New in GMS 10.1 is support for the CLN (Connected Linear Network) Process of MODFLOW-USG. From the MODFLOW-USG documentation:
The CLN Process was developed for MODFLOW–USG to provide the framework for incorporating one-dimensional connected features into a structured or unstructured threedimensional GWF Process grid. A one-dimensional CLN feature is any hydrogeologic or hydrologic water conveyance feature that has a cross-sectional dimension which is much smaller than the longitudinal flow dimension and the size of the encompassing GWF cell. Flow is computed in the longitudinal direction of the network of connected one-dimensional features using specified cross-sectional properties; flow between CLN cells and GWF cells is computed across the wetted perimeter of the one-dimensional CLN feature. The CLN Process thus provides a mechanism for including features with small cross-sectional areas, relative to GWF cell sizes, without having to build this level of detail into the grid used for the GWF domain.