Strategies for Condition Assessment of Sewer Systems

The inspection of sewers can take place whether by means of fixed-intervals in a conventional surface-covering inspection, or by means of need-oriented strategies. Those need-oriented strategies can be differed between a selective inspection, an evaluation of the present sewer condition based on a representative samples and a failure-oriented forecasting strategy. By setting up and implementing a numerical model it is now possible to carry out a comparison between strategies. Herewith, the potential of success from every single strategy concerning different boundary conditions has been evaluated. For larger Sewer Systems a failure-oriented forecasting strategy presents a more reasonable alternative than the conventional surface-covering one. The reason is because the holding time from every sewer in a critical condition can be reduced considerably within this kind of oriented-need inspections compared to the conventional ones. Similarly, this method meets the ability to estimate the whole condition of a sewer for a given term in the minimum time, which usually could not be achieved by a conventional inspection. Oriented-need inspection strategies offer even superior advantages when the crop and the ground water pollution regulation controls have been followed from the beginning, in order to reduce holding times within sewers in a critical class-condition.