Aggregated hydraulic sensitivity indicators for irrigation system behavior

Abstract Knowledge of the way perturbations propagate and/or attenuate along free-flow irrigation delivery systems is crucial for monitoring and effectively operating a system. With this knowledge sections of the canal system which are identified as sensitive to flow perturbations should be targeted for more frequent inspection and operational decisions than others. The steady-state hydraulic approach for canal operation design is well understood by irrigation agencies, but it has limited practical application and is unsuitable for studying the propagation of perturbations. The unsteady flow approach is more powerful but rather complex. A third intermediate way is proposed here through the development of hydraulic sensitivity indicators. These indicators allow the characterization of the response of a structure, or a set of structures, to any input change. Local sensitivity indicators are first estimated for the main hydraulic structures, i.e. offtakes and cross-regulators, for delivery and conveyance. Aggregation processes are then proposed for the computation of lumped sensitivity indicators at reach and canal levels. These sensitivity indicators are designed to improve the knowledge of canal behavior and to lead to improved monitoring and operation of irrigation canals. A case study of the application of a sensitivity analysis at system level is carried out, describing the behavior of two different irrigation canals in Sri Lanka.