O. Debreczyi?
Kept running in circles aimlessly :(
Could this be a badger spoil heap? Right on a river bank? Badgers prefer well-drained sites for setts, on elevated ground, to avoid flooding of the sett. Hence the riverbank location is a bit unlikely- but not impossible, especially if they have been disturbed by recent operations which is suggested at this site given the installation of a new wire and post fencing system. Could this potentially be water vole? The ground was not stable enough for me to get a better look.
With Heidi Eaton.