Deterioration Rates of Sewers (UKWIR Project)

Current rates of investment in sewer replacement, renovation and maintenance represent only a small fraction of the value of the asset base. Concerns have been raised over the sustainability of such low levels of investment and the continuing ability of the sewer stock to deliver long-term stable serviceability to customers and the environment. The key objectives of this project were to assess current deterioration rates of sewers, to produce a sewer deterioration model for use in the next business planning cycle, to identify data gaps and to recommend how CCTV and other data can be better used.

This work has developed a process and methodology to robustly model the deterioration of sewer performance. This can be used both in the business planning process to determine appropriate future investment strategies, and as part of ‘business as usual’ sewer operational management. Much time was spent in the project considering the benefits of defining sewer deterioration at the pipe level or at a small-area level. A survey of the data that water companies hold on sewer attributes, performance failures and interventions showed that for most companies at the present time a pipe-level approach to sewer performance modelling could not be used. This project has successfully developed an area-based approach in which the sewer assets in areas of similar age are characterised by indicators that do not require such detailed information. For those companies with more comprehensive data sets the methodology can be applied at a pipe level with equal effectiveness.