Calibration and Sensitivity Analysis of Hydraulic Behavior in Qazvin Plain Aquifer

In a national plan of salt marsh lands’ drainage in Qazvin، in order to have the water table lowered، and to prevent the progress of saltmarsh، an interceptor drain equipped with hydraulic structures was constructed. A number of 99 observation wells، in the direction perpendicular to the drain were constructed in 9 directional sections. The hydraulic behavior of the aquifer and the effect of the interceptor drain، while using PMWIN Model، (in transient flow and monthly time steps)، hydrodynamic coefficients were calibrated through PEST code plus trial and error method. In sensitivity analysis، the model was run in a three step increase and three steps decrease without any changes in the other hydrodynamic coefficients. The results indicate that error variance of before and of after model calibration were respectively 0. 336 and 0. 127 meter. Furthermore results of sensitivity index revealed that the highest sensitivities were respectively recorded for، hydraulic conductivity coefficient، recharge and specific yield، while the effect of hydraulic conductivity coefficient being observed more around observation wells adjacent to the channel within the radius of influence drain، with little effect on the other parts of the aquifer.