ASEA Ecology Mitigation and Flood Defence Project

This summer we continued our work creating and improving flood defences near the Bristol Port at Avonmouth, with the installation of huge boulders, known as rock armour at Holes Mouth Outfall.

You can watch a short video of the rock armour installation at the foot of this article.

Holes Mouth Outfall is operated and maintained by Wessex Water Services Limited and discharges water treated by its dedicated Water Recycling Centre. It is therefore critical that this infrastructure is protected from scour. Around 5,000 tonnes of ‘rock armour’ have been installed. The wider scheme will reduce the risk of tidal flooding across the Avonmouth and Severnside area.

Each of the boulders, weighing between one and three tonnes, have been transported from Cornwall. Skilled contractors ensure that each of the rocks interlock together to dissipate wave energy help to reduce erosion and flood risk. The project team has chosen rock armour at Holes Mouth because of its durability. The flood defences here will need almost no maintenance and will sit in place protecting the outfall culvert and adjacent flood defences for this century and beyond.

Colin Taylor, Senior Flood & Coastal Risk Management Advisor at the Environment Agency, said: “This section of the flood defence is the result of dialogue with Wessex Water, over how best to construct the flood defences without compromising the outfall structure”.

The rock armour is just one type of flood techniques being used for the project. Construction of earth embankments, sheet piling, flood walls and gates continues along the line of flood defences. The project is a partnership between South Gloucestershire Council, Bristol City Council and the Environment Agency.

The largest of its kind in the region, the £80m project will provide 17km new and improved flood defences, from Lamplighter’s Marsh in the south to Aust in the north, once complete in 2026/27. The defences will help reduce flood risk to around 2,500 homes and businesses over the scheme’s lifetime. It will also create a minimum of 80 hectares (the equivalent of around 112 football pitches) of new wetland habitats for the internationally important Severn Estuary’s bird species.

The project will boost the regional and national economy by enabling development within the 1,800 ha Avonmouth and Severnside Enterprise Area, helping to unlock 12,000 new jobs by 2026. Funding for the project has come from the West of England Local Enterprise Partnership, administered by the West of England Combined Authority. Other funding sources are Government’s Flood Defence Grant in Aid, and Local Levy raised by the Wessex Regional Flood and Coastal Committee. The contractor is BMMjv.