Hertfordshire County Council have installed a series of leaky woody dams on headwater streams in Bishop's Wood in the Colne Valley as part of DEFRA-funded Natural Flood Management programme. The aim of the dams is to attenuate flooding and so reduce the flood risk downstream. The FreeStations are monitoring the effectiveness of the two furthest downstream structures before the woodland stream disappears underground and reappears a few miles away in a flood risk area near Rickmansworth.

Upstream of upper dam 1

Downstream of upper  dam 
Upstream of lower dam 
Downstream of lower dam