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Determination of the maximal run off in the constantly changing urbanized territory often is very different compare to the natural conditions. There are many approaches to reflect the new conditions of flows formation including the extremes. Sometimes the level of urbanization is so quick that the conditions of flows formation could be altered in the frame of several years. The determination of the maximum flows is additionally complicated in case there is not a suitable hydrological monitoring network or a lack of any observations. The last years the rapid growth of the capital Sofia, the biggest city in the Bulgarian Danube catchment area, urgently imposes the new methodological issues for characteristic maximum flows determination necessary for new infrastructural constructions and floods protection activities. Floods are a potential danger for any urban territory where there are river streams. All rivers inflowing trough Sofia urbanized territory spring in the northern slopes of Vitosha Mountain and have a similar hydrological regime. But hydrological observations exist only in one hydrometric station located at the beginning of the city with still low level of urbanization. On the other hand some of the Sofia rivers are heavily impact on the urbanization. The present material considers the determination of maximum characteristic flows of Sofia rivers reflecting the new hydrological conditions in the urban areas. The suitable methodological approaches are discussed and examples with different urbanizations levels on the territory are demonstrated. Landuse mapping is used to identify the existing and expected future land uses. The timely information about the changing pattern of urban land use plays significant role in urban landuse planning and sustainable urban development. The article presents the re-assessment of the maximum natural flows based on the natural flow in the unique monitoring station and generalizing of new hydrological time series depending on the urbanized level. [ABSTRACT FROM AUTHOR]