It took long enough (and hundreds of thousands if not millions wasted) patching up the Conwy Valley every year or two before they saw sense and went down the "enhancement" line, dumping a load of massive rocks a bit like a sea wall alongside it, since which there has been flooding but there have been no washouts at all that I can recall.
As for Ardwick I think making it accessible would be horribly expensive due to its location, and post-development you might not even want the entrance where it is now, but development might provide an alternative if there's a suitable building to run a bridge to later, so for now "like for like" probably did make sense. Enhancements could even be funded via planning gain given the amount of development likely.