Sustainable Track Drainage, Buckinghamshire (Light case study)

Where

A forward-thinking approach to sustainable track drainage and maintenance, pioneered by London Underground, has set new standards for personnel safety, whilst successfully managing flooding and pollution risk.

Flooding had become an increasingly frequent problem for homes and businesses that back onto the track at the north-western end of the Metropolitan line at Amersham in Buckinghamshire.

Investigation work found the existing track drainage to be in relatively poor condition, with poor ballast, deteriorating pipes and, most of all, existing deep bore soakaways that had completely silted up and which were in a poor state of repair.

The existing deep bore soakaways were 6-7 m deep and posed a health & safety risk for a maintenance operative to attempt to rehabilitate. Disturbing them could have increased the risk of groundwater pollution. They were therefore left unmaintained to reach the end of their service life. New deep bore soakaways were constructed, which, although expensive, are necessary solutions in space-constrained sites. Other options, including above ground SuDS and connecting to the sewer network were considered, but rejected on technical grounds.