Welcome to the forum, yes Alderbottom is as you have described, there is a footpath coming from Strongstry which passes under the viaduct and ends up in Irwell vale, this path was damaged in the 2012 flood and was never officially reopened, that is a contentious issue as is the flattened mill, we still use the path as it leads to some very good habitat.
Give me a ring anytime if you want to have a wander round the area, you will find in the general discussion page a list of events for the next six months, you would be more than welcome to join the group on any of these, there is a private message service built into the forum if you wish to discuss anything.
