
Run-of-river hydroelectricity (ROR) or run-of-the-river hydroelectricity is a type of
hydroelectric
Hydroelectricity, or hydroelectric power, is Electricity generation, electricity generated from hydropower (water power). Hydropower supplies 15% of the world's electricity, almost 4,210 TWh in 2023, which is more than all other Renewable energ ...
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
Pondage usually refers to the comparably small water storage behind the weir of a run-of-the-river hydroelectric power plant. Such a power plant has considerably less storage than the reservoirs of large dams and conventional hydroelectric station ...
. A plant without pondage is subject to seasonal river flows, so the plant will operate as an
intermittent energy source
Variable renewable energy (VRE) or intermittent renewable energy sources (IRES) are renewable energy sources that are not dispatchable due to their fluctuating nature, such as wind power and solar power, as opposed to controllable renewable ener ...
. Conventional hydro uses
reservoir
A reservoir (; ) is an enlarged lake behind a dam, usually built to water storage, store fresh water, often doubling for hydroelectric power generation.
Reservoirs are created by controlling a watercourse that drains an existing body of wa ...
s, which regulate water for
flood control
Flood management or flood control are methods used to reduce or prevent the detrimental effects of flood waters. Flooding can be caused by a mix of both natural processes, such as extreme weather upstream, and human changes to waterbodies and ru ...
,
dispatchable electrical power, and the provision of
fresh water
Fresh water or freshwater is any naturally occurring liquid or frozen water containing low concentrations of dissolved salt (chemistry), salts and other total dissolved solids. The term excludes seawater and brackish water, but it does include ...
for
agriculture
Agriculture encompasses crop and livestock production, aquaculture, and forestry for food and non-food products. Agriculture was a key factor in the rise of sedentary human civilization, whereby farming of domesticated species created ...
.
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
A penstock is a sluice or gate or intake structure that controls water flow, or an enclosed pipe that delivers water to hydro turbines and sewerage systems. The term is of Scots origin, and was inherited from the earlier technology of mill pond ...
pipes that lead to the
turbines
A turbine ( or ) (from the Greek , ''tyrbē'', or Latin ''turbo'', meaning vortex) is a rotary mechanical device that extracts energy from a fluid flow and converts it into useful work. The work produced can be used for generating electrical ...
, 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)
[Knight Piesold Consulting]
Plutonic Hydro Inc. Bute Inlet Project. Summary of Project Intake and Turbine Parameters
Knight Piesold Consulting. through a pipe and/or tunnel leading to electricity-generating turbines, then return the water back to the river downstream.
[Douglas T, Broomhall P, Orr C. (2007)]
Run-of-the-River Hydropower in BC: A Citizen's Guide to Understanding Approvals, Impacts and Sustainability of Independent Power Projects
/ref>
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
A reservoir (; ) is an enlarged lake behind a dam, usually built to store fresh water, often doubling for hydroelectric power generation.
Reservoirs are created by controlling a watercourse that drains an existing body of water, interrup ...
, 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.[Hydromax Energy Limited]
Hydromax Energy Limited website
/ref>
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 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
The Bureau of Indian Standards (BIS) is the National Standards Body of India under Department of Consumer affairs, Ministry of Consumer Affairs, Food and Public Distribution, Ministry of Consumer Affairs, Food & Public Distribution, Government ...
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.[Plutonic Power (2008)]
Revised Project Description for Bute Inlet Hydroelectric Project Requirements. P1
Plutonic Power. For example, the Beauharnois Hydroelectric Generating Station
The Beauharnois generating station is a run-of-the-river hydroelectric power station along the Saint Lawrence Seaway on the Saint Lawrence River, in Quebec, Canada. The station was built in three phases, and comprises 36 turbines, capable of gene ...
in Quebec is rated at 1,853 MW. 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
The La Grande-1 (LG-1) is a hydroelectric power station on the La Grande River that is part of Hydro-Québec's James Bay Project. The station can generate 1,436 MW and was commissioned in 1994–1995. A run of the river generating station, ...
. Previous upstream dams and reservoirs were part of the 1980s James Bay Project
The James Bay Project () involves the construction of a series of hydroelectricity, hydroelectric power stations on the La Grande River in northwestern Quebec, Canada by government-owned corporation, state-owned public utility, utility Hydro-Qué ...
.
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
Hydroelectricity, or hydroelectric power, is Electricity generation, electricity generated from hydropower (water power). Hydropower supplies 15% of the world's electricity, almost 4,210 TWh in 2023, which is more than all other Renewable energ ...
. 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
Electricity generation is the process of generating electric power from sources of primary energy. For utilities in the electric power industry, it is the stage prior to its delivery ( transmission, distribution, etc.) to end users or its stora ...
and thereby creates electricity. Prototypes by commercial producers are generating power on the Middle Rhine
Middle Rhine (, ; kilometres 529 to 660 of the Rhine) is the section of the Rhine between Bingen and Bonn in Germany. It flows through the Rhine Gorge (), a formation created by erosion, which happened at about the same rate as an uplift i ...
river in Germany and on the Danube
The Danube ( ; see also #Names and etymology, other names) is the List of rivers of Europe#Longest rivers, second-longest river in Europe, after the Volga in Russia. It flows through Central and Southeastern Europe, from the Black Forest sou ...
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
Electricity generation is the process of generating electric power from sources of primary energy. For electric utility, utilities in the electric power industry, it is the stage prior to its Electricity delivery, delivery (Electric power transm ...
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
Natural gas (also fossil gas, methane gas, and gas) is a naturally occurring compound of gaseous hydrocarbons, primarily methane (95%), small amounts of higher alkanes, and traces of carbon dioxide and nitrogen, hydrogen sulfide and helium ...
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
Natural gas (also fossil gas, methane gas, and gas) is a naturally occurring compound of gaseous hydrocarbons, primarily methane (95%), small amounts of higher alkanes, and traces of carbon dioxide and nitrogen, hydrogen sulfide and helium ...
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
"Unfirm" power
Run-of-the-river power is considered an "unfirm" source of power: a run-of-the-river project has little or no capacity for energy storage[Douglas, T. (2007)]
"Green" Hydro Power: Understanding Impacts, Approvals, and Sustainability of Run-of River Independent Power Projects in British Columbia
Watershed Watch. and so cannot co-ordinate the output of electricity generation to match consumer demand. It thus generates much more power when seasonal river flows are high (spring freshet
The term ''freshet'' is most commonly used to describe a snowmelt, an annual high water event on rivers resulting from snow and river ice melting.
Description
A spring freshet can sometimes last several weeks on large river systems, resulting ...
),[Wilderness Committee]
Wilderness Committee Comments on the Draft Terms of Reference, Bute Inlet Hydroelectric Private Power Project. Letter to Kathy Eichenberger, Project Assistant Director. P1
Wilderness Committee. and depending on location, much less during drier summer months or frozen winter months.
Depending on location and type, the plant will most likely have a lower head of water than from a dam, and will thus generate less power.
Availability of sites
The potential power at a site is a result of the head
A head is the part of an organism which usually includes the ears, brain, forehead, cheeks, chin, eyes, nose, and mouth, each of which aid in various sensory functions such as sight, hearing, smell, and taste. Some very simple ani ...
and flow of water. By damming a river, the head is available to generate power at the face of the dam. A dam may create a reservoir hundreds of kilometres long, but in run-of-the-river the head is usually delivered by a canal, pipe or tunnel constructed upstream of the power house. The cost of upstream construction makes a steep drop desirable, such as falls or rapids.
Environmental impacts
Small, well-sited run-of-the-river projects can be developed with minimal environmental impacts. Larger projects have more environmental concerns. For fish-bearing rivers, a ladder may be required, and dissolved gases downstream may affect fish.
In British Columbia
British Columbia is the westernmost Provinces and territories of Canada, province of Canada. Situated in the Pacific Northwest between the Pacific Ocean and the Rocky Mountains, the province has a diverse geography, with rugged landscapes that ...
, the mountainous terrain and wealth of big rivers have made it a global testing ground for 10–50 MW run-of-river technology. As of March 2010, there were 628 applications pending for new water licences solely for power generation, representing more than 750 potential points of river diversion.[IPPwatch.com website]
IPPwatch.com
.
In undeveloped areas, new access roads and transmission lines can cause habitat fragmentation
Habitat fragmentation describes the emergence of discontinuities (fragmentation) in an organism's preferred environment (habitat), causing population fragmentation and ecosystem decay. Causes of habitat fragmentation include geological proces ...
, allowing the introduction of invasive species.
Vulnerable to climate change
Run-of-the-river projects strongly depend on the consistent flow of water, as they lack reservoirs and depend on the natural flow of rivers. Consequently, these projects are more vulnerable to climate change compared to storage-based projects. Short-term climate anomalies such as the El Niño Southern Oscillation (ENS
can significantly disrupt the flow and can have a profound impact on the operation of these projects. Thus, incorporating climate change considerations into the initial design and location selection of run-of-the-river projects can help mitigate the vulnerability of these projects to climate-related disruptions.
Major examples
* Jirau Dam
The Jirau Dam is a rock-fill dam with an asphalt-concrete core, in the Madeira River in the state of Rondônia, Brazil. The dam's hydroelectric power stations have 50 turbines each 75 MW resulting total installed capacity of 3,750 MW. The power p ...
, Rondônia
Rondônia () is one of the 26 states of Brazil, located in the northern subdivision of the country (central-western part). It is bordered by Acre (state), Acre in the west,
Amazonas, Brazil, Amazonas in the north, Mato Grosso in the east, and Bo ...
, Brazil
Brazil, officially the Federative Republic of Brazil, is the largest country in South America. It is the world's List of countries and dependencies by area, fifth-largest country by area and the List of countries and dependencies by population ...
3750 MW
* Santo Antônio Dam
The Santo Antônio Dam is a hydroelectric dam on the Madeira River southwest of Porto Velho in the state of Rondônia, Brazil. The dam's run-of-the-river hydroelectric power station has 50 turbines, each rated at 71.6 MW resulting in a total inst ...
, Rondônia
Rondônia () is one of the 26 states of Brazil, located in the northern subdivision of the country (central-western part). It is bordered by Acre (state), Acre in the west,
Amazonas, Brazil, Amazonas in the north, Mato Grosso in the east, and Bo ...
, Brazil
Brazil, officially the Federative Republic of Brazil, is the largest country in South America. It is the world's List of countries and dependencies by area, fifth-largest country by area and the List of countries and dependencies by population ...
3580 MW
* Chief Joseph Dam
The Chief Joseph Dam is a concrete gravity dam on the Columbia River, upriver from Bridgeport, Washington. The dam is upriver from the mouth of the Columbia at Astoria, Oregon. It is operated by the U.S. Army Corps of Engineers, USACE Chief Jose ...
, Washington
Washington most commonly refers to:
* George Washington (1732–1799), the first president of the United States
* Washington (state), a state in the Pacific Northwest of the United States
* Washington, D.C., the capital of the United States
** A ...
, United States
The United States of America (USA), also known as the United States (U.S.) or America, is a country primarily located in North America. It is a federal republic of 50 U.S. state, states and a federal capital district, Washington, D.C. The 48 ...
2620 MW
* John Day Dam
The John Day Dam is a concrete gravity run-of-the-river dam spanning the Columbia River in the northwestern United States. The dam features a navigation lock plus fish ladders on both sides. The John Day Lock has the highest lift (at ) of any ...
, Oregon
Oregon ( , ) is a U.S. state, state in the Pacific Northwest region of the United States. It is a part of the Western U.S., with the Columbia River delineating much of Oregon's northern boundary with Washington (state), Washington, while t ...
/Washington, United States
The United States of America (USA), also known as the United States (U.S.) or America, is a country primarily located in North America. It is a federal republic of 50 U.S. state, states and a federal capital district, Washington, D.C. The 48 ...
2160 MW
* Beauharnois Hydroelectric Power Station, Quebec
Quebec is Canada's List of Canadian provinces and territories by area, largest province by area. Located in Central Canada, the province shares borders with the provinces of Ontario to the west, Newfoundland and Labrador to the northeast, ...
, Canada
Canada is a country in North America. Its Provinces and territories of Canada, ten provinces and three territories extend from the Atlantic Ocean to the Pacific Ocean and northward into the Arctic Ocean, making it the world's List of coun ...
, 1903 MW
* The Dalles Dam
The Dalles Lock and Dam is a concrete-gravity run-of-the-river dam spanning the Columbia River, east of the city of The Dalles, Oregon, United States. It joins Wasco County, Oregon, with Klickitat County, Washington, upriver from the mouth o ...
, Oregon/Washington, United States 1878 MW
* Teles Pires Dam
The Teles Pires Dam is a run-of-the-river hydroelectric dam on the Teles Pires River, upstream of the confluence with the Tapajós river, on the border of the Brazilian states of Mato Grosso and Pará. The dam impounds a reservoir ( origina ...
, Brazil 1820 MW
* Inga Dams
The Inga Dams (French language, French: ''Barrages d'Inga''; Dutch language, Dutch: ''Ingadam'') are two hydroelectric dams connected to one of the largest waterfalls in the world, Inga Falls. They are located in the western Democratic Republic o ...
, Democratic Republic of the Congo
The Democratic Republic of the Congo (DRC), also known as the DR Congo, Congo-Kinshasa, or simply the Congo (the last ambiguously also referring to the neighbouring Republic of the Congo), is a country in Central Africa. By land area, it is t ...
1775 MW
* Satluj Jal Vidyut Nigam Ltd, Satluj River
The Sutlej River or the Satluj River is a major river in Asia, flowing through China, India and Pakistan, and is the longest of the five major rivers of the Punjab region. It is also known as ''Satadru''; and is the easternmost tributary of th ...
, Shimla
Shimla, also known as Simla ( the official name until 1972), is the capital and the largest city of the northern Indian state of Himachal Pradesh. In 1864, Shimla was declared the summer capital of British India. After independence, the city ...
, India
India, officially the Republic of India, is a country in South Asia. It is the List of countries and dependencies by area, seventh-largest country by area; the List of countries by population (United Nations), most populous country since ...
, 1500 MW
* Ghazi-Barotha Hydropower Project
Ghazi-Barotha Hydropower Project () is a 1,450 MW run-of-the-river hydropower project on the Indus River in Pakistan. It is located about west of Attock in the Punjab province. Construction of the project began in 1995. It consists of five ...
, Khyber Pakhtunkhwa
Khyber Pakhtunkhwa (; ; , ; abbr. KP or KPK), formerly known as the North West Frontier Province (NWFP), is a Administrative units of Pakistan, province of Pakistan. Located in the Northern Pakistan, northwestern region of the country, Khyber ...
, Pakistan
Pakistan, officially the Islamic Republic of Pakistan, is a country in South Asia. It is the List of countries and dependencies by population, fifth-most populous country, with a population of over 241.5 million, having the Islam by country# ...
1450 MW
* Gezhouba Dam
The Gezhouba Dam or Gezhouba Water Control Project () on the Yangtze River is located in the western suburbs of Yichang, in central China's Hubei province. One of the largest run-of-the-river dams, it sits several kilometers upstream from downto ...
, Yichang
Yichang ( zh, s= ), Postal Map Romanization, alternatively romanized as Ichang, is a prefecture-level city located in western Hubei province, China. Yichang had a population of 3.92 million people at the 2022 census, making it the third most pop ...
, Hubei
Hubei is a province of China, province in Central China. It has the List of Chinese provincial-level divisions by GDP, seventh-largest economy among Chinese provinces, the second-largest within Central China, and the third-largest among inland ...
, China 2715 MW
See also
*Environmental impact of electricity generation
Electric power systems consist of generation plants of different energy sources, Electric power transmission, transmission networks, and Electric power distribution, distribution lines. Each of these components can have Biophysical environment, ...
*Environmental impacts of reservoirs
The environmental impact of reservoirs comes under ever-increasing scrutiny as the global demand for water and energy increases and the number and size of reservoirs increases.
Dams and reservoirs can be used to supply drinking water, generate ...
*Hydropower
Hydropower (from Ancient Greek -, "water"), also known as water power or water energy, is the use of falling or fast-running water to Electricity generation, produce electricity or to power machines. This is achieved by energy transformation, ...
*Small hydro
Small hydro is the generation of hydroelectric power on a smaller scale as compared to traditional large-scale hydro. Exact definitions vary by country, but small hydro power (SHP) projects are typically less than 50 megawatts (MW) and can be furt ...
*Micro hydro
Micro hydro is a type of hydroelectric power that typically produces from 5 kW to 100 kW of electricity using the natural flow of water. Installations below 5 kW are called pico hydro. These installations can provide power to an ...
*Pico hydro
Pico hydro is a term used for hydroelectric power generation of under 5 kW. These generators have proven to be useful in small, remote communities that require only a small amount of electricity for example, to power one or two fluorescent l ...
* Gravitation water vortex power plant
The gravitation water vortex power plant is a type of micro hydro vortex turbine system which converts energy in a moving fluid to rotational energy using a low hydraulic head of . This technology is based on a round basin with a central drain. Ab ...
* Tidal power
Tidal power or tidal energy is harnessed by converting energy from tides into useful forms of power, mainly electricity using various methods.
Although not yet widely used, tidal energy has the potential for future electricity generation. T ...
* Marine current power
Marine currents can carry large amounts of water, largely driven by the tides, which are a consequence of the gravitational effects of the planetary motion of the Earth, the Moon and the Sun. Augmented flow velocities can be found where the underw ...
Notes
References
* Freedman, B., 2007, Environmental Science: a Canadian Perspective; 4th edition, Pearson Education Canada, Toronto, pp 226,394.
{{DEFAULTSORT:Run-Of-The-River Hydroelectricity
Hydroelectricity