A £27 million project in Comrie has demonstrated the advantages of permanent steel sheet pile walls as effective flood defences.
Working alongside main contractor Balfour Beatty, Sheet Piling (UK) Ltd installed over 3km of steel sheet piles to mitigate flood risks in the village.
Perth & Kinross Council deemed that Comrie, situated six miles west of Crieff, was a priority for flood protection. The village lies at the confluence of three rivers – the Water of Ruchill, the River Earn and the River Lednock. The area had experienced significant flooding, with notable incidents occurring in 1993, 1997, 2006, and twice in 2012.
The severity of these events prompted the implementation of flood protection works in 2013. However, these initial measures did not fully address the ongoing threat, as they failed to tackle the risk of destructive floodwaters originating from the River Earn and River Lednock. Furthermore, the vulnerability to simultaneous flooding from all three rivers persisted.
Sheet Piling (UK) Ltd utilised its knowledge of other flood alleviation projects in Scotland and suggested a maximised use of sheet piles within the scheme design. This sheet pile solution has helped create flood defences designed to protect the village against a 1-in-200-year flood event.
The project will safeguard around 190 homes and businesses, with over 3km of steel sheet piles forming river walls and embankments.
Circa 3,000 Z-section steel sheet piles, totalling 13,400m2, were installed to create the flood walls. The steel sheet piles were a mix of ArcelorMittal and Emirates Steel (EMSTEEL), the latter drawn directly from the piling contractor’s stock holding.
Continuous noise and vibration monitoring was undertaken during all sheet pile installation when conducted close to residential properties. Piling trials and pre-augering were performed at the outset to help prevent issues from boulders and obstructions buried deep along the pile line.
The sheet piles were driven to around six metres using a Kobelco SK380 SRLC piling rig with a Movax side-grip vibratory hammer. They were left exposed to heights of between 1.2 and 1.8 metres on the floodplain side.
Thanks to the use of sheet piles, the final height of the defences is described as being 250mm lower than if a clay core had been used.
To create a pleasant aesthetic, the sheet pile flood walls were reinforced with mesh and had 40mm-thick natural stone cladding applied.
Aside from one flood gate, there are no moving parts, largely due to the use of sheet piles.
Sheet Piling stated that In the event of a flood, the village is not reliant on someone being available to operate any flood systems.
