River restoration

Upper Woodford - The Broads

At Upper Woodford, the River Avon is extremely wide with a heavily silted bed and little in-channel vegetation. The object of the restoration is to demonstrate a range of techniques that increase flow and substrate variation, providing a toolkit of techniques that fishing clubs could use. The work was completed in November 2006 and involved:

• use of brushwood, flint and chestnut stakes to create vegetated islands
• construction of a causeway just above water level to narrow the channel and create a sheltered backwater area
• use of log weirs and deflectors to encourage variation in flow depth and speed
• creation of d-shape deflectors made of brushwood to prevent bank erosion and to vary flow

Since completion of the works, two of the three wettest summers in 28 years have been experienced, combined with very high weed growth around the catchment. Bank inundation has occurred at Upper Woodford and other locations in the Avon catchment which are normally reasonably dry. The bank inundation at Woodford made access unsafe and meant that it could not be effectively used as a demonstration site.

Potential sustainable solutions included modification of restoration works, stabilising discrete areas of the right bank, and potential modification of downstream structures. Bank works were carried out in spring 2009 to secure the angler access. In deciding on solutions, the ecological benefits of retaining the in-channel restoration works, reinstating a narrow angler access, and the low-lying nature of the site were considered.

Fovant - Iron hatches

The River Nadder at Fovant was historically dredged and is over sized compared to flow. As a result, hatches are used to maintain water levels, leading to slow flows and heavy siltation. The object of the work is to modify the channel to a more appropriate width and shape, allowing the impoundment to be reduced, improving in-channel and marginal habitats. The work was completed in November 2006 and involved:

• selective coppicing of trees on the adjacent south river bank to allow light to reach the channel and enhance bankside vegetation
• use of felled trunks to create current deflectors to vary flow and narrowing the river. Deflectors filled with brash and topped with pre-planted matting to allow them to vegetate
• redistribution of silt laden gravel from the right bank to the centre of the channel bed to improve substrate quality

Hale

Due to past dredging, the main channel is over-sized at Hale, as a result of which habitat is very limited for spawning and young salmon, and there is little water crowfoot. A lack of riparian shrubs and trees means there is very little large woody debris present in the reach, which should be characteristic of the river at this location. The object of this work is to re-energise the river, varying flow and channel shape, promote local sediment transport and increase spawning habitat and amount of large woody debris present. The work was completed in November 2007 and involved:

• creation or rehabilitation of spawning riffles using a combination of existing and imported gravels
• selective felling of trees, to build deflectors, varying flow speed and direction and introducing large woody debris

Seven hatches

The River Wylye was historically dredged at Seven hatches and is over sized compared to flow. In the top part of the site, large hatches used to control flow between channels results in slow flows. Below the hatches major dredging combined with the presence of various structures downstream means the channel has no slope, little or no flow speed in summer and heavy siltation. The object of the work is to modify the channel to a more appropriate width, shape and slope, and to re-introduce woody debris resulting in increased and varied low speed and sediment movement. The work was completed in November 2007 and involved:

• reducing impounding effect of sluices
• narrowing channel width in suitable locations, using hazel coppice bundles and pre-planted coir
• reinstating the historic river bed to create spawning habitat and increase physical habitat diversity
• introducing large woody debris by selectively felling/pollarding non-native trees, replanting with suitable riparian species

Amesbury

Historical dredging, road bridges and weirs mean that the River Avon at Lords Walk in Amesbury has no slope, little or no flow speed in summer and the bed is heavy silted. The river bed lacks spawning habitat for salmon and lamprey, and the growth of water crowfoot is generally poor. The old water meadow system on the south bank was until recently planted with non-native poplars, which shaded the river and limited adjacent wet grassland habitat.

The aim of the restoration was to work with natural processes to modify the channel to a more appropriate width, shape and slope, and re-introduce woody debris to vary flow speed and direction, and sediment movement.

The Environment Agency designed and built the scheme in autumn 2008. The restoration work included:

• re-grading part of the bank to make a more gently sloping river bank (good for plants and fly-life)
• raising the river bed level with gravel to provide spawning habitat for salmonids and lamprey
• selectively felling trees and anchoring them securely in the river - this was the main focus of the restoration work.

Dockens Water

This small tributary of the Avon drains the acid sands and gravels of the New Forest. The river has been diverted from its natural course, being predominantly straight and 'confined' by flood banks. The river is highly shaded and vegetation within the channel is very sparse.

The works will complement river restoration that has already been completed at Hampshire and Isle of Wight Blashford Lakes wildlife reserve. The objective of this work is to improve the connection between the river and its floodplain, reduce shading, and restore a more dynamic channel. The work was completed in August 2008 and included:

• forming a small (approximately 15 metres long) floodplain pool connected with the river via a small channel that mimics a natural chute
• decreasing heavy shading by felling a small number of non-native trees alongside and around the chute (there is increasing concern about the effect on Atlantic salmon of rising temperatures in the Avon catchment; tree work must aim to leave patchy shade)
• creating brushwood barriers between the new path and pool to ensure safe public access to the area.