STAGE-DISCHARGE RELATIONSHIP IN TIDAL RIVERS FOR TIDAL FLOOD CONDITION

Estimation of the water level in river's tidal reach is a suitable tool for the tidal flood risk and environmental management and design for rivers that are located in coastal area. The reaches of the river that affected by river flow and tidal wave are called as tidal limit and water level in this limit is a function of flood discharge and water level in upstream and downstream, respectively. In tidal limit, tidal waves propagate along the river to the upstream and combination of these waves and upstream flood discharge leads to an increase in water level. This mechanism increases flood plain limit and potential of damage and the risk. In this study, the reach between Ahvaz and Khorramshahr in Karun River in Iran is selected as case study and different linear models for the prediction of water level in tidal flood condition are investigated. Results show that the simple linear regression is not acceptable because of its variable variance of residuals. Transformed nonlinear models that are a form of linear models are used for modeling too. Two equations (Logarithmic and Power) with improved coefficient of determination, relatively constant variance and normal distribution of residuals of models are concluded from detailed analysis. These selected models are used for preiction. Prediction's results confirm the acceptability of these models considering their simplicity.