Report No FR0413
NON CRITICAL SEWER MAINTENANCE FEASIBILITY STUDY
The development of proposals for the use of planned maintenance,
outlined in this report, should lead to savings in operational costs on maintenance of
The objective of this study was to identify a more cost-effective
approach to the maintenance of non-critical sewers, and to identify future research
requirements if appropriate.
There are approximately 235,000km of non-critical sewers in
England and Wales, representing approximately 80% of the total length of sewers.
Maintenance is currently carried out on a reactive basis. The total expenditure on the
maintenance of non-critical sewers in England and Wales is approximately £6.5 million per
year to deal with failures and approximately £30 million for clearing blockages. There is
concern that the reactive maintenance approach may not prove cost effective in the long
- The are approximately 4000 sewer failures a year on non-critical sewers
in England and Wales. These cost an average of £1600 per failure. The number of failures
per year does not appear to have changed since the early 1980's.
- Pre-emptive inspection and repair of defects in non-critical sewers to
prevent failures is unlikely to be economic except for a very small percentage of
non-critical sewers. This is based on current repair costs.
- New methods of trenchless repair for isolated defects in sewers may
significantly reduce planned repair costs. This may make a pre-emptive approach to
maintenance of a much larger proportion of non-critical sewers economic.
- Data from a limited study suggests that there are approximately 200,000
blockages each year. Up to 20% of these may be recurring more than once a year. The cost
of clearing these blockages is estimated at approximately £30 million per year.
- A pre-emptive approach to removing the cause of recurrent blockages is
likely to be cost effective in a significant proportion of cases. However further
information on the number of blockages and their recurrence is required to confirm this.
Information on the extent to which identifiable sewer defects cause recurrent defects is
- Planned maintenance of non-critical sewers should only be considered to
reduce the number of collapses in a small number of areas where the failure rates are
- Further research should be carried out to study the impact that emerging
trenchless repair methods will have on the economics of planned maintenance to reduce
collapses on non-critical sewers.
- Planned maintenance should be considered to reduce expenditure on
blockages where they are recurring more than once per year.
- Further research should be carried out investigate the extent and causes
of recurrent blockages in more detail and to develop detailed guidance on the use of
This report describe the results of a desk study to determine the
feasibility of a new approach to the maintenance of non-critical sewers. The technical and
economic appraisals are described and proposals for research to produce definitive methods
Copies of the report are available from FWR, price £15.00, less 20% to FWR Members.