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Sweco UK


Sweco recently undertook a number of Pilot Studies for Northumbrian Water (NWL), to assess the viability of alternative solutions that could reduce spills from combined sewer overflows.

The studies, in Berwick-upon-Tweed, Burn Valley and Washington North, formed part of Ofwat’s Acceleration Programme, and were briefed with a view to providing data and direction for Northumbrian Water’s wider activity across 485 drainage areas (c.1,000 overflows need attention over the next 30 years), in particular 37 drainage areas that will be addressed during AMP8. Below, Sustainable Drainage Manager at Northumbrian Water Richard Woodhouse reflects on our work in Berwick.

The ‘why’

“We had two existing framework suppliers for our DWMP work, but we wanted to look at a couple of areas with ‘fresh eyes’ to see if we were missing a trick on anything. From our point of view it was a very deliberate move to see if those fresh eyes – not blinkered by ongoing day-to-day problem-solving or being too close to what had previously been done – would in turn open our eyes to better strategies or savings.

We have a very open-minded view when it comes to interrogating the way we do things, and we wanted a partner with an equally brave approach when it comes to exploring different methods of engineering and asset management.”

The wastewater networks sector is a very small world, with a small pool of truly competent advisors. Having worked with them in the past, we knew that Sweco is one of those, so we were keen to get their perspective on our challenges.

Richard Woodhouse Sustainable Drainage Manager at Northumbrian Water

The ‘where’

“With 485 drainage areas in our portfolio, it’s impossible to cast the net over all of them in detail, to find gains and potential efficiencies. We therefore chose Berwick as a ‘sample’ site within Ofwat’s Acceleration Programme, in order to uncover solutions that would in turn give us a model for how we go on to tackle issues across our wider infrastructure over coming years.

We chose Berwick-upon-Tweed because of the proportion of catchments there in relation to the size of the town and its population, as well as some of the complexities the geography throws up for us, and also intricate challenges such as the need to work around ancient monuments and walls. The thinking being that if we could identify the things that were on track in this complex area, as well as those that we need to change course on, we could identify universal ‘things that work’ and better prepare our strategies across other projects within the areas we’re looking at in AMP8.

Berwick is also a bathing area, so we knew that we could potentially make a big difference to a lot of people fairly quickly by prioritising our focus there.”

The UK faces a huge challenge in reducing storm overflow spills to protect our environment. As an industry we must think differently and embrace systems thinking and Nature-based Solutions in water consultancy to tackle this problem in the most efficient and sustainable way possible.


These studies with Northumbrian Water have demonstrated Sweco’s unique ‘Thinking in the Whole’ approach, which has identified a range of smart, sustainable, catchment-wide solutions that have significantly reduced the need for the additional ‘grey’ storage identified by other consultants as part of the DWMP process.


This will result in reduction of Whole Life Carbon, TOTEX and disruption to customers during construction and increased opportunity for Biodiversity Net Gain.

Tom Rathmell Water Director at Sweco UK

The ‘what’

“The data and insights from Sweco’s feasibility & Options report were hugely valuable, especially when presenting plans and business cases to stakeholders as well as decision-makers like MPs or local authorities.

Having well thought out plans and alternatives breeds confidence, and ‘proof of concept’ we achieved in Berwick means we’re more certain of outcomes across other areas when we come to repeat the process and employ the same solutions – without the cost and disruption of having to scope each area out in detail every time.

We’ve got 1,000 overflows that need attention within the next 30 years, so it’s essential that we eliminate guesswork in favour of clear ideas that we have all the ‘workings out’ for.”

Benefits of work undertaken

The benefit of our work and resulting solutions at Berwick-upon-Tweed is the reduction of flows in the network, which leads to reduced pumping and treatment costs as well as a reduction in catchment flooding. The ‘non-grey’ solutions proposed, will also generally bring value to society and the environment. Smart network solutions utilised existing capacity within the sewerage network and reductions in OPEX will also result from the reduction of flow volumes in the network.

  • Smart, sustainable catchment-wide solutions versus traditional DWMP solutions
  • Reduced overflow spills to required levels
  • Reduced flows in catchment
  • Reduced treatment and pumping to lower OPEX costs
  • Reduced TOTEX solutions
  • Reduction in catchment flood risk
  • Lower carbon solutions
  • Less disruption to local residents through lower levels of construction required
  • CAPEX either less than or comparable to DWMP solutions

The ‘how’

“The review of our existing assets, especially pumping stations and what they should be doing and what they actually do and was very worthwhile, You would expect most suppliers can do that…but expectations are not always met. In Sweco’s case they certainly were.

Communication at every stage was open, and there was constantly good dialogue. You can find great engineers fairly easily, but finding technical excellence AND communication skills is more difficult.

For us to be able to understand and acknowledge where the team were in their process, know what they were doing and what the next steps were was you know…the customer experience was as good as any we’ve had.”

A unique approach

Sweco’s Thinking in the Whole approach to systems thinking in water consultancy is most useful for root cause analysis and particularly useful for  problem solving network issues as we see in water and wastewater. For example, when trying to solve a problem at a specific point in a network such as available capacity, throughput or resilience,  we consider the wider network (or part) as a system with inputs and outputs to expose alternative solutions. Our experts approached these studies by undertaking catchment wide analysis, assessing the opportunity for the following:

  • The utilisation of available storage within the network using smarter flow management and/or flow diversions.
  • Returning key pumping assets to their original designed performance.
  • Modification of existing CSOs to allow them to operate more effectively.
  • Use of swales / earth bunds to prevent overland flow entering the combined sewer network.
  • Surface water separation.
  • Provision of impounding areas on watercourses
  • Nature-based treatment of storm flows at the treatment works

Thinking in the Whole

The regulatory driver of “Resilience in the round” is one of the key themes for AMP7 set by Ofwat. We believe this needs to be tackled by “Thinking in the Whole”, as opposed to the “thinking in the hole” approach traditionally driven across the industry by commercial models that primarily focus on delivery efficiencies.

As a result of the successful study in Berwick-upon-Tweed, NWL asked us to look at another two catchments – Burn Valley and Washington North. For both of these catchments, Sweco was able to find smarter, more sustainable solutions as had been achieved in Berwick-upon-Tweed, significantly reducing the required storage volume and significantly reducing CAPEX and OPEX costs while meeting the required overflow spill reduction.