Denarii Cut As Votive Offerings

Last night I was browsing through photos I took in the coin gallery of the British Museum last month.
I noticed a photo that showed two examples of Denarii that had been deliberately cut and then thrown into the River Tees, south of Hadrian's wall.
A photo of that exhibit is shown below.

Last year by fate I ended up buying a number of Denarii of Septimius Severus, that had been cut.
The second photo shows them, note that the first Denarius came from a lot I bought from Hungary.
All others were found in England, most in Yorkshire.
Hungary included the Roman frontier province of Pannonia Inferior.

I had thought at first that these coins had been cut to get the silver to make Fourrees (ancient Denarii forgeries).
Seeing that exhibit, I wonder if most of these cut Denarii and others that are out there, are more the result of being cut for an offering to the gods, being cast into a river.

I also wonder if this was some Celtic tradition that continued into the Roman era, since we know the Celts made very elaborate offerings to their gods, casting fine wares into the rivers.
http://www.britishmuseum.org/explor..._shield.aspx

If it is a celtic only tradition, then how to explain Denarii being cut as votice offerings in Pannonia inferior?
On the opposite side of Pannonia inferior, across the Danube, the Celtic "Boii" tribe had inhabited the region of the modern Czech republic, known until a hundred years ago as "Bohemia".
http://en.wikipedia.org/wiki/Boii
Perhaps locals enlisted into the frontier garrisons on that part of the Danube were descended from such Celts, however by the era of Septimius, "Bohemia" had come under Germanic control, namely the powerful "Marcomanni" tribe.