PERFORMANCE EVALUATION OF IRRIGATION CONVEYANCE SYSTEMS USING DYNAMIC SIMULATION MODELS

Abstract

The sustainability of irrigation projects, which use extensive open channel conveyance systems to distribute water, depends to a great extent on the ability of the system to economically satisfy farm water needs and to ensure maximum utilization of water commanded for irrigation purposes. The delivery of water from supply to farm normally incurs a significant proportion of project costs in terms of real currency, (i.e. actual costs), lost water resources, (i.e. water diverted but not used for crop production or other beneficial uses), land taken out of production, (eg. due to system right-of-way requirements and waterlogging and salinization), and suboptimal farm productivity, (i.e. due to inadequate farm water delivery). Each of these costs are a complex function of conveyance system design, method of operation, management practice, and maintenance programs. The relative significance of system costs is determined using appropriate performance evaluation criteria. Assessment of project sustainability requires that performance be measured or reliably estimated by engineers, agronomists, economists, bankers, governments, farmers and other professionals and stakeholders.For assessments to be useful, costs used in performance evaluation need to be related to the specific physical and operational characteristics of the conveyance system being evaluated. Historically, conveyance system performance evaluation has been seriously inhibited by the lack of data. Even if existing systems were monitored to the required extent, the impacts of proposed changes to design, operations, etc. could have only been surmised. These difficulties may be overcome using recent developments in dynamic simulation of irrigation conveyance system hydraulics, operation and hydrologic environment. Unlike water balance models, dynamic simulation models provide the opportunity to relate specific system characteristics to actual costs and selected performance evaluation criteria. The impact of irrigation water distribution system design, management, operations and maintenance on the sustainability of existing or proposed irrigation projects may now be readily assessed.