Hi, When I try to merge multiple coverages that have specified observed flow to a specific arc group, the merged coverage does not contain all arc groups from the original coverages, but only some of them (not the same arcs every time). Any suggestions how to deal with this, or a different approach to assigned multiple instances of observed flow to complex arc groups? I know there are ways to manually group the arcs in a single coverage and take it from there, but I have an intricate system of streams that is classified according to stream width. The 'observed flow' is used as a workaround by setting its weight to 0, as I need the jacobian matrix calculated by PEST for further analysis; manually grouping all these arcs is not really a workable option. Any advice is appreciated, thanks in advance. Pytrik