Reservoir projects

The alternative to the run-of-river is the reservoir project. This will involve a major civil engineering undertaking, construction of a dam. If a dam is to be constructed, then a very careful geological survey of the underlying rock will be needed and any faults identified. Geological faults or unsuitable substrata need not prevent construction of a dam but if they are only discovered during construction they are likely to result in massive additional costs and will delay construction for months or years.

The purpose of a dam is to create a reservoir of water which builds up behind it. Once created, the reservoir allows some measure of control over the flow of water in the river beyond the dam and consequently the flow through the turbines in the powerhouse. Water can be conserved during periods of high flow and used up when rainfall is low. A dam can also be used for flood control.

Headrace

Intake (pipeline or tunnel) Surge chamber

Headrace

Intake (pipeline or tunnel) Surge chamber

Figure 8.2 Hydropower scheme with dam and reservoir. Source: Mott MacDonald

There are three principle types of dam used for hydropower projects, concrete dams, arch dams and embankment dams. A concrete dam is basically a massive concrete structure which, as a result of its weight, resists the pressure of water behind it. Care must be taken, however, to prevent water flowing around or beneath the dam. Concrete construction is normally employed where a high dam can be built across a narrow ravine.

Where conditions permit, the sides of such a ravine can be used as part of the construction. If the rock either side of dam site is sound and strong, it is possible to build an arch dam. In principle this acts in exactly the same way as an arch in a building, but with the bow of the arch facing upstream to resist the pressure of water behind it rather that vertically, supporting the weight of a building. Provided the sides of the arch dam are anchored securely to the rock at each side, the arch is incredibly strong and requires much less material than other types of dam.

When a broad, shallow dam is required, an embankment dam is the more normal choice. This is constructed from a mixture of materials but the major component is usually earth if this is available locally. The dam allows a certain amount of water to seep through it. This must be carefully controlled to prevent damage to the structure. It is also vital to ensure that the water in the reservoir does not flow over the top of the dam; if it does it could wash the structure away.

The cost of a dam is a major factor in the financing of a hydropower project. The dam is also the part of the project which is likely to cause the most controversy. A reservoir behind a dam will inundate a large area of land, displacing people and destroying habitats. Downstream habitats may also be effected by the reduced flow of water, at least while the dam is filling. Detailed environmental impact studies will normally be required before such a project can proceed.

Solar Stirling Engine Basics Explained

Solar Stirling Engine Basics Explained

The solar Stirling engine is progressively becoming a viable alternative to solar panels for its higher efficiency. Stirling engines might be the best way to harvest the power provided by the sun. This is an easy-to-understand explanation of how Stirling engines work, the different types, and why they are more efficient than steam engines.

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