Pond lining in Somerset

Limestone hills and wet moors

Carboniferous limestone on the Mendips is riddled with joints and swallets, which is how Cheddar and Wookey Hole came to have their caves. A pond dug into that rock has nowhere to hold its water, and even a clay bed can be lost into an opening fissure. A continuous welded liner is the dependable answer on the hills around Wells, Shepton Mallet and Cheddar.

Down on the Levels and Moors the ground is wet clay and peat with water close to the surface. There the risk is groundwater lifting the liner when the pond is drawn down, and soft ground under the formation. Your designer sets the formation and any underdrainage, and we lay the lining to match it.

What Somerset ponds are for

Irrigation reservoirs for growers and orchards, fishing lakes, estate and garden ponds, and wet SuDS ponds on the housing that keeps spreading around Taunton, Bridgwater and Yeovil make up most of the work. Wildlife ponds on farms along the Quantock and Blackdown foothills are another part of it.

A SuDS pond on a new estate has a job set by the planning condition: hold a permanent pool, take the storm on top, and release it no faster than the agreed rate. Where the ground under it is permeable, or contaminated, the drainage design calls for a lining so the permanent water level stays put.

Membranes we install

The survey settles the material. For a big irrigation reservoir with long exposed banks, HDPE is normally right. LLDPE conforms better to an irregular formation and still welds well. PP handles awkward shapes and many pipe details. EPDM suits smaller ornamental and wildlife ponds. A fishing lake that sees anglers' platforms, boats or a bank-side mower may need a thicker sheet or protection over the liner on the margins, and we take that into account at survey. Where a natural clay bed and self-sealing behaviour would serve the pond better, a GCL may be the better choice, and we install those as well.

Building the lining

Your contractor digs and shapes the pond; we don't excavate. Once the formation is trimmed we check it, then lay a geotextile underlay to protect the liner from stones in the limestone brash or roots in the clay.

• Wedge welds along the panel seams, extrusion welds around corners and pipes
• A sample weld peel-tested on site and logged for every pond
• Pipework through the membrane sealed at the inlet, outlet and overflow
• The sheet edge buried in an anchor trench around the top of the bank
• A final walk of the seams, then weld records and handover documents