Dams and barrages

Once a site for a hydropower scheme has been identified, there are normally two ways of exploiting it. The first is to build a dam and create a reservoir behind it from which water is taken to drive hydraulic turbines in the project's powerhouse. The second, called a run-of-river scheme, does without a reservoir, though it will usually involve some sort or barrage. Instead it takes water directly from the river to the powerhouse where the turbines are installed.

Run-of-river project

A run-of-river scheme is the simplest and cheapest hydropower project to develop. Since it requires no dam, a major constructional cost is avoided.

Intake from river

Headrace (canal, pipeline or tunnel)

Surge chamber

Intake from river

Headrace (canal, pipeline or tunnel)

Surge chamber

Tailrace - discharge to river (canal, pipeline or tunnel)

Figure 8.1 Run-of-river hydropower scheme. Source: Mott MacDonald

Tailrace - discharge to river (canal, pipeline or tunnel)

Figure 8.1 Run-of-river hydropower scheme. Source: Mott MacDonald

Geological problems associated with dam construction (see above) are avoided too. However some sort of diversion structure will be required to direct water from the river into a channel and pipework which will carry the water to the powerhouse. And if, in order to generate a significant head of water, the powerhouse is a long way from the point where the water is taken from the river (the distance can be tens of kilometres in some cases) then the geology of the route will need to be studied carefully too.

The simplicity of the run-of-river scheme is attractive but it is also the main weakness of this type of development. With no dam to conserve water, the power plant must rely exclusively on the flow of water in the river. As this fluctuates, so will the amount of power that can be generated. Under drought conditions the plant will be able to generate no power, whereas when the river is in flood, much water will have to be allowed to flow past the diversion system without being exploited. Nevertheless this type of project does have significant advantages besides cost, particularly because of the small amount of environmental disruption it causes.

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