Hi @dgw_awf -
This is caused by the way the MFD flow direction algorithm works. It’s great for defining flood plains, but it is problematic when the resulting modeled stream network is not realistic and cuts into riparian restoration defined in the land use map, it’s happened to me more than once. For what it’s worth, we’re working on adding the option of using the D8 flow direction algorithm to the freshwater models, which is much more likely to produce streams that are just 1-2 pixels wide (except in large, totally flat areas, where most flow direction algorithms have trouble), but it hasn’t been released yet.
Jesse pointed to the Working with the DEM section of the User Guide, which is useful for sanity-checking your DEM. But if it’s just the case that your riparian zone is actually naturally flat, and the DEM is pretty accurate, one thing you could try (that we don’t really talk about in the User Guide) is “burning” a thin (1-2 pixel) stream network into the DEM, which might create an equally thin output stream. Here’s a previous forum post that addresses the topics of wide streams and riparian buffers in some detail.
~ Stacie