Hi David

The key thing you need to know is the flow of the stream. Should be relatively easy to measure this if it currently flows through a tunnel. Ideally you'll need to be able to estimate the mean flow and the flow exceeded for 95 percent of the time. Flow and the hydraulic head, ie difference between water level and turbine determine the power you can generate. Without an idea of the flow it's difficult to tell if you're talking about a few watts or something substantial.

cheers
Mike

With hydro-electricity, anything less than mega-mega-projects are uneconomic unless the head (distance the water falls) is very large: say 100ft or more. The basic economic problem is that electricity potential is proportional to head x flow rate, but the machinery cost is proportional to flow rate alone. In theory rivers with a high flow rate but a small fall offer considerable power (as much as a small stream with a high fall) but the problem is that the machinery has to be much larger to cope with the great flow and is vastly more expensive. (Low-head machinery is usually of a totally different design.)

Quercus, you need to get involved with the British Hydro Association. http://www.british-hydro.org/ Don't be put off by the nay-sayers.

Good job there are some numerate eco-freaks about ;)

There is a project in Sheffield to do this:

http://sheffieldcommunityrenewables.org.uk/hydro.php

Nothing built yet, but there is one built here:

http://www.torrshydro.co.uk/Scheme.htm

Erm, its not my stream.
The reason i am asking for the forum's advice is so i can be a bit more credible when approaching the town council about thinking about a hydro scheme. The sceptics on here can play devils advocate for me - funcrusher!
The other reason i thought this was an ideal place for a hydro scheme is that because there will be a dam there is less of an issue with low flow rates. There will be a small lake behind a dam so you can smooth out the highs and lows a bit. Useful for other reasons as the park downstream flooded last week.

Anyway, the not my stream is roughly 3 meters wide. Depth ranges from 6 inches when low rainfall to 2 feet or more when high rainfall. Creates a flood and ford over a road which gets closed sometimes after heavy rain - another reason planners might be amenable to any scheme which controls the flow of the river.

Because of public location unlikely to be possible to make a V weir just yet - would probably need buy-in from Tory town council first.
Looks like I'll be playing lots of pooh sticks over the next few months.....

Posted By: Quercus Creates a flood and ford over a road which gets closed sometimes after heavy rain - another reason planners might be amenable to any scheme which controls the flow of the river.

Researching flooding in our Kent town for the last 200+ years, we discovered millers locked in battle with the town council until mid last century [edited - I'm a little behind the rest of the universe...]. Millers want to eke out the water for a steady supply: residents want low river levels in anticipation of winter rain. Modern flood reports say, "Risk of flooding much reduced since the disappearance of the mills and their damn leats." Or words to that effect...

Might be different for hydroelectric if a) it can efficiently use varying speeds of water, and b) it's supplementary to another source (eg grid).

Sorry, I meant "your" in the most general sense, as in the stream you'd mentioned. Re the dam, its useful for increasing the head and decreasing short term fluctuations, but you'll need to do some calculations to estimate the storage capacity of the lake to compare to the flow rate. Unless the lake is very large compared to the inflow, your storage capacity isn't going to help much regarding low flows. This is because low flow periods tend to be extended in time. Also worth considering is if your lake is at all ornamental then level fluctuations produce unsightly muddy areas round the edge when the level is low.
cheers
Mike

I recall from my geogrpahy A level (20 years ago) that to measure flow we held a tape measure across the river , and then at 1 m intervals took depth readings, and flow readings using a flow meter. You repeat this over a couple of sections say 10m apart. We also noted the position of recent flood levels to establish the flow rate likely in a flood!

Back at your desk you then plot a cross section of the river, work out the area, and then mutiply by the averaged flow rate to get an overall m3/s.

I wouldn't be suprised if someone has invented a Laser flow meter now that you just shine at the top of the river and it does the whole lot for you. But that would be no fun!

Simon

Hmm, latest news is nearly two years old. Not a good sign:

http://www.beck-mickle-hydro.co.uk/index.php?id=bmh_news

A flow meter? That's posh. I recall from my geogrpahy A level (40 years ago) that to measure flow we dropped an orange into the river and timed its passage along a measured distance. An orange floats deeply enough to be unaffected by wind, is the right shape for not getting stuck and is coloured brightly enough to be easily visible. Such equipment is renewable and at the end of the experiment it can be eaten with all wastes being compostable.