Totnes Weir Archimedean Screw hydropower turbines and fish pass
The Totnes Weir hydropower scheme was developed by Dart Renewables and when completed it is estimated that the two Archimedean Screw hydropower turbines rated at 150kW each will generate 1,200 MWh of renewable energy every year, enough to power the equivalent of around 400 homes and saving 500 tonnes of C02. It is expected that around two thirds of the electricity generated will be used to power King Edward VI Community College, which serves around 1,700 students, and Atmos Totnes, a community development involving the construction of 60 to 70 social housing units and housing for older people.
The environment
Numbers of migratory salmon and sea trout are in decline in the river Dart, in part due to difficulty in passing the Totnes weir. The species are currently being held at the weir, where seals predate, leading to mortality of the fish. The construction of the Totnes Weir scheme will include the installation of a modern fish pass which allows the fish to pass the weir and continue their journey upstream to spawn. It is expected that this will reduce salmon and sea trout losses in the river Dart and over time increase the population of these species in the river Dart catchment. The scheme would also encompass an additional Larinier type fish pass, alongside the repair of the existing pool-and-traverse fish pass. Underwater cameras and a fish counter will estimate Salmon and Trout migration to spawning grounds in the Upper Dart. This will provide valuable data on the species in the river Dart which will be shared with both the Dart Angling Association and the Environment Agency.
Community benefits
Dart Renewables developed the Totnes Weir scheme in close conjunction with the local community in Totnes and the scheme will benefit the community in a variety of ways. Around two thirds of the power generated by the Totnes weir scheme will be used to power the local school in Totnes, King Edward VI Community College (KEVICC), and a community development of affordable homes and community facilities for the Totnes area which is being managed by the Totnes Community Development Society (TCDS). Electricity will be sold to these organisations at a mutually beneficial rate compared to prevailing market rate.
The Environment Agency, the Dart Angling Association, the TCDS and TRESOC (the Totnes Community Energy Society) have been closely involved in the consultation process for the Totnes Weir scheme and are very supportive of the project. A small classroom complex is proposed for the site next to the weir to be used by a KEVICC educational trust.
Larinier fish pass
Fishtek were responsible for the design of the new Larinier fish pass and the improvements and modifications to the existing fish pass on the far side of the river from the hydropower scheme. A few images of the turbines and fish pass are shown below.
The fish pass can be seen in the images above (running at a very high level as the turbines were temporarily turned off when these images were taken). A fish counter is to be added at the upstream end of the fish pass very shortly and this will provide invaluable data for the ongoing monitoring of fish populations in the river.
Funding
Triodos Bank helped Dart Renewables raise the £1.3 million needed to build the hydro power scheme through a Bond Issue. Local investors were offered the opportunity to invest a minimum of £2,000, with the minimum for those living further than 15 miles from Totnes being £10,000. Investors could earn up to 8% return a year for up to 8 years.
Once again we see the Ancient power of Archimedes being used for hydropower generation because if it’s fish-friendly credentials. The Archimedean Screw turbine provides a fish-friendly alternative to conventional turbines, ideally suited to low-head (1m-10m) sites, and sites with fish protection issues. Extensive fish passage tests have conclusively demonstrated that the large water chambers and slow rotation of the Archimedean Screw allow fish of all sizes, and debris, safe passage through the turbine. As a result, the Environment Agency has agreed that no screening is required.
