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.

Figure 12.20. Layout for eighty-acre field irrigated with a traveler.

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.

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).

Hose Diameter (in)	Hose Length (ft)	Maximum Travel Distance (ft)	Maximum Capacity (gpm)	Maximum Irrigated Area (acres)	Sprinkler Pressure (psi)	Typical Lane Spacing (ft)	Area Covered per Pass (acres)	Maximum Hose 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