Statistical limitations of holistic approaches for sewer network maintenance and rehabilitation planning

Today inspection is accepted as the basic need for the preparation of short-, mid- and long-term planning of reconstruction and maintenance of water distribution networks and sewer systems. In Germany this is even defined by the relevant standard DIN EN 752–5. Nevertheless, it is still under discussion what kind of inspection is needed. The control of the whole sewer system now being planned by many cities is a challenging task, which on the one hand has the benefit that environmental hazards will certainly be detected. But on the other hand this kind of inspection is in itself a hazard: it is quite expensive. Therefore it is necessary to ask if this kind of inspection is always needed, or if it could be restricted to regions with high environmental risks. Is a limited inspection — based on a statistical choice of parts inspected — sufficient for the purpose of long-term planning? The two different approaches are partly realized in two different commercial planning models applied in a study for a part of the sewer system in the city of Berlin.