Investigation on the impoundment effects of the constructed dams on the hydrodynamics and distribution of salinity in Urmia Lake (by Mike 3 Flow Model FM).

Urmia Lake is the second most saline lakes in the world after the Dead Sea that is located in Northwestern Iran. Urmia Lake has been facing serious environmental crisis, because of mismanagement in water uses. To solve this problem, an analysis of the hydrodynamic behavior and salinity distribution is important. The three-dimensional numerical model Mike 3 Flow Model FM was employed in this study. Model sensitivity analyses revealed that wind speed and friction coefficient and vertical eddy viscosity are effective parameters on flow velocities and on salinity distribution. Bottom roughness height is less influent and negligibly affects surface velocities. Using a very low vertical eddy viscosity improved flow velocities estimation, but deteriorated the reproduction of salinity distribution. Use of the UNESCO equation for density implemented in Mike 3 Flow Model FM for hypersaline Urmia Lake leads to density overestimation. Model accuracy in prediction of salinity is acceptable. Model simulations of Urmia Lake revealed that the salinity difference between North and South basins significantly increased after the draining process, peaking in May by arriving of fresh waters from snow melting. This study proved that the present model of Urmia Lake could be run for any time period in natural and drought conditions and can satisfactorily simulate the hydrodynamics and salinity distribution. The resultant direction of water flow was from the South to North basin for simulated 1986-1987 and 2004-2005, strongly reducing in the exchanged discharge is caused to increased salinity difference with lake draining.