I'm having a problem related with assigning specified flow boundary conditions to my UGrid / Modflow-USG model. The error appears when I do the '' Map to MODFLOW'' option while converting my conceptual model to UGrid numerical model. I have read the helping document saying that If you want to use ''Specified flow boundary condition'' the UGrid must be a stacked grid. A stacked grid is one in which there is no vertical discritization of layers and the horizontal discritization of all layers is the same. (i.e. the Index of Vertical Sub-Discretization (IVSD) in the UnStructured Grid Discretization (DISU) package could be set to -1) (See the Figure attached).
Firstly, I did not understand what this means and how to find the IVSD in the DISU package and set it to -1 to be able to use specified flow boundary condition. In my model there are 2 groundwater divide boundaries which must be zero flow and 2 formation boundaries where the aquifer feeds from neighboring formations with a specified flow value. If I ll have to change my specified flow bound. cond. with something else or If there is a way to use them, could you please help me to find the solution?