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Using a canal/aqueduct system for hydroelectric power rather than a dam

The hydroelectric power extracted by a river dam is related to the height of the water at the dam (with greater heights translating to higher water pressure at the bottom of the dam, and so more hydroelectric power), as well as to the river flow rate (the volume of water per minute flowing down the river at the dam location).

With this water height and water flow rate in mind, why not just tap the river several miles upstream, and run the river's water near horizontally along the mountain sides of the valley (via a horizontal canal or aqueduct built into the mountain side), and then some miles downstream, let this channelled water cascade down some large-bore vertical pipes, at the bottom of which you place hydroelectric turbines.

The water pressure and water flow rate at the bottom of the vertical pipes should be similar to that created by the dam. So a comparable amount of hydroelectric power could be extracted by this canal/aqueduct system.

The advantage of this canal/aqueduct approach is that you will not change the local environment like a dam does (via flooding the area behind the dam). And you do not have the hazard of a dam failure, which can lead to great damage to buildings and a loss of life.

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  • $\begingroup$ And you won’t be able to generate more based on the dam capacity, ie a larger Q over shorter time compared to river. $\endgroup$
    – Solar Mike
    Commented Sep 27, 2022 at 15:48
  • $\begingroup$ @SolarMike A much smaller (and vastly shallower) reservoir would suffice to tide over daily variations. $\endgroup$
    – SF.
    Commented Sep 27, 2022 at 15:50
  • $\begingroup$ @SF. but what about seasonal variations like producing power through the winter? 4 months... $\endgroup$
    – Solar Mike
    Commented Sep 27, 2022 at 15:54
  • $\begingroup$ @SolarMike Well, "slow-reaction" facilities like nuclear or coal plants can pick up the slack. Dam might be the optimal solution if you want to squeeze every last watt available from the river. If you accept some efficiency losses in order not to create a huge disruption to the ecology and the area in general (in form of creating a big lake) - this is a good alternative. $\endgroup$
    – SF.
    Commented Sep 28, 2022 at 8:31
  • $\begingroup$ @SF. So Dinorwig can go from no output to maximum output in under 12 seconds, can you do that with nuclear? or coal? Which is why it is used (and designed for) matching the changing demand. Oh, and as for ecology - check out where the lakes are... $\endgroup$
    – Solar Mike
    Commented Sep 28, 2022 at 8:35

2 Answers 2

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This is in fact quite common. It's called a diversion hydro facility as opposed to an impoundment (dam) facility or pumped storage facility.

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  • $\begingroup$ Of course, one drawback is that there's no capacitance, whereas a dam provides a pretty good "low-pass" filter. $\endgroup$
    – Carl Witthoft
    Commented Sep 28, 2022 at 11:56
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You need to remember that the daily electricity demand is not constant or deterministic (you don't know it exactly in advance). Generally through the day has fluctuation similar to the following:

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**Figure: energy demand daily profile (source: energymag))

So not all electricity generation units are created equal. For the purposes of this discussion, you can identify:

  • base units: these are units that are more efficient than other but you can't turn them on/off quickly enough. So these are units that usually work all the time and they get shutdown mainly for maintenance.
  • peak units: these are units that can quickly change their output power, to follow the demand. Hydro is one of the best cases there.

So, the main reason is that hydroelectric power units are usually units that deal with the peaks in the production. I.e. they can be turned from off to 100% output capacity in a matter of seconds. So in a sense they need to be able to store and release the energy when they are not used, hence the dams.

There is the concept of run-of-the-river hydroelectricity, , where by little or no storage water is provided. However, this is subject to seasonal river flows, thus the plant will operate as an intermittent energy source.

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  • $\begingroup$ It is more than a concept. I participated in the design of a run-the-river powerhouse in Ohio. I think TVA has a few as well. $\endgroup$
    – r13
    Commented Sep 27, 2022 at 16:54

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