Spencer ECA

August 2018

Spencer ECA has returned to Llanishen Reservoir to undertake additional work, this time to restore the 1886 Victorian internal wall stone pitching to its former glory, following decades of mothballing the facility and the subsequent tree and vegetation growth.

The famous north Cardiff Grade II listed landmark is a designated Site of Special Scientific Interest (SSSI), so Spencer ECA was able to bring the necessary specialist expertise needed to undertake such a sensitive task. Working on behalf of Lewis Civil Engineering and Dŵr Cymru/Welsh Water, the works involved undertaking repairs to the existing stone pitching where stones were missing and where trees and vegetation had grown through the stone pitching pushing the stones out. It’s a very delicate job, employing a grab machine to lift some of the heaviest Victorian pitching stones. Each stone has to be lifted, debris/tree roots removed completely, stones cleaned and placed back securely. And lifting each stone isn’t easy, as they have been placed in contact with adjacent stones, specifically to prevent them moving when submerged in water.

Clearing vegetation varies from pulling out small plants, cutting out small saplings and removing larger saplings – where the root system has to be dug out, sometimes to a depth of 500mm, to remove the root ball. In these cases the hole is then backfilled with well-compacted puddle clay to within 25mm of the underside of the pitching level, before 25mm of well-graded aggregate is added and the pitching stones placed precisely back in position.

Each process ensures the vegetation cannot grow back and the pitching stones are repaired and replaced as securely as they were originally placed there 132 years ago.

Llanishen Reservoir’s embankment is 10 metres (33ft) high and 1,173 metres (3,848ft) long, and care is taken to ensure that the repaired pitching stones have a uniformed surface, a total of nearly 700m2 of repairs have been carried out.