Wastewater overflow events into the Loughor Estuary have been reduced; Wastewater overflow events into the Loughor Estuary have been reduced;

Halfway and Northumberland Sewage Pumping Stations, Carmarthenshire, Wales

How can digital tools and green infrastructure create cleaner waterways?

Clean waterways and safety from flooding are fundamental to maintaining thriving communities alongside our rivers and coastlines. In Llanelli, South Wales, local waterways are a critical natural asset. As well as being used for recreational and commercial fishing, swimming and sporting events, this area on the Loughor Estuary is ecologically sensitive – it includes waters that must meet rigorous legal standards for shellfish production as well as prized saltmarshes and a designated special area of conservation.

Home to over 50,000 people, this part of Wales has historically suffered from repeated flooding by wastewater, an experience that is devastating to local people. To protect homes, businesses and roads at times of heavy rainfall, wastewater from the area’s combined sewerage system has historically been discharged into the estuary via combined sewer overflows. To safeguard the environment, and in line with its long-term vision, our client Welsh Water committed to reducing the number of these overflow events from 120 to 30 per year.

Arup’s water engineers used a catchment-wide approach to provide a resilient, environmentally sustainable and cost-effective solution.

Project Summary

75% reduction in wastewater overflow incidents per year

£15m+savings in capital expenditure, compared to traditional methods

450hourssaved in modelling and engineering design time

A catchment-wide approach to water management

Traditional approaches to wastewater management rely on an end-of-pipe solution – transporting wastewater to be stored and treated. In Llanelli, this technique would have required an increase in wastewater storage capacity of 22,000m³. Welsh Water had for some years been developing more strategic, sustainable approaches to surface and wastewater management, enabling us to work together and take a catchment-based approach to the problem – using green infrastructure to deal with water close to where it is collected and maximising the efficiency of existing assets. The impact of this approach was significant, with only 2,700m³ of new wastewater storage capacity required. This 88% reduction is calculated to have saved Welsh Water £15m in construction costs.

3D models were created using data collected via digital surveys 3D models were created using data collected via digital surveys

Digital modelling and design

Designing an effective catchment solution requires a substantial amount of modelling to balance the many variables involved. Our team developed an optimised optioneering tool to transform the efficiency of this process. The tool models key parameters and combines results with sensitivity analysis. Machine-learning-driven algorithms generate a solutions matrix, which allows the tool to optimise a catchment solution. This innovation saved the projects 450 hours of modelling and engineering time, increasing our engineers’ capacity to analyse the catchment holistically and propose the most robust, sustainable solution.


Digital tools were also key to improving efficiency and safety during the surveying stage. At both pumping station sites, confined spaces, deep wells and the presence of hydrogen sulphide gas pose serious safety risks. We reduced the need for entry into these areas during the project’s design phase by using point cloud surveys to capture all the necessary information from these chambers. Using remotely-operated 360º panoramic cameras and Spike – a mobile laser measurement attachment for smart phones that captures dimensional information via photography – we were able to avoid the need for multiple surveys and remove the arduous task of measuring large confined-space areas by hand.


The Halfway and Northumberland SPS scheme is a perfect example of outcome-focused thinking in line with our 2050 vision. The feasibility and design work undertaken has created a solution which improves the local environment and provides future resilience in a technologically-smart, environmentally-sensitive and cost-effective manner. 

Martin Hennessey Head of Capital Delivery Alliance, Welsh Water

Digital solutions to maximise wastewater assets

Part of our design team’s solution incorporated digital technologies to maximise existing assets – utilising Victorian structures and upgrading pumps, mechanical equipment, electrical infrastructure and digital interfaces to create “smart assets” that bring the network into the 21st century. This eliminated the requirement for a new installation that would have represented a significant financial cost and embodied carbon footprint. Smart sensors now inform Welsh Water’s operations teams of potential problems within the network and trigger appropriate responses, such as pump shut-down or flow diversions. These technologies help to maximise network capacity by identifying areas of spare capacity and diverting flows. The result is assets that are more resilient, with headroom created for future growth.

Green infrastructure has been used to reduce the volume of surface water entering the network

RainScape sustainable drainage

The final element in the catchment solution incorporated an investment in using green infrastructure retrofits to reduce the amount of surface water entering the sewer system. Our team deployed Welsh Water’s existing RainScape strategy and demonstrated how green infrastructure could be woven into designs to complement the catchment strategy and unlock greater overall value - reducing demand for wastewater storage capacity and enabling storage systems to be gravity operated instead of needing to be pumped.

Rainscape not only contributes to an efficient wastewater system, but also delivers wider benefits – increasing biodiversity protection, public amenity, operational safety and energy savings. In Llanelli, the green infrastructure systems deliver a community learning and amenity feature for a local primary school that provides opportunities to educate future generations about water conservation.

A sustainable long-term solution

Since the new and improved assets in Llanelli became operational, evidence from a number of significant rainfall events has proven that flooding incidents from the sewer network are no longer frequent. In addition to drastically reducing the regularity and severity of wastewater flooding, this solution is forecast to save Welsh Water £35m over 60 years of operation through reductions in energy consumption, operational costs and avoided re-investments.


Constructing Excellence in Wales 2019, Value Award

Constructing Excellence National Awards 2019, Value Award

Sustainable Futures: Arup Annual Report 2020

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