Interesting comments - thank you. I'm still trying to resolve pptential
difficulties.

One problem is that the existing bank isn't well compacted. I've just
dragged the soil outwards so far. I think I may have to remodel the
bank, trying to compact it as I go, otherwise it will be difficult to
tend to the plants around the edges.

One other problem that I'm struggling with a bit is the planned shore
section. A wildlife pond has to have a gentle incline, and I'm not sure
how easy this will be to achieve with banked sides.

And the edging? As has been mentioned, grass will be difficult to mow,
but I'm struggling to imagine how I could use my original preferred
edging - some sort of paving or gravel - with a banked pond. I suppose
with a wildlife pond it would be more than acceptable to allow the
grass to grow long immediately round the edge.

Hmm. The convenience of not having to shift the soil or dig too far
down are still making the idea appealing, but I need to resolve some of
these things. Looks like the pond project might stretch forward for
quite a while yet....