The refinement geometry is a polygon that must be contained within the domain geometry. Typically, it is defined around the river’s area of interest that should also be included inside the polygon. However, some rivers may have tributaries or other features requiring multiple polygons to accurately represent the pre-processor geometry and input. Unlike the domain, multiple refinement definitions can exist within the same context, optionally nested inside each other, with each defined by a polygon with individual property values. The only property of this geometry is also named CL, and if multiple refinements are defined for the same context, each refinement has its own CL value. To improve accuracy, the user can change the resolution of the computations by specifying refinements in the context.