Two Dimensional Modeling of Net Water Renewal Time in Gorgan Bay

Net Renewal Time is one of the most important indicators for water quality analysis in the water bodies. In this study, in order to investigate the Net water Renewal Time in Gorgan Bay, two modules from two dimensional Mike21FM model including Advection-Dispersion and Hydrodynamic were coupled.
Modeling was performed under 4 different scenarios with inclusion of some factors such as wind stress, river input, precipitation, evaporation and water fluctuations in spans of Ashoradeh-Bandaretorkaman.
Findings: The modeling results showed that integral Net Renewal Time in Gorgan Bay was 0.0181 per days. Variations in the amounts of Net Renewal Time were strongly influenced by prevailing hydrodynamic regime in Gorgan Bay. Net Renewal Time in distance of 1 km from the input spans was less than one day. This time index rate decreases by moving along longitudinal axis of the bay from east to west. Net Renewal Time in northeastern area was more than the corresponding areas in southeastern part. There was no significant difference in the Net Renewal Time for southern and northern parts of the west area. The modeling results in the four seasons showed that the Renewal amounts in winter and spring were more than those in summer and fall, and these results were consistent with increasing and decreasing inter-annual water level trend in the Caspian Sea, respectively.
Due to the low water Net Renewal Time in Gorgan Bay, it can be concluded that the water flushing system has very low speed in this water body and any use of it must be done with further studies and arrangements.