I've got a copy of 'A Flat Place' by Noreen Massud. Check out the GeoLibrary for some more.
She contributed a piece to The Guardian's feature on holidays to explain why she likes to visit flat places.
There's some excellent descriptions of the value of flatness and why other places leave her cold and anxious. Excellent for units exploring the distinctive landscape of this area, and the value of flatness in areas such as the Somerset Levels and elsewhere.
Can I also recommend that you subscribe to Drew's Fenland on Film YouTube channel. Drew does fantastic work collating, sharing and restoring films about the Fens and places such as Ely.
Here's one of his latest projects: a restored film from 1945 which gives a tantalising glimpse into another (lost) world of the old Fen.