Irrigation & Drainage Systems Engineering

Slope Effects on the Pressure Head Profile Patterns of Sprinkler Irrigation Laterals, I. Theoretical Analysis

Abstract

Zerihun D, Sanchez CA and Bautista E

The pressure head profile of an irrigation lateral is a function of the hydraulic and geometric characteristics of the lateral and its slope. Slope effects on pressure variability along a lateral are typically limited. However, for a lateral with a spatially invariant parameter set well-defined relationships can be discerned between lateral slopes and the spatial patterns of the lateral pressure profiles. Thus, a comprehensive understanding of these relationships can be useful in the evaluation of lateral hydraulic simulation models and design recommendations. Existing studies have examined slope effects on the locations of pressure head extreme, along a lateral, in the context of hydraulic design of laterals. This paper presents a comprehensive analysis of slope effects on lateral pressure head profile patterns. The monotonic properties, with respect to distance from inlet, of lateral slope and friction slope profiles coupled with the pressure slope equation are used here to determine the full range of variation of lateral pressure head profile patterns as a function of lateral slope. Overall, the analysis show that the pressure profile patterns of a lateral, and possibly the locations of the pressure extreme along the lateral, can be determined by comparing the negative of the lateral slope with the corresponding friction slope at the upstream and/or downstream ends of the profile. The results also show that the full range of variation of the pressure profile patterns of a lateral, as affected by slope, consists of three distinct categories. These include a profile pattern that is increasing or decreasing, with distance from the inlet, over the entire length of the lateral and one that combines both trends within the length of the lateral. The relationships between lateral slopes and pressure profile patterns, deduced here through theoretical analysis, will be evaluated in a companion paper based on simulations.