Renewal Programs

When any authority starts to tackle its ageing asset problem, completing the program as it is required or "just in time" is desirable.

It is critical to know what the real replacement/rehabilitation program is, that it is properly based on "needs" and "levels of risk", and not "gold plated". Renewals accounting provides Asset Managers with a vital tool for determining level of service and the cost of the service.

Unlike some dynamic mechanical or electrical assets, where the probability of failure is able to be predicted with a high degree of accuracy, many of the long lived passive assets such as roads, drains, water, sewerage and building infrastructure has a degradation profile of over eighty years.

Throughout this time, the level of service offered by these assets will reduce considerably, but the assets may not fail as a whole eg. roads will continue to deteriorate until they are totally unserviceable. Some other assets such as drains, sewers, water mains and some structural elements of buildings, bridges, etc., fail more catastrophically.

For those assets with a high consequence of failure, such as bridges and other structural components of buildings, etc., a far greater safety margin is required than is the case where gradual failure occurs.

The failure of drains, sewers, water mains and electrical distribution systems can have high consequences of failure, and could result in significant cost to the community, and substantial loss to the authority responsible for those assets.

One method of managing the "just in time" theory is to adopt the minimum service level eg. two bursts per kilometre per annum for water mains.

This is all very well; however, most passive assets fail randomly. In some cases the water supply, sewerage and drainage assets will have effectively lasted 100 years or more before catastrophic events start to occur. The frequency and occurrence of catastrophic events will depend on many factors beyond the control of the responsible authority, for example:

• Weather conditions eg. droughts, floods, cyclones, and freak storms may place stress on ageing assets.
• Operational stresses caused on parts of the system by the unpredicted failure of components, for example:
  • Burst water mains causing water hammer stress
  • Blocked drains causing upstream surcharge
  • Electrical overload in systems caused by component failure.

These unplanned scenarios result in lost time and other inefficiencies that are costly and disruptive. If replacement is required, this is more so because of the high capital costs involved the inefficiencies and costs will be far greater.