12.5.5: Other Issues
- Page ID
- 44657
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\(\newcommand{\avec}{\mathbf a}\) \(\newcommand{\bvec}{\mathbf b}\) \(\newcommand{\cvec}{\mathbf c}\) \(\newcommand{\dvec}{\mathbf d}\) \(\newcommand{\dtil}{\widetilde{\mathbf d}}\) \(\newcommand{\evec}{\mathbf e}\) \(\newcommand{\fvec}{\mathbf f}\) \(\newcommand{\nvec}{\mathbf n}\) \(\newcommand{\pvec}{\mathbf p}\) \(\newcommand{\qvec}{\mathbf q}\) \(\newcommand{\svec}{\mathbf s}\) \(\newcommand{\tvec}{\mathbf t}\) \(\newcommand{\uvec}{\mathbf u}\) \(\newcommand{\vvec}{\mathbf v}\) \(\newcommand{\wvec}{\mathbf w}\) \(\newcommand{\xvec}{\mathbf x}\) \(\newcommand{\yvec}{\mathbf y}\) \(\newcommand{\zvec}{\mathbf z}\) \(\newcommand{\rvec}{\mathbf r}\) \(\newcommand{\mvec}{\mathbf m}\) \(\newcommand{\zerovec}{\mathbf 0}\) \(\newcommand{\onevec}{\mathbf 1}\) \(\newcommand{\real}{\mathbb R}\) \(\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}\) \(\newcommand{\laspan}[1]{\text{Span}\{#1\}}\) \(\newcommand{\bcal}{\cal B}\) \(\newcommand{\ccal}{\cal C}\) \(\newcommand{\scal}{\cal S}\) \(\newcommand{\wcal}{\cal W}\) \(\newcommand{\ecal}{\cal E}\) \(\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}\) \(\newcommand{\gray}[1]{\color{gray}{#1}}\) \(\newcommand{\lgray}[1]{\color{lightgray}{#1}}\) \(\newcommand{\rank}{\operatorname{rank}}\) \(\newcommand{\row}{\text{Row}}\) \(\newcommand{\col}{\text{Col}}\) \(\renewcommand{\row}{\text{Row}}\) \(\newcommand{\nul}{\text{Nul}}\) \(\newcommand{\var}{\text{Var}}\) \(\newcommand{\corr}{\text{corr}}\) \(\newcommand{\len}[1]{\left|#1\right|}\) \(\newcommand{\bbar}{\overline{\bvec}}\) \(\newcommand{\bhat}{\widehat{\bvec}}\) \(\newcommand{\bperp}{\bvec^\perp}\) \(\newcommand{\xhat}{\widehat{\xvec}}\) \(\newcommand{\vhat}{\widehat{\vvec}}\) \(\newcommand{\uhat}{\widehat{\uvec}}\) \(\newcommand{\what}{\widehat{\wvec}}\) \(\newcommand{\Sighat}{\widehat{\Sigma}}\) \(\newcommand{\lt}{<}\) \(\newcommand{\gt}{>}\) \(\newcommand{\amp}{&}\) \(\definecolor{fillinmathshade}{gray}{0.9}\)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.