Small dams in UK

Hi there.  I've just acquired c1Ha of land which I'm keen to turn into a wonderful resilient ecosystem in all the usual ways.
It has a small stream which enters my land through a 19th century drainage conduit and runs in a deep gully, through a pipe under a large earthen bank and then continues in the gully on the other side.
I'm very interested in damming the stream at the point it goes through the pipe under the bank to create a water reservoir for irrigation and a habitat for waterfowl.

I'm wondering if anyone here has any experience with doing this kind of thing in the Uk.  In particular:
- Where to get advice on how to make it strong enough to be safe
- How to deal with the inevitable bureaucracy (I'm in Scotland so I think SEPA is the relevant body for me)

Any and all advice much appreciated!

Hi Jacob, welcome to Permies! And hello from Skye.
Sepa can really give you a headache, depending on your purposes, but I think just damming the water is not so much an issue as diverting it and using it in another way. After all, if the culvert happened to get blocked......
Without seeing the earth bank, I wonder about it: why it was put across the gully for instance. Unless it is designed to hold water (clay layer etc.) the bank is likely to be porous and that could cause structural problems down the line. Does the stream run all the time? Where do you need the irrigation water and how will you get it there?
Lots of questions rather than answers I'm afraid!