Two people have offered theories about rain in tunnels, and in a flash of the blindingly obvious I have just thought of another.
My good friend David, aka Rainman – who sent in a reply on the wrong post (Doh)- reckons the dripping in Crick tunnel is seepage from ground water running down through a permeable layer underground and moving downhill over a non permeable layer. He is probably right and I may find out for sure on our sailing weekend next month when I hope to be joined by another old friend PDS who does in fact know everything, especially about geology. (and cement).
Which means I have to doubt the word of another kind contributor Bobr, all the way from N Carolina who reckoned it was condensation. Sorry Bob. What leads me to this conclusion is that there are a fair few canal tunnels of similar length, but they have widely varying amounts of rainfall inside. Some are virtually dry, whereas Crick in particular is very wet.
Which leads us to the question, why are some tunnels wetter than others? For example Husbands Bosworth tunnel, not far from Crick is generally bone dry. Can it be to do with air supply? I don’t think so, although that one is 1100 odd yards long and Crick tunnel is nearly a mile. Interestingly I haven’t noticed any air shafts in Crick tunnel. Air shafts generally make good waterfalls as anyone going through Braunston tunnel will testify. Is the geology at HB different from Crick? Possibly but I have a better idea.
Tunnels have been built by all sorts of engineers over the years and many of them have been repaired and relined since. Could the variation in wetness simply be due to how well the tunnel was lined? I reckon that might have a lot to do with it. Some of them just keep the water out better.
But, going back to where this all started, I’m still amazed that Crick is still dripping after 20 odd months with hardly any rain!