River Colne, Uxbridge Moor

Background Information

This project focused on a reach of the River Colne where it splits into two sections in the town centre of Uxbridge. One arm is the river’s natural course and the second is a man-made channel created to bring power to the former Bell Punch Co. premises where a dynamo was formerly housed. The two channels flow on either side of Uxbridge Moor Nature reserve, which is owned by The London Borough of Hillingdon and managed by London Wildlife Trust and Gerrards Cross and Uxbridge Angling Society.

Scope of the Project

The natural river was lacking in depth variation and in-channel habitat features; and the man-made channel was prone to heavy siltation, due to its modified nature and regular low flow conditions. Marginal berms and large pieces of wood were strategically placed in the watercourse to diversify the flow of the river and to provide complex marginal habitat for aquatic wildlife to take refuge. Pools were created to provide varied depths and conditions suitable for a variety of coarse fish species including the much sought after specimen Barbel for which the fishery is famed. The river channel now offers good habitat for both fish spawning, recruitment and adult life phases.

Our Solution

Various river restoration techniques were used across the numerous different sites of the Colne at Uxbridge. These included installing large brash berms and woody debris to narrow the overwide and sluggish channel. Speeding upflows and encouraging natural scour to wash the river bed clean of decades of deposited silt. Previously unmanaged trees were thinned to allow light back into the channel and encourage marginal vegetation to establish.

At the confluence with the Grand Union Canal and the site of the former mill, a specialist amphibious excavator was used to overcome the deep water and poor access. The mill pool was dredged and the sediment was used to backfill large berms, providing a soft frontage to the hard urban revetments previously encasing the channel.

Pools were dug throughout the original channel and the arising gravel was deposited as riffles and berms to create diverse fish habitat and complex flow regimes within the channel.