Pond lining in Solihull

Why a clay borough still lines its ponds

People often assume a pond dug in Solihull clay will hold water by itself. Some do. Many don't, because the clay here is mixed with lenses of sand and gravel, and a single sandy seam in a bank can drain a pond to half its depth over a summer.

Clay also shrinks and cracks when it dries. A pond whose level drops in a hot spell can open fissures in its own banks, then lose water through them when it refills. With a welded sheet laid on a geotextile cushion, the way the clay behaves no longer decides the water level.

The ponds we get asked about

Each brings its own detail. A reservoir has a pump intake and a draw-off. A balancing pond on an estate has inlet and outlet headwalls. An ornamental lake may have a bridge pier or a fountain base standing in it. Every one of those is formed and sealed into the sheet, and round the crest the membrane is turned down into a trench and buried.

• Irrigation reservoirs on the borough's golf courses
• Ornamental lakes on business parks and country house grounds
• Wildlife ponds and fishing pools in the green belt
• Lined SuDS ponds and basins on new housing estates
• Relines of existing ponds that have started to leak

Picking the membrane

The right sheet depends on the pond: how big it is, how it is shaped, what stands in it and how much of the edge will sit in sun. EPDM suits small, curved garden and wildlife ponds. LLDPE and PP give weldable panels that follow awkward shapes. HDPE is our choice for big reservoirs and for edges that will see sun for years.

All of them go onto a geotextile underlay first. Panels are joined on site with wedge and extrusion welders, a trial weld is made and written up, and no joint anywhere relies on tape.

Relining a pond that has given up

Plenty of the calls we take from Solihull are about older ponds: a garden lake lined thirty years ago with a sheet that has gone brittle, or a pool in the grounds of a big house whose puddled clay has dried and split. We look at the old lining, find out why it failed, and put a new system in over fresh protection. Drained ponds in the borough often have silt and roots to clear first, which the owner's landscaper or groundworker deals with before we arrive.

A pond just down the road

Our nearest recent pond is on the HS2 route near Coventry, a few miles east of the borough boundary. Three rolls of 1mm Atarfil HDPE went over a geotextile underlay, the liner was sealed around two concrete headwalls, and every seam was tested and marked before we signed off. A golf reservoir or an estate basin in Solihull gets the same method.