Run-of-the-river Hydroelectricity in Simple Terms

Run-of-the-river Hydroelectricity

Run-of-the-river Hydroelectricity Run-of-river hydroelectricity (ROR), sometimes known as run-of-the-river hydroelectricity, is a type of hydroelectric power facility in which there is little or no water storage. Run-of-the-river power plants may have no or very little water storage, in which case the storage reservoir is referred to as pondage. Without pondage, a plant will be vulnerable to seasonal river flows, making it an unreliable energy source. Reservoirs, which regulate water for flood control, dispatchable electrical generation, and the provision of fresh water for agriculture, are used in traditional hydro.

Run-of-the-river Hydroelectricity
A sample of an Elements of Run-of-the-river Hydroelectricity (Reference:


Concept of Run-of-the-river Hydroelectricity

With large hydropower’s widespread success as the world’s largest renewable energy source, it’s only natural that countries pursue small hydro, or run-of-river, development as well. Large hydro dams are expensive to construct, and new facilities necessitate lengthy consultation, planning, environmental assessments, and construction timeframes. Small hydro has risen to prominence as a result of these considerations. Small hydro is intriguing because of its decreased environmental consequences, the possibility for lower development costs, and the abundance of possible sites. It is an old technology with numerous modern developments.

Find out More about Renewable Energy Device & Equipment in Linquip

When it comes to small hydro, the public sometimes confuses the reduction of environmental and social problems with their eradication. It’s crucial to remember that though small hydro has a lower impact on aquatic ecosystems and local populations, like all kinds of energy, it can’t totally eliminate stress on the plant, animal, and human health. Furthermore, the negative, cumulative impact of multiple river systems functioning inside the same river network may cause further issues, and study in this area is critically inadequate.

Small hydro, while not yet cost-competitive with large hydro, can nonetheless produce lower costs per kWh than some alternative sources, such as diesel-electric. Small hydro has found a place in some nations, such as Canada, in replacing polluting diesel generators in isolated, often First Nations, settlements. However, because the risk of changing river ecosystems is closely linked to the stability of traditional livelihoods, this development must be done with caution. In many regions, social and environmental concerns are inextricably linked.

Small hydro has been hindered by long and often  permitting processes, as well as apprehension caused by unmet social and environmental issues. If research and development (R&D) becomes a higher priority, small hydro will likely establish a bigger presence in the following years. In order for expansion to actually take root, improvements in the technology’s overall efficiency, as well as its environmental status, must be made.

For a better understanding of the concept of Run-of-the-river Hydroelectricity, watch this video.


Working Principle of Run-of-the-river Hydroelectricity

Two key features must be considered for run-of-the-river hydroelectricity:

See List of all Renewable Energy Manufacturing Companies in Linquip
  • The water storage capacity of run-of-river power facilities is limited.
  • They generate far less electricity than hydroelectric dams since they can’t hold water.

Running water is diverted from a flowing river and steered down a conduit, or penstock, that flows to a generating house in a run of the river system. The force of moving water turns a turbine, which drives a generator. The water is returned to the main river, a short distance downstream. Run-of-river systems differ from big hydroelectric systems in this respect that they do not dam the river to construct a water reservoir. Most run-of-river systems employ a tiny dam, or weir, to guarantee that adequate water reaches the penstock, as well as a tiny reservoir known as pondage, to store small amounts of water for immediate use. They cannot, however, store considerable amounts of water for later use.

The lack of a significant reservoir has two major consequences. The first is that if or when the river’s water levels are diminished due to drought or water extraction, the “fuel” for the river system’s operation is diminished or unavailable totally. There is no stored power without a dam to hold water. This indicates that the capacity factor of run-of-river projects ranges between 40% and 80%.

Due to the lack of a reservoir, the capacity of a run-of-the-river plant is limited, and they are only practical on rivers with high year-round flow rates. The second implication is that the lack of a significant reservoir minimizes the run-of-river plants’ environmental burden.

The formation of a reservoir in big hydro projects floods formerly dry terrain, affecting local residents as well as plant and animal life. Salmon, for example, can be traumatized and their migration pathways impeded, while stagnant water in a reservoir can degrade overall water quality. These consequences are not entirely avoided in run-of-river systems, but they are reduced to a level that is frequently considered bearable.

Run-of-the-river Hydroelectricity
An illustration of Run-of-the-river Hydroelectricity (Reference:

There must be two essential geographical elements in order for a run-of-the-river system to be feasible in a given place. The first is that there must be a significant flow rate, which might come from rain or melting snow. In addition, the river must be tilted enough to dramatically increase the speed of the water. As a result, run-of-the-river systems work best in bodies of water with a consistent flow rate. Suppose they are constructed in areas where the flow rate is relatively low for a period of time before rapidly increasing. In that case, there will be a significant volume of “wasted” water during peak flow periods as the excess water flows through the spillways. Because these systems are designed to handle the lowest flow rate, they will not be able to handle much higher flow rates.

Running water from a river is steered down a channel or penstock in a run-of-the-river system. There may be some change in height at this point (due to a minor dam or the natural environment), thus “falling water” may still play a role. The diverted water is sent to a power plant to generate electricity. Running water in this house powers a turbine, which drives a generator and creates electricity. Water is returned to the river downstream after it has been consumed.

Although run-of-the-river systems rely mostly on river flow rates to generate energy and do not have a considerable quantity of water storage, some systems use a small-scale dam or weir to ensure that enough water enters the system. Pondage (a little amount of water kept below the dam) is sometimes employed, which makes them more reliable because it compensates for any differences in water flow. This water isn’t like a reservoir in that it only stores enough for “same day use,” not for future usage.


Comparison to Traditional Hydroelectricity Generation

There are several advantages to employing run-of-the-river hydro rather than traditional dam-based hydro. To begin with, traditional hydro dams are costly and time-consuming to construct. Run-of-the-river systems, on the other hand, are less expensive to construct and may be completed in less time. Furthermore, many of the current attractive hydropower sites have been created in various locations where large hydro is regularly employed. Because the pondage is much less than the lakes used in traditional hydro, run-of-river systems avoid some of the environmental issues connected with flooding.

Although run-of-the-river hydro has several advantages, its output is much lower than that of large-scale hydro. Despite the higher initial investment, dam-based hydroelectric generating often has a lower cost per kWh. As a result of the lack of a major dam and reservoir, the power plant’s electricity generation will be less reliable. There is more limited water to run the hydroelectric system if the water levels upstream are reduced, possibly owing to dry conditions.


Environmental Issues

Because run-of-the-river hydro systems don’t have a reservoir, they cause much less ecosystem disruption than hydroelectric dams. Studies prove that run of river generators damage fish populations in the rivers where they’re situated.

Run-of-the-river Hydroelectricity
Ambro Creek is a typical example of the type of run-of-river facilities created in Carboni. (Reference:

Unlike huge hydroelectric dams, which flood enormous areas of land and substantially alter river ecosystems, run of river facilities do not require dams that flood significant areas of land and release greenhouse gases, and unlike fossil fuel plants, they do not generate greenhouse gases.

Despite this, a growing corpus of scholarly research reveals that run-of-river plants do have a significant deleterious influence on river ecosystems. They frequently result in decreases in water flow and variations in water temperature, both of which contribute to fish population losses. Access roads and electricity lines fragment and destroy habitat while also increasing sedimentation in the river. All of these things have a negative impact on the land and river ecosystems.

These are important issues that require to be addressed. The Pacific Salmon Foundation discovered that almost all of the run-of-river projects they looked at in British Columbia, Canada, were on portions of the river where salmon were present, according to a research published in 2013. Almost every one has the potential to harm the salmon populations.

The Fraser River salmon fishery was forced to close due to the 2016 salmon run collapsing to its lowest level in recorded history. The main cause was rising Pacific Ocean temperatures as a result of climate change. The enormous need for safeguarding one of the Pacific Northwest’s iconic species means the run of river plants must be given a free pass, even though they are not created by the run of river initiatives.

River ecosystems are extremely vulnerable and reliant on a complex web of interconnections among the animals that dwell in and around the river. Even small changes in water flow, turbidity, sedimentation, or temperature can have a significant impact on river ecology. Unfortunately, developing run-of-river initiatives that don’t mess with all of these highly tuned ecological knobs is difficult.

Run-of-river projects work by diverting a portion of a river’s flow through a tunnel or penstock. The water is reintroduced to the river at a later time downriver. Water depletion has occurred along the stretch of the river in between. A study published in the Water and Environment Journal in 2014 looked at ten case studies of different run-of-river projects of various sizes and types. It was established that there were fish population decreases in water-deprived locations in all cases, ranging from small to catastrophic.

Small dams, or weirs, that are used in run-of-river systems have been found to be an obstacle to salmon and trout migration, preventing them from reaching their spawning sites. The weirs have been found to have an impact on the ecology upstream and downstream over several kilometers. Furthermore, many run-of-river facilities lack adequate screening to prohibit fish from entering the penstock and being drawn into the turbines as they travel downstream.

Some of these issues can be mitigated with the use of certain strategies. Fish passages or ladders can be created in a variety of ways to help fish get past weirs and to their spawning areas, though the authors of the 2014 study point out that little research has been done on their effectiveness. Improved penstock screens have been shown to effectively prevent fish from swimming into turbines. The major conclusion is that run-of-river facilities have the potential to have a huge influence on fish and that much more research is needed before we can fully assess their overall impact.

Run-of-the-river Hydroelectricity
A fish ladder at a run of river plant (Reference:

The land effects of run-of-river projects can be significant as well. Roads and transmission corridors can cause more erosion in the river, resulting in more sedimentation and a change in the river’s delicate ecosystem. Animal habitats can be fragmented and separated by roadways. Bears, in the example, have been known to avoid highways, therefore building a network of roads near a river could limit their access to the river, and the fish that live there are an important component of their diet.

Many of these projects are on the logged property, and instead of building new roads, they restore existing logging roads, reducing the amount of extra damage. Only 3% of the roadways utilized for a big complex of run-of-river generators were new, according to a UBC graduate paper. The rest were all logging roads that had been repaired.

While there are good grounds to claim that run-of-river plants have a low environmental impact compared to many alternatives, it is crucial to emphasize that the impacts of these facilities build up. When a group of run-of-river generators is erected in a single location, the impact is magnified. Bute Inlet plan by Plutonic Power Corporation was denied “There were 17 river diversions totaling over 60 kilometers of diverted water. This would necessitate the building of 476 kilometers of transmission line, 250 kilometers of permanent roadways, and more than 150 bridges.”

Economic Aspects of Run of River Hydroelectricity Generation

In general, run-of-river power is slightly more expensive than power generated by hydroelectric dams, but it can be less expensive in remote places.

The great bulk of the costs of a run-of-river plant, like all renewable energy technologies, are incurred during the construction phase. Building the facility accounts for around a third of the total cost, while the transmission and distribution cables that connect the frequently faraway facilities to the grid account for another third. If the plant is located near a rural community that it is intended to serve and the cables only need to go a short distance, the size of that slice of the pie can be significantly decreased.

The turbine, which accounts for 20 to 50 percent of the total project cost, is a crucial component in the price. Turbines, like the majority of the other equipment, have a 25-year life cycle and can be reconditioned.

The water ‘fuel’ is free once the plant is built. The facility requires very little upkeep, and major components are rarely changed for decades. The majority of the maintenance costs are spent on tree pruning along the power lines. The fact that the run of the river is intermittent hurts the economic case because backup power is occasionally required, especially in the late summer after the snowpack has melted. This can be avoided by ensuring that rivers always have a minimum flow that corresponds to electricity requirements, especially in off-grid isolated areas.

The cost of run-of-river plants is low when compared to major hydroelectric facilities with their dams and reservoirs. The run of the river, on the other hand, is more expensive because it generates less power. In 2008, the average cost per installed kW was $2,000 to $5,000, equating to $0.04 to $0.10 per kilowatt-hour. In rural areas, investments of roughly $6000 per kWh of capacity, or $0.12 per kWh, are usual. Electricity from run-of-river projects might be confined to $0.07 per kWh, according to a research by Natural Resources Canada. When you consider that most Oregonians spend $0.09 per kWh and Californians pay $0.15 per kWh and that most of their electricity comes from fossil fuels, this is still a bargain.

Another economic consideration is the influence of climate change. Even though the run of river plants contribute little to climate change, they will not be immune from it. This means that in the late summer and early autumn, run-of-river projects will be increasingly deprived of water fuel. Droughts that are becoming increasingly severe may render minimum flow calculations obsolete when rivers dry up, and run-of-river plants can only operate at a quarter of their capacity. They may be left high and dry in the extreme—yet conceivable—cases. Climate change must be integrated into all run-of-river project proposals, if for no other reason than economic rationality.

Advantages and Disadvantages of River Hydroelectricity Generation


Run-of-the-river hydro projects can produce sustainable energy while reducing impacts on the surrounding environment and community when designed with consideration to footprint size and location. The following are some of the benefits:

Less Flooding

The higher part of the river does not flood because there is no reservoir. As a result, people continue to live along the river’s edge or near it, and established habitats are not swamped. Any pre-existing flooding patterns will be maintained, posing a flood danger to the facility and downstream areas.

Cleaner Power and Fewer Greenhouse Gases

Run-of-the-river, like all hydroelectric generation, uses the natural potential energy of water to produce energy for consumers and businesses, avoiding the need to burn coal or natural gas. Furthermore, because run-of-the-river hydroelectric plants do not have reservoirs, the methane and carbon dioxide emissions caused by the decomposition of organic waste in a traditional hydroelectric dam’s reservoir are avoided. This is especially beneficial in tropical climates, where methane production can be a concern.



“Unfirm” power

Typical-of-the-moment River power is regarded as an “unreliable” source of energy since it has little or no energy storage capacity. It hence cannot coordinate the output of electricity generation to match customer demand. It creates substantially more electricity when seasonal river flows are strong (spring freshet), and much less during the drier summer months or frozen winter months, depending on location. The plant will most likely have a lower water head than a dam and so produce less power.


Environmental impacts

Small, well-located run-of-the-river projects can be created with little influence on the environment. Environmental concerns are more prevalent in larger projects. A ladder may be required for fish-bearing rivers, and dissolved gases downstream may impact fish.


Availability of sites

The head and velocity of water determine the potential power at a location. When a river is dammed, the head of the river can be used to generate electricity at the dam’s face. A dam can create a reservoir that is hundreds of kilometers long, but in a run-of-the-river system, the head is normally delivered via a canal, pipe, or tunnel built upstream of the power plant. A steep descent, such as falls or rapids, is desired due to the high cost of upstream development.


Suitable Sites of Run of River

Two geographical features are required for a run-of-river system to function. One is a large flow of water, which can come from either rainfall or snowmelt. The other is enough hydrostatic head to boost the energy of the water. A higher drop in height implies the water is subjected to more gravitational force, which increases its kinetic energy. It is also critical that the river has a substantial and consistent flow throughout the year.

Run of river systems can be built at existing dams, as standalone generators, or as private systems that power local settlements. Plants are sometimes built-in conjunction with water-level management and irrigation systems for rivers and lakes.

Run-of-the-river Hydroelectricity
A 1 MW run of river generator (Reference:

To precisely calculate all of the numbers in the above equation for a given place, extensive fieldwork is required. Because of the daily and yearly variations in flow, observations must be made over time to calculate river flow averages. When a plant is not connected to the grid and is used to power a small isolated town, the minimum year-round flow rate must surpass the community’s power requirements; otherwise, they will have to rely on a backup source of power such as diesel generators.

Nonetheless, the required characteristics of a constantly flowing river and an elevation drop can be found in many locations worldwide.

Run-of-the-river Hydroelectricity
The penstock at an Australian run-of-river facility has a severe slope (Reference:

Buy Equipment or Ask for a Service

By using Linquip RFQ Service, you can expect to receive quotations from various suppliers across multiple industries and regions.

Click Here to Request a Quotation From Suppliers and Service Providers

Read More In Linquip

Print Friendly, PDF & Email
Looking for Renewable Energy Device & Equipment Prices?

Here at Linquip you can send inquiries to all Renewable Energy suppliers and receive quotations for free

Leave a Comment

Your email address will not be published. Required fields are marked *