Zerihun D and Sanchez CA
An equation that expresses lateral pressure as an explicit function of distance from the lateral inlet is derived for linear-move sprinkler irrigation systems. The equation takes into account the effects of both field slope and span geometry on lateral pressure. The proposed equation is not intended for predictive use. Instead, it is used here in an additional evaluation of the validity of the unique pressure profile variability patterns, of linear-move laterals, produced in an earlier study through numerical simulations. Accordingly, the pressure profiles computed with the equation are compared with those obtained through simulations. Six data-sets, covering a range of field slopes and lateral parameters, are used in the evaluation. The results show that pressure profiles computed with the equation closely match those obtained through simulations. Overall, the spatial patterns of the pressure profiles computed here, with the equation, confirm observations made in an earlier study that the variability attributes of the pressure profiles of linear-move laterals exhibit dual characteristics, consisting of local span-scale variability patterns and inter-span/ lateral-wide trends. Analysis of the pressure head equation shows that pressure head profile of a lateral is a stepwise linear function of distance from the inlet with discontinuities at computational nodes. The practical significance of this observation in the computation and description of lateral pressure head profile is highlighted. The pressure head equation derived here is also used to define a pressure slope function that can potentially be used to characterize the full range of variation of the pressure profile patterns of linear-move laterals.
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