Severn Trent sewerage management plans

  • Location: Gloucestershire, UK
  • Location: United Kingdom
  • Client: Severn Trent Water
  • Project status: Ongoing

Project overview

Severn Trent Water has procured the services of Binnies to help manage its sewerage catchments – our remit covers the Gloucestershire area and we are required to gain an understanding of the risks and issues in that area. This framework includes the requirement to update, maintain, and where necessary, re-verify the hydraulic models of the sewerage networks. It calls for the proactive identification of emerging performance issues, risks and improvement opportunities. The framework also involves provision of support to operational teams responding to flooding and pollution events as they occur. Growth is one of the key risks affecting asset performance and the framework includes the requirement to assess the impact of growth from individual confirmed developments and to conduct strategic assessments that look at the cumulative impact of multiple confirmed or provisional developments.

Our role

We have two catchment planners heading our team who have built up an in-depth knowledge of the Gloucestershire catchments and issues. There are multiple aspects to our role under this framework and we have a degree of flexibility in prioritising the various aspects, depending on current need. Some of these aspects are to:

  • keep models up to date with recent growth, capital schemes, updated trader consents and new asset surveys
  • maintain an up-to-date suite of model simulations for dry weather and various rainfall return period storms to enable the provision of flood risk and other performance information
  • work with Severn Trent’s service delivery team to resolve customer complaints around flooding and pollution incidents – this contributes to Severn Trent achieving its outcome delivery incentive (ODI) targets
  • track catchment risks as they evolve and identify any trends that might be of concern
  • scope and supervise asset surveys
  • commission flow surveys targeted to deliver key system performance data to improve model accuracy
  • investigate hydrogen sulphide impacts
  • perform carbon and energy assessments using pumping station power data to identify opportunities for improving efficiency
  • assess sewer capacity, looking at the impact of growth on system performance, flood risk and combined sewer overflow (CSO) spill frequencies
  • carry out modelling assessments to inform the national drainage and wastewater management plans (DWMP) process
  • use detailed catchment knowledge to assist Severn Trent in developing catchment strategies to help target future investment to meet the challenges of the key risks facing the catchments
  • provide information, such as dry weather flows, CSO spill frequencies and predicted flooding return periods at trouble spots to inform solution development
  • assess flow velocities in sewers to estimate the risk of siltation and requirements for planned cleansing
  • update and improve Severn Trent’s modelling specification procedures.


  • Improving the quality of Severn Trent’s model stock within the budget constraints
  • Enabling Severn Trent to respond to customers quickly following an event
  • Working to Severn Trent’s specifications and procedures
  • Escalation of issues within some catchments


  • Prioritising locations for new flow surveys and asset surveys
  • Providing a response to queries or RFIs in a timely manner
  • Updating and improving many of Severn Trent’s procedures
  • Monitoring trends in growth, incidents and asset health to proactively predict future issues

Benefits and Achievements


Our modelling expertise in the use of InfoWorks ICM to construct, verify and update hydraulic models has led to an improvement in the quality of Severn Trent’s modelling stock at an acceptable cost.

An improved understanding of the hydraulic and operational performance of network and assets has helped to identify the root causes of issues.

We have supported Severn Trent in meeting its ODI targets on flooding and pollution.


We have used our in-depth knowledge of the catchments to support operatives rapidly responding to customer-impacting events.


We have developed an innovative approach to understand the cause of exploding manholes from trunk sewers across Gloucester. We produced a spreadsheet to assess the risk and tested solutions. We provided recommendations for a manhole cover design to prevent lifting.

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