If the bridge had not startled Hazel, the river did. He remembered the Enborne, its surface broken by gravel spits and plant growth. The Test, a weed-cut, carefully-tended trout stream, seemed to him like a world of water. A good ten yards wide it was, fast-flowing and smooth, spangling and dazzling in the evening sun… The water was very clear, with a bed of clean, yellow gravel, and even in the middle was hardly four feet deep. As the rabbits stared down they could discern, here and there, a very fine scour, like smoke – chalk and powdered gravel carried along by the river as dust is blown on the wind.
Richard Adams, Watership Down
This one isn’t so much a newsletter as a lame excuse note for why I didn’t get around to writing one. I’ve been busy physicsing, jobhunting, procrastinating from jobhunting, and trying to finish blog posts. It’s annoying because I’m building up a massive backlog of things I want to talk about, but I don’t have time.
Thanks very much for all the perturbations last month! I’m still feeling in need of perturbation, so please add more if you want. Work has been calmer this month, so I’m feeling less stressed out, but I do need to make a plan to get out soon. I’m sort of assuming that I’m going to end up getting another programming job, and I’m making (slightly lacklustre) attempts in that direction, but I’m still open to hearing weird ideas.
In lieu of a proper newsletter, please accept this infodump on chalk streams.
Infodump on chalk streams
Apparently I’m interested in chalk streams now. They look like this:
This is the River Test in Hampshire. It’s not a great photo, but it’s what I took so it’ll have to do. It’s very shallow compared to its width, only a few inches deep. And it’s VERY clear – like tap water. Or like gin – apparently the phrase is ‘gin clear’. There’s no sediment, no thick weeds, and no debris being carried down. These are classic features of chalk streams. In fact, it’s pretty much the canonical chalk stream, along with its near neighbour the Itchen.
I crossed the Test while walking last weekend. I went to a wedding last Saturday, woke up the next morning with no hangover and decided it would be more fun to walk the eight miles to the nearest station rather than getting a taxi. Most of it was fairly unremarkable walking across fields, but I was intrigued by the Test and started reading about chalk streams when I got back. Here is my infodump (if I didn’t give a source it probably came from Wikipedia or this page on the Chilterns):
- Chalk streams are fed from groundwater held by chalk, which absorbs water like a sponge. This slow release of water helps regulate the flow rate, which is very stable. The water also stays at a very regular temperature year round, about 10 °C – I guess because the temperature is more stable underground?
- If the water table drops then the river starts from somewhere lower. So higher stretches may not exist in summer. These seasonal stretches are called winterbournes. There are lots of villages called Winterbourne Something in Dorset.
- They’re clear because chalk doesn’t produce sediment, it dissolves in water instead. Also the steady flow is less likely to pick up debris.
- The stones on the bottom are flint gravel – flint is common in chalk.
- Most chalk streams are in the south and east of England (a bunch of places say about 85% of them, but there must be some slop in exactly how they’re defined), with some others in north west Europe.
- I’m from Sussex, and I wondered why we didn’t have chalk streams, given that we have chalk. This source explains that we do have three chalk streams, but they aren’t quite the classic type as they have a much steeper gradient, flowing from the South Downs to the sea in quite a short distance. So they have more debris and stuff in them.
- The Test features in Watership Down, one of my favourite books. The rabbits escape in a punt, and Adams points out that the plan only works because the Test is so free-flowing, with no debris to impede it.
- Fly fishing is popular on chalk streams. I saw a lot of trout.
- Chalk streams are under pressure from overuse of water (this is called ‘over-abstraction’ apparently). Threats include FOREIGN SALAD:
- More importantly, the main threat is normal domestic water use. There are a lot of people in the south east.
I definitely will finish up my posts on negative probability. Maybe even today! It’s ended up as two posts, one assuming no particular maths or physics background and one that goes into the details. It’s a lot more comprehensible than the very muddled newsletter version, so if you suffered through that one, this will be better.
Other than that I will continue being perturbed. And maybe write a proper newsletter.
Cheers, and thanks for reading,