Reducing the Occurrence of Flooding through the Effective Management of Sewer Blockages

Abstract

Sewer blockages are responsible for the majority of sewer flooding incidents. They cause the discharge of raw sewage effluent into homes and into natural watercourses and are immensely expensive to the water industry. The number of sewer blockages suffered on public sewer networks is steadily increasing. This trend is likely to continue with deteriorating sewer networks and increased water efficiency both likely to contribute to an increased numbers of reported blockages. Previous research examining the potential for reducing blockage numbers has primarily been concerned with interrogating historical sewer blockage records, and scheduling proactive sewer cleansing to target the worst performing parts of the network. Whilst this approach has represented some success in reducing the rate at which blockages are increasing, a new approach is required to deliver further reduction. The aim of this project is to enable sewerage undertakers to reduce the number of sewer blockages in small bore (i.e. < 225mm) sewers. To achieve this aim, an improved approach based on active identification and management of potential blockages is proposed. Sewer blockages data records and the existing blockage management practices of five water service providers have been analysed. The resulting evidence base has been used to develop a conceptual decision support tool to predict blockage potential and the impact of blockage management interventions. The tool includes a framework that not only takes into account a range of causal factors contributing to blockage formation, but also systematically integrates expert views in the overall assessment of blockage likelihood. The tool also identifies the relative importance of each variable in influencing blockage formation. The tool has been calibrated using data from four case study catchments. The calibrated model has been subjected to a validation exercise, and the model predictions on blockage rates are broadly in agreement with the available data. This thesis outlines an approach which attempts to a) deliver improvements to the way in which sewer blockages are managed reactively and b) provide a decision support tool for sewerage undertakers to undertake proactive removal and prevention of sewer blockages. It is anticipated that through applying the approaches 3 outlined in this thesis, sewerage undertakers will be able to deliver a reduction in the number of blockages suffered on public sewer networks.