Run of the river hydroelectricity is a type of hydroelectric generation whereby the natural flow and elevation drop of a river are used to generate electricity. Power stations of this type are built on rivers with a consistent and steady flow, either natural or through the use of a large reservoir at the head of the river which then can provide a regulated steady flow for stations down-river.

The Concept of run of the river method

Run-of-river hydroelectricity is a type of hydroelectric generation whereby the natural flow and elevation drop of a river are used to generate electricity. Such 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. A dam – smaller than used for traditional hydro – is required to ensure there is enough water to enter the “penstock” pipes that lead to the lower-elevation turbines.

Run-of-river projects are dramatically different in design and appearance from conventional hydroelectric projects. Traditional hydro dams store enormous quantities of water in reservoirs, necessitating the flooding of large tracts of land. In contrast, most run-of-river projects do not require a large impoundment of water, which is a key reason why such projects are often referred to as environmentally-friendly, or “green power.”

In recent years, many of the larger run-of-river projects have been designed to a scale and generating capacity rivaling some traditional hydro dams. For example, one run-of-river project currently proposed in British Columbia (BC) Canada – one of the world’s new epicenters of run-of-river development – has been designed to generate 1027 megawatts capacity.

Advantages using run of the river method

When developed with care to footprint size and location, run-of-river hydro projects can create sustainable green energy that minimizes impacts to the surrounding environment and nearby communities. Advantages include:

Cleaner Power, Less Greenhouse Gases

Like all hydro-electric power, run-of-river hydro harnesses the natural energy of water and gravity – eliminating the need to burn coal or natural gas to generate the electricity needed by consumers and industry.

Less Flooding/Reservoirs

Substantial flooding of the upper part of the river is not required for smaller-scale run-of-river projects as a large reservoir is not required. As a result, people living at or near the river don't need to be relocated and natural habitats and productive farmlands are not wiped out.

Disadvantages using Run of the river method

"Unfirm" Power

Run-of-River power is considered an “unfirm” source of power: a run-of-the-river project has little or no capacity for energy storage and hence can't co-ordinate the output of electricity generation to match consumer demand. It thus generates much more power during times when seasonal river flows are high (i.e, spring freshet), and much less during drier summer months.

Environmental Impacts

While small, well-sited run-of-river projects can be developed with minimal environmental impacts, many modern run-of-river projects are larger, with much more significant environmental concerns. For example, Plutonic Power Corp.’s Bute Inlet Hydroelectric Project in BC will see three clusters of run-of-river projects with 17 river diversions; as proposed, this run-of-river project will divert over 90 kilometres of streams and rivers into tunnels and pipelines, requiring 443 km of new transmission line, 267 km of permanent roads, and 142 bridges, to be built in wilderness areas.

British Columbia’s mountainous terrain and wealth of big rivers have made it a global testing ground for run-of-river technology. As of March 2010, there were 628 applications pending for new water licences solely for the purposes of power generation – representing more than 750 potential points of river diversion.

Many of the impacts of this technology are still not understood or well-considered, including the following:

• Diverting large amounts of river water reduce river flows affecting water velocity and depth, minimizing habitat quality for fish and aquatic organisms; reduced flows can lead to excessively warm water for salmon and other fish in summer. As planned, the Bute Inlet project in BC could divert 95 percent of the mean annual flow in at least three of the rivers).

• New access roads and transmission lines can cause extensive habitat fragmentation for many species, making inevitable the introduction of invasive species and increases in undesirable human activities, like illegal hunting.

• Cumulative impacts – the sum of impacts caused not only by the project, but by roads, transmission lines and all other nearby developments – are difficult to measure. Cumulative impacts are an especially important consideration in areas where projects are clustered in high densities close to sources of electricity demand: for example, of the 628 pending water license applications for hydro-power development in British Columbia, roughly one third are located in the south-western quarter of the province, where human population density and associated environmental impacts are highest.

• Water licenses – which are issued by the BC Ministry of Environment enabling developers to legally divert rivers – have not included clauses that specify changing water entitlements in response to altered conditions; this means that conflicts will arise over the water needed to both sustain aquatic life and generate power when river flow becomes more variable or decreases in the future.