Pond lining in Sheffield

A city of mill dams

Before steam, the Rivelin, Loxley, Porter and Sheaf drove hundreds of grinding wheels and forges, each fed from a dam pond. Plenty of those ponds survive in parks and wooded valleys, and they are a reminder that holding water on sloping, stony ground has always taken work.

Today the requests are more varied. Developers want wildlife and amenity ponds as part of the landscaping on new housing. Farms and smallholdings on the moorland edge want storage for livestock or irrigation water. Fishing lakes, garden ponds on large plots and old ponds that have begun to leak make up the rest.

Choosing the sheet

The pond decides the liner. EPDM is soft and forgiving, which suits a smaller wildlife or ornamental pond with curves and shelves. LLDPE welds into large panels and follows an uneven bed well. PP handles fiddly outlines and detailing. HDPE is the tough option for a big reservoir or one with long, exposed banks. Where a natural clay bed is wanted, a GCL may suit better, and that has its own page.

Thickness follows the same logic, from around 1mm on a modest garden pond to 2mm on a farm store that cattle may walk to the edge of.

Stones in the formation, slopes at the edge

Sheffield ground throws up sandstone slabs, gritstone boulders and broken brick, and any of them will work through a liner given time. The groundworker trims and clears the formation; we look it over, then lay a protective geotextile underlay before the membrane goes anywhere near it.

Banks here are often steeper than the textbook would like because the land is. A membrane can be dressed up a steeper bank than a clay liner can, and its outer edge is buried in a trench dug along the crest so it can't creep down into the water.

• Panels laid out and wedge or extrusion welded on site
• A trial weld made first and written up, on every pond
• Inlets, overflows and pipe penetrations sealed into the liner
• The crest trench backfilled over the edge, then weld records handed to you

When an old pond starts leaking

Many leaking ponds we hear about were lined with taped joints or laid straight onto stony ground with no underlay. We inspect what is there, find the likely cause, and put a new welded system in over fresh protection, rather than patching a liner that is failing along its seams.