A comprehensive water balance methodology for collective irrigation systems

Abstract

This paper presents the development and application of a comprehensive methodology for the systematic water balance calculation in collective irrigation systems (CIS), applicable to pressurized pipelines or open canals. Existing approaches focus solely on the assessment the water resources use efficiency of CIS single components (e.g., leakage in some canal reaches), without a system-wide approach. A water balance approach allows accounting for the different system volume inputs (i.e., water abstraction, imported water, water volume due to precipitation or surface runoff), authorized and non-authorized consumptions and water losses either in canal, mixed or pressurized CIS, which has never been presented in literature. The proposed methodology allows the assessment of different water loss components (i.e., evaporation losses, unauthorized uses, metering errors, leakage and discharges) and the calculation of water loss performance indicators that allow the identification of the main problems in terms of water losses and provides guidance about measures to control water losses. Although based on the existing and consolidated water balance schemes specifically developed for urban water supply systems, the proposed methodology includes novel components in terms of system input volume, authorized consumption and water loss that are specific of CIS. The methodology is tested and applied to a mixed collective irrigation system. Results show that the water losses due to discharges in canal systems can be one of the most relevant component of the non-revenue water, representing approximately half of its total volume, followed by leakage in canals and metering errors. These results highlight the importance of improving daily operation of these systems and also rehabilitating ageing infrastructures.