Hairy Mallow (Malva setigera) is a rare species that is only reliably found at five or six sites in the warmer southern counties of England. It is protected under Schedule 8 of the Wildlife and Countryside Act 1981. Its presence on the reservoir overburden has earned the area an SSSI designation.
The repair to a reservoir roof involved approximately 70 metres of overbanding. Though this was a relatively minor job for Stonbury, due to the presence of Hairy Mallow, the project required a full adaptation of the usual working methodology to suit the environmental restrictions and protect the species present within the topsoil.
Prior to commencing the project, Stonbury was required to produce a Construction Environmental Management Plan (CEMP) describing how the environmental issues would be managed. An SSSI assent and license was issued from Natural England, outlining terms which were strictly followed. Environmental monitoring, auditing, and reporting was also undertaken throughout the works.
A toolbox talk was delivered at the start of the project by specialist ecologists to outline the site’s significance as an SSSI, appropriate storage and access areas, and the overburden-removal methodology. All equipment and vehicles were stored on a hardstanding area, and the teams used a pedestrian walkway to access the reservoir roof.
To expose the concrete and complete the overbanding, the team removed the topsoil in a series of turves and excavated a channel just over half a metre wide. As there were restrictions on the use of plant, equipment and vehicles which could damage the grass, excavations were completed by hand and matting was used to protect the surrounding ground.
The turves and soil were stored carefully adjacent to the excavated strip on geotextile matting to protect the underlying flora. To ensure the turves were lifted for no more than five days, the repair was carried out in 15 to 20-metre-length sections at a time and soil and turves were reinstated immediately before moving on to the next section.
Once the repairs to the roof crack were complete and the soil and turves were replaced, the disturbance around the reinstated strips was left to re-seed naturally, as no soil or vegetation was allowed to be imported on to the site. Stonbury demobilised from the site within the two-week window stipulated in the assent.