Summary (by AI): Kemble, Gloucestershire; Official source of River Thames; Dry field due to porous geology; Stone monument 108m above sea level; Thames Head Inn parking; 15-20 minute walk to site; Seven Springs tributary debate; River Severn is longest; Pumping station lowered water table; Canal failed due to porous rock.
Blog: This one amused me: I’m walking a river in a completely dry field in the middle of Gloucestershire. The field is near Kemble, and it’s officially recognised as the source of the River Thames. Because of the local geology, though, there’s actually no water there at all for a large proportion of the time. It doesn't bubble up from this spot; the water only really starts about three or four miles down the valley.
Still, there’s a stone monument marking the spot. It sits at 108 metres above sea level, exactly 185 miles from the other end of the Thames Path, which finishes in Woolwich. Arguably, you could walk a bit further, because obviously the Thames doesn't stop in Woolwich—it goes all the way to the sea between Essex and Kent.
It’s definitely worth visiting, and it was absolutely gorgeous when I went. I stopped off and had a pint at the Thames Head Inn and left my car there. From the pub, it’s about a 15- to 20-minute walk to the monument. While I was walking, there was a farmer out in the field—not so much mowing his grass and hay, because that had already been felled, but doing that bit with the circular machine that essentially turns the grass over to dry it out. It was cool to see.
It turns out there is a bit of an argument as to whether or not this is the correct place to source the River Thames. Further down the course, there is a junction where another tributary turns off, going up to a place called Seven Springs. That branch is actually about 10 or 15 miles longer. If that had been designated as the official Thames as opposed to the tributary, the Thames would actually be the longest river in England. As it is, starting where it does at the spring, it’s only the second longest, with the River Severn taking the top spot. (I guess I’ll have to go and find the source of the Severn at some point on my travels—does anyone know what county that’s in?)
Anyway, one final point was what the Victorian engineers decided to build across the Cotswolds at that point. They dug the Thames and Seven canal without realising that the rock itself was incredibly porous. This brand-new canal just kept losing all its water. The solution wasn't to abandon the canal, though; it was to build a massive pumping station. Not far from the source of the Thames, they built a steam-powered water pumping unit, drilling down many metres to pump water straight into the canal.
The consequence was that the canal effectively filled with water, although it didn't actually last that long—there’s no canal left there now. But it permanently and dramatically affected the water table in that area. If you can imagine it, they sucked so much water out that it created a massive depression in the rocks, which still retains water today. Because of that, there’s even less chance of the river naturally popping up at the spring than there was before they built it.
I don’t know when the last time water actually flowed from the source of the Thames. Given some of the biblical rain we had at the beginning of the year, I’d like to think it might have been doing it then, but it wasn’t obvious.
Yeah, interesting.
The Map: