Sidmouth Amphitheater: Flood defenses with a theatrical twist

A new flood alleviation scheme to protect residents and properties in Sidmouth, U.K. from future flooding doubles up as an amphitheater for the local community.

Sidmouth Amphitheater

The Sidmouth Amphitheater

For many years Sidmouth, a town on the southwest coast of England, has suffered regular stormwater flooding, with overland flowpaths draining to a low point directly in the town center, putting up to around 150 residential properties and businesses at risk. If a rare, major storm were to take place many local residential and commercial properties would be at risk of flooding.

Devon County Council brought Jacobs in to develop a flood management scheme that would overcome this and navigate the town’s drainage challenges including a dense town center, narrow streets and historic buildings with shallow foundations.

But the team went further and were inspired to turn the flood defenses into an amphitheater, providing a public space for local communities to visit. They also reinstated a wildflower meadow and planted 11 new trees. Now over 300 people at any one time can enjoy local events in a unique natural setting, so long as the weather stays dry!

  • 64

    properties will be protected from flooding in the event of a rare, major storm

  • 24720

    cubic feet (700 cubic meters) of storage provided by the amphitheater and sub-surface tank

  • 3000

    recycled plastic geocellular crates used to store water below the ground

  • 11

    new trees planted

  • 3724

    US gallons per minute (235 liters per second) of reduction to flow reaching the South West Water sewer network

The challenge

The project needed to consider how to intercept surface water flows on a busy highway and provide a flood storage solution to mitigate flood flows, while reducing flows into the town center. More traditional approaches to mitigate flood risk were not viable with the town’s narrow streets and historic buildings, so the storage scheme needed to be located further upstream in an area of open parkland, that was acceptable to the local community and sensitive to the impact on the mature trees. 

A blue-green infrastructure solution

Favoring Sustainable Drainage Systems (SuDS), our team focused on creating an environmentally-friendly solution that would diversify the flora and support the needs of nature, while creating a useful asset for the community. A landscape vision for the storage area was developed with an amphitheater as the focal point of the scheme, creating a venue for community and festival events.

With a strong focus on using recycled, upcycled and sustainable materials wherever possible, our Jacobs team developed a broader system design comprising two “crossdrains”, which take water off the highway and towards the parkland area, with the outfall discharging into a swale. This leads to the flood storage area – the amphitheater – designed for dual use. In normal weather conditions the storage area is a stunning outdoor amphitheater for general amenity use, festivals and other town events. 

During extreme rainfall events, water intercepted from the highway will flow along the swale and infiltrate through the surface of the amphitheater into a sub-surface geocellular crate system. Once the sub-surface storage is full, water will pond on the surface of the amphitheater. Water can leave the amphitheater through a combination of the infiltration system and a piped outflow to the nearby surface water sewer network at a greatly reduced rate. In the event of a blockage of the outlet, a spillway can direct flows safely overland into the adjacent area of the parkland.

Using this blue-green infrastructure solution helps improve the water quality of the runoff as it filters through grass and stone media. Our team incorporated several innovative features and designs including a carefully developed step design to the tiered seating with state-of-the-art, plastic-free grass product and reinforced earth techniques to resist erosion. A lockable, self-raising cover and frame was developed to protect the central flow control chamber from any movement and make for easy-access maintenance.

This culturally relevant solution integrates the vital stormwater management into a creative, environmentally sensitive, climate-resilient design – enhancing the local landscape and biodiversity, while functioning as a delightful performance venue and community recreation space now being fully enjoyed by all.

“No one imagined that a scheme requiring such a significant volume of water to be intercepted and stored before it gets to the town could in effect be hidden in plain sight, giving the community a real asset that will be a draw for people.”

Cllr Stuart Hughes

Sidmouth Town Council

Sidmouth Flood Alleviation Scheme

“The dual-use approach used here is a model for how all projects should be conceived. Flood defenses should benefit the community all year round as opposed to simply when there is a flood event. Maximizing the use of blue-green infrastructure in our public realm will provide wildlife habitats, local amenities, and mitigate some of the effects of our changing climate. Our green spaces are enormously valuable to local communities, providing mental health benefits, cleaning the air and water, and reducing the urban heat island effect for those living in our cities and urban spaces.”

Paul Hargreaves

Paul Hargreaves

Senior Associate Director, Jacobs

Meet the team

  • Paul Hargreaves
    Paul Hargreaves, Lead Designer

    Responsible for developing the overall Sustainable Drainage Systems (SuDS) design concept and ensuring the various disciplines involved coordinated their efforts to deliver a holistic design. Paul also supervised the site during construction.

  • Andy Craven
    Andy Craven-Webb, Lead Landscape Artchitect

    Lead landscape architect responsible for developing hard and soft landscaping proposals from the outline to detailed design stages.

  • Angela Sims
    Angela Sims, Project Manager

    Project manager from the outline design stage through to construction.

  • Dave Bellamy
    Dave Bellamy, Senior Engineer

    Lead ground and hydraulic modeler responsible for overseeing 3D modeling of the ground surface and creating a representative hydraulic model to check performance.

  • Gloria Rigual Munoz
    Gloria Rigual Munoz, Designer

    Designer of the cross drains to capture surface water, conveyance pipeline, and the outfall connection.

  • James Scott
    James Scott, Site Supervisor

    Main supervisor at the construction site.

  • Jennifer Roberts
    Jennifer Roberts, Landscape Architect

    Landscape architect responsible for artist impressions, public information boards and various architectural detailing.

  • Steve Bishop
    Steve Bishop, Geotechnical Engineer

    Lead geotechnical engineer responsible for the steel sheet pile designs and reinforced earth steps from the outline design stage to supervision during construction.