Let me start by introducing myself to you all, my name is Alasdair Brewster and I run a small consultancy business, as part of this one of my main clients is The Scottish Environment Protection Agency or SEPA. I mainly look at river restoration from an engineering perspective to do with the EU water framework directive, however my background includes amongst other things hydro and I currently advise SEPA on applications. I have been working in hydro on and off since the early 90's.
One important part with any hydro project is the passage of fish, and in particular Salmon trout and eels. The requirement for a fishpass is usually a requirement of any scheme. Don't underestimate the cost of a fish pass, to give you an example on a small weir circa 15m across with a head difference of 1.2m the cost of design procurement and installation will be circa £80-100k.
I cant speak for any projects south of the border under the EA, but if anyone needs advice from north of the border i can probably help.
The biggest issue with 99% of all weirs i come into contact with is they were originally built 100's of years ago and usually have been bodged together ever since. most owners of structures don't relise that if the structure fails and causes damage they will be liable. Ive yet to find anyone who has their weir insured!
Mini schemes are fine even at 2kw you can still make money, its all down to the site. if you are lucky enough to have a water fall below your site and its impassable to fish (this will have to proved) you can avoid a fishpass.
Before you do any river works remember you need to have, a licence, silt control measures and if plant is used hydrocarbon booms, this is regardless of where you live in the UK.
if you need any help, PM me.