Improvement of the Volume Balance Model by Adjusting Water Surface Storage Term in Furrow Irrigation System

Generally irrigation efficiency is reported too low in most fields of Iran. It can be increased when the design input parameters such as infiltration opportunity and advance time are estimated accurately. Volume balance model (VBM) is introduced as an appropriate model for evaluation of the surface irrigation system and its application in designing the irrigation system. However, the predicted values from this model are not strongly correlated to the hydraulic model due to the model assumptions. The purpose of this research was to develop an improved volume balance model (IVBM) for furrow irrigation system. The IVBM is based on a combination of the VBM and the Zero-Inertia model (ZIM) that was used to desing border irrigation system. For evaluation of the model, it used five series of field data with a differente range of soil texture and the field properties. The data included geometric/hydraulics coefficients, advance time, inflow/outflow discharges, Manning’s coefficient, bed slope and Kostiakov infiltration coefficient. The comparison of the models (VBM and IVBM) has been done with root mean squared error (RMSE) with the observed data. The result shows an increasing of 15-40% accuracy for advance distance estimation of IVBM in comparison with the VBM.