Errors in computing flows are caused by uncertainties about input data as well as uncertainties about appropriate models and model parameters.

It is investigated how errors of the input “rainfall”, especially errors in spatial resolution, propagate by computation of sewer flows.

Results of a case study about a sewer system with a catchment area of 2 km2 and ca. 1000 reaches between manholes show

  • that mean errors in rainfall event depths of about 20 % occur even with five raingages within or close to the catchment

  • that the errors by disregarding the spatial distribution are amplified rather than damped by the rainfall-runoff transformation and

  • that using spatially homogeneous rainfall input for flow computations cause systematic errors due to the wrong assumption of spatially homogeneous initial losses and due to dominating directions of storm movement.

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