Current modelling and water level fluctuations in Arvandrud

In this research, fluctuations of water level at the mouths of Arvandrud and Bahmanshir rivers are studied. COHERENS which is a three-dimensional hydrodynamic model is employed to simulate salinity and temperature in three dimensions. In this model, Cartesian coordinate for the horizontal and sigma coordinate with three layers is used for the vertical profile. At open boundaries variations of salinity, temperature as well as four main tidal constituents (,M2, S2, O1, K1) are applied. Monthly mean atmospheric parameters (speed and wind direction, temperature, rainfall, relative humidity and cloud coverage) are also employed in the model. In this study, uniform grid of 491× 690 is used which covers the region of 40×55 square kilometers of both Arvandrud and Bahmanshir estuaries. In order to validate the results of the model, outputs of the model are compared whit confirmed Admirality Tide Tables and found a very good agreement between them. To compare water level fluctuations of Arvandrud river with Bahmanshir river, some stations were selected along rivers with equal distances from the river mouths. Results of this comparison show that, the speed of tidal wave at Arvandrud river is higher than Bahmanshir river. Also tidal range in the Bahmanshir river found lower than Arvandrud river.