science

Run-of-the-river hydroelectricity

Run-of-the-river hydroelectricity is a science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Run-of-the-river hydroelectricity rather than just read about it. In short: Run-of-river hydroelectricity (ROR) or run-of-the-river hydroelectricity is a type of hydroelectric generation plant whereby little or no water storage is provided. Run-of-the-river power plants may have no water storage at all or a limited amount of storage, in which case the storage reservoir is referred to as pondage.

Key takeaways

Run-of-the-river hydroelectricity belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Run-of-the-river hydroelectricity to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Run-of-the-river hydroelectricity from memory before moving on to harder problems.

Reference excerpt

Run-of-river hydroelectricity (ROR) or run-of-the-river hydroelectricity is a type of hydroelectric generation plant whereby little or no water storage is provided. Run-of-the-river power plants may have no water storage at all or a limited amount of storage, in which case the storage reservoir is referred to as pondage. A plant without pondage is subject to seasonal river flows, so the plant will operate as an intermittent energy source. Conventional hydro uses reservoirs, which regulate water for flood control, dispatchable electrical power, and the provision of fresh water for agriculture.

Concept

Run-of-the-river, or ROR, hydroelectricity is considered ideal for streams or rivers that can sustain a minimum flow or those regulated by a lake or reservoir upstream. A small dam is usually built to create a headpond ensuring that there is enough water entering the penstock pipes that lead to the turbines, which are at a lower elevation. Projects with pondage, as opposed to those without pondage, can store water for daily load demands. In general, projects divert some or most of a river's flow (up to 95% of mean annual discharge) through a pipe and/or tunnel leading to electricity-generating turbines, then return the water back to the river downstream. Run-of-the-river projects are dramatically different in design and appearance from conventional hydroelectric projects. Traditional hydroelectric dams store enormous quantities of water in reservoirs, sometimes flooding large tracts of land. In contrast, run-of-river projects do not have the disadvantages associated with reservoirs and so cause fewer environmental impacts.

The use of the term "run-of-the-river" for power projects varies around the world. Some may consider a project run-of-the-river if power is produced with no water storage, but limited storage is considered run-of-the-river by others. Developers may mislabel a project run-of-the-river to soothe public perception about its environmental or social effects. The European Network of Transmission System Operators for Electricity distinguishes run-of-the-river and pondage hydropower plants, which can hold enough water to allow generation for up to 24 hours (reservoir capacity / generating capacity ≤ 24 hours), from reservoir hydropower plants, which hold far more than 24 hours of generation without pumps. The Bureau of Indian Standards describes run-of-the-river hydroelectricity as:

A power station utilizing the run of the river flows for generation of power with sufficient pondage for supplying water for meeting diurnal or weekly fluctuations of demand. In such stations, the normal course of the river is not materially altered. Many of the larger run-of-the-river projects have been designed to a scale and generating capacity rivaling some traditional hydroelectric dams. For example, the Beauharnois Hydroelectric Generating Station in Quebec is rated at 1,853 MW (Megawatts). Some run-of-the-river projects are downstream of other dams and reservoirs. The reservoir was not built by the project but takes advantage of the water supplied by it. An example would be the 1995 1,436 MW La Grande-1 generating station. Previous upstream dams and reservoirs were part of the 1980s James Bay Project. There are also small and somewhat-mobile forms of a run-of-the-river power plants. One example is the so-called electricity buoy, a small floating hydroelectric power plant. Like most buoys, it is anchored to the ground, in this case in a river. The energy within the moving water propels a power generator and thereby creates electricity. Prototypes by commercial producers are generating power on the Middle Rhine river in Germany and on the Danube river in Austria.

Major types The advantages and disadvantages of run-of-river dams depends on the type, the following sections generally refer to Dam-Toe unless otherwise stated. These are listed in order of least impact to most impact, as well as (on average) requisite project size.

Dam-Toe Dam-toe has no flow regulation and utilizes the natural flow of the river to turn the turbines. Electricity generation is heavily dependent on river flow.

Diversion Weir Diversion Weir has very little flow regulation, which is generally used to cover exclusively short-term peak times electricity demand. Diversion Weir is also heavily dependent on the natural river flow.

Pondage Similar to a regular dam, water is stored from lull periods to be used during peak-times. This allows for the pondage dams to provide for the regulation of daily and/or weekly flows depending on location.

Advantages When developed with care to footprint size and location, run-of-the-river hydro projects can create sustainable energy minimizing impacts to the surrounding environment and nearby communities. Run-of-the-river harnesses the natural potential energy of water by eliminating the need to burn coal or natural gas to generate the electricity needed by consumers and industry. Advantages include:

Cleaner power and fewer greenhouse gases Like all hydro-electric power, run-of-the-river harnesses the natural potential energy of water by eliminating the need to burn coal or natural gas to generate the electricity needed by consumers and industry. Moreover, run-of-the-river hydroelectric plants do not have reservoirs, thus eliminating the methane and carbon dioxide emissions caused by the decomposition of organic matter in the reservoir of a conventional hydroelectric dam. That is a particular advantage in tropical countries, where methane generation can be a problem.

Less flooding Without a reservoir, flooding of the upper part of the river does not take place. As a result, people remain living at or near the river and existing habitats are not flooded. Any pre-existing pattern of flooding will continue unaltered, which presents a flood risk to the facility and downstream areas.

Low-Impact implementation Due to their low impact, run-of-the-river dams can be implemented in existing irrigation dams with little to no change in the local fluvial ecosystem.

Disadvantages

… excerpt ends here. Continue reading the full article.

Illustrations

Worked examples

Example 1 — a first encounter with Run-of-the-river hydroelectricity

Start with the simplest possible case. Write down what Run-of-the-river hydroelectricity claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Run-of-the-river hydroelectricity before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Run-of-the-river hydroelectricity ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Run-of-the-river hydroelectricity

In research: Run-of-the-river hydroelectricity appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Run-of-the-river hydroelectricity in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Run-of-the-river hydroelectricity is common in secondary-school and first-year university syllabi. It links to neighbouring topics Hydroelectricity, so understanding it makes those chapters shorter.
In everyday life: Look for Run-of-the-river hydroelectricity outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Run-of-the-river hydroelectricity in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Run-of-the-river hydroelectricity means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Run-of-the-river hydroelectricity out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Run-of-the-river hydroelectricity in simple terms?

Why does Run-of-the-river hydroelectricity matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Run-of-the-river hydroelectricity?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Run-of-the-river hydroelectricity.