Thomson’s freshwater ecology team has completed the most recent round in a major survey programme under the Storm Overflow Assessment Framework (SOAF). This storm risk assessment work provided valuable insight into the condition and environmental impact of 55 storm overflow sites.
SOAF surveys play a key role in the industry’s drive to reduce pollution and safeguard the environment. They are vital in allowing water companies to monitor the performance of storm overflows, comply with the Urban Waste Water Treatment Regulations, and target investment where it will make the most difference.
Working on behalf of a water company, AECOM commissioned Thomson to carry out SOAF surveys at a diverse range of sites. The objective was to gather high-quality evidence on the operation of overflow structures and assess their potential effects on local watercourses.
Project requirements
Thomson was tasked with delivering two key areas of work across all 55 sites. Firstly, aesthetic assessments were required to record the condition of each storm overflow structure.
It was also important to provide a biological measure of water quality, both upstream and downstream of the overflow. Macroinvertebrate samples were collected for laboratory identification to inform River Invertebrate Classification Tool (RICT) analysis.
The survey data needed to meet strict accuracy standards and align with the methodology set out in the Storm Overflow Assessment Framework. This involved using approved field techniques and ensuring that the results could be repeated seasonally and used in conjunction with other project datasets.
What we did
Our water ecologists, all trained in SOAF methodology and water safety, carried out surveys in line with industry standards to ensure consistency. Visual assessments documented the condition of each asset, checking for signs of pollution, untreated water, or sewage debris in the surrounding area, indicating poor storm overflow performance.
Macroinvertebrate kick or sweep sampling was undertaken using standardised techniques. Samples were preserved for laboratory analysis to support the River Invertebrate Classification Tool (RICT) assessment.
All survey results were compiled into a centralised database for efficient review and integration with AECOM and the water company’s wider reporting.
Project challenges and solutions
The programme involved several challenges, which were addressed through planning and adaptability:
Land access
Many sites were on private property. Therefore, early coordination with AECOM and direct contact with landowners ensured permissions were in place ahead of visits.
Location accuracy
Some sites could not be located using the supplied coordinates due to outdated databases. Thomson was able to assess the area for potential outfalls and provide feedback to clients on whether outfalls were present at the provided location. Additionally, the team also identified additional outfalls in proximity to the mapped outfall locations, which may cause cumulative impacts.
Weather and flooding
Bouts of heavy rain caused safety and access difficulties. Thomson’s surveyors, trained in water safety, ensured health and safety were thoroughly considered, particularly during flood conditions.
The outcome
The surveys produced a detailed picture of storm overflow performance across all of the sites visited, offering comprehensive datasets of the visual assessments and biological water quality data. Additionally, the findings and ongoing monitoring will support AECOM and the water company in:
- Identifying underperforming assets
- Prioritising improvement works
- Meeting environmental compliance requirements.
By securing access early, responding quickly to challenges, and applying rigorous quality controls, Thomson delivered the programme to the agreed specification and timescale. The resulting data will play a key role in protecting and improving watercourses.
Emily Trill, Principal Hydrologist at Thomson, adds:
“We are proud to have delivered detailed surveys across 55 storm overflow sites within a tight programme window. Our team’s expertise and knowledge allowed us to provide the required data to allow overflow performance assessment. This storm risk assessment data will help AECOM and the water company to prioritise investment and drive improvements in water quality across the region”.
