12.5.4: Management
- Page ID
- 44656
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\(\newcommand{\avec}{\mathbf a}\) \(\newcommand{\bvec}{\mathbf b}\) \(\newcommand{\cvec}{\mathbf c}\) \(\newcommand{\dvec}{\mathbf d}\) \(\newcommand{\dtil}{\widetilde{\mathbf d}}\) \(\newcommand{\evec}{\mathbf e}\) \(\newcommand{\fvec}{\mathbf f}\) \(\newcommand{\nvec}{\mathbf n}\) \(\newcommand{\pvec}{\mathbf p}\) \(\newcommand{\qvec}{\mathbf q}\) \(\newcommand{\svec}{\mathbf s}\) \(\newcommand{\tvec}{\mathbf t}\) \(\newcommand{\uvec}{\mathbf u}\) \(\newcommand{\vvec}{\mathbf v}\) \(\newcommand{\wvec}{\mathbf w}\) \(\newcommand{\xvec}{\mathbf x}\) \(\newcommand{\yvec}{\mathbf y}\) \(\newcommand{\zvec}{\mathbf z}\) \(\newcommand{\rvec}{\mathbf r}\) \(\newcommand{\mvec}{\mathbf m}\) \(\newcommand{\zerovec}{\mathbf 0}\) \(\newcommand{\onevec}{\mathbf 1}\) \(\newcommand{\real}{\mathbb R}\) \(\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}\) \(\newcommand{\laspan}[1]{\text{Span}\{#1\}}\) \(\newcommand{\bcal}{\cal B}\) \(\newcommand{\ccal}{\cal C}\) \(\newcommand{\scal}{\cal S}\) \(\newcommand{\wcal}{\cal W}\) \(\newcommand{\ecal}{\cal E}\) \(\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}\) \(\newcommand{\gray}[1]{\color{gray}{#1}}\) \(\newcommand{\lgray}[1]{\color{lightgray}{#1}}\) \(\newcommand{\rank}{\operatorname{rank}}\) \(\newcommand{\row}{\text{Row}}\) \(\newcommand{\col}{\text{Col}}\) \(\renewcommand{\row}{\text{Row}}\) \(\newcommand{\nul}{\text{Nul}}\) \(\newcommand{\var}{\text{Var}}\) \(\newcommand{\corr}{\text{corr}}\) \(\newcommand{\len}[1]{\left|#1\right|}\) \(\newcommand{\bbar}{\overline{\bvec}}\) \(\newcommand{\bhat}{\widehat{\bvec}}\) \(\newcommand{\bperp}{\bvec^\perp}\) \(\newcommand{\xhat}{\widehat{\xvec}}\) \(\newcommand{\vhat}{\widehat{\vvec}}\) \(\newcommand{\uhat}{\widehat{\uvec}}\) \(\newcommand{\what}{\widehat{\wvec}}\) \(\newcommand{\Sighat}{\widehat{\Sigma}}\) \(\newcommand{\lt}{<}\) \(\newcommand{\gt}{>}\) \(\newcommand{\amp}{&}\) \(\definecolor{fillinmathshade}{gray}{0.9}\)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 positioned 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.
Figure 12.22. Traveler Management Spreadsheet for traveler irrigation systems.
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.
qs = Cd Pa Dnb
where: qs = gun discharge, gpm
Cd = 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.