The drainage system of sewage in Graz is in large part a combined system. Along the Mur river and the streams in Graz 89 combined sewer overflows are attached, which discharge the unexplained mixed water in wet weather conditions into the river. Because of knowledge that combined sewer overflows contribute to the pollution of waters, its the Holding Graz Services Wasserwirtschaft aim, to adapt the mixing water management on the state of art in Graz. The construction of a central memory channel (zentraler Speicherkanal) with a capacity of 100.000 m, the requirements of ÖWAV-Regelblatt 19 met and the pollution load emissions into the Mur are reduced. The drain in the sewer pipe in wet weather conditions depends largely on intensity of the rain and soil sealing, which is why these parameters are analyzed in terms of the city in Graz. The aim of this Master thesis is on the one hand to find out whether the frequency of precipitation has changed in the area of Graz since 1950 and secondly to evaluate the development of the sealing degree, which are based on aerial data of individual years. In addition the urban drainage systems of Graz, the quality status of the Mur river and the structural design and relevance of the central memory channel are discussed.