Closure to “Field-Scale Assessment of Uncertainties in Drip Irrigation Lateral Parameters” by Yeboah Gyasi-Agyei

Abstract

The discusser appreciates the author for providing a methodology Gyasi-Agyei 2007 for estimating the effective parameter values in drip irrigation laterals under field conditions. The topic of this research mainly deals with a field-scale assessment of the uncertainties of lateral parameters k, x, and and evaluation of the manufacturer’s supplied values. The present methodology gives an opportunity to design engineers to clearly analyze and decide the real performance of the lateral emitter parameters effective field values in comparison with their supplied values by the manufacturers due to manufacturer’s variability. However, the discusser calls attention to the following important points, which still need to be clarified. Note that, to avoid any notation conflict, the notations and definitions are the same as those in the original paper. The first section of the paper presents general hydraulic modeling formulations for the following three sections: Single lateral, subunit of multiple laterals, and irrigation bay with multiple subunits. 1. In the subsection “Single Lateral” under the general title “Hydraulic Modeling,” the paper says: “Emitter discharge varies along the lateral with maximum value at the upstream and zero at the end.” In a micro-irrigation system, a major hydraulic design criterion is the minimization of the emitter flow, qi or emitter discharge variation, which means the maximization of water application uniformity along a micro-irrigation line lateral or submain Yildirim 2008a . The emitter flow variation is mainly controlled by the pressure head Hi variation along the line, as given by the paper’s Eq. 1 . When the kinetic energy is considered to be small and neglected in a microirrigation line, the pressure variation will be simply a linear combination of the inlet pressure head H0 , energy drop due to friction, and total energy change gain or loss due to uniform line slope s0 Wu and Gitlin 1973, 1974; Howell and Hiler 1974; Gillespie et al. 1979 . In line with this concept, there are five typical pressure profiles in three general types, as shown in the discussion Fig. 1, that can be expressed as follows Gillespie et al. 1979; Wu et al. 1983; Wu and Barragan 2000 : • Pressure Profile Type I: The pressure decreases with respect to the lateral length. This type occurs when the lateral line is laid on zero or uphill slopes. Energy is lost by both elevation change due to upslope and to friction. The maximum pressure head, Hmax or maximum emitter discharge, qmax is at the inlet Hmax=H0 , and the minimum pressure