Flowing with facts

I JUST love statistics and facts. I’m afraid I’m one of those real nerds who enjoys sitting down with an encyclopedia or a reference book and just soaking up interesting information about – well – virtually anything at all really.

So when I was casting around for something to write about for this week’s Riverwatch, my good lady wife said: “Why don’t you do something on interesting facts about the Thames?” So here goes…

For a start, did you know that the Thames, that symbol of Britishness and one of our proudest national assets, started its watery life as nothing more than a tributary of the mighty German River Rhine?

True enough, way back 25,000 years ago, during the last ice age, Britain was still joined to the Continent and the Thames, running slightly north of its current position, weaved its way across East Anglia and joined the Rhine as it flowed into what it now the North Sea close to the Dogger Bank.

When the ice began to melt and the sea levels rose, the low-lying land to the south and east was inundated and Britain became an island – which was when the Thames took on an independent life of its own.

The river rises in the Cotswold Hills at a place called Trewsbury Mead at a height of 364 feet above sea level and then follows a winding course of approximately 215 miles to the point where it officially becomes the sea at Sea Reach Buoy No.1, midway between the Essex and Kent shorelines.

One thing that never ceases to amaze me is the volume of water the river carries on its way down to the sea.

The Environment Agency has a number of flow monitoring stations set up along the river’s course, which provide data on the quantities of water passing along at any given time. There are 38 main tributaries on the non-tidal Thames above Teddington – and the catchment area for the river is a staggering 9,950 square kilometres (3,840 square miles). It’s clear that those tributaries play a major role in feeding the Thames.

Up at Buscot Lock (close to Lechlade) the average flow is about 176 million gallons of water a day. But by the time the river reaches Kingston, that figure has gone up to 1,253 million gallons a day.

At Teddington, where the Thames changes into a tidal river, the average rate of flow over the weir is around 1,145 million gallons a day.  During times of drought, that can fall as low as 200 million gallons a day whilst at the other end of the spectrum, during the winter when heavy rains throughout the catchment area feed the river, the flow rate can rise to 6,600 million gallons a day!

With that volume of water passing along its length, it’s perhaps no surprise that the river carries approximately 300,000 tonnes of sediment every year, depositing most of it on the ever-shifting mudbanks in the estuary.

Just in case you haven’t yet had your fill of Thames statistics, I’ve provided a box with a few more fascinating facts for your delectation. (Right, I’d better go and have a lay down in a darkened room after all those figures!)