In 1978, a dredging gang working for British Waterways was struggling with a problem. They were trying to clear obstacles on the Chesterfield Canal so they could stabilise a concrete wall — not an easy day’s work. But what really had them stumped was a heavy iron chain on the canal bottom. After various attempts, they hooked the chain to their dredger. That did the trick. A firm pull removed the chain and the block of wood on the end of it. The gang took a well-earned break for tea.

The tea break was rudely interrupted by a policeman in a state of some excitement. He had been passing the normally tranquil waterway when he could not help but notice a large whirlpool. By the time the crew returned to the scene, the canal had gone. “We didn’t know there was a plug,” protested one workman. And, in fairness, the canal was two centuries old, and so was the plug. Whatever records there may have been had been destroyed in the Blitz. The moral of the story: institutional memory is valuable, and if an organisation starts forgetting important matters (such as the existence of the plug) bad things happen.

Expertise drains away alarmingly fast if not refreshed by activity. Anyone who has filed tax returns can attest that a year is easily enough time to forget how to do any complex process

It’s not easy, though. I was recently taken on a tour of the Bodleian Library’s portrait collection, and was struck by how hard our tour guides had had to work to recover basic information about the sitter and the artist, even in portraits just a few decades old. This wouldn’t be so remarkable, except that the entire reason for the Bodleian Library to exist is to preserve information in an accessible form. (Bodley’s librarian, Richard Ovenden, has written Burning the Books: A History of the Deliberate Destruction of Knowledge and is president of the Digital Preservation Coalition.) But the Bodleian is a library, not a portrait museum, and without constant attention, the natural order of things is not to remember, but to forget.