Purple Small-Reed. New to Calderdale?

Walking the canal towpath this afternoon at Walsden, I saw a tall grass which I haven't seen before in Calderdale; in fact the last time I saw it in the wild was at the SSSI at Leven Canal near the river Hull, East Yorks.

This Purple Small-Reed, Calamagrostis canescens at Walsden must have been there a while as it has covered a large area with its rhizomatous roots. It is a lovely grass with its long purplish flower heads and is dominating the vegetation, as seen in the photo.

Can anyone say if this grass has any local records? I wonder how it got to Walsden?