Hello, thank you for your question. My name is Tony and I can assist you with your question.
If this attaches to a wall that acts as a boundary between the two properties, then before he did any work like this, he should have followed the Part Wall Act etc. 1996 procedure. If he has not done this, then there is the prospect of being able to seek a court injunction to force him to remove it.
The whole point of the 1996 Act is that it prevents issues like this arising, because where neighbours disagree about something, a surveyor is appointed and they decide what can and cannot be done.
The idea being that the surveyor acts as adjudicator and adjudicates what is reasonable, what needs to be done to protect structures, and what materials etc. should be used.
Additionally, you might have a cause of action based in the law of nuisance, as a result of the noise that now occurs when it trains and the fact water is being retained, which may cause actual physical damage.
I believe that, from what you've said, there are grounds here to look at suing him, to force him to remove what he has put up.
I would always recommend you use a solicitor when taking this kind of action against somebody, because it's not like suing for a small debt, and so it can be pretty complicated.
Does this answer your question, is there anything you would like to chat through with me? If so, just let me know and when I'm back on I will answer it for you. Otherwise, could I ask you to rate the answer for me please. Thank you!