I measured the following and came out with an approximate potential power- I would appreciate it if someone could take a look over the numbers and advise where Ive gone wrong / or otherwise.

The existing feeder is a stone flag lined water channel = 1200mm wide x 35mm water depth - running at an average of 7.167 seconds to travel 4 meters = 0.018 cu mtrs / sec

The remains of the wheel suggest an overshot design, with the wheel 6ft in diameter x full channel width.

I have assumed a head of 1.8 mtrs (wheel diameter), and efficiency of 80% (wheel, inverter etc)

Which based on the flow rate recorded would generate 255 watts/hr - does this seam about right for what looks like a big wheel ?

OK - just trying to repeat the calculation, for fun:

Volume of water in 4 meters of channel 1200mm wide x 35mm water depth = 4 * 1.2 * 0.035 = 0.168 cu mtrs.

This is the amount flowing in 7.167 seconds, so divide by that to get 0.023 cu mtrs / sec (you said 0.018, but perhaps this is where you applied the 80%?).

Mass of water (assuming 1 cu mtr = 1000 kg) 23 kg/sec.

Gravitational potential energy (m * g * h) in that, for a fall of 1.8 meters: 23 * 9.8 * 1.8 = 406 joules / sec = 406 watts.

I've not allowed any 80% there, but still I'm getting a slightly larger number than you - albeit in the same ballpark. Don't say e.g. "255 watts/hr". It's just 255 watts or whatever (no hours involved). One could say "255 watt hours per hour" but that would be silly.

Once we agree on the figure (I'm just as likely to have messed up), then at least we know that if you could use 10 meters head instead of 1.8, then the output would be 5.5 times more.

Just out of interest: thought I'd see what the amount of kinetic energy in the moving water is (that's not saying that you'd necessarily extract ths, after all the water is still moving afterwards...). This time, it's 0.5 * m * v * v.

Velocity is 4 / 7.167 = 0.558 m/sec, so 0.5 * 23 * 0.558 * 0.558 = 3.6 watts. So insignificant in comparison to potential energy.