Strategic sewer rehabilitation planning with AQUA-WertMin 6.x

Conventional, comprehensive rehabilitation concepts of a ten-year inspection program are only significant at the time of inspection and at least 50 percent of the data is already obsolete by the time the inspection is completed.

Thus, these rehabilitation concepts are not suitable to illustrate network-specific, dynamic condition processes with reliable statements about the corridors of condition development, rehabilitation requirements and financial flows, as they are only based on a snapshot.

Periodic inspections at intervals of fifteen years are also not suitable to manage the different network-specific deterioration speeds, as the reaches are either inspected too early or too late.

Dynamic rehabilitation strategies must be developed whenever the elimination of conditional or functional deficits is paramount and if a sewer network operator cannot eliminate the determined rehabilitation tail-back on a timely basis due to financial reasons.

Ageing and condition forecast models allow for strategic considerations for the medium and long-term condition development and rehabilitation and financing requirements, if data about the state of construction is available from a comprehensive inspection or selective inspection projection.

Sewer ageing is not (only) a question of time, as the sewer damage is the result of various network-specific influencing factors at different points of time.

These ageing models are not magical, but - similar to hydrodynamic sewer network simulation models - they can provide a good overview of the consequences of current and future rehabilitation activities and the development of sewer conditions as well as cost trends at relatively low financial investment.

An ageing and condition forecast model provides the sewer network operators with useful information

• for the determination of the current and projected net asset value,
• of the total and remaining service life of each reach and manhole,
• for condition-dependent periodic inspection dates for the individual reach / manhole before they reach the next condition class (recommendation of the Baden-Württemberg Guidelines 2001),
• for the development of a rehabilitation strategy for various scenarios (DWA-M 143-14:2005-11),
• for the evaluation of long-term consequences of the current maintenance routine for past hydraulic and constructional replacement and renovations (success control),
• for the determination and forecast of rehabilitation budgets, and
• for recommendations for specific measures in the short and medium term.