WATCHING THE WORLD PIPELAYERS HOLD BACK FOR BREEDING TOADS

British Gas plc recently gassed up a section of pipeline built using a technique developed for crossing environmentally sensitive sites. A major section of the project was planned around the breeding habits of a rare species of British toad. Natterjack toads spend most of the year away from water. Every spring, though, they collect in their home ponds for breeding. Minimal parental duties fulfilled, they scatter again for the rest of the year.

March 1, 1993

2 min read

British Gas plc recently gassed up a section of pipeline built using a technique developed for crossing environmentally sensitive sites.

A major section of the project was planned around the breeding habits of a rare species of British toad.

Natterjack toads spend most of the year away from water. Every spring, though, they collect in their home ponds for breeding. Minimal parental duties fulfilled, they scatter again for the rest of the year.

British Gas wanted to lay a 12 in. pipeline in Cumbria, linking a new plant at Sellafield to the U.K. national grid near Ulverston, 35 miles away. This involved crossing the River Duddon estuary, home to natterjacks, which live in sandy soil around the estuary, and overwintering birds.

Directional drilling was used to help install the pipeline in a series of shallow loops that were later joined. Eight loops were required to cross the 1 1/2 mile wide estuary.

ENVIRONMENTAL SURVEY

A survey carried out by British Gas satisfied government environmental agency English Nature the project would cause little disturbance to wildlife in the sand dunes and mudflats.

A small drilling rig was set up on a movable platform for the river crossing. Using a 4 in. bit, the contractor first drilled downward and away from the platform. Then the bit was pointed upward, to emerge about 1/2 mile away.

A reamer enlarged the hole, with several passes often required. Once the hole was large enough, a prewelded pipe string was attached to the reamer so the pipe could be pulled into position.

Immediately after installation, the ends of the drillpipe overlapped like crossed swords. To enable joining of pipe sections, sheet piling was built to form a 150 ft by 15 ft coffer dam around the ends. The exposed pipe was cut back, then a joining section of pipe was dropped into place and welded.

WILDLIFE WINDOW

The river crossing took place from last June 1, shortly after the toads had finished breeding, until the end of October, just before the birds returned for the winter.

Conduits were laid to allow toads to travel through construction unhindered. Plastic sheet fencing was erected along the pipeline route to prevent the toads taking a shorter, more dangerous path.

A study of long term effects on bird feeding areas will be carried out.

The toads seemed largely untroubled by the project, however.