Author: Matthew Roberts

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Significant savings on cost and carbon, new research finds

Significant savings on cost and carbon, new research finds

A flood defence trial embankment for ASEA has made significant savings on cost and carbon, new research has revealed.  

 

The trial embankment at Aust in South Gloucestershire was part of initial ground investigation work for the project. The research, by Gareth Mason, Geotechnical Project Lead, at contractor BMMJV, was presented to the International Symposium on Field Monitoring in Geotechnics in London in September 2022. 

 

Stretching along the coast of the Severn Estuary and the River Avon, the ASEA project will provide 17km of flood defences to reduce flood risk to 2,500 homes and businesses over its lifetime and help to unlock 12,000 new jobs for the West of England when completed in 2026/27. The project, a partnership between South Gloucestershire Council, Bristol City Council and the Environment Agency, is being constructed by a Bam Nuttall Mott MacDonald joint venture (BMM JV).  

 

Ground settlement had already been identified as being one of the greatest geotechnical hazards for the scheme. Geotechnical design of embankments on soft ground requires a high level of accuracy in the determination of subsurface parameters. Unreliable parameters can lead to underestimation of settlement and potential embankment failure or overestimation of settlement and unnecessary additional fill. These projects demand a detailed understanding of the subsurface. A trial embankment can help to refine subsurface parameters predicted from ground investigation and laboratory tests. 

 

For the ASEA project, the project team constructed a trial embankment approximately 200m in length in summer 2020 to understand and obtain actual rates of settlement. The trial embankment contained instruments such as vibrating wire piezometers, settlement plates, magnet extensometers and surface settlement monitoring points to measure the response of the underlying ground to embankment loading.   

 

Monitoring of the instruments was undertaken during construction and for 12 months afterwards.  

 

To begin with, the BMM JV team conducted a review of the existing ground investigation information, followed by an investigation along the alignment of the proposed flood defence to determine the conditions of the ground where existing information was sparse.   

 

The team then developed a conceptual model using Leapfrog Works geological modelling software. Analysis of insitu and laboratory test data established characteristic geotechnical parameters.  

  

The trial embankment results indicated that the settlement was greater, and the rate quicker than anticipated from laboratory data, allowing the embankment construction level to be optimised.  

 

These conclusions were a significant benefit to the project as most of the settlement occurs before one year after takeover, which allowed a review of the embankment construction level to be undertaken. Optimisation of the embankment construction levels and increased confidence in the geotechnical parameters resulted in less imported fill and a significant cost and carbon savings. The team calculated a saving of 5000m3 reduction in imported embankment fill which is equivalent to 100,000kg of equivalent CO2. 

 

“The results of the trial allowed the settlement parameters to be refined and increased confidence in the settlement estimations, resulting in carbon and cost savings,” explained Gareth, “The risk of additional remedial works following demobilisation was also significantly reduced.” 

By enabling development within ASEA, the project is expected to boost the regional and national economy with 12,000 new jobs by 2026.  

 

As well as providing flood defence, the ASEA project will also create a minimum of 80ha of new wetland habitats at Northwick in South Gloucestershire and Hallen in Bristol, the equivalent of 112 football pitches, to support Severn Estuary’s bird species, and improve walking routes.   

 

Project funding comes from the West of England Local Enterprise Partnership, administered by the West of England Combined Authority, the Government’s Flood Defence Grant in Aid, and local levy raised by the Wessex Regional Flood and Coastal Committee.  
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Apprentices and graduates talk about their ASEA experience

Apprentices and graduates talk about their ASEA experience

Are you thinking about next steps after school or university? We’ve been talking to the young apprentices and graduate trainees on the ASEA project to find out what it’s like to work on the project. Hear about their exciting experiences and career paths in our series of short videos. You can find out more about apprentice and graduate programmes with The Environment Agency here and our contractors BAM Nuttall here.

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Innovation

New rock armour flood defence to protect water treatment infrastructure

New rock armour flood defence to protect water treatment infrastructure

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.

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News

ASEA joins in with Severn Beach centenary celebrations

ASEA joins in with Severn Beach centenary celebrations

6 July 2022. In June we were excited to take part in an exhibition hosted by the Pilning and Severn Beach History Group, one of the Severn Beach centenary celebration events.

As part of the very well organised and extensive exhibition that displayed images spanning 100 years, our team had a display and handouts showing the history of flooding and flood defences in the area.

Over 200 people came to view the exhibition and stop to chat with us. Some residents recalled being present at some of the flooding events on our board such as the 1976 floods on Beach Road and the 1990 floods in New Passage.

Many commented that completed sections of the scheme, including the precast walls at Severn Beach North, were working well and many people had walked along the newly reopened footpath at this section. Our newly installed glass panels at New Passage were also popular and people appreciated that views across the estuary would be maintained. Residents said that they were looking forward to that section being reopened later this year.

We would like to thank the Pilning and Severn Beach History Group for giving us the opportunity to take part in such an excellent event and we look forward to attending future events in the community.

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West of England leaders visit Bristol Port as vital flood defences take shape

West of England leaders visit Bristol Port as vital flood defences take shape

25 March 2022. In March we marked another milestone, with work having started in earnest at the Bristol Port. Following extensive survey works carried out last year, leaders from around the West of England gathered to see for themselves the installation of new sheet piled flood defence walls that will help protect homes and businesses from flooding and unlock new jobs, delivering a significant boost to the local and regional economy.

The sheet pile walls are one of several forms of flood defence used throughout the 17km project area. These are steel sheets that are driven deep into the ground and are well-suited to the area around the port as they take up only limited space in the industrial area, with installation causing little disruption to the operations of the port. The sheet piles, delivered directly to the port via boat, have the additional benefit of a reduced carbon footprint compared to a reinforced concrete wall.

The ASEA project is a partnership between Bristol City Council, South Gloucestershire Council and the Environment Agency.

Cllr Don Alexander, Cabinet Member for Transport at Bristol City Council and Avonmouth and Lawrence Weston ward member, said: “The start of flood defence work at the port is a major milestone for the project, which continues to progress on schedule. Around 2,500 homes and businesses will be better protected as part of the scheme, a significant number of which are in Avonmouth and Lawrence Weston ward. I’m delighted to see the progress of work taking place here that will help protect against the increasing challenges of climate change for decades to come.”

Cllr Toby Savage, Leader of South Gloucestershire Council and Cabinet Member with responsibility for Climate Change, said: “This work taking place at Bristol Port will deliver significant benefits for the whole of the Avonmouth and Severnside area and beyond, and is critical for the future economic prosperity of the wider West of England region. The new and improved flood defences here will help give businesses the confidence they need to further invest and deliver 12,000 new jobs by 2026/27 when the overall project is scheduled to be completed.”

John Chaplin, The Director of External Affairs & Special Projects at Bristol Port Company, said: “The new flood defences are of the utmost importance to Bristol Port, which is a major economic driver for the South West and supports over 10,000 jobs through port-based businesses.”

Colin Taylor, Senior Flood & Coastal Risk Management Advisor at the Environment Agency said: “The stretch of coastline through Bristol Port and Lamplighter’s Marsh is the longest continuous area of flood defence for the entire project. We have been hard at work throughout the area, not only at the port but also at Lamplighter’s Marsh where we have been clearing vegetation in preparation for the building of new flood defences.”

The largest of its kind in the region, the £80m project will provide 17km of 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.

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 the Government’s Flood Defence Grant in Aid, and Local Levy raised by the Wessex Regional Flood and Coastal Committee. The contractor is BMMjv (https://asea-flood-ecology.co.uk/bmmjv-explained/). 

Watch our video below to see the defences being installed.

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Innovation News

Innovative new hybrid glass panel flood defence in place

Installed section of hybrid glass panel flood defence - February 2022

Innovative new hybrid glass panel flood defence in place

24 February 2022. We have achieved another milestone this month with an innovative hybrid glass flood defence at New Passage, South Gloucestershire. The glass panels, on a concrete base, were installed at New Passage because of its location as a popular viewpoint and birdwatching spot on the Severn Way footpath. 

You can watch a short video of the panels’ installation here.

The panels mean that residents and visitors will still be able to enjoy the breath-taking views of the Severn Estuary, while providing robust flood defence for years to come. Manufactured off-site, they were delivered directly to New Passage, minimising disruption to the public. Each panel has been fitted individually so that, if one were to be damaged, it could be repaired or replaced quickly without disrupting the rest of the flood defence.  

The glass panels are one of the innovative flood defence techniques being used along the project’s 17km stretch of coastline. 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.   

Colin Taylor, Senior Flood & Coastal Risk Management Advisor at the Environment Agency, said: “This section of flood defence is the result of long-term consultation and dialogue with the local community. The plans have evolved extensively to create a hybrid form of flood defence with a concrete base and glass panel installed above. Not only will this help significantly reduce flood risk to the community here at New Passage from flooding in the years ahead, but it will also preserve the stunning views of the Severn Estuary.”  

Cllr Toby Savage, Leader of South Gloucestershire Council and Cabinet Member with responsibility for Climate Change, said: “It is fantastic to see these glass panel flood defences installed at New Passage. Their innovative design was in direct response to feedback received from the community. This is a clear marker of the progress that we are making to help protect the Avonmouth and Severnside area from flooding for decades to come.” 

Cllr Nicola Beech, Cabinet lead for Climate, Ecology and Waste, Bristol City Council, said: “The completion of this part of the flood defence project is a great milestone for such an ambitious project, as well as a showcase of one of the innovative solutions that will better protect residents and businesses from flooding in the future, while preserving views of a landscape that is being improved to provide a better home for internationally significant species of bird, such as curlew and shelduck.” 

The largest of its kind in the region, the £80m project will provide 17km of 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 the area from the increased risk of flooding from climate change and rising sea levels, reducing 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 the Government’s Flood Defence Grant in Aid, and Local Levy raised by the Wessex Regional Flood and Coastal Committee. The contractor is BMMjv (BMMjv Explained – Avonmouth and Severnside Enterprise Area (asea-flood-ecology.co.uk).  

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Innovation News

Innovation in techniques: Creating natural refuges for wildlife

Work in progress to create hibernacula at Northwick

Innovation in techniques: Creating natural refuges for wildlife

17 December 2021. We are creating network of natural new refuges for local wildlife as part of our work on wetlands at Northwick, all part of the minimum of 80 hectares (the equivalent of around 112 football pitches) of new wetland habitat along the internationally important Severn Estuary.

The new refuges at the Northwick wetlands are made from grass, mud and other natural materials. Also known as hibernacula, they make a warm, moist and safe habitat for Great Crested Newts, other amphibians, reptiles and insects. Hibernacula also act as a well-stocked larder, with earthworms, slugs and spiders on offer, and provide protection from predators too.

During winter, the hibernaculum offers a safe place for reptiles and amphibians to hibernate. This is particularly important for Great Crested Newts who are largely inactive in winter.

Hibernacula are useful at many other times of year too. They offer shelter for breeding and from hot weather. The network at Northwick will give animals safe passage from the refuges to other areas. The hibernacula are an important part of our work to create and provide locations for wildlife to thrive. You can find out more about the project’s ecological mitigation work here. 

Work in progress to create hibernacula at Northwick

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News

Update: Significant successes for West of England flood defence and ecology project in 2021

Concrete finishing to installed precast concrete flood defence units

Update: Significant successes for West of England flood defence and ecology project in 2021

16 December 2021. The Avonmouth and Severnside Enterprise Area (ASEA) Ecological Mitigation and Flood Defence Project has achieved significant successes this year, including the completion of the main phase of construction of a minimum of 80ha of new wetlands.

When complete, the project will provide 17km of flood defences to reduce flood risk to 2,500 homes and businesses and help to unlock 12,000 new jobs for the West of England. Watch our new video on our progress, above.

Wetland construction: creating a wildlife haven

A major milestone has been met with the completion of the main phase of construction work at Hallen Marsh and Northwick wetlands. Scrapes (small ponds), flow control structures and ditch crossings, and new embankments have all been constructed. Work has also included creating natural refuges, or hibernacula, for local wildlife such as Great Crested Newts, other amphibians, reptiles and insects.

Cllr Nicola Beech, Bristol City Council Cabinet Member for Climate, Ecology, Waste and Energy, said: “These two new wetlands, one of which is in the Bristol area, are fantastic news and will play a major role in achieving our climate and environmental goals, as well as making our city a healthier place to live.”

New flood defences

Over 2021, there has been significant progress on installing new flood defences throughout the project area. The project reached a key milestone over the summer with the installation of approximately one kilometre of precast concrete flood defence wall units in the Severn Beach area.

To the north of the project area at Aust Wharf Road, we have completed sections of the new flood defence wall, with built-in habitat shelves for plants, part of the commitment to enhance wildlife where possible during the project.

Emma Baker, Environment Agency Director Wessex, said: “Climate change is already happening, it’s happening now. Climate change will mean wetter winters, drier summers, greater intensity of rain and therefore greater flood risk. Large parts of Avonmouth and Severnside are already at risk of flooding so we need this scheme to protect the area now and for future generations.”

Cllr Toby Savage, South Gloucestershire Council Leader and Cabinet Member with responsibility for Climate Change, said: “We need to act now to ensure we are resilient against the effects of climate change. The newly constructed flood defences will help encourage businesses to invest in the area and are expected to unlock 12,000 new jobs by 2026. This will deliver a significant boost for our regional and national economy and thousands of homes and businesses in our area will be better protected against the risk of flooding.”

What’s next: 2022

  • Following the completion of much of the construction work, we will carry out landscaping of the new wetland areas at Northwick and Hallen Marsh in Spring 2022.
  • Work at Lamplighter’s Marsh and the Avonmouth Docks will start in earnest in early 2022, with new flood defence walls, outfall structures and embankments constructed. This is the project’s longest stretch of flood defence.
  • The completion of a new flood defence low-level wall incorporating a glass panel at New Passage. This will have two purposes, firstly it will play an important role in reducing the risk of flooding for homes in the area. Secondly, this form of flood defence will preserve the stunning views of the Severn Estuary for residents and people walking along Severn Way.
  • The flood defences at Aust Wharf Road will progress towards completion in Spring 2022, with the installation of new flood gates to complement the new retaining wall that has been built this year. These measures, when installed, will provide much-needed reassurance to residents in the event of flooding.

Richard Bonner, West of England Local Enterprise Partnership Chair, said: “To see so much visible progress being made, with flood defences being built and work taking place all along the coastline, is fantastic. The project is on schedule and going from strength to strength. I’m excited to see what 2022 will bring.

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Innovation News

Innovation in techniques: A new flood defence wall with special features- stone render-effect finish and built-in habitats for plants

Innovation in techniques: New flood defence wall with special features - stone render-effect finish and built-in habitats

22 November 2021. A section of our recently completed flood defence wall at Aust Wharf Road has some special and unusual features. 

The section is part of a stretch of reinforced concrete wall at the most northern part of our project. It has a stone render-effect finish on one side and, on the other, facing onto the Severn Estuary, built-in habitat shelves for plants. The shelves are made from oak. Natural materials make a better and more sustainable habitat for many reasons. They suit small amounts of natural planting which flourishes; invertebrates prefer them; and they are also renewable, durable and strong. 

The stone render-effect finish was a design response to comments from local residents, as well as South Gloucestershire Council’s technical officers, and the requirements of the planning application. The location of the wall is a rural area, overlooked by homes. Officers and neighbours wanted a structure that fitted with these surroundings. 

In response, we devised a design for a stone render-effect finish that would look natural. We then sent this to a form liner manufacturer. Form liners are the liners, or moulds, used in the preparation of designs of concrete walls. As they are available in many different shapes, the manufacturer was able to recreate our design. The resulting finish has a stone and masonry texture with a horizontally running pattern of ‘rocks’ of different sizes. 

The render-effect finish also has considerable environmental benefits. It has meant we have avoided importing stone material, reducing CO2 emissions in the construction process. The finish makes the wall much easier to maintain compared to stone which would have needed repairing over its lifetime. 

As we pride ourselves on being good neighbours, we are delighted that the design fits well with its surroundings, offers a habitat for plants, and is environmentally friendly.

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Local resident discusses flood defence benefits for Severn Beach

Severn Beach North flood defence wall – September 2021

Local resident discusses flood defence benefits for Severn Beach

18 November 2021. John Miller, owner of Salthouse Farm Park retirement community, has lived and worked in the Severn Beach area for over 60 years. Here he talks about how the new ASEA project flood defences at Severn Beach, which are nearing completion, will secure the community’s future.

My business, Salthouse Farm Park retirement community, is an eight-acre private residential estate for retired and semi-retired people aged 50+. We are located on the edge of Severn Beach and have 57 park homes on-site. Originally a dairy farm and holiday site, the park as it is now, was completed in 2006. The park has since grown into a friendly and neighbourly community.

Since I’ve lived here, the risk of flooding has been managed with the building of flood defences. Now, with the possibility of rising sea levels over the coming decades, these new flood defences will lower the risk of flooding.

The new flood defences are great news because they offer protection for the estate in the long-term as climate change and rising sea levels increase the risk of flooding. The main benefit for us is the extra flood security that we’ll have, knowing that flooding is something we’ll need to worry about less in the years ahead.

We are very lucky that the Severn Way runs through Severn Beach. It has always been a pleasant stretch on which to take a stroll or ride a bike. The most important thing for me is the knowledge that its views onto to the Severn Estuary are not being spoilt by the new flood defences, which is really good to know.

The flood defence scheme will really help ensure the village’s survival.