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Flood and Ecology

Avonmouth Severnside Enterprise Area (ASEA) Ecology Mitigation and Flood Defence Project


This project is a partnership between South Gloucestershire Council, Bristol City Council and the Environment Agency and focuses on helping to support the growth of the Avonmouth Severnside Enterprise Area and protecting the existing communities from flooding. The project will help towards unlocking the economic potential of the Enterprise Area and benefit the local community by:

  • Managing the risk of flooding to keep pace with climate change and rising sea levels.
  • Ensuring that sufficient wetland habitat for birds is created to protect the internationally important habitats and species of the Severn Estuary site.

ASEA Project Partnership Team

Creation of New Pond

Current status of the project

December 2020 Update: A year of delivery – a plan for even more

Over the past year, despite challenging circumstances, we have made excellent progress to start the construction of the 17km of flood defences that will reduce flood risk to 2,500 homes and businesses and help to unlock 12,000 new jobs for the West of England. Our contractors, BMMjv, introduced a range of safety measures so that construction work could continue throughout the Covid-19 restrictions.

Next year promises to be even more exciting as we begin flood defence work both in the south and north areas. We will also continue work on the new wetlands at Northwick and start in Hallen Marsh. We are creating a minimum of 80 hectares of new wetland habitat to provide “high-tide roosts” for the birds.

Watch our new video  about what we’ve done so far and what’s next.

Future of flood defence: Aust 

Our achievements so far include substantial new earth embankments alongside Passage Road near Aust. The new, larger embankments replace the existing lower flood defence to further reduce flood risk to the area.
Watch this flythrough video showing what the most northerly area will look like when complete. As well as flood defence, the improvements also provide the opportunity for people to walk near the coastline to discover nature from vantage points overlooking the Severn Estuary.

The year ahead in 2021

What next? Looking twelve months ahead

Subject to Covid-19, we expect an acceleration of progress on the construction which includes a combination of starting main works and new trial panels – where we test the effectiveness of the materials and design used in specific locations before building on a larger scale. The table below contains the current programme of new works. We will also complete the flood defence sections at Aust Wharf Road, Passage Road and Cake Pill, including new road ramps and flood gates.


Work & location Estimated start

Area 1

Flood defence walls on Aust Wharf Road at Old Passage; Severn Beach North; Severn Beach South. From Winter 2020/21 throughout 2021
Earth embankment flood defence upgrade from Passage Road to New Passage Spring to Summer 2021
Six-metre trial panel of the new flood defence at Severn Beach (South of Station Road) on the existing flood defence Spring 2021
Six-metre trial panel of the new flood defence low-level wall and glass panel at New Passage  Autumn 2021

Area 2

Flood defence wall at Lamplighter’s Marsh, near River Avon (two-year project) Spring 2021

Area 4

Hallen Marsh wetland creation Spring 2021

Unlocking future economic growth

A key purpose of the flood defences is to enable the mix of industrial and former industrial areas and greenfield sites in ASEA to become viable for commercial development and generate 12,000 new jobs by 2026. You can find out more about this potential opportunity in our short video.

Temporary road and lane closures

As part of the works to construct the flood ramps and associated structures on Passage Road unfortunately part of Passage Road will remain closed until autumn/winter 2021.

The road closure is between the southern junction of Passage Road with the A403 and just beyond BMMjv’s site compound entrance, south of the junction with Aust Wharf Road. A diversion route is currently in place for both vehicles and cyclists, and an alternative footpath diversion route is sign posted. We apologise for the inconvenience whilst we undertake these works safely.

In addition, temporary traffic signals have been installed on the A403. These will be part time vehicle activated signals, that will only be used when we transport material across the A403.

Reinvigorating the natural environment


The complexity of this project requires changes to the natural environment – but we are planting much more in terms of high-quality tree numbers, wetland areas and shrubs than we must remove. Work will continue to create the Hallen Marsh and Northwick Wetlands across 80 hectares of land as locations for wildlife to thrive. We will:

  • Construct new ponds, areas of shallow water, and ‘high-tide roosts’ for birds;
  • Start to plant a combined total of two hectares (equivalent to about three football pitches) of native, mature species of trees, including silver birch and hornbeam, and shrubs. We will plant a significant number of trees that could last for centuries as part of our tree replacement programme
  • There is a line of hybrid poplar trees along the Severn Way footpath near Northwick that is near the end of its approximate 40-year lifespan. The trees in this location prevent us from constructing the new, larger flood defence embankment south of Cake Pill outfall which is why our approved planning application covered their removal. We will start to replace the poplars with high quality, longer living, native species, to be planted on a raised bank behind the location of the existing poplar trees and protected by the new flood defence embankment, later next year.


We are reviewing all site operations and, where necessary, ceasing operations where we are unable to adhere to the guidelines. For example, we have suspended ground investigation works on site, where we considered that we were unable to comply with the social distancing guidelines. We are currently reviewing our procedures and methods for ground investigation to determine if with the correct Respiratory Protective Equipment (RPE) and Personal Protective Equipment (PPE) operations could recommence.

Bristol City Council and South Gloucestershire Council have both granted planning permission for 17km of improved sea defences and around 85 hectares of wetland areas for ecological mitigation:

  • You can access the planning application documents submitted to South Gloucestershire Council here. Should you need to search for it, the planning application number is: PT18/2505/R3F.
  • You can access the planning application documents submitted to Bristol City Council here. The planning application number is: 18/02847/FB.

BMM JV have been appointed by Bristol City Council, South Gloucestershire Council and the Environment Agency to undertake the detailed design of the flood defences and construction of the flood defences and wetland areas. BMM JV have been undertaking site investigation, survey and ecological mitigation works across the area since October 2019, with the main construction work scheduled to start in Summer 2020 on a phased basis until 2024. Please read our latest e-newsletter for the latest information


Figure 1 – ASEA scheme proposals

The proposed flood defence upgrade involves raising existing earth embankments and walls as well as innovative techniques using glass panels to ensure views out to the Severn Estuary are retained. Figure 1 provides an overview. For full details, please refer to the drawings contained within our full planning application. The new flood defences will allow for sea level rise caused by anticipated climate change to ensure flood risk is reduced for at least 60 years.

The new wetland habitat being created at Northwick and Hallen Marsh is to help protect the internationally important bird species that live on the Severn Estuary. The new wetland must be delivered to replace and expand any that is lost or disturbed by the development in the Avonmouth Severnside Enterprise Area.

The planning applications gives consent to raise the height of the flood defences between Aust and Avonmouth. The method we propose to use to do this varies from place to place (as shown on Figure 1) and includes:

  • Raising the height of existing flood banks
  • Building new, higher concrete flood walls
  • Building new, higher flood defences from steel sheet piles

Watch our short videos that explains the project, Click here.

Please refer to our Frequently Asked Questions page if you have any queries.

Avonmouth and Severnside Enterprise Area Ecology Mitigation and Flood Defence Project short video


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