Even in urban areas reliable and precise information about possible floods and related water levels as well as inundation areas are needed to minimize potential damages. One main requirement for this issue is to correct the stage-discharge relations which are sometimes not available. This paper reconsiders the use of historical hydrologic data in urban areas which have fundamentally changed even concerning the river beds, cross sections and floodplain areas. By means of an historical approach the flood statistics has been updated with surprising results.