Project

Morden weir project at Cotehele Mill

The collapsed weir on the Morden stream | © James Dobson

Torrential rain and flooding destroyed the weir on the Morden stream in late 2020, causing the water to stop flowing down the leat to Cotehele Mill. Without this water supply, the wheel at the mill can’t turn and the hydro-electric plant is unable to generate electricity. However, a project is now under way to get water running to the leat so that Cotehele Mill can continue working.

What happened to the weir?

The weir on the Morden stream was over 200 years old. It acted as a barrier, directing water through the leat to Cotehele Mill where it turned the wheel.

Most of the weir was damaged and washed away during the floods. The hydropower plant at the mill was also flooded, but didn’t suffer major damage.

Cotehele Mill weir project: A timeline

19 December 2020

Weir is washed away

The flooding damaged the weir and finally washed most of it away. This photo, also taken by ranger George, shows the extent of the damage to the weir once much of it was washed away.

The remains of Morden Weir after it was damaged by flooding in December 2020 at Cotehele Mill, Cornwall — Morden Weir after flooding damage at Cotehele Mill | © National Trust / George Holmes

What’s next?

Although European Smelt and Allis Shad are present in the River Tamar, further research suggests that there is a possibility that both may not venture this far up the stream. As they are significant species of conservation concern, additional survey work will take place from spring 2023 to ascertain their presence. This will include DNA testing with results expected in the autumn.

The outcome from these surveys will impact the design and construction of the weir structure, however its necessary to take this step to ensure any decisions we make do not harm species which are already under significant threat and that the structure is good for the long term.

Being within a Site of Special Scientific Interest (SSSI) there are limitations on when any construction work can take place to ensure wildlife is protected. This means it is unlikely that we will be able to use water to operate the wheel at the mill until late 2024