IN HIS letter (February 7), John Macallister refers to a lake south of Oxford.

This lake was, in fact, the River Thames which, to the west of Oxford, was very wide, shallow and slow-moving and stretched from the rising ground at Jericho to the hills to the west and from Wolvercote to Radley.

Being slow-moving it allowed sediment, from farms in the Cotswolds, to settle out and be formed into unstable islands.

Normally the river was only a few centimetres deep, making this stretch easy to ford but, if there was heavy rain in the Cotswolds, even the islands would be under water.

When Oxford was first built, the Anglo-Saxons made the first deep cut along the western edge of the town (now known as the Trill Mill Stream) which, I believe, was the town’s main form of defence for the south and west. John is probably right in thinking that there were no ramparts in this area and therefore no gates but, I’m sure that there would have been gates in the 13th century wall.

Further cuts were made to make the islands useable including a deep navigation channel which we now identify as the Thames.

With more fossil fuels being burnt and the rain forests being cut down, global warming can only increase, resulting in more rain.

It’s difficult to see an easy answer to the flooding in this area.

Fortnam Close
Headington, Oxford