Application of unsteady flow hydraulic-model to a large and complex irrigation system

Canal hydraulic-models can be used to understand the hydraulic behavior of large and complex network, to evaluate their performance and to improve the operation and management of such systems at low cost. In this study, the canal hydraulic-model (CANALMAN) was applied to the right bank main canal (RBMC) of the Kangsabati irrigation project, West Bengal, India. The canal is 33.17 km in length and has eight distributaries. The model was calibrated for the irrigation period of 19 July–1 August 1997 and validated for 18–28 October 1997 and 23 July–5 August 1996. The observed and simulated inflow-rates were in close agreement with each other for both the calibration and validation periods. The calibration parameters, Manning’s roughness-coefficient and seepage-loss rate, were found to be 0.016 and 160 mm per day, respectively. The means of observed and simulated inflow-rates were not statistically different at 1% level of significance for both the calibration and validation periods. The calibrated model was subsequently used to study the adequacy of water supply during Kharif (rainy) season for the year 1996. Comparison between simulated (required) and observed (supplied) inflow-rates revealed that the supply of irrigation water was in excess most of the time. The average water supply during the entire Kharif season was about 13% higher than the model-simulated required flow-rate, which establishes the fact of over-irrigation in the head reach of the main canal system. The simulation results suggest that the CANALMAN-model can be successfully used for the operation and management of the RBMC of the Kangsabati irrigation project.