Estimation of rating curve in river’s tidal limit using long term and tidal flood data

Estimation of the water level in river’s tidal limit is a suitable tool for the tidal flood management for rivers that are located in coastal areas. In this limit, propagation of tidal waves along the river to the upstream and combination of these waves and upstream flood discharge leads to an increase in flood plain limit and risk of damage. In this study, the reach between Ahvaz and Khorramshahr in Karun River is selected as case study and different linear and non-linear models are investigated for prediction of water level as a function of flood discharge of upstream. The analysis is performed for two cases considering the nature of tidal flood. In first case, total recorded data is investigated while in second case tidal flood data is extracted based on peak over threshold series analysis. Analysis of residuals of models in two cases show that the linear models are not acceptable, therefore the transformed nonlinear models that are a form of linear models are considered for modeling too. The power equations with improved coefficient of determination, relatively constant variance and normal distribution of residuals of models are concluded from detailed analysis in calibration parts for two cases. These selected models are used for validation part for two cases. The results confirm the acceptability of these models considering their simplicity and better efficiency for first case than second case.