Restoring Toddbrook Reservoir

Overview

Following damage to the auxiliary spillway at Toddbrook Reservoir, the Canal & River Trust has invested in significant restoration works designed by Arup and in construction with Kier.

The works involve the removal of the auxiliary spillway, restoring the eroded section of the embankment, and construction of an enlarged spillway, along with providing draw off upstream control, remote instrumentation monitoring, and increased drawdown provision. 

The evening meeting will cover the complexities of the design, innovation and flood management required during the construction, and the extensive mitigation works and remote monitoring to assure reservoir safety. The failure mechanism has been covered extensively in previous events.

The Toddbrook auxiliary spillway failed during a storm event in 2019. The failure mode was investigated and determined to be a defect in the design of the auxiliary spillway built in 1971.

Following intense heavy rainfall at the end of July 2019, several concrete panels on the auxiliary spillway collapsed. Around 1,500 residents of Whaley Bridge were evacuated from their homes for up to six nights as a safety precaution.

 Trust staff, volunteers and our contractors worked around the clock with the local emergency services, including Derbyshire Fire & Rescue, Derbyshire Police and the Environment Agency, supported by the armed services, to stabilise the embankment and empty the reservoir.

Toddbrook Reservoir was constructed in the 1830s and opened in 1840 to feed the Peak Forest and Macclesfield canals and remains one of England’s most important canal supply reservoirs.

The dam is 23.8m high and stores 1,238,200 m3. The reservoir is essential to keep these canals open and alive for the benefit of the communities who live along the canals, the many visitors who enjoy them and the ecological and environmental benefits they provide.

The Canal & River Trust is a charity looking after 2,000 miles of canals and rivers, with 74 statutory reservoirs, across England and Wales.

Arup have designed the new spillway to carry the probable maximum flood, removing the need for the over-dam spillway. Arup’s design utilized a tumble bay feeding into a stepped chute with final energy dissipation using 6m high “turrets” to form a flume, preventing the need for a deep chamber in the final stilling basin.

Kier has excavated more than 15,000 tonnes of soil, installed over 500 concrete piles and 1,000 sheet piles to support the new spillway structure resist both flotation and seismic loading. The ramp is now in place and work has commenced to repair the face of the embankment. 

When the spillway is complete, and before refill, an array of instruments will remotely monitor both thermal change and the phreatic surface within the embankment, supporting reservoir safety management of the restored reservoir. After a staged refill, Toddbrook will then commence supply to the canal network for summer 2026.