Channelling Works
2017
Tewkesbury, Gloucestershire
Severn Trent Water
CiM6 (JV of Costain & MHW Global)
Maccaferri Ltd
Mythe Water Treatment
Flood protection bund during construction in 2010/11
April 2012 – The Mythe STW
Existing structure before the repair works Flooding of the site during the repai
External side of the structure during construction – Nov 2016
Reno mattress placed over the top of the bund
View of the external side of the completed repair works – Feb 2017
Problem
The nearby rivers, the River Severn and River Avon flooded the waterworks in the summer of 2007, which interrupted the water supply which lead to loss of water for over 150,000 homes. In 2010/11 a flood bund was constructed to protect the Mythe Water Treatment Works near Tewkesbury, Gloucestershire. The bund was a double-sided geogrid-wrapped structure. In April 2012 Tewkesbury was subject to very serious flooding. The area surrounding the bund was flooded, although the bund did perform as expected, protecting the treatment plant from being flooded. Floods lasted over six weeks and during that time the outer face of the bund suffered damage. It is believed that the damage was due to wind waves acting over the six weeks on the structure.
Solution
Following the event and the damage caused, repair works were proposed. CiM6 requested that Maccaferri carry out a design covering the stability of a gabion face covering the existing reinforced soil structure. The aim of the exercise was to provide a new, low-maintenance surface to the existing bund which will be more resistant to erosion, on both faces, than the original vegetated face In addition a long-term solution to prevent UV degradation of the existing geogrid-made bund reinforcement material was provided.
The long-term solution proposed was polymeric-coated woven gabion walls, which are to stand on either side of the flood defence bund. The walls on either side of the bund vary in height from 2m to 3.5m (including embedment). The gabion facing will be found above the existing bund foundation level at levels designed/detailed to maintain a minimum of 300mm approx. buried depth. The length of each wall is 312m and the gabions will terminate at each end of the bund by butting up to the existing concrete flood walls.
In addition to the gabions, a 230mm thick Reno Mattress was placed over the existing crest of the bund. The presence of the Reno Mattress will therefore increase the freeboard above the maximum static water level for additional security against over-topping. Maccaferri has carried out stability analysis on the proposed gabion facing, considering it as a gravity walls.
Used Products
