River Sow Flood Alleviation Scheme

Feb 11, 2008 - 4:17:27 PM
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Background:    
     
 

The River Sow Flood Alleviation Scheme was completed in 2004 with the aim of reducing flooding in the centre of Stafford. Timber piling was installed to create a formal edge through a public park. Environment Agency conservation officers required that a margin of aquatic vegetation be established in front of the piling in order to link two known water vole habitats. Salix were approached by the main contractor to find a practical way of quickly introducing a marginal corridor.
  River Sow before works (above).
 

 

  
     
 

Design:

  

 

 
Marginal plants installed along the River Sow to provide water vole habitat (above).  

 

 Due to regular weed cutting the system needed to be resistant to different mechanical cutting method. Pre-planted coir rolls were considered but would not stand up to such maintenance. The solution was to install galvanised wire baskets filled with compressed coir fibre and retained by a well-established coir pallet. A diverse mix of native wetland plants was chosen and grown into the coir pallets. Wildfowl fencing was then placed in front of the margin to prevent grazing and nesting while the plants became fully established.
 
Coir Pallets:

In order to withstand potential flood inundation and grazing pressure by waterfowl, as well as providing instant water vole habitat “well-established” coir pallets were used. These are extremely well rooted and are grown into the coir for 3-4 months prior to installation.

  •  - Iris pseudacorus 15%
  •  - Lythrum salicaria 5%
  •  - Juncus effusus 15%
  •  - Mentha aquatica 15%
  •  - Veronica beccabunga 15%
  •  - Mysotis palustris 15%
  •  - Glyceria maxima 20%
  •  - Caltha palustris 5%
 
Pre-established coir pallets used at River Sow, Stafford (above).
Willow Spiling:    

A 30-metre section of the channel needed to be protected where the channel split and a lower energy backwater was created. Willow spiling was installed to create a vertical 1m high living retaining wall.

Willow spiling at the Rover Sow immediately after installation (left) and one year later (right).
     
Results:    
     

The well-established coir pallets provided instant cover and habitat for water voles. A 300m vegetative corridor has been created linking two areas with known water vole activity. Visually the “hard” timber edge has been softened and once the temporary waterfowl fencing is removed the bank will appear even more natural.
Marginal plants at the River Sow immediately after installation (left) and one year later (right).


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  PROJECT BY SALIX