Under the conditions of climate change, exceptional flooding events are becoming more frequent. In order to reduce the impacts of extreme flooding, EDF’s Hydro Engineering Centre (CIH) develops a new technological solution for increasing the discharge capacity of spillways: the piano key weir (PKW).

The name of this solution refers to its innovative design, with distinctive rectangular discharge tanks which look like the keys of a piano. Their shape provides a larger surface area for the flow of water, dramatically increasing the discharge capacity of spillways. This is particularly important for dams which are situated in narrow gorges, where it can be essential to rapidly evacuate excess water from flooding.

In 2015, EDF received a Climate Solutions Award, a scheme launched in the wake of COP21, for the company’s role in the development of PKW technology. Yves Giraud, director of EDF’s hydro division, received this prize in the “adaptation to climate change” category from Ségolène Royal, the French minister of ecology, sustainable development and energy. This award demonstrates the increased international recognition for PKW technology.

In 2012, EDF installed PKW technology at the Malarce dam in Ardèche, France. To date, this is the largest PKW project installed in EDF’s hydropower fleet. Situated on the Chassezac River, the Malarce dam is exposed to an unpredictable and extreme hydrological regime from September to June. Twelve “piano keys” are now installed at the dam, increasing the discharge capacity to 4,600 m³ of water per second, enough to evacuate a millennial flood.

There are very few technological innovations in hydropower that have spread so quickly around the world."

EDF has already installed this technology at a further eight dams in France. The solution has also been implemented at other sites in France, as well as in Vietnam, Sri Lanka, Australia and Scotland (UK). EDF is now incorporating the concept into the study phase of international projects, particularly in Africa. Other developers are currently implementing the technology in Algeria, the USA and South Africa. There are very few technological innovations in hydropower that have spread so quickly around the world.

Why has the global uptake of PKW technology been so rapid? In a sense, PKW is an “open source” technology. The concept was first proposed by HydroCoop, a non-profit organisation, and the University of Biskra (Algeria). Then EDF and other institutes, such as the Swiss Federal

Institute of Technology in Lausanne, the University of Liège and the Vietnamese Comitee of Large Dams, took part in further development. In parallel, EDF designed and built the first PKW at Goulours dam, France. While none have sought to protect or patent this important solution, stakeholders have rather been working collaboratively to share the PKW design with the wider hydropower community.

PKW builds on an earlier solution: the labyrinth spillways which were developed in the 20th century. Labyrinth spillways can only be implemented in certain types of dams, and they must generally be included in the project design from the earliest stages of development.

By contrast, PKW technology can be installed at an existing dam. Another advantage is that it is suitable for a wider range of dam types, including far narrower dams than the labyrinth spillways, where the need to increase discharge capacity is of far greater importance.

This case study is featured in the 2016 Hydropower Status Report. You can download the full report here.