Myrke Ditch Flood Alleviation Scheme, Maidenhead.

Client: Tilhill Landscapes for the EA

Background: The Myrke Ditch is a 400-metre section of the Jubilee River Flood Alleviation Channel close to Eton. The entire section had eroded at the outer bend below a bridge structure. Salix were invited to tender for the specialist installation of the reinforced wildflower turf installation and the contract growing of the Pre-Planted Coir Pallets.

Design: The wildflower turf was reinforced with a three dimensional erosion control geotextile to enable the turf to be installed in large rolls (2m by 20m). Access to the top of the bund was limited to a small mini digger, which could only install off cuts of the wildflower turf but not the full rolls. Additionally, a contaminated stream lay between the access road and the bund.

Salix utilised a 25 tonne long reach excavator, with an extended reach of 22 metres) to reach over the stream and allow the turf to be pulled out by hand install the 1 tonne rolls of wildflower turf directly onto the bund. The entire 5000 m2 of reinforced wildflower turf was installed in just 4 days.

The reinforced wildflower turf was laid directly onto a woven geotextile. Previous trials demonstrated that a wildflower mix was capable of growing through this geotextile. The grass and wildflower mix would not have been able to withstand the regular inundations around the marginal fringe of the river. Salix were asked to contract grow a specific mix of native wetland plants into 1m by 2m Coir Pallets.

Coir Pallets:

Glyceria maxima; Sweet Reed Grass

Phalaris arundinacea; Reed Canary Grass Juncus effusus; Soft Rush

Lythrum salicaria: Purple Loosestrife

Phragmites australis: Common Reed

Iris pseudacorus: Yellow Flag Iris
Carex acutiformis: Lesser Pond Sedge

In order to withstand immediate winter flooding and intense grazing pressure by waterfowl, “well-established” Coir Pallets were used. These are extremely well rooted and are grown into the coir for 3-4 months prior to installation. The use of well established coir stock also meant that they could be installed out of season in October 2004.

Results: The project was an instant success with the bank appearing green from day one. By June 2005 the wildflower and wetland plants had firmly rooted and had begun to flower. The project had met all the engineering and ecological objectives with the entire installation completed in just one week.

 

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Materials used: Shear Strength Turf

 

Myrke Ditch during works (left) and after works with well established wildflower turf (right)