The paper demonstrates application of the Fuzzy Set Theory in risk and uncertainty assessment, associated with hydraulic overloading and flooding Of urban drainage networks. The case study with the town of Novi Iskar, Bulgaria has been chosen as ail example, because it was among the settlements in the Country, drastically damaged by the heavy rains and floods in August 2005. Modeling has been performed by means of MOUSE software, based oil the available electronic cadastre Of the urban drainage network oil ArcView platform. Different scenarios and technical measures have been checked for coping with the problem with flood mitigation, which have been assessed on the base of cost analyses. Risk for the sewer networks vulnerabilities of hydraulic overloading and flooding at the relevant scenarios was assessed, based oil selected criteria.
