The interpolation of the initial heads in Modflow yields values above the ground surface. I supplied a grid file of initial heads, containing the already interpolated head values using rigging with external drift to ensure the ground surface elevation is also taken into account. However, MODFLOW still interpolates the head values. However,, the result is not good. I do not have Groundwater Vistas to convert the grid file into .HEADS file. I checked the .VIH and .BAS files, but I don't think I will be able to edit these files since the study area is vast and very confusing. Has anyone faced a similar problem? Please help.