.2.1 Types of Systems
Figure 12.2. Hand-moved sprinkler system. (Photos a and b are courtesy of USDA-NRCS. Figures c and d were adapted from Turner and Anderson, 1980)
Moved-lateral sprinkler systems are composed of a lateral that is periodically repositioned across the field. The lateral consists of individual pieces of pipe connected with a coupler and latching system. Individual pieces of pipe are often referred to as a joint, a length, or a section of pipe. The simplest sprinkler system is a hand-move system where the lateral joints are carried from set to set by hand and the lateral is reassembled at the new set (Figure 12.2a and 12.2b). In some cases, aluminum pipe is used for the mainline (Figure 12.2c). In other cases, the mainline is buried and risers with hydrants are connected to the lateral (Figure 12.2d). While these systems are versatile, they require considerable labor, especially if the soil surface remains muddy after irrigation or the soil surface is not protected by the crop. Moving laterals is also difficult when crops are tall. Moving the lateral is much easier when the soil is covered such as with grass or alfalfa. Once the lateral reaches a field boundary it must be disassembled and transported to the next location to be irrigated. The lengths of pipe, sprinkler types and nozzle sizes are usually the same for all joints of the lateral to avoid confusion when repositioning the lateral. The substantial effort required to move the lateral promotes large application depths per irrigation to minimize the number of moves.
Hand-move irrigation systems are the cheapest to buy and maintain. Maintenance involves replacing gaskets used to seal adjoining lengths of pipe—usually replaced biennially or triennially. Sprinklers and nozzles should also be replaced periodically. Sprinkler replacement depends on the amount of annual use; however, sprinklers often last more than five years. The pipe has a long life; thus, investment and maintenance costs are small while labor requirements are quite high. In some cases, hand-move systems are used for special purposes such as leaching salts during the off-season where surface methods are used during the irrigation season. Hand-move systems are extremely portable so they can be used on fields where supplemental irrigation is not required every season.
Figure 12.3. Tow-line sprinkler system and components. (Diagram of tow-line with wheel stabilizers is courtesy of Turner and Anderson, 1980. Plan view of field and tow-line system is adapted from Turner and Anderson, 1980.)
To alleviate the labor of carrying laterals, several mechanical adaptations were developed to reposition the lateral to the next set. One method uses a tractor, or other power source, to pull the lateral across the field from one set to another. This type of system is called a tow-line, skid-towordrag-line system. The components and plan view of the system as shown in Figure 12.3. As shown in the plan view, the pipeline is towed in a zigzag fashion across the field. The lengths of pipe are held together with tow-line couplers that connects two lengths of pipes. Connecting pins were used within the coupler to allow quick disassembly when relocating laterals to the starting set. A skid pan held the pipe above the soil and protected the drain that was included in the coupler. The pipeline is supported by devices, called outriggers or stabilizers, that are clamped onto the pipeline to prevent the lateral from twisting during movement which prevents sprinkler risers from tipping over and breaking. Wheels were also used as shown in Figure 12.3 to provide stability; thus, some systems are called wheel-tow systems. To reduce abrasion on the aluminum pipe—especially for rough terrain—steel skid pans can be clamped at the midpoint of the joints to carry the pipe above the soil.
Tow-line systems work well on low-growing crops where the lateral pipe can slide freely across the soil and crop surface. The pipe must be pulled between the rows when the system is used for row crops. This is easily done for low-growing crops such as soybeans or grain sorghum. For tall crops, such as corn, the tractor will flatten one or two rows of corn when the pipe is pulled. Sometimes producers plant a few rows of a low-growing crops in the alley where the pipe is pulled. Others plant the tow alley to a permanent grass. In any case there will be a loss of production area for tall crops. The end cap and hitch shown in Figure 12.3 are installed on both ends of the lateral. The lateral is connected to the mainline using a flexible hose.
Tow-line systems are more expensive to purchase and maintain than hand-move systems. The same pipe and sprinklers are needed as for hand-move systems, but stabilizers and couplers increase investment cost. Friction between the soil and the pipe often causes wear that shortens the life of tow-line systems. Less labor is needed to move laterals from one set to the next than for hand-move systems; however, more time is needed to disassemble and reposition the pipeline once the lateral reaches the field boundary.
Figure 12.4. Side-roll sprinkler system and components. (The plan view shown in drawing a is adapted from Turner and Anderson, 1980. Picture c is courtesy of Rain for Rent and picture d is courtesy of Wade Rain, Inc.).
The third type of moved-lateral systems is the side-roll, wheel-move, wheel-line, or hand-roll system. With this system wheels are clamped directly onto the lateral pipeline (Figure 12.4c). Pipe used on side-roll systems is usually thicker walled than for hand-move or tow-line systems. The joints of the lateral are rigidly fastened—sometimes using gears between joints—to remain connected while applying torque when moving the system. The pipeline is moved by rotating the pipeline directly or in some cases to a drive shaft that runs parallel to the lateral. For mechanically powered systems torque is applied by an engine located on a chassis (Figure 12.4b) located either at one end of the lateral or along the center of the lateral where access is convenient. The engine slowly turns the pipeline or drive shaft, and the wheels rotate across the field. Hand-roll systems do not have an engine and the wheels are rotated by hand. The clearance below side-roll systems is typically about 3 feet but can be as much as 6 or 8 feet for special large diameter wheels. Sometimes braces are needed to keep the lateral in place after moving. Some alignment by hand to straighten laterals may be needed after moving. Sprinkler levelers (Figure 12.4d) include a swivel that kept sprinklers vertical if the pipeline did not rotate to the perfect angle. All moved-lateral systems should be drained prior to moving as demonstrated with the drain shown in Figure 12.4d for side-roll systems.
12.2.2 Operational Characteristics
Managing sprinkler irrigation systems involves adjusting several variables to meet crop water needs, avoid deep percolation and align with management goals and constraints. Moved-lateral systems are repositioned from set to set across the field. The time that the lateral is in one location is called the set time. These systems require significant effort and labor to move each set; therefore, the minimum set time acceptable to operators is about 8 hours with a maximum of 3 sets per day. The most common set time is 12 hours, but 24-hour sets may be used for high clay content soils or for salinity management—low application rates over long periods enhance leaching and minimize runoff. Laterals must be drained before moving which can take up to 1 hour. Therefore, the time that water is applied, the application time, will be less than the set time.
The depth of water applied is often large for periodically moved systems. The depth is determined by the average application rate (A_r) and the time of application as described from Equations 11.3 and 11.4. The application rate is determined by the flow rate from the sprinkler (q_s), the spacing of sprinklers along the lateral (S_L) and the spacing between lateral sets along the mainline (S_m):
(12.1)
where: d_g = the gross depth of application (in),
A_r = the average application rate, inches/hour,
q_s = the sprinkler discharge rate (gpm),
S_L = the spacing of sprinklers along the lateral (ft), and
S_m = the spacing of lateral locations along the mainline (ft), and
T_o = the application time (hr).
The depth of water applied per hour (i.e., the application rate) for typical sprinkler and lateral spacings are listed in Table 12.3 for a range of sprinkler flows. For example, a typical system using a 40 ft × 60 ft spacing with a sprinkler discharge of 10 gpm applies 0.4 inches per hour. If four inches of water are needed, then water should be applied for 10 hours. This is the gross depth of application and must be multiplied by the application efficiency for the low quarter (E_LQ) to determine the net depth (d_n):
(12.2)
The irrigation interval (I_i) is the amount of time required to irrigate the field. This can be thought of as the time between consecutive irrigations of the first set of the field. Periodically moved laterals are operated to utilize the longest possible irrigation interval to minimize labor input. The irrigation interval depends on the average crop water use rate during the interval and the amount of water that can be stored in the root zone without causing deep percolation. The net depth of water required for an irrigation is the product of the irrigation interval and the average net crop water use during the interval. The net water use rate equals the evapotranspiration minus the expected effective rainfall during the interval. This is analogous to the net system capacity (C_n, in/d) discussed in Chapter 4. Thus, the required net depth of application is given by:
(12.3)
Table 12.3. Depth of water applied per hour (i.e., the application rate), (in/hr).
Lateral
Spacing,
S_L (ft) Spacing
Along
Mainline,
S_m (ft) Representative
Area,
S_L x S_m(ft²) Sprinkler Discharge, q_s (gpm)
4 6 8 10 12 15 20 25
20 40 800 0.48 0.72 0.96 1.20 1.44 1.81
30 40 1200 0.32 0.48 0.64 0.80 0.96 1.20 1.61
40 40 1600 0.24 0.36 0.48 0.60 0.72 0.90 1.20 1.50
20 50 1000 0.39 0.58 0.77 0.96 1.16 1.44 1.93
30 50 1500 0.26 0.39 0.51 0.64 0.77 0.96 1.28 1.61
40 50 2000 0.19 0.29 0.39 0.48 0.58 0.72 0.96 1.20
50 50 2500 0.15 0.23 0.31 0.39 0.46 0.58 0.77 0.96
20 60 1200 0.32 0.48 0.64 0.80 0.96 1.20 1.61
30 60 1800 0.21 0.32 0.43 0.54 0.64 0.80 1.07 1.34
40 60 2400 0.16 0.24 0.32 0.40 0.48 0.60 0.80 1.00
50 60 3000 0.13 0.19 0.26 0.32 0.39 0.48 0.64 0.80
60 60 3600 0.11 0.16 0.21 0.27 0.32 0.40 0.54 0.67
30 70 2100 0.18 0.28 0.37 0.46 0.55 0.69 0.92 1.15
40 70 2800 0.14 0.21 0.28 0.34 0.41 0.52 0.69 0.86
50 70 3500 0.11 0.17 0.22 0.28 0.33 0.41 0.55 0.69
60 70 4200 0.09 0.14 0.18 0.23 0.28 0.34 0.46 0.57
70 70 4900 0.12 0.16 0.20 0.24 0.29 0.39 0.49
40 80 3200 0.12 0.18 0.24 0.30 0.36 0.45 0.60 0.75
50 80 4000 0.10 0.14 0.19 0.24 0.29 0.36 0.48 0.60
60 80 4800 0.12 0.16 0.20 0.24 0.30 0.40 0.50
70 80 5600 0.10 0.14 0.17 0.21 0.26 0.34 0.43
80 80 6400 0.09 0.12 0.15 0.18 0.23 0.30 0.38
The net application depth must be less than or equal to the allowable depletion (AD) determined from scheduling:
(12.4)
where: AD = allowable depletion before irrigating, in,
R_d = root depth for scheduling, ft
AWC = available water capacity, in/ft, and
f_dc = allowable depletion, fraction.
The relationship between the allowable depletion and the net crop water use is shown in Figure 12.5. The solid blue lines represent the cumulative net crop water use during an irrigation interval. The horizontal dashed lines represent the allowable depletion for six soils using a critical allowable depletion of 50%, a management root zone depth of 4 ft, and the available water capacities consistent with Table 2.3. For example, the allowable depletion for a silt loam soil for these conditions is 4.3 inches. Applying more water would cause deep percolation. If the average crop water use rate was 0.30 inches/day, then the longest acceptable irrigation interval would be (4.3 in ÷ 0.3 in/d = 14.3 days) or rounding down to 14 days. Sandy loam soils only hold about 2.9 inches for these conditions. Also, since the irrigation interval will be shorter than for the silt loam you would expect that the net water use rate would be higher for the shorter period. So, for a water use rate of 0.35 inches/day the maximum irrigation interval for sandy loam would be about eight days. Sandy soils have small water holding capacities which leads to short irrigation intervals, requiring short set times or more laterals in an equally sized field. The irrigation intervals shown in Figure 12.5 represent the maximum acceptable values. Shorter intervals could be used such as seven days for the sandy loam soil so that scheduling activities are more tractable. The irrigation interval is based on the more extreme water use periods during the season. The actual irrigation interval will depend on irrigation scheduling during the season.
Figure 12.5. Maximum allowable irrigation interval for 4-ft root zone depth and 50% allowed depletion.
Water quantities in Figure 12.5 represent net irrigation depths and must be increased to determine the gross depth to apply. The application efficiency for well managed systems could be about 75% (see Table 5.4). Therefore, the gross depth for the silt loam soil is 5.6 inches (i.e., 0.3 in/d × 14 d ÷ 0.75) and 3.7 inches (i.e., 0.35 in/d × 8 d ÷ 0.75) for the sandy loam soil. If using the seven-day interval for the sandy loam soil, the gross depth would be 3.3 inches.
The irrigation interval accounts for time that water is applied, time for draining and moving laterals, and time to relocate the lateral to the starting set. If relocating the lateral takes one day, then water would only be applied for 13 days for the silt loam and 7 days for the sandy loam soil—assuming an eight-day interval. If an irrigator selected a 12-hour set time, then two sets can occur per day and the total sets possible for one lateral for the silt loam would be 26 (i.e., 13 days × 2 sets/day). One lateral would only allow 14 sets per lateral for the sandy loam soil.
The number of laterals required for the field depends on the irrigation interval and the field dimensions. The number of laterals also depends on the number of sets in the field and the number of sets possible during the irrigation interval for one lateral. Since fields for periodically moved systems are usually rectangular, the amount of land irrigated per set is usually constant. An example of a moved-lateral system is shown in Figure 12.6. This is an eighty-acre field with laterals on the left and right halves with the mainline running down the middle of the field. The left side of the sketch shows the layout of the sets, and the right side shows the lateral position and field information.
Figure 12.6. Plan view of field layout for moved lateral examples. Note that both sides of the field are irrigated.
The amount of area per set (A_s) is shown in Figures 12.1 and 12.6 and is given by:
(12.5)
where: A_s = the area irrigated per set, acres
L = the length of the lateral, ft, and
S_m = the spacing of laterals along the mainline, ft.
Then the number of sets (N_s) in the field is the area of the field (A_f) divided by the area per set:
(12.6)
The number of sets must be an integer, so the value from Equation 12.6 should be rounded up to the nearest integer.
For example, the area of the field in Figure 12.6 is 80 acres (2640 ft × 1320 ft ÷ 43560 ft²/acre) and the area per set is 1.82 acres; thus, 80 acres ÷ 1.82 acres/set gives 44 sets for the field. Equation 11.15 can be expanded for when the lateral length is less than the field length to also give the number of sets:
(12.7)
where the length and width of the field are illustrated in Figure 12.6. Equation 12.7 and the layout in Figure 12.6 show that 44 sets are required for this field. The spacing of 60 feet between laterals is common for moved lateral systems as that is the length of two pipe sections for portable mainline pipe.
The number of laterals depends on the number of sets that can be irrigated with one lateral during the interval:
(12.8)
where: N_p = the number of sets per lateral
I_i = the irrigation interval, d
T_m = time required to reposition lateral to the first set, hr, and
T_s = set time, hr/set.
The number of sets per lateral must be an integer; so, round the number from Equation 12.8 down to the nearest whole number. Then the number of laterals (N_L) for the field is:
(12.9)
The number of laterals must be an integer, so you need to round up for the number of laterals. Rounding of results to integer values may require relaxation of some management criteria to provide reasonable configurations. For example, increasing f_dc to 55% on a sandy loam soil allows one more day for the irrigation interval which may provide a more acceptable number of laterals. Such compromises would not threaten crop yields in most cases.
12.2.3 Management Plan
The large number of variables and calculations needed to describe moved-lateral systems can be perplexing. Managing irrigation systems usually involves an existing system. Therefore, the first process is to describe the characteristics of the existing system. Second, the existing conditions should be evaluated to determine if the system is capable of efficient irrigation. The third step is to develop a plan to meet crop needs and achieve efficiency.
A management spreadsheet such as in Figure 12.7 can help alleviate confusion and facilitate development of a management plan. Users enter parameter values into the shaded boxes and then compute results for the unshaded cells. These data are critical, but they are characteristics of the system and only need be considered once unless major changes are made which would require redesign and new investment.
The Moved-Lateral Management Spreadsheet is divided into four portions. The first portion is an inventory of field characteristics. The values entered for this example are from the field shown in Figure 12.6—an actual field from western Nebraska. The second portion includes design variables which represent the considerations made when designing the system. These are choices made during design; however, these values are generally constant once a system has been installed. Designs can be modified which would result in changing parameters, but once changes were made the variables would be constant again. Thus, design variables are only defined once and are not modified routinely by managers. You can think of field characteristics and design variables as a description of the system you are called upon to manage.
The third portion represents the parameters that describe system performance based on field characteristics and design parameters. These boxes contain either calculation results or parameter values derived from earlier sections. Values in these boxes do not represent choices. The fourth portion includes management variables which can be changed annually or within the season. These values are adjusted to provide the desired performance. Conflicts can arise in selecting management values and issues must be resolved when compromise is needed.
Values for the mainline portion of the operation results section include the total inflow which equals the flow per lateral times the number of laterals. The remaining values are based on application of procedures developed in Chapter 8 for friction loss and flow velocity. One should check values against guidelines for friction loss and velocity.
The lateral information represents calculations described in Chapters 8 and 11. Note that the friction loss calculations are for the most critical lateral that runs uphill—the lateral north of the mainline. This example is for 5-inch aluminum pipe for the side roll. The Hazen- Williams C value is taken as 120 and the wall thickness for the side-roll pipe is 0.072 inches.
Figure 12.7. Example of the Moved-Lateral Management Spreadsheet.
Four-inch pipe can also be used for the side-roll lateral and the wall thickness is the same as for the 5-inch pipe. The spacing limits between sprinklers and laterals are derived from Table 11.3. The application rate is also computed. The number of sets in the field and per lateral are also shown. Completion of these sections and validation that characteristics meet established guidelines establishes the foundation for managing the system.
The fourth section of the sheet is for management choices. These parameters are frequently changed or adjusted to achieve short-term management goals for crop and system performance. The management decisions must be entered into the shaded cells. Management choices vary throughout the season and annually. The following examples illustrate the computation process for the field in Figure 12.6. The second example illustrates computation of the parameter values for the lateral information portion of the operation results in Figure 12.7. The last section in the Moved-Lateral Management Spreadsheet involves the core of managing the system. Example 12.3 illustrates the decision-making process for the management section.
The side-roll system is designed to meet crop water use during the middle of the season when water use rates are at the peak value. During other times of the year the system will have excess capacity. Early in the growing season the root depth will be less than 4 feet, so the root zone would not store a net application of 3.38 inches. When the system has excess capacity the irrigation interval can be extended through accurate scheduling. Timers can also be used to shutoff the pump for a shorter application time for the same set time. This will reduce the net depth when the root zone is swallower or when water demands are less. Once a management plan has been developed it is important to ensure that the system is operating properly—as designed.
12.2.4 Pressure Distribution
Figure 12.8. Locations along a lateral where pressure measurements should be made.
You will recall from Chapter 11 that the pressure variation along the lateral should not vary more than 20% of the average pressure. When a larger pressure range occurs, irrigation is not applied uniformly; therefore, excess water must be applied to adequately irrigate the drier portions of the field. The best way to evaluate the pressure variation along the lateral is to measure the pressure at critical points. The sketch in Figure 12.8 shows locations along a lateral that should be monitored. Usually, the highest pressure will occur near the inlet to the lateral. It could occur directly at the inlet or at a low-lying sprinkler close to the inlet. The lowest pressure locations will generally be near the distal end of the lateral. This could be at the end or at a high elevation near the end. These are good locations to measure the pressure.
The pressure can be measured in several ways. First a good quality pressure gauge that is accurate to within 1 or 2 psi should be used. The gauge can be attached to a pitot tube as shown in Figure 12.9 to measure the pressure. Care must be taken to place the pitot tube directly in the center of the jet from the sprinkler. The tube can be moved around in the jet to determine the maximum pressure reading. The maximum pressure read on the pitot is generally the true pressure. The pitot tube can be made from ¹/₈-inch flexible copper tubing attached to the gauge with an appropriate tube fitting. The pressure can also be measured by removing the sprinkler from the riser and directly attaching the pressure gauge. This, however, will require more time to conduct the test.
Figure 12.9. Pressure gauge connected to a pitot tube to measure nozzle pressure.
Instead of measuring pressure you can also measure the discharge from the sprinkler at selected locations along the lateral. This can be done by placing a soft, flexible hose over the nozzle and measuring the time required to fill a container to a specified volume. Several measurements should be made on each nozzle to determine the mean flow rate. While pressure can vary 20% of the mean along the lateral, discharge is only allowed to vary 10%.
After performing the pressure tests, you should compute the average pressure. The average pressure (P_a)for the lateral will be approximately:
P_a = P_min + 0.25 (P_max – P_min) (12.10)
As previously stated, the maximum acceptable range of pressure for the four points shown in Figure 12.8 is 20% of the average pressure. If the flow rate was measured the variation should be less than 10% of the average discharge. The average discharge equals the minimum discharge plus about 40% of the variation in flow that you measured.
Suppose that the pressure or discharge variation is too large, what could the problem be and how can you correct the situation? First compare the pressure or discharge at the lateral inlet to the design value. If the pressure or discharge is too small the problem may be with the pump or mainline system and the entire lateral is simply under pressurized.
Excessive variation in pressure may be due to a lateral that is too long, or the pipe diameter may be too small. The lateral could also run up a hill that was not considered in design. Correcting problems can be difficult. It is probably infeasible to replace the lateral unless the variation is bad, or the lateral is worn and will be replaced soon anyway. Recall from Chapter 11 that about half of the pressure loss occurs in the first third of the lateral. Thus, the initial section of the lateral could be replaced with larger diameter pipe to reduce the pressure loss. This is practical for side-roll and hand-move systems where the larger pipe will always be located near the mainline. This solution will not work for tow-line systems since the larger pipe would be at the distal end of the lateral half of the time.
The nozzles could be replaced with a smaller size to reduce the average flow rate of the lateral and to increase pressure at the downstream end. This will reduce the average discharge along the lateral. Some will think that this will reduce the ability to meet crop water requirements. However, the critical area along the lateral is the area receiving the smallest amount of water. Assuming that this area was used for scheduling, the poor uniformity contributed to deep percolation or runoff in the early portions of the lateral. If the flow rate at the critical distal end is not reduced, the depth of water applied at the critical area will be the same or more than when the nozzles were too large. Smaller nozzles could be used on sprinklers near the mainline if the smaller nozzles provide an adequate diameter of coverage.
Another alternative is to install either flow control nozzles or pressure regulators in the sections of the lateral that are likely to have excess pressure. These devices reduce the discharge in the high-pressure areas and produce better uniformity. It may not be necessary to install regulators along the entire lateral. Keep in mind that there is a pressure loss of about 5 psi across regulators, so you may not want to install them in the areas already low in pressure. You may also need to change the nozzle(s) in the sprinklers equipped with pressure regulators. Pressure regulators are more expensive than flow control nozzles, but they also operate over a wider range of pressures. Pressure regulators may be needed all along a tow-line lateral since the sprinklers are changing locations on the landscape every set.
An example may help illustrate the evaluation of lateral distribution and some alternatives for solving pressure distribution problems (Example 12.4).
Analyzing solutions for existing laterals is complex, so a spreadsheet program was developed to assist evaluation. The program is called Lateral Analysis. Performance for an existing lateral is shown in Figure 12.10. The shaded cells are where operators input data about the lateral. The unshaded areas cannot be changed. The variation of nozzle pressure for the existing lateral is 14.7 psi which represents about 40% of the average pressure—double the guideline.
Suppose pressure regulators are used to minimize variation. Examining the data for the sprinklers along the lateral in Figure 12.10, the pressure at the distal end of the lateral is about 33 psi. A 35-psi pressure regulator would give about the same nozzle pressure. Additionally,
Figure 12.10. Existing conditions in the Lateral Analysis program for the example lateral.
regulators cause about 5 psi loss when regulation is not active. Thus, a nozzle pressure of 38 psi without regulation will give an outlet pressure of about 33 psi. The first ten sprinklers have a nozzle pressure above 38 psi when regulators were not used. So, regulators are installed on the first ten sprinklers.
Table 12.4. Comparison of sprinkler lateral performance with and without regulators.
Values LateralPressure (psi) NozzlePressure (psi) SprinklerDischarge(gpm)
Performance—No Regulators
Maximum
49.7 47.6 10.96
Minimum
35.0 32.8 9.11
Average
38.8 36.7 9.62
Variation
14.7 14.7 1.85
Percent variation
38% 40% 19%
Performance—With Regulators for First 10 Sprinklers
Maximum
49.4 37.7 9.76
Minimum
35.0 32.8 9.11
Average
38.8 34.3 9.32
Variation
14.4 4.9 0.65
Percent variation
37% 14% 7%
The lateral analysis program was used to evaluate the results when using the ten regulators. Table 12.4 shows a comparison of the performance analysis when no regulators were used on the lateral and when 10 regulators were used at the inlet of the lateral. The results show that using regulators reduced the nozzle pressure variation to 14% and the discharge variation to about 7%. Both quantities are within the acceptable guidelines for uniformity. Ten regulators represent an investment of approximately $100 which would work for a long time, so pressure regulation is a relatively inexpensive and efficient way to achieve the uniformity goals. Of course, it is essential that the regulators are always used at the inlet to the lateral which would require some organization for hand-move systems. The spreadsheet can be used to analyze laterals and refining designs for special needs. Laterals with two pipe diameters can also be evaluated.
12.2.5 Uniformity Issues
Poor uniformity is evidenced by plant water stress in areas receiving less water. The problem can be due to pressure distribution, but other factors are possible. One issue is stretching the spacing between laterals or sprinklers along the lateral. When the spacing is excessive for prevailing wind conditions the overlap is inadequate to provide uniformity. Poor uniformity may also arise from worn sprinklers and nozzles. The sprinkler bearing may be worn causing the sprinkler to rotate slowly or stick in locations during rotation. Bearings can be replaced but it is often best to replace the entire sprinkler with this amount of wear. Wear of brass straight-bore nozzles can be evaluated by matching the diameter to a drill bit of that size. If the nozzles are worn significantly, they can be replaced very economically; however, sprinklers should be checked to ensure that they should not also be replaced.
The diameter of coverage of some sprinklers can be increased by inserting straightening vanes. The straightening vane shown in Figure 11.2 decreases turbulence and increases the diameter of coverage which may provide the coverage needed for acceptable uniformity. The sprinkler jet with a vane does not breakup as quickly as sprinklers without vanes. This also provides more throw and helps fight wind effects; however, vanes may lead to poorer distributions about an individual sprinkler resulting from a doughnut pattern. Straightening vanes are inexpensive and easily installed, so vanes can be evaluated for a few sprinklers. If vanes do not improve performance, then other alternatives should be considered.
The spacing between lateral sets is often limited by the length of mainline pipe. Aluminum pipe is commonly available in either 20-, 30- or 40-ft lengths. This dictates the width of sets and ultimately the uniformity. Operators can adapt to this problem by offsetting the lateral each set. Suppose that mainline joints are 30 ft long and two joints are used for a set width of 60 feet. For odd numbered irrigations, the lateral could be placed at locations of 30, 90, 150, etc., feet from the field boundary. The lateral is then placed between these setting for even numbered irrigations or at locations of 0, 60, 120, 180, etc. feet from the field boundary. Offsets place laterals halfway between the previous set and the cumulative uniformityof water application generally improves. Offsetting may cause issues when the first and/or last set is along the field boundary or where lanes are required for tow-line systems in tall crops.
12.2.6 Uniformity Evaluation
The ultimate evaluation of uniformity is to measure the distribution using an array of collector cans to compute the coefficient of uniformity as described in Chapter 5. It is impractical to measure the distribution along the entire lateral; thus, a representative area should be selected near the downstream end of the lateral where uniformity will be lowest. The configuration of catch cans is illustrated in Figure 12.11 for a lateral with sprinklers 40 ft apart along the lateral and a set width of 60 ft. The spacing of cans should be selected so that each container represents the same area. A common denominator should be determined that is convenient—either 5, 10 or 20 ft for Figure 12.11. In this case a ten-foot spacing was selected for collector spacing. Initially, the column of cans is placed one-half of the nominal can spacing from the lateral and the first row is one-half the can spacing from the sprinkler— i.e., first can is placed 5 ft from the lateral and 5 ft from the sprinkler. The remaining rows and columns of cans are space the full distance (10 ft) apart. This orientation ensures that each container represents the same area (10 ft × 10 ft) which simplifies computation of uniformity. Cans are placed on both sides of the lateral to evaluate the effect of wind. Tests should be conducted when wind, temperature, and humidity conditions are representative of the area.
Figure 12.11. Layout for testing the uniformity of application using catch can collectors.
It is impractical to measure the depth of water applied by all laterals for moved-lateral systems, so it is necessary to numerically overlap the catch data from one lateral. The lateral for the second set in Figure 12.11 should be operated for the test. Water is measured on both sides of the lateral. An adequate distance along the lateral should be tested to avoid bias from one or two sprinklers. Sprinklers should be evaluated to ensure they represent the system. However, the number of containers increases quickly. For example, the layout in Figure 12.11 requires 112 catch cans. Cans should be placed at least one row beyond adjoining laterals if wind is expected during the test. The system should be operated long enough to provide adequate water to accurately measured the depth in the cans. The water caught in cans is measured with a graduated cylinder. The diameter of the top of several catch containers should also be measured. The volume caught is converted to a depth by dividing the volume by the area of the top of the container.
The depth of water from the second lateral must be overlapped to determine the depth applied to the area by adjoining laterals. The depth of water applied during successive sets is computed based on the distance of the lateral from the point of interest. The following example shows how to overlap depths to evaluate the uniformity.
The coefficient of uniformity in Table 12.5 is 90, which is good, even though the application ranges from a minimum of 0.98 to a maximum of 1.57 inches over a relatively small distance. The areas between the sprinklers along the lateral (i.e., those 15 and 25 ft east and west of the central sprinkler) seem to be the driest. The DU for this area is about 84%, so you would need to apply about 20% more water than the average depth (i.e., 1.26 ÷ 0.84 = 1.5 in) to adequately irrigate the dry spots. The CU for the entire lateral will be less than for the area of the test.
A great deal can be learned about the operation of sprinkler systems with catch-can tests; however, evaluations are quite time consuming and wind conditions make tests difficult. When a catch can test is conducted, the pressure and flow rate measurements described in earlier sections should also be conducted. This is a short overview of evaluating sprinkler systems. Merriam and Keller (1978) developed a good reference on system evaluation that provides examples and charts for computation.
Table 12.5. Results of catch can evaluation for an example system. Red and blue cells are used in example.
Diameter of Top of Can (in) = 4 Area of Container (cm²) = (6.452 p D²/4) = 81.08
Distance North of Central Sprinkler (ft) Distance East of Central Sprinkler (ft)
-35 -25 -15 -5 5 15 25 35
Volume of Water Caught (cm³)
65 23 20 19 23 24 19 18 22
55 76 63 60 73 76 61 58 70
45 118 98 94 114 119 94 90 109
35 160 134 127 154 161 128 123 147
25 191 160 153 185 193 153 147 176
15 212 177 169 205 214 170 163 196
5 233 195 186 225 235 187 179 215
-5 210 176 167 203 212 168 161 194
-15 191 160 152 184 192 154 147 176
-25 163 136 129 156 163 132 125 149
-35 112 93 87 105 111 93 87 100
-45 50 40 35 43 47 45 39 41
-55 22 17 12 15 19 23 18 14
-65 0 0 0 0 0 0 0 0
Depth of Water Applied (in)
65 0.11 0.10 0.09 0.11 0.12 0.09 0.09 0.11
55 0.37 0.31 0.29 0.35 0.37 0.30 0.28 0.34
45 0.57 0.48 0.46 0.55 0.58 0.46 0.44 0.53
35 0.78 0.65 0.62 0.75 0.78 0.62 0.60 0.71
25 0.93 0.78 0.74 0.90 0.94 0.74 0.71 0.85
15 1.03 0.86 0.82 1.00 1.04 0.83 0.79 0.95
5 1.13 0.95 0.90 1.09 1.14 0.91 0.87 1.04
-5 1.02 0.85 0.81 0.99 1.03 0.82 0.78 0.94
-15 0.93 0.78 0.74 0.89 0.93 0.75 0.71 0.85
-25 0.79 0.66 0.63 0.76 0.79 0.64 0.61 0.72
-35 0.54 0.45 0.42 0.51 0.54 0.45 0.42 0.49
-45 0.24 0.19 0.17 0.21 0.23 0.22 0.19 0.20
-55 0.11 0.08 0.06 0.07 0.09 0.11 0.09 0.07
-65 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
Overlapped Depth for the Three Sets (in)
55 1.39 1.16 1.10 1.34 1.40 1.11 1.06 1.28
45 1.50 1.25 1.19 1.45 1.51 1.20 1.15 1.38
35 1.57 1.31 1.24 1.51 1.57 1.26 1.20 1.44
25 1.47 1.23 1.17 1.41 1.48 1.19 1.14 1.34
15 1.27 1.05 0.99 1.20 1.27 1.04 0.98 1.15
5 1.35 1.13 1.05 1.28 1.35 1.11 1.04 1.22
Absolute Deviation from Mean Depth (in)
55 0.13 0.10 0.16 0.08 0.14 0.15 0.20 0.02
45 0.24 0.01 0.07 0.19 0.25 0.06 0.11 0.12
35 0.31 0.05 0.02 0.24 0.31 0.00 0.06 0.18
25 0.21 0.03 0.10 0.15 0.22 0.07 0.12 0.08
15 0.01 0.21 0.27 0.06 0.01 0.22 0.28 0.11
5 0.09 0.13 0.21 0.02 0.09 0.15 0.22 0.04
Coefficient of Uniformity = 90
12.3 Solid-Set Systems
Two forms of solid-set systems are available. One is a permanently installed system as illustrated in Figure 12.12. A typical design includes buried mainline and laterals, often with PVC pipe. Special risers are used to bring sprinklers to the required height for the crops irrigated. Risers usually include some type of flexible connection near the soil surface to prevent rupturing the lateral if sprinkler risers are damaged during farming operations. Solenoid valves are used at the inlet to allow irrigation of a set as frequently as desired and with a variable irrigation interval. Solenoid valves may be above ground, as shown in Figure 12.12, or can be buried in irrigation valve boxes to provide access for repair. The solenoid valves are connected to an electronic controller that can be programmed to open and shut valves for desired frequency and duration. The solenoid valves may be connected to the controller with direct wiring or by wireless control. Controllers with web access can communicate to office computers or portable devices for real-time control. Some controllers now allow integration of irrigation scheduling into the controller programming as described by Davis and Dukes (2016) and Haghverdi et al. (2021). Controllers can also interface with soil water monitoring to provide information on the crop water status.
Portable solid-set systems are also available as shown in Figure 12.13. These systems are essentially a series of hand-move laterals connected to a mainline. Some systems such as shown in Figure 12.13c can be move mechanically to allow field operations and to reposition laterals. Manual or automatic values can be used to turn on and off laterals which allows for varying set times and irrigation intervals as needed. These systems are cheaper and more flexible than permanently installed systems. Many characteristics of portable solid-set systems are the same as periodically moved laterals.
Figure 12.12. Plan view and some components of a permanent solid-set system. (Lower right photo is courtesy of Senninger Irrigation.)
Figure 12.13. Examples of portable solid-set systems (photos a and b are courtesy of Hunter Industries; photo c is courtesy of Westlake Pipe & Fittings).
12.3.1 System Design
Solid-set systems, especially permanent systems, are expensive to install and, therefore, should be carefully designed. Permanent solid-set systems can be tailored to specific fields conditions to minimize installation and operation costs. The size of mainlines, manifolds and laterals can be reduced in an incremental fashion to achieve pressure loss and flow guidelines while saving investment costs. For example, the pipe for the distal portion of the lateral may be smaller than at the inlet since flows decrease along the lateral. One lateral in the system will ultimately determine the maximum pressure required from the pump. Mainline, submain and lateral sizes for other portions of the system may be smaller to reduce investment cost. The size of nozzles along the lateral can be varied for solid-set systems which allows for enhanced uniformity with little investment.
Each lateral can be specifically designed for local conditions. Thus, some laterals may operate at different average pressures depending on the location in the network and elevation of the lateral. The discharge and application rate can be designed to apply the desired depth at the appropriate application rate to avoid runoff and erosion. The set time can be short to apply small depths each irrigation. The cost of solid-set systems depends on the number of laterals that are needed. Therefore, a common problem is that the distance between laterals is extended to reduce investment costs. This is critical because once the system is installed it is expensive to retrofit the system to operate appropriately.
The piping network in buried solid-set systems will probably be PVC. This has proven to be an economical pipe for construction and operation. However, the pipe cannot take large pressure surges. Therefore, special precautions should be taken to prevent pipeline damage due to water hammer or vacuum. Vacuum relief valves must be installed at the high locations in the field to allow air to enter when the system is shutdown. High-pressure surges can be dealt with in several ways. A high-pressure relief valve can be installed in areas where pressure reached peak values. Surge tanks can be installed, especially at the pump, to absorb some of the pressure surge ahead of the PVC pipeline. Special valves can also be used to throttle the flow at the pump until pressure develops in the mainline. This prevents the pressure surge that occurs when flowing water reaches the end of an enclosed pipeline. These valves can also be adjusted to maintain a constant downstream pressure. This is useful when a reduced number of laterals are operated. The pressure control of the valve keeps the operating pressure of the pipeline within an acceptable range. Depending on the characteristics of the pump, the pressure ahead of control valves may rise to high levels when a small flow rate is pumped; therefore, variable speed pumps or other controls may be needed.
Lateral spacing is not contingent on the length of mainline pipes for permanent solid-set systems; therefore, the lateral spacing should align with farming equipment operation. One of the major inconveniences with solid-set systems is that you must farm around the risers. If the lateral spacing is adjusted to match typical or critical equipment width, then farming practices are easier.
Laterals must be designed to prevent frost damage. The laterals should be drained when cold weather threatens. Drain valves can be used to drain the pipelines every irrigation, but this may not be desirable, especially if the laterals and mainlines are large containing substantial amounts of water. In this case, a long time is required to drain the pipes and drainage accumulates at lower elevations along the lateral or mainline. Thus, a good deal of water drains, and wet areas can develop that are difficult to accommodate. An alternative is to use compressed air to force water out of the system. The end of the mainline and laterals can be equipped with a manual ball valve. The valve is shut when irrigating. The valve is opened when the pipeline is drained, then compressed air is supplied into the mainline. Water in the mainline can be expelled first. Then valves for the laterals are sequentially opened to force water from the laterals. Valves may be needed on some risers to prevent compressed air from bleeding through sprinklers on rolling terrain. Pipelines must also be installed deep enough so that farming operations do not either crush or damage the pipe while tilling. Any control or power cabling should be installed consistent with local codes.
Obviously, solid-set systems must be carefully designed and installed. An experienced designer should be employed for sophisticated systems. Intricate software programs are available to customize designs to local needs.
12.3.2 Management Problems
Management problems with solid-set systems are the same as for moved laterals. The spacing of sprinklers is too large for the selected sprinkler, the lateral is too long or small to meet pressure guidelines, etc. These are more difficult to correct for solid-set systems since the system is often installed below ground. However, solid-set systems are usually not limited by the set time or irrigation interval. So, sprinklers and nozzles can be changed to meet performance requirements and then the set time can be adjusted to provide the depth of water needed. Pressure regulators and flow control nozzles are still a viable option if changes are necessary.
Maintenance requirements for solid-set systems are more demanding than periodically moved systems. There are more electromechanical components in the system that periodically fail. The operator should conduct periodic inspections to ensure that the automatic system is working properly. This is critical because solid-set systems are often used on valuable crops where stress is expensive.
Many solid-set systems are connected to automatic controllers that allow producers to start the system anytime they desire. The controller must be programmed so that each lateral is operated at the desired time. Many controllers have more than one program that can be stored so that different depths can be easily applied. These functions work well. The controller can start irrigating any time on any day of the week without operator assistance. Unfortunately, this automatic operation is often not well linked with scheduling so that the system operates when it does not need to or does not operate when it is needed. Thus, systems have the potential for efficient operation if users take the time to learn how to operate the system and train assistants.
12.4 Guns
Large sprinklers called guns have been developed for stationary and moving irrigation systems. A gun has a single large diameter nozzle that discharges large flows and throws water long distances. Stand-alone guns can be portable or installed at a fixed site (Figure 12.14). Water can be supplied from buried pipelines with valves that allow the gun to be moved from riser to riser, or water can be supplied from portable pipes. Guns can be operated to provide overlap and uniform irrigation. In other cases, guns may be used for irregular areas where uniformity is a secondary objective.
Big guns are also useful for distribution of wastewater from animal feeding operations or effluent from processing centers. An example of animal wastewater application is illustrated in Figure 12.14d. Guns are well suited to wastewater application because the nozzle are large, high pressures are used and all discharge is through one nozzle, so the flow velocity remains high minimizing clogging or plugging.
The performance of Model 150 and 200 guns from Nelson Irrigation Corporation is listed in Table 12.6. The performance includes the discharge and wetted diameter for some nozzle sizes and a range of pressures. Three types of nozzles are included. Taper nozzles are shaped to minimize turbulence and provide high flows and large throw distances. The ring nozzle creates more turbulence which reduces flow and throw (Figure 12.15). A hybrid nozzle called the tapered-ring nozzle falls between the tapered and ring nozzles. The jet from a tapered nozzle does not break up as completely and provides larger droplets. Large droplets travel further and retain their velocity longer than small drops. This provides increased throw but also causes a donut pattern and compacts bare soils. Conversely, ring nozzles provide more breakup; thus, the wetted diameter is less than for tapered nozzle and the water application from ring nozzles is gentler. The discharge of the ring nozzle varies from 60 to 75% of the flow from the tapered nozzle. The wetted diameter of the ring nozzle is about 85% of that for the tapered nozzle (Figure 12.15).
Data in Table 12.6 show that the discharge ranges from 100 to over 1200 gpm from a single gun. Simultaneously the wetted diameter varies from 250 to over 600 feet depending on the nozzle size and operating pressure. Such a large operating range makes guns flexible and adaptable to many conditions. The large jet can compact bare soil surfaces and reduce infiltration rates. Energy in large drops moving at high velocity may cause leaf damage for sensitive plants. Operating pressures range from 50 to 130 psi making gun-based systems expensive to operate. These systems also experience significant pressure loss in conveyance systems because large flows must be delivered to the end of the supply pipeline. These systems also require pipe with higher pressure ratings which increases investment costs. Guns may apply water at high application rates that cause runoff and erosion, especially on steep slopes and clayey soils.
Figure 12.14. Illustration of gun sprinklers (photos a and b are courtesy of Nelson; photo c is courtesy of Wade Rain, Inc.).
Table 12.6. Performance of 150 and 200 guns from Nelson Irrigation Corp.
150 Series Big Guns—24° Trajectory^[a] 150 T Taper Bore Nozzles
Size: 0.7 in 0.8 in 0.9 in 1.0 in 1.1 in 1.2 in 1.3 in
Press. Flow Diam Flow Diam Flow Diam Flow Diam Flow Diam Flow Diam Flow Diam
(psi) (gpm) (ft.) (gpm) (ft.) (gpm) (ft.) (gpm) (ft.) (gpm) (ft.) (gpm) (ft.) (gpm) (ft.)
50 100 250 130 270 165 290 205 310 255 330 300 345 350 360
60 110 265 143 285 182 305 225 325 275 345 330 365 385 380
70 120 280 155 300 197 320 245 340 295 360 355 380 415 395
80 128 290 165 310 210 335 260 355 315 375 380 395 445 410
90 135 300 175 320 223 345 275 365 335 390 405 410 475 425
100 143 310 185 330 235 355 290 375 355 400 425 420 500 440
110 150 320 195 340 247 365 305 385 370 410 445 430 525 450
120 157 330 204 350 258 375 320 395 385 420 465 440 545 460
150 Series Big Guns—24° Trajectory^[a] 150 R Ring Nozzles
Size: 0.86 in 0.97 in 1.08 in 1.18 in 1.26 in 1.34 in 1.41 in
Press. Flow Diam Flow Diam Flow Diam Flow Diam Flow Diam Flow Diam Flow Diam
(psi) (gpm) (ft.) (gpm) (ft.) (gpm) (ft.) (gpm) (ft.) (gpm) (ft.) (gpm) (ft.) (gpm) (ft.)
50 100 245 130 265 165 285 205 300 255 320 300 335 350 350
60 110 260 143 280 182 300 225 315 275 335 330 350 385 365
70 120 270 155 290 197 310 245 330 295 350 355 365 415 380
80 128 280 165 300 210 320 260 340 315 360 380 380 445 395
90 135 290 175 310 223 330 275 350 335 370 405 390 475 405
100 143 300 185 320 235 340 290 360 355 380 425 400 500 415
110 150 310 195 330 247 350 305 370 370 390 445 410 525 425
120 157 315 204 335 258 360 320 380 385 400 465 420 545 435
200 Series Big Guns—27° Trajectory^[a] 200 T Taper Bore Nozzles
Size: 1.05 in 1.2 in 1.3 in 1.4 in 1.5 in 1.6 in 1.75 in 1.9 in
Press. Flow Diam Flow Diam Flow Diam Flow Diam Flow Diam Flow Diam Flow Diam Flow Diam
(psi) (gpm) (ft.) (gpm) (ft.) (gpm) (ft.) (gpm) (ft.) (gpm) (ft.) (gpm) (ft.) (gpm) (ft.) (gpm) (ft.)
60 250 345 330 375 385 390 440 410 515 430 585 445 695 470 825 495
70 270 360 355 395 415 410 480 430 555 450 630 465 755 495 890 515
80 290 375 380 410 445 430 515 450 590 470 675 485 805 515 950 535
90 310 390 405 425 475 445 545 465 625 485 715 505 855 535 1005 555
100 325 400 425 440 500 460 575 480 660 500 755 520 900 550 1060 575
110 340 410 445 450 525 470 605 495 695 515 790 535 945 565 1110 590
120 355 420 465 460 545 480 630 505 725 530 825 550 985 580 1160 605
130 370 425 485 465 565 485 655 515 755 540 860 560 1025 590 1210 620
200 Series Big Guns—27° Trajectory^[a] 200 R Ring Nozzles
Size: 1.29 in 1.46 in 1.56 in 1.66 in 1.74 in 1.83 in 1.93 in
Press. Flow Diam Flow Diam Flow Diam Flow Diam Flow Diam Flow Diam Flow Diam
(psi) (gpm) (ft.) (gpm) (ft.) (gpm) (ft.) (gpm) (ft.) (gpm) (ft.) (gpm) (ft.) (gpm) (ft.)
50 230 325 300 355 350 370 410 390 470 405 535 420 640 435
60 250 340 330 370 385 390 445 410 515 425 585 440 695 455
70 270 355 355 385 415 405 480 425 555 440 630 455 755 475
80 290 370 380 400 445 420 515 440 590 455 675 470 805 490
90 310 380 405 415 475 435 545 455 625 470 715 485 855 505
100 325 390 425 425 500 445 575 465 660 480 755 500 900 520
110 340 400 445 435 525 455 605 475 685 490 790 510 945 535
120 355 410 465 445 545 465 630 485 725 500 825 520 985 545
130 370 415 485 450 565 470 655 490 755 505 860 525 1025 550
^[a] The diameter of throw is approximately 2% less for the 24° trajectory angle and 5% less for the 21° trajectory angle.
Figure 12.15. Performance of types of nozzles for guns. (Data from Nelson Irrigation Corp.)
12.5 Travelers
Figure 12.16. Soft-hose traveler irrigation system. (Photos at top are courtesy of Yüzüak Irrigation Sprinklers.)
A semi-automated sprinkler system was developed in the 1960’s to reduce labor and to adjust application depths to match soil and crop requirements. The early versions consisted of rotating booms mounted on a cart that was periodically moved. That design was replaced with a towable cart that could be pulled continuously across the field to provide a moving sprinkler system. Initially the travelers were pulled by winding up cable on a cart. The other end of the cable was anchored at the end of the travel lane. Big guns were developed that operated at high pressures but could throw water hundreds of feet. Utilization of traveler systems has decreased in the United States to about 2% of the sprinkler irrigated land. However, systems are utilized more extensively internationally.
A modern cable-tow, or soft-hose, traveler is shown in Figure 12.16. Water is supplied to the traveler with a flexible hose, called a lay-flat hose. The hose is looped behind and to the side of the traveler when positioning the cart to the edge of the field. This avoids interference with the cart when moving toward the center of the field. This style of traveler is pulled by a winch that rolls cable from the field boundary toward an anchor—often the tractor used to reposition the cart for subsequent irrigations. The water source can also be in the middle of the field. This allows a hose that is half the length of the cable. The effective diameter of the cable reel increases as cable is rewound on the cart. This could cause variable speed of movement as the cart moves along the towpath. Special controls are used to vary the speed of the cable winch to provide uniform speed of travel. The traveler stops when it reaches the anchor point. The hose is then drained and rewound onto the hose reel. The cart is then located at the edge of the next towpath and the process repeats. Guns apply water beyond the edge of the traveler set as shown in Figure 12.16.
Figure 12.17. Hard-hose traveler diagram with photo of a traveler with a gun (photo a is courtesy of Cadman Power Equipment) and with large boom (photo b is courtesy of Bauer Group).
Later designs of travelers eliminated the cable and used a fortified hose to drag the sprinkler cart along the path (Figure 12.17). Hoses were designed to supply water to the cart and with enough tensile strength to pull the sprinkler cart through the field. This eliminates the need for a cable to move the gun through the field. The sprinkler cart is smaller than the cart for the soft-hose traveler; therefore, less effort is needed to move the gun across the field. These hoses are generally polyethylene and are referred to as hard hoses because they are quite rigid. Hose diameter can be as big as six inches and the length can be up to 2,000 feet; however, most systems use hose smaller than five inches. Manufacturer recommendations should be carefully followed when selecting the hose diameter and length to have adequate strength and to minimize friction loss. The hard-hose traveler requires less time to reposition to the next set than a soft-hose traveler because the hose is rewound onto the reel as the sprinkler cart is towed across the field. Additionally, the hard hose is not drained during rewinding which prevents the hose from collapsing as it is rewound onto the cart. The hose-reel cart is generally equipped with a lift to carry the sprinkler cart while repositioning the system or for storage. Once a set has been irrigated the sprinkler cart is lifted with the primary cart and the system is repositioned for the next set. In many cases the hose reel can be rotated in place to irrigate the set opposite of the one just completed. The host cart is slowly pulled from the hose reel to the far end when positioning for the next set. The diameter of the coiled hose on the reel increases as the hose is rewound, increasing the effective diameter of the hose reel. Just like with cable tow systems, the change of diameter can cause a variation of travel speed along the towpath; therefore, these travelers must adjust the speed of rotation of the reel to maintain a constant sprinkler cart velocity.
Recently a large boom has become available which replaces the big gun (Figure 12.17b). The advantage of the boom, which does not rotate, is that uniform application of water is more achievable, and less pressure is required to apply water across the set (Peters and McMoran, 2008). Friction loss in the hose remains the same as for a gun with equal flow; however, the operating pressure is less. Wind effects are also diminished with a boom configuration.
All travelers have slope limitations. Slope along the towpath changes the effort required to transport the gun. Slope perpendicular to the towpath may cause the cart to slide downslope. Slope also affects the acceptable application rate to avoid runoff. Manufacture recommendations should be followed regarding slope.
The traveler has little clearance and the hose and/or cable must be pulled across the soil surface. Therefore, the traveler operates along a travel lane. This is often a grass or alfalfa strip for row crops so that the hose can move easily.
The big gun does not make a complete circle during operation (Figure 12.18). The gun is designed to operate over an arc and then it automatically reverses to the starting position of the arc. The arc and starting position should be set according to the manufacturer's recommendations to provide uniform irrigation. If the arc is too large, excess water will be applied near the lane where the traveler is towed.
Figure 12.18. Operational characteristics of a big gun traveler.
12.5.1 Gun Performance
Efficient irrigation with travelers depends on understanding the characteristics of the moving gun. Table 12.6 lists the discharge and wetted diameter for guns with varying nozzle sizes and pressures. Certainly, these are important characteristics; however, the distribution of water about the gun is also critical. This distribution is affected by settings of the angles of operation for the gun as illustrated in Figure 12.18. The aerial view of the sprinkler pattern shows that two angles are involved. The gun begins rotation at the initial angle and progresses through the central angle. When the gun completes rotation through the central sector the gun reverses rotation. The reversal continues until it reaches the initial angle. The initial angle can be arbitrary relative to the line of travel. The central angle of the sector can be independently adjusted also. The water application process is complicated because the gun is moving at a relatively constant velocity. The plan view of the gun in Figure 12.18 includes two lines equidistant from the towpath. The initial angle was set so that the bottom portion of the circular sector, along line 1, receives more water than the area along line 2. The upper portion of the sector, along line 2, receives water about 60% of the time compared to line 1.
The water application rate for the gun is illustrated in the upper portion of Figure 12.18. Consider a point on each line. As the traveler moves the water pattern reaches the point on line 1 (at time t₁) earlier than line 2 (time t₂) because of the initial angle. After time t₂ the water application rate is the same for both points. The same amount of water is applied at each point after time t₂. However, the amount of water applied between time t₁ and t₂ (the unshaded portion of the application rate curve) enlarges the application at point 1 relative to point 2.
Ge et al. (2018) and Prado and Colombo (2020) analyzed the distribution of water for a pass of a traveling irrigation system using either a small or medium size gun (Figure 12.19). The depth of application was divided by the average depth applied for the ratio on the vertical axis. The distance perpendicular to the towpath was normalized by dividing the distance by the wetted radius of the gun. These authors estimated the distribution of water perpendicular to the towpath for one pass of a traveler irrigation system equipped with a small gun with a central angle of 270° and with a medium gun with a central angle of 270° and 320°. The initial angle was set so that the pattern was symmetrical about the towpath. So, the initial angle was 45° for central angles of 270°, and 20° for the 320° central angle. Results show that the application depth peaks about 45% of the wetted radius away from the gun. The patterns from these guns are similar. However, the 320° rotation applies more water near the gun than the same gun with a central angle or 270°. Some manufacturers recommend the central angle be between 220° and 320°. The central angle should be greater than 180° to maintain gun thrust so that the hose and/or cable rewind properly.
The uniformity of application in the field depends on overlapping the water distribution for two passes of the traveler. The degree of overlap depends on the wetted radius of the gun and the spacing between towpaths for the traveler. An example of the overlap for the medium sized gun with the central angle of 270° is shown in the lower portion of Figure 12.19. The dashed line on the left represents the application when the traveler makes one pass for the gun that has a wetted radius of 150 feet. The mirror image of the application occurs for the second pass as shown by the dash line on the right. In this case the spacing between paths and therefore the distance between guns during each pass is 260 feet. The percent overlap is the ratio of the spacing of the towpath relative to the wetter diameter of the gun. In this case the towpath spacing is 260 feet and the wetted diameter of the gun is 300 feet; therefore, the percent overlap is 87%. The blue dots in the diagram represent the depth of water applied as result of overlapping the distribution from each pass of the traveler. The distribution is reasonably uniform. All water comes from the first pass for the first 110 feet, and all water comes from the second pass from 150 to 260 feet. The patterns overlap from 110 feet to 150 feet, so the depths are added for this region. The average depth of application after overlapping was 0.7 inches and the uniformity coefficient which was 91 which is good.
These results were based upon computer simulation for low wind speeds. The authors simulated windy conditions, but those results are site specific. In lieu of predicting the distribution pattern for each traveler and gun configuration, general recommendations have been made for the maximum spacing between towpaths based on the wetted diameter of the gun and the prevailing wind speed (Table 12.7). The recommended maximum spacing for a gun with a wetted diameter of 300 feet under no wind conditions is 240 feet or 80% of the wetted diameter from Table 12.7. Wind distorts the water distribution pattern for sprinklers and especially for guns which throw water high into the air for hundreds of feet. Thus, as the wind speed increases the amount of overlap must increase to maintain uniformity as illustrated in Table 12.7. For example, if wind speeds are over 10 mph, Table 12.7 recommends that the maximum path spacing would be 50% of the wetted diameter of the gun. Therefore, the maximum spacing in windy conditions would be 150 feet for the gun in Figure 12.19.
Figure 12.19. Distribution of water from a single pass of a traveler for three types of gun settings, and the overlapped patterns for the medium size gun with a central angle of 270°. Based on data from Ge et al. (2018) and Prado and Colombo (2020).
Table 12.7. Maximum spacing for traveler irrigation systems for ring nozzles (smaller percentages) and tapered nozzles (larger percentages) based on guidelines from USDA-NRCS (2016).
Sprinkler
Wetted
Diameter(ft) Percent of Wetted Diameter
50 55 60 65 70 75 80
Wind over 10 mph Wind up to 10 mph Wind up to 5 mph No Wind
Spacing (ft)
200 100 110 120 130 140 150 160
250 125 137 150 162 175 187 200
300 150 165 180 195 210 225 240
350 175 192 210 227 245 262 280
400 200 220 240 260 280 300 320
450 225 248 270 292 315 338 360
500 250 275 300 325 350 375 400
550 275 302 330 358 385 412 440
600 300 330 360 390 420 - -
12.5.2 Field Layout
Water application with travelers can be uniform if properly designed and operated. The traveler constantly moves which reduces areas of high or low application that can occur with stationary sprinklers. A gun must be selected that provides the required diameter of coverage for the layout of the sets and local wind conditions. Sets need to be spaced so that they evenly fit within the field boundaries. A final set that is a fraction of the width of other sets should be avoided since this area is difficult to irrigate with travelers. If narrow sets are required, it is best to locate them in the interior of the field because conflicts can arise when guns operate on a narrow set at the edge of a property.
The location of travel lanes and the mainline are the most critical aspects of the layout. The field should be divided into sets of equal width as shown in Figure 12.20. The set is the area located on either side of a travel lane which is in the center of the set. The 80-acre field in Figure 12.20 requires five sets across the field width. The field was also divided down the middle where the mainline is located, so ten total sets are required. Fields are typically split with the mainline in the center of the field so that the traveler can operate from the field edge back toward the mainline. This minimizes the length of hard hose needed for the traveler.
After the set width has been determined the width should be compared to spacing limitations from Table 12.7. The gun in Figure 12.20 has a wetted diameter of 440 feet and the path width is 264 feet. This provides 88 feet of overlap along each side of the towpath. The overlap area would then be 176 feet wide. The ratio of the tow lane spacing to the wetted diameter of the gun is 60% (i.e., 264 ÷ 440) which is adequate for wind speeds up to 10 mph in Table 12.7.
Travelers apply water beyond the area intended for irrigation as represented by the green areas on the right side of Figure 12.20. Water will be applied well beyond the boundary of the field along all edges. This may not be acceptable to neighbors or the public if a road lies along the property. The angle of operation of the gun can be changed to reduce overthrow along field edges in the direction of travel. This maintains uniformity for the edge sets but will increase the application rate so the speed of travel would need to increase for field uniformity.
Travelers throw water beyond the ends of the field. There is also a deficit area near each end of the towpath because the wetted pattern cannot fully pass over those areas without throwing water long distances beyond the field boundary. Small dry areas also occur if the traveler is stopped exactly at the center of the field. If the hose reel can be moved beyond the centerline the dry areas could be reduced. If water cannot be thrown beyond the ends of the lane, then the traveler should be positioned further into the field which causes larger deficit zones along the ends of the field.
The traveler is flexible as it can irrigate many shapes of fields. The length of the towpath can be adjusted to match fields with variable boundaries. The traveler shuts off automatically when it returns to the hose reel; thus, variable operation times are possible for irregular lengths of lanes.
Figure 12.20. Layout for eighty-acre field irrigated with a traveler.
Traveler systems can only pull a maximum length of hose. The length depends on the model of traveler, the type and size of hose, and the type of movement system (cable or hose reel). Typical characteristics for cable-tow traveler systems for the southeastern area of the United States are listed in Table 12.8. These results assume that the travel lane can be twice the length of lay-flat soft hose. The capacity listed in Table 12.8 is based on approximately five gpm/acre which may be insufficient in more arid regions. Manufacturer specifications should be used for specific conditions and designs.
Table 12.8. Typical characteristics for cable-tow traveler irrigation system from Harrison et al. (2015).
HoseDiameter(in) HoseLength(ft) Maximum TravelDistance(ft) MaximumCapacity(gpm) Maximum IrrigatedArea(acres) Sprinkler Pressure(psi) TypicalLaneSpacing(ft) AreaCoveredper Pass(acres) MaximumHose Pull Range(lbs)
2.5 660 1,320 165 33 60–70 180 5.5 1,300–1,900
3 330 660 250 50 70–80 210 3.2 1,000–1,500
3 660 1,320 250 50 70–80 210 6.4 2,000–3,000
3.5 660 1,320 375 75 80–90 240 7.3 3,000–4,000
4 660 1,320 535 107 90–100 300 9.1 3,500–5,000
4 1,320 2640 535 107 90–100 300 18.2 7,000–10,000
4.5 660 1,320 730 145 90–100 300 9.1 4,000–6,000
4.5 990 1,980 730 145 90–100 300 13.6 6,000–9,000
4.5 1,320 2,640 730 145 90–100 300 18.2 8,000–12,000
5 660 1,320 960 192 100–120 330 10 5,000–7,000
12.5.3 Operational Characteristics
The depth of water applied with a traveler can be computed by:
(12.11)
where: d_g= average depth of application (in),
q_s = discharge from the gun (gpm),
T_o = time of operation for one lane (hr),
W_p = width of the travel lanes = set width (ft),
L_l = length of the travel lane (ft), and
v_t = speed of travel of the traveler (ft/hr).
The speed of travel is v_t = L_l / T_o which is represented in equation 12.11. Most travelers are designed to allow several specific speeds of travel or a variable range of speeds which allows a range of application depths.
The average rate of water application is given by:
(12.12)
where: A_r = average application rate (in/hr),
q_s = discharge from the traveler gun, (gpm),
W_r = wetted radius of gun, (ft), and
ß = central angle of gun operation (degrees).
Consider the following example.
The flow rate needed for the traveler (q_s) is determined by revising Equation 11.14 to:
(12.13)
where: C_n = net system capacity requirement (gpm/ac),
E_a = application efficiency (decimal fraction),
W_p = width of the travel path (ft),
L_l = Length of the travel length (ft),
Ns = number of sets in the field,
N_t = number of travelers used,
T_s = set time between moving traveler to next travel lane (hr),
T_o = time of operation, i.e., time water is applied for the travel lane (hr),
I_i = irrigation interval (time between irrigations of the field) (days), and
T_d = down time between irrigations (days).
Equation 12.13 is applied to the system in Figure 12.20 in the following example.
Table 12.9. Pressure loss (psi/100 ft) for lay-flat hose when operated at 100 psi (USDA-NRCS, 2016).
Flow(gpm) Nominal Inside Diameter (in)
2.5 3 4 4.5 5
100 1.6 - - - -
150 3.4 1.4 - - -
200 5.6 2.4 - - -
250 - 3.6 0.9 - -
300 - 5.1 1.3 0.6 -
400 - - 2.3 1.3 -
500 - - 3.5 2.1 1.1
600 - - 4.9 2.7 1.6
700 - - - 3.6 2.1
800 - - - 4.6 2.7
900 - - - - 3.4
1000 - - - - 4.2
Table 12.10. Friction loss in hard hose, psi/100 ft (Hazen-Williams resistance coefficient = 150).
Flow
(gpm) Hose Inside Diameter (in)
2.5 2.7 3.0 3.3 3.7 4.0 4.5 5.0
75 1.45 1.00 0.60 - - - - -
100 2.48 1.70 1.02 0.64 - - - -
125 3.74 2.57 1.54 0.97 0.56 - - -
150 5.24 3.61 2.16 1.36 0.78 0.53 -
175 6.98 4.80 2.87 1.81 1.04 0.71 0.40 -
200 8.94 6.14 3.68 2.31 1.33 0.91 0.51 0.31
250 - 9.29 5.56 3.50 2.00 1.37 0.77 0.46
300 - - 7.80 4.90 2.81 1.92 1.08 0.65
350 - - 10.37 6.52 3.74 2.56 1.44 0.86
400 - - - 8.35 4.79 3.28 1.85 1.11
450 - - - - 5.95 4.07 2.30 1.38
500 - - - - - 4.95 2.79 1.67
550 - - - - - 5.91 3.33 1.99
600 - - - - - - 3.91 2.34
650 - - - - - - 4.54 2.72
700 - - - - - - 5.21 3.12
750 - - - - - - - 3.54
800 - - - - - - - 3.99
The pressure loss in the hoses used to supply travelers can be quite high due to the use of hoses that are relatively small for the required flow rates. Small hoses are used because large diameter hoses are harder to pull and much more expensive. The friction loss for a range of diameters of hose and flow rates is given in Table 12.9 and 12.10. Friction loss for the lay-flat used with a cable-tow traveler is shown in Table 12.9. The diameter of lay-flat hose varies depending on the pressure. Values in Table 12.9 are for a tube pressure of about 100 psi. Comparison of losses for hard hoses is slightly higher than for lay-flat hoses. However, hard hose systems are by far the most common system today.
Pressure losses in the sprinkler cart must be computed. The pressure loss in the traveler depends on the flow rate, speed of travel, type of power unit, and machine design. Performance for a specific machine must be obtained from the manufacturer. Some travelers use water pressure through a turbine to power the hose reel to rewind the hard hose. Other systems use an engine to power the reel. About ten psi is required to power the turbine.
Figure 12.21. Pressure versus discharge and friction loss relationships for a traveler with a 1.83-inch nozzle.
The pressure and discharge relationships for a typical traveler powered with a turbine is shown in Figure 12.21. The upper portion of the figure shows the pressure discharge relationships for the 1.83-inch nozzle used with the gun and the input pressure required for a given discharge from the traveler—developed from manufacturer’s data. The difference in the pressure between the nozzle and inlet to the hose reel for the same discharge represents the friction loss in the hose reel, turbine, hard hose, and the sprinkler cart. The pressure loss is quite substantial for travelers. The pressure requirement of the traveler is significant, so operating costs for travelers are high. The lower portion of Figure 12.21 shows the friction loss in the 4.5-inch hard hose and the cart and the reel system with a turbine powered traveler. Most of the loss occurs in the hose, especially at high flow rates.
12.5.4 Management
As with other systems, management should start with an assessment of the properties of the existing system and then evaluation of the characteristics of the system compared to crop water needs and guidelines for efficient irrigation with traveler systems. The Traveler Management Spreadsheet is shown on Figure 12.22. This analysis is based on the traveler depicted in Figure 12.20. The 80-acre field was divided into towpaths (sets) that are 1300 feet long and 264 feet wide. This allows 40 ft in the middle of the field to rotate the traveler to irrigate the alternate side of the field and gives an irrigated area of 78.8 acres. The traveler will be posi-
Figure 12.22. Traveler Management Spreadsheet for traveler irrigation systems.
tioned 88 feet from the field boundary when starting a set. The layout provides substantial overspray which assumes that transboundary conflicts are immaterial. This layout provides five sets on each side of the mainline that fits the field boundary.
The characteristics of the traveler are based on an actual model available from a manufacturer. This system uses a 4.5-inch inside diameter hard hose that is 1250 feet long. This provides the ability to irrigate a length of up to 1,338 feet (1250 + 88). The traveler used a water turbine to recoil the hose and the gun was set to a central angle of 270 degrees. The nozzle is about 9 ft above the ground. The elevation at the west end of the lane is 8 ft higher than the mainline. The manufacturer shows that the pressure at the inlet to the hose reel should be 126 psi to produce 60 psi to the gun nozzle. The wetted radius of this gun and nozzle configuration is 220 feet (440-ft wetted diameter). The application provides 88 feet of overlap on each side of the set when the set width is 264 feet, and the wetted diameter is 440 feet. The gun discharge computed from equation 12.14 for a nozzle pressure of 60 psi is 584 gpm for this nozzle and gun.
(12.14)
where: q_s = gun discharge, gpm
C_d = discharge coefficient,
a = pressure exponent when pressure is in psi, and
b = the nozzle diameter exponent when the size is in inches.
As listed in Figure 12.22 the discharge coefficient was 16.0, and exponents a and b are 0.50 and 2.566 respectively for this gun and nozzle.
The average wind speed at this location was listed as 7 mph. The maximum set width for this wind speed is given as 65% of the wetted diameter of the gun in Table 12.7. Since the wetted diameter is 440 feet the maximum width is 286 feet. The actual set width of 264 feet is 60% of the wetted diameter which is less than the maximum. Most of the rest of the inputs and operational results have been discussed.
The soil and plant information for the management variables are the same as for the moved lateral systems. The time inputs are as previously discussed. This combination results in a down time of approximately 17%. The irrigation interval is 5.5 days since there are ten sets and two sets are irrigated a day, plus one-half of a day is needed to reposition the traveler. The velocity of travel, application rate and gross depth were computed in previous examples. The net irrigation depth is the product of the gross irrigation depth and the application efficiency giving a net depth of 1.45 inches. The 1.45-inch net depth would support a net crop water use rate of 0.26 in/d over the 5.5-day irrigation interval. This capacity should be compared to regional needs. The data in Figure 12.22 summarizes the capability of the traveler and the outcome of management choices for this field. It also illustrates critical issues for travelers.
Computer simulation programs have been developed to predict the performance of traveler systems. Programs such as that by Rolim and Teixeira (2016) or Smith et al. (2008) can be used to design and evaluate traveler systems and as decision support systems to enhance management. Those resources should be examined for advanced management.
12.5.5 Other Issues
Areas at the ends of the towpaths receive less water than in the middle of the field. These deficits occur because the entire water pattern cannot traverse these areas due to boundary limitation as illustrated in Figure 12.20. Some operators adapt to this issue by leaving the traveler stationary for a period before starting movement of the traveler when irrigating. This will reduce the deficit but results in deep percolation in areas that are watered while the traveler is stationary and receive a full pass of the water pattern.
Uniformity issues due to set widths that exceed recommendations for windy conditions may require system modifications. Towpath spacing does not need to be permanent. If travel lanes are too far apart, they can be changed after harvesting the current crop. Modifications may be needed if mainline risers are at the wrong location, but this is not particularly troublesome. Excessive wind drift may result because towpath spacings are too far apart. Wind drift problems can be partially alleviated by altering the time of day that irrigation is started on the field. Usually, winds are highest during the day. When 12-hour set times are used, the starting time for irrigating the field can be altered by half a day each irrigation so that a set irrigated during the day one irrigation and is irrigated at night the next irrigation.
The speed of travel along the towpath may vary for several reasons. The effective diameter of the reel used to rewind cable or hose increases as more material is pulled in. If the rotation speed of the reel is the same, then the traveler will speed up as more cable or hose is rewound. This use to be a major problem with earlier designs but has been mostly assuaged in modern systems. The amount of drag for soft hoses increases as the traveler moves toward the anchor point. Resistance increases with length so the travel speed may decrease as more power is needed as the length of towed hose increases. The inverse occurs with hard hose systems as the maximum length of towed hose is largest at the start of the set. Rolling terrain also contributes to uneven drag of on the hose. Increased drag exerts more stress on the reel system and can slow rotation due the increased load.
Mainline operation and protection can be troublesome for travelers. Travelers require high operating pressures. Since there is only one sprinkler per lateral pressures increase rapidly when the system is started. This can lead to high pressure surges. The mainline needs to be protected from pressure surges as described for solid-set systems. Valves can be used with electrically powered pumps to prevent the surge. Internal combustion engine powered pumps can be started at a slow speed to minimize the pressure surge.
Safety is more of a concern with travelers than moved-lateral systems. The high pressure required of these systems poses some threat if proper operations are not followed. The large diameter hoses are difficult to move and may require assistance to prevent injury. There are many moving parts on the traveler where operators could become entangled. Safety shields and proper operation and maintenance are required to maintain a safe machine. A unique feature of travelers is that water is propelled great distances from the machine. Research has shown that if the water jet impinges on electrical power lines, some current can be transmitted back to the traveler. This, of course, poses severe safety concerns and should be unconditionally avoided.
12.6 Summary
This chapter describes the characteristics and operational requirements for moved-lateral irrigation systems which includes hand-move, tow-line, and side-roll systems. Solid-set, stationary gun-based systems, and travelers are also discussed. These systems collectively represent about 15% of the irrigated area in the United States in 2018. So, while the extent is not large, they still represented significant areas of irrigated land in the United States and a much more significant footprint around the world. Management of these systems requires a thorough understanding of their attributes, familiarity with the operational characteristics including the friction loss, discharge, overlap, and soil-plant interactions.
The focus of this text is on management of systems therefore little emphasis is placed on designing systems. However, the characteristics of the system related to the design must be understood for proper management. The initial step in developing a management plan is to describe the field layout of the system. Then the current conditions of the irrigation system must be inventoried and analyzed. The performance of the system should then be computed to ensure the system will meet acceptable management and industry guidelines. Finally, a management plan should be developed to operate the system to meet current crop soil and environmental demands. There is also discussion about monitoring of existing systems to ensure that they are performing as expected from the analysis.
Questions
1. Describe the advantages and disadvantages of hand-move, towline, and side-roll irrigation systems. Discuss any issues that would limit the adequacy at these types of systems.
2. Discuss two of the general management problems associated with moved lateral irrigation systems (e.g., side-roll, hand-move, towline).
3. Determine the required set time for a side-roll irrigation system with the following characteristics:
Spacing along the lateral is 40 ft.
Spacing along the mainline 60 ft.
Sprinkler discharge is 8 gallons per minute.
Application efficiency is 75%.
Soil water depletion at irrigation is 2 ¹/₂ in.
4. A tow-line irrigation lateral has a sprinkler spacing of 40 ft. The spacing between adjacent positions for the lateral is 70 ft. The diameter of coverage (d_c) for the sprinklers is 103 ft, and the average wind speed is 7 miles per hour. Is the sprinkler spacing and distance between laterals acceptable for good water distribution?
5. Determine the maximum acceptable irrigation interval for a silty clay loam soil where the root depth is 4 feet deep, f_dc is 45% and the anticipated net crop water used rate is 0.3 in/day.
6. Determine how the management plan would change in Figure 12.7 for a crop that had a root depth of 2.5 ft and the soil was a sandy loam soil.
7. How would you change the orientation of the mainline and laterals in Figures 12.6 and 12.7 if three laterals were required for the field? What sizes of mainline would you recommend and what total length of pipe would be needed to minimize investment cost?
8. A lateral in an existing solid-set irrigation system consists of 2½-inch PVC pipe that runs up a hillside with a 2% slope. Sprinklers are 30 feet apart on the 600-ft long lateral. Impact sprinklers with a single ³/₁₆-inch nozzle are used. The design called for an average nozzle pressure of 55 psi. Your client has complained about dry areas at the distal end of the lateral.
a. Do you expect uniformity to be an issue with this system?
b. How could pressure regulators be used to improve uniformity? Where would you put them and how many would you recommend?
c. Suppose you decided to change nozzles in the lateral to achieve acceptable uniformity without regulators. What size of nozzle would you recommend at the distal end of the lateral?
9. The gun on a traveler irrigation system discharges 400 gpm and the towpath spacing is 240 feet.
a. What travel velocity is required to apply a gross depth of 2 inches?
b. What is the application rate if the wetted radius of the gun is 200 ft?
10. How many gallons of diesel fuel are required to apply an acre-inch of water with the traveler system shown in Figure 12.22?
11. The design net system capacity (C_n) for a moved-lateral irrigation system on an alfalfa field is 0.21 in/d. The system is moved every 12 hr (set time = T_s = 12 hr), with downtime to move the system being 1 hr. Downtime allowed for harvesting alfalfa is 10%. The E_LQ is 75% (allows for 10% drift & evaporation; assumes no runoff). Determine the gross system capacity (C_g) in gpm. If the area of the field is 33 ac, what is the minimum flow rate (Q_min) needed for the system?
12. Your client purchased a field identical to the one in Figure 12.6, except the soil is a silt loam and the field has a hard-hose traveler. The traveler has the characteristics listed below. You will need to determine mainline orientation and size, length and width of towpath, and times for management. Justify any additional assumptions you require.
a. Develop a traveler management spreadsheet and plan for the field.
b. Discuss any issues you foresee for this field and propose solutions as needed.
Traveler and field characteristics are as follows:
The soil is predominately silt loam.
A hard hose traveler uses a 1.46-inch diameter nozzle operated at 60 psi.
Characteristics of the gun are available from Table 12.6.
Parameters for gun discharge equation are C_d = 15.97, a = 0.50, and b = 2.586.
The inlet pressure for the hose reel should be 104 psi for 60 psi at the nozzle.
Hard hose is 1320 feet long.
Cart and turbine losses as a function of flow can de determine from Figure 12.21.
The irrigator plans to irrigate field beans with a root depth of 3.5 feet and and critical depletion fraction of 45%.
References
Davis, S. L., & D. Dukes, M. D. (2016). Importance of ET controller program settings on water conservation potential. Appl. Eng. Agric., 32(2), 251-262.
Ge, M., Wu, P., Zhu, D., & Zhang, L. (2018). Analysis of kinetic energy distribution of big gun sprinkler applied to continuous moving hose-drawn traveler. Agric. Water Manag., 201, 118-132.
Haghverdi, A., Singh, A., Sapkota, A., Reiter, M., & Ghodsi, S. (2021). Developing irrigation water conservation strategies for hybrid bermudagrass using an evapotranspiration-based smart irrigation controller in inland southern California. Agric. Water Manag., 245, 106586.
Harrison, K., Porter, W. M., & Perry, C. (2015). Factors to consider in selecting a farm irrigation system. University of Georgia Ext. Bull. 882. 1-12.
Keller, J., & Bliesner, R. D. (1990). Sprinkle and trickle irrigation. Van Nostrand Reinhold Publ.
Merriam, J. L., & Keller, J. (1978). Farm irrigation systems evaluation. Logan: Utah State University.
Morgan, R. M. (1993). Water and the land: A history of American irrigation. Fairfax, VA: Irrigation Association.
Peters, R. T., & McMoran, D. (2008). Boom-type carts vs. big-guns in northwestern Washington. Proc. Int. Irrigation Show, (pp. 27-38).
Prado, G. D., & Colombo, A. (2020). Asymmetric wetted sector angle in water distribution of traveling gun irrigation systems. Engenharia Agricola, 40(4), 443-452.
Rolim, J., & Teixeira, J. L. (2016). The design and evaluation of travelling gun irrigation systems: Enrolador software. Engenharia Agricola, 36(5), 917-927.
Smith, R. J., Gillies, M. H., Newell, G., & Foley, J. P. (2008). A decision support model for travelling gun irrigation machines. Biosyst. Eng., 100(1), 126-136.
Stetson, L. E., & Mecham, B. Q. (2011). Irrigation (6th ed.). Falls Church, VA: Irrigation Association.
Turner, J. H., & Anderson, C. L. (1980). Planning for an irrigation system (2nd ed.). Athens, GA: American Association for Vocational Instructional Materials.
USDA-NRCS. (2016). Sprinkler irrigation. Chapter 11 in Part 623 National engineering handbook. Washington, DC: USDA-NRCS.
USDA (2019). 2018 Irrigation and water management survey. Vol. 3. Special Studies, Part 1. AC-17-SS-1. Washington, DC: USDA.

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Table 12.1. Data on sprinkler irrigation from USDA (2019).
Type ofSprinkler System	Number of Farms	Total Area(acres)	Acres per Farm	Percent ofSprinkler Area
Center Pivot	49,923	26,800,613	537	85%
Side Roll	16,130	1,788,443	109	6%
Solid Set	18,216	1,206,860	66	4%
Traveler	7,518	596,059	79	2%
Linear Move	3,669	469,408	122	1%
Other	8,673	401,318	46	1%
Hand Move	22,266	394,194	17	1%
Total	126,395	31,656,895		100%

Table 12.2. Rank of top ten states for each type of periodically moved system (data from USDA, 2019).
Rank	Side Roll		Hand Move		Solid Set		Big Gun
Rank	State	Acres	State	Acres	State	Acres	State	Acres
1	Idaho	406,429	Oregon	115,405	California	454,924	Oregon	112,182
2	Utah	258,816	Idaho	73,733	Washington	253,939	Michigan	61,636
3	Montana	198,603	California	50,262	Oregon	88,463	Washington	48,632
4	Oregon	196,155	Washington	44,429	Arizona	58,051	Georgia	43,631
5	Texas	86,163	Montana	33,825	Idaho	46,463	Texas	36,217
6	California	83,396	Utah	13,745	Florida	42,564	Florida	31,256
7	Washington	82,373	Colorado	6,973	Texas	38,368	Missouri	24,766
8	Colorado	79,972	Texas	6,714	Wisconsin	34,903	California	24,433
9	Illinois	42,338	Wyoming	6,548	Georgia	29,471	New Jersey	22,336
10	Wyoming	36,645	New Jersey	5,106	Michigan	18,995	N. Carolina	21,305

Table 12.3. Depth of water applied per hour (i.e., the application rate), (in/hr).
Lateral Spacing, S_L (ft)	Spacing Along Mainline, S_m (ft)	Representative Area, S_L x S_m(ft²)	Sprinkler Discharge, q_s (gpm)
Lateral Spacing, S_L (ft)	Spacing Along Mainline, S_m (ft)	Representative Area, S_L x S_m(ft²)	4	6	8	10	12	15	20	25
20	40	800	0.48	0.72	0.96	1.20	1.44	1.81
30	40	1200	0.32	0.48	0.64	0.80	0.96	1.20	1.61
40	40	1600	0.24	0.36	0.48	0.60	0.72	0.90	1.20	1.50
20	50	1000	0.39	0.58	0.77	0.96	1.16	1.44	1.93
30	50	1500	0.26	0.39	0.51	0.64	0.77	0.96	1.28	1.61
40	50	2000	0.19	0.29	0.39	0.48	0.58	0.72	0.96	1.20
50	50	2500	0.15	0.23	0.31	0.39	0.46	0.58	0.77	0.96
20	60	1200	0.32	0.48	0.64	0.80	0.96	1.20	1.61
30	60	1800	0.21	0.32	0.43	0.54	0.64	0.80	1.07	1.34
40	60	2400	0.16	0.24	0.32	0.40	0.48	0.60	0.80	1.00
50	60	3000	0.13	0.19	0.26	0.32	0.39	0.48	0.64	0.80
60	60	3600	0.11	0.16	0.21	0.27	0.32	0.40	0.54	0.67
30	70	2100	0.18	0.28	0.37	0.46	0.55	0.69	0.92	1.15
40	70	2800	0.14	0.21	0.28	0.34	0.41	0.52	0.69	0.86
50	70	3500	0.11	0.17	0.22	0.28	0.33	0.41	0.55	0.69
60	70	4200	0.09	0.14	0.18	0.23	0.28	0.34	0.46	0.57
70	70	4900		0.12	0.16	0.20	0.24	0.29	0.39	0.49
40	80	3200	0.12	0.18	0.24	0.30	0.36	0.45	0.60	0.75
50	80	4000	0.10	0.14	0.19	0.24	0.29	0.36	0.48	0.60
60	80	4800		0.12	0.16	0.20	0.24	0.30	0.40	0.50
70	80	5600		0.10	0.14	0.17	0.21	0.26	0.34	0.43
80	80	6400		0.09	0.12	0.15	0.18	0.23	0.30	0.38

Table 12.4. Comparison of sprinkler lateral performance with and without regulators.
Values	LateralPressure (psi)	NozzlePressure (psi)	SprinklerDischarge(gpm)
Performance—No Regulators
Maximum	49.7	47.6	10.96
Minimum	35.0	32.8	9.11
Average	38.8	36.7	9.62
Variation	14.7	14.7	1.85
Percent variation	38%	40%	19%
Performance—With Regulators for First 10 Sprinklers
Maximum	49.4	37.7	9.76
Minimum	35.0	32.8	9.11
Average	38.8	34.3	9.32
Variation	14.4	4.9	0.65
Percent variation	37%	14%	7%

Table 12.5. Results of catch can evaluation for an example system. Red and blue cells are used in example.
Diameter of Top of Can (in) = 4				Area of Container (cm²) = (6.452 p D²/4) = 81.08
Distance North of Central Sprinkler (ft)	Distance East of Central Sprinkler (ft)
	-35	-25	-15	-5	5	15	25	35
	Volume of Water Caught (cm³)
65	23	20	19	23	24	19	18	22
55	76	63	60	73	76	61	58	70
45	118	98	94	114	119	94	90	109
35	160	134	127	154	161	128	123	147
25	191	160	153	185	193	153	147	176
15	212	177	169	205	214	170	163	196
5	233	195	186	225	235	187	179	215
-5	210	176	167	203	212	168	161	194
-15	191	160	152	184	192	154	147	176
-25	163	136	129	156	163	132	125	149
-35	112	93	87	105	111	93	87	100
-45	50	40	35	43	47	45	39	41
-55	22	17	12	15	19	23	18	14
-65	0	0	0	0	0	0	0	0
	Depth of Water Applied (in)
65	0.11	0.10	0.09	0.11	0.12	0.09	0.09	0.11
55	0.37	0.31	0.29	0.35	0.37	0.30	0.28	0.34
45	0.57	0.48	0.46	0.55	0.58	0.46	0.44	0.53
35	0.78	0.65	0.62	0.75	0.78	0.62	0.60	0.71
25	0.93	0.78	0.74	0.90	0.94	0.74	0.71	0.85
15	1.03	0.86	0.82	1.00	1.04	0.83	0.79	0.95
5	1.13	0.95	0.90	1.09	1.14	0.91	0.87	1.04
-5	1.02	0.85	0.81	0.99	1.03	0.82	0.78	0.94
-15	0.93	0.78	0.74	0.89	0.93	0.75	0.71	0.85
-25	0.79	0.66	0.63	0.76	0.79	0.64	0.61	0.72
-35	0.54	0.45	0.42	0.51	0.54	0.45	0.42	0.49
-45	0.24	0.19	0.17	0.21	0.23	0.22	0.19	0.20
-55	0.11	0.08	0.06	0.07	0.09	0.11	0.09	0.07
-65	0.00	0.00	0.00	0.00	0.00	0.00	0.00	0.00
	Overlapped Depth for the Three Sets (in)
55	1.39	1.16	1.10	1.34	1.40	1.11	1.06	1.28
45	1.50	1.25	1.19	1.45	1.51	1.20	1.15	1.38
35	1.57	1.31	1.24	1.51	1.57	1.26	1.20	1.44
25	1.47	1.23	1.17	1.41	1.48	1.19	1.14	1.34
15	1.27	1.05	0.99	1.20	1.27	1.04	0.98	1.15
5	1.35	1.13	1.05	1.28	1.35	1.11	1.04	1.22
	Absolute Deviation from Mean Depth (in)
55	0.13	0.10	0.16	0.08	0.14	0.15	0.20	0.02
45	0.24	0.01	0.07	0.19	0.25	0.06	0.11	0.12
35	0.31	0.05	0.02	0.24	0.31	0.00	0.06	0.18
25	0.21	0.03	0.10	0.15	0.22	0.07	0.12	0.08
15	0.01	0.21	0.27	0.06	0.01	0.22	0.28	0.11
5	0.09	0.13	0.21	0.02	0.09	0.15	0.22	0.04
					Coefficient of Uniformity = 90

Table 12.6. Performance of 150 and 200 guns from Nelson Irrigation Corp.
150 Series Big Guns—24° Trajectory^[a]									150 T Taper Bore Nozzles
Size:	0.7 in		0.8 in		0.9 in		1.0 in		1.1 in		1.2 in		1.3 in
Press.	Flow	Diam	Flow	Diam	Flow	Diam	Flow	Diam	Flow	Diam	Flow	Diam	Flow	Diam
(psi)	(gpm)	(ft.)	(gpm)	(ft.)	(gpm)	(ft.)	(gpm)	(ft.)	(gpm)	(ft.)	(gpm)	(ft.)	(gpm)	(ft.)
50	100	250	130	270	165	290	205	310	255	330	300	345	350	360
60	110	265	143	285	182	305	225	325	275	345	330	365	385	380
70	120	280	155	300	197	320	245	340	295	360	355	380	415	395
80	128	290	165	310	210	335	260	355	315	375	380	395	445	410
90	135	300	175	320	223	345	275	365	335	390	405	410	475	425
100	143	310	185	330	235	355	290	375	355	400	425	420	500	440
110	150	320	195	340	247	365	305	385	370	410	445	430	525	450
120	157	330	204	350	258	375	320	395	385	420	465	440	545	460
150 Series Big Guns—24° Trajectory^[a]									150 R Ring Nozzles
Size:	0.86 in		0.97 in		1.08 in		1.18 in		1.26 in		1.34 in		1.41 in
Press.	Flow	Diam	Flow	Diam	Flow	Diam	Flow	Diam	Flow	Diam	Flow	Diam	Flow	Diam
(psi)	(gpm)	(ft.)	(gpm)	(ft.)	(gpm)	(ft.)	(gpm)	(ft.)	(gpm)	(ft.)	(gpm)	(ft.)	(gpm)	(ft.)
50	100	245	130	265	165	285	205	300	255	320	300	335	350	350
60	110	260	143	280	182	300	225	315	275	335	330	350	385	365
70	120	270	155	290	197	310	245	330	295	350	355	365	415	380
80	128	280	165	300	210	320	260	340	315	360	380	380	445	395
90	135	290	175	310	223	330	275	350	335	370	405	390	475	405
100	143	300	185	320	235	340	290	360	355	380	425	400	500	415
110	150	310	195	330	247	350	305	370	370	390	445	410	525	425
120	157	315	204	335	258	360	320	380	385	400	465	420	545	435
200 Series Big Guns—27° Trajectory^[a]									200 T Taper Bore Nozzles
Size:	1.05 in		1.2 in		1.3 in		1.4 in		1.5 in		1.6 in		1.75 in		1.9 in
Press.	Flow	Diam	Flow	Diam	Flow	Diam	Flow	Diam	Flow	Diam	Flow	Diam	Flow	Diam	Flow	Diam
(psi)	(gpm)	(ft.)	(gpm)	(ft.)	(gpm)	(ft.)	(gpm)	(ft.)	(gpm)	(ft.)	(gpm)	(ft.)	(gpm)	(ft.)	(gpm)	(ft.)
60	250	345	330	375	385	390	440	410	515	430	585	445	695	470	825	495
70	270	360	355	395	415	410	480	430	555	450	630	465	755	495	890	515
80	290	375	380	410	445	430	515	450	590	470	675	485	805	515	950	535
90	310	390	405	425	475	445	545	465	625	485	715	505	855	535	1005	555
100	325	400	425	440	500	460	575	480	660	500	755	520	900	550	1060	575
110	340	410	445	450	525	470	605	495	695	515	790	535	945	565	1110	590
120	355	420	465	460	545	480	630	505	725	530	825	550	985	580	1160	605
130	370	425	485	465	565	485	655	515	755	540	860	560	1025	590	1210	620
200 Series Big Guns—27° Trajectory^[a]									200 R Ring Nozzles
Size:	1.29 in		1.46 in		1.56 in		1.66 in		1.74 in		1.83 in		1.93 in
Press.	Flow	Diam	Flow	Diam	Flow	Diam	Flow	Diam	Flow	Diam	Flow	Diam	Flow	Diam
(psi)	(gpm)	(ft.)	(gpm)	(ft.)	(gpm)	(ft.)	(gpm)	(ft.)	(gpm)	(ft.)	(gpm)	(ft.)	(gpm)	(ft.)
50	230	325	300	355	350	370	410	390	470	405	535	420	640	435
60	250	340	330	370	385	390	445	410	515	425	585	440	695	455
70	270	355	355	385	415	405	480	425	555	440	630	455	755	475
80	290	370	380	400	445	420	515	440	590	455	675	470	805	490
90	310	380	405	415	475	435	545	455	625	470	715	485	855	505
100	325	390	425	425	500	445	575	465	660	480	755	500	900	520
110	340	400	445	435	525	455	605	475	685	490	790	510	945	535
120	355	410	465	445	545	465	630	485	725	500	825	520	985	545
130	370	415	485	450	565	470	655	490	755	505	860	525	1025	550
^[a] The diameter of throw is approximately 2% less for the 24° trajectory angle and 5% less for the 21° trajectory angle.

Table 12.7. Maximum spacing for traveler irrigation systems for ring nozzles (smaller percentages) and tapered nozzles (larger percentages) based on guidelines from USDA-NRCS (2016).
Sprinkler Wetted Diameter(ft)	Percent of Wetted Diameter
	50	55	60	65	70	75	80
	Wind over 10 mph		Wind up to 10 mph		Wind up to 5 mph		No Wind
	Spacing (ft)
200	100	110	120	130	140	150	160
250	125	137	150	162	175	187	200
300	150	165	180	195	210	225	240
350	175	192	210	227	245	262	280
400	200	220	240	260	280	300	320
450	225	248	270	292	315	338	360
500	250	275	300	325	350	375	400
550	275	302	330	358	385	412	440
600	300	330	360	390	420	-	-

Table 12.8. Typical characteristics for cable-tow traveler irrigation system from Harrison et al. (2015).
HoseDiameter(in)	HoseLength(ft)	Maximum TravelDistance(ft)	MaximumCapacity(gpm)	Maximum IrrigatedArea(acres)	Sprinkler Pressure(psi)	TypicalLaneSpacing(ft)	AreaCoveredper Pass(acres)	MaximumHose Pull Range(lbs)
2.5	660	1,320	165	33	60–70	180	5.5	1,300–1,900
3	330	660	250	50	70–80	210	3.2	1,000–1,500
3	660	1,320	250	50	70–80	210	6.4	2,000–3,000
3.5	660	1,320	375	75	80–90	240	7.3	3,000–4,000
4	660	1,320	535	107	90–100	300	9.1	3,500–5,000
4	1,320	2640	535	107	90–100	300	18.2	7,000–10,000
4.5	660	1,320	730	145	90–100	300	9.1	4,000–6,000
4.5	990	1,980	730	145	90–100	300	13.6	6,000–9,000
4.5	1,320	2,640	730	145	90–100	300	18.2	8,000–12,000
5	660	1,320	960	192	100–120	330	10	5,000–7,000

Table 12.9. Pressure loss (psi/100 ft) for lay-flat hose when operated at 100 psi (USDA-NRCS, 2016).
Flow(gpm)	Nominal Inside Diameter (in)
Flow(gpm)	2.5	3	4	4.5	5
100	1.6	-	-	-	-
150	3.4	1.4	-	-	-
200	5.6	2.4	-	-	-
250	-	3.6	0.9	-	-
300	-	5.1	1.3	0.6	-
400	-	-	2.3	1.3	-
500	-	-	3.5	2.1	1.1
600	-	-	4.9	2.7	1.6
700	-	-	-	3.6	2.1
800	-	-	-	4.6	2.7
900	-	-	-	-	3.4
1000	-	-	-	-	4.2

Table 12.10. Friction loss in hard hose, psi/100 ft (Hazen-Williams resistance coefficient = 150).
Flow (gpm)	Hose Inside Diameter (in)
Flow (gpm)	2.5	2.7	3.0	3.3	3.7	4.0	4.5	5.0
75	1.45	1.00	0.60	-	-	-	-	-
100	2.48	1.70	1.02	0.64	-	-	-	-
125	3.74	2.57	1.54	0.97	0.56	-	-	-
150	5.24	3.61	2.16	1.36	0.78	0.53		-
175	6.98	4.80	2.87	1.81	1.04	0.71	0.40	-
200	8.94	6.14	3.68	2.31	1.33	0.91	0.51	0.31
250	-	9.29	5.56	3.50	2.00	1.37	0.77	0.46
300	-	-	7.80	4.90	2.81	1.92	1.08	0.65
350	-	-	10.37	6.52	3.74	2.56	1.44	0.86
400	-	-	-	8.35	4.79	3.28	1.85	1.11
450	-	-	-	-	5.95	4.07	2.30	1.38
500	-	-	-	-	-	4.95	2.79	1.67
550	-	-	-	-	-	5.91	3.33	1.99
600	-	-	-	-	-	-	3.91	2.34
650	-	-	-	-	-	-	4.54	2.72
700	-	-	-	-	-	-	5.21	3.12
750	-	-	-	-	-	-	-	3.54
800	-	-	-	-	-	-	-	3.99

Moved-Lateral, Gun, and Traveler Sprinkler Systems

Pages 233-275 (doi: 10.13031/ISM.2021.12) in Irrigation Systems Management. ,

12.1 Introduction

12.2 Periodically Moved Laterals

12.2.1 Types of Systems

12.2.2 Operational Characteristics

12.2.3 Management Plan

12.2.4 Pressure Distribution

12.2.5 Uniformity Issues

12.2.6 Uniformity Evaluation

12.3 Solid-Set Systems

12.3.1 System Design

12.3.2 Management Problems

12.4 Guns

12.5 Travelers

12.5.1 Gun Performance

12.5.2 Field Layout

12.5.3 Operational Characteristics

12.5.4 Management

12.5.5 Other Issues

12.6 Summary

Questions

References