The allocation was carried out largely automatically based on the connections located in each block and block segment area, depending on the type of connection. Due to the different mapping scales of the block and block segment areas and the drainage network plans, positions had to be adjusted slightly. The documentation (HYDOR 2023) presents the methodology in more detail. The catchment areas of the rainwater drainage system were largely assigned based on available catchment area data of the BWB’s individual rainwater drainage systems (HYDOR 2023). Block and block segment areas as displayed on the map were always allocated as a whole to one of the categories or one of the first-receiving water bodies, even in the rare case that individual properties or block segments are drained differently from the rest of the block area. The block and block segment areas were automatically assigned to exactly one type of sewerage system based on the type of
connections present and the information as to whether these are connected to combined systems, waste water or rainwater drains. In ambiguous cases, they were allocated based on the predominant type of connection. This means that a new processing method was used compared to the 2017 edition. The reason for this was that in the current edition, data on connection points was available for the first time. In contrast to previous editions, all block and block segment areas were taken into account, including green and open spaces. The process of categorising blocks and block segment areas into the prevailing drainage system in the area was refined using available data on land use and the degree of imperviousness for blocks and block segment areas. This was followed by a manual check and corrections where necessary. Whether and to what extent the properties are actually connected to a drainage system or the rainwater from the impervious surfaces is actually discharged into rainwater
drains varies greatly at times. The accompanying text to the Map “Surface Runoff from Precipitation” (02.13.1) documents the corresponding data, based on information from the BWB and contains generalised connection rates for a variety of building structure types (SenStadtWohn 2017, Table 1). The proportion of the impervious area that is actually connected to the drainage system depends on the location within the city, the building structure and the degree of imperviousness.
In some cases, the data bases do not provide information on the type of drainage. This is especially true of large-scale industrial and commercial areas, where the type of waste water and/ or rainwater disposal is not evident from the BWB’s maps of the drainage networks. Some of these areas discharge their rainwater directly into water bodies via private drains.
In areas with separate sewerage systems, rainwater is discharged into water bodies. For every block or block segment area with rainwater drains, the first-receiving water body into which the rainwater drain discharges its water was defined. As part of the 2022 update, the information on the first-receiving water bodies was reassigned and subjected to random checks in the process. The results are presented in two Environmental Atlas maps on the topic of “Catchment Areas of Rainwater Drainage”. In the map “Catchment Areas of Rainwater Drainage differentiated”, 259 sections of first-receiving water bodies are presented into which rainwater is discharged. The second Environmental Atlas map “Catchment Areas of Rainwater Drainage”, combines these first-receiving water bodies into groups for a better overview. The map therefore shows the catchment area sections that are connected to the water body via the rainwater drainage system.
