The main trench is a brick built bypass channel running parallel to the river to allow it to flow when locks were in use and to provide a water supply for the various processes used in making fertilizer. There are 3 tunnels along the channel, a human skull bone was found in the downstream tunnel end in 2015 and the tunnel exit was discovered and restored in 2016. Trench walls were rebuilt in November 2017. The channel also runs behind the Blacksmith area and boiling house. Bats are known to roost in the tunnels in winter.