all the water is falling at 9.8 m/s/s
it just travels horizontaly because it cant travel verticaly.
Well, actually it isn't falling at 9.8 m/s/s, it is accelerating at that rate. And the actual flow rate at the bottom of the run won't match that acceleration, because of friction with the sides of the stream.
so almost as soon as the water is released from the system back into the river the water will accelerate back to its original or close to its original speed , because of gravity.
Actually it will come out of the bottom of the penstock at a significantly lower speed than it has when it enters the turbine. The turbine extracts a great deal of the energy from the flow and thus slows it down. I'm not sure of the details because I don't know exactly what the flow equations would be. But it is possible that the flow from the penstock would actually have a lower speed than the flow in the original stream bed. That would depend on a number of factors, including the percentage of the stream that was passed through the penstock.
We should also keep in mind that the flow rate in the original bed would be lower than just the percentage that is drawn off to feed the generator. That is if 50% of the water is drawn off to the generator then the flow will be 50%, but the stream beds area will not be cut in half. So the resistance to flow will not be cut in half. So the stream may not gain as much energy as it would at full flow.
I keep looking at that and thinking I should add some more to it, but I think that should be enough to think about for right now.
Bill Gill
