Arash Adib - Assistant Professor, Civil Engineering Department, Engineering Faculty, Shahid Chamran University, Ahvaz, Iran
Mohammad Vaghefi - Assistant Professor, Civil Engineering Department, Engineering Faculty, Persian Gulf University,Bushehr, Iran

Tidal surges and fluvial flows influence tidal rivers interactively, while fluvial flow is only an influential factor in ordinary (non-tidal) rivers. It is therefore imperative to consider both return periods of the upstream flood condition and the downstream tidal surge condition in order to determine the combined return period for design flood analysis in tidal rivers. Tidal surges and fluvial floods are usually considered to be independent phenomena. The task of obtaining a suitable and practical combination of the two encompasses preparation of an interactive scenario most closely and practically verified against the actual design event. In the present research, a combination coefficient has been introduced by the use of the joint probability method. The combination coefficient is used to combine return periods of tidal surges and fluvial floods. A numerical and stochastic model has been developed for hydraulic routing in tidal rivers. The model is applied to the River Severn in the U.K. The model can be generally utilised for river management and determination of safe bank height for tidal rivers.

Combination coefficient, Tidal surges, Floods, Joint probability method, The RiverSevern