Saddlers Mill Stream culvert is mapped from Enfield Town Park to near Progress Way, Enfield. From there it seems likely that it goes in a straight line parallel to Elmcroft Avenue to somewhere near Boundary House and joins the unnamed stream running parallel to Sandhurst Road, which goes into Brimsdown Ditch. I've looked where it's publicly accessible and not noticed visible surface confirmation of the missing section of this route. Brimsdown Ditch does flow into Salmons Brook about 300m east of your marker.