The type of sewerage system of the block and block segment areas has been updated using the information presented in the chapter “Statisical Base”. By reference to the types, courses, and slopes of sewage drains, it was possible to mark off catchment areas of combined sewerage and of separate sewerage systems, respectively. It is not possible, however, to exactly match individual roof and courtyard areas to the catchment areas of rainwater sewers by reference to maps of the sewerage network. Entire blocks and block segment areas as represented on the map were always allocated in their entirety to one of the categories or one of the first receiving water bodies, even if individual properties or block segments are drained differently from the remaining block area under specific circumstances Depending on how far they are located from the canal (max. 25 metres), the block and block segment areas were semi-automatically categorized as combined systems, waste water or rainwater sewers. For this, several GIS tools were used. A new processing method was thus applied, as compared to that of the year 2012. The process of categorizing blocks and block segment areas into different sewerage systems was fine-tuned using available data on land use and the degree of impervious soil coverage for blocks and block segment areas. This was followed by a manual check and, if required, a correction step. At times, there are considerable differences regarding the extent to which properties are actually connected, if they are connected at all, and whether rainwater from impervious surfaces is actually discharged into rainwater sewers. The text accompanying Map 02.13.1 “Surface Runoff from Precipitation” documents the corresponding data, based on information from the BWB and contains generalized connection rates for different building structure types (SenStadtUm 2013). The proportion of impervious areas actually connected to the canal depends on the location within the city, the building structure (e.g. airports) and the degree of impervious soil coverage. As part of de-coupling measures or alternative rainwater management measures, which have often already been used in the planning of new construction areas in recent years, the rainwater from impervious areas is not always discharged into bodies of water but managed locally. The exact locations of these areas have yet to be determined.
To some extent, data on the type of sewers cannot be derived from the documentation available. This is especially true of large-scale industrial and commercial areas, where maps of the sewerage networks of the BWB do not provide any information as to the the type of disposal of rainwater. The rainwater of some of these surfaces is drained directly into water bodies via private drains.
Parts of the city with green and open spaces which may be considered unconnected to sewers were not included in this analysis and are therefore not included in the catchment area presented.In areas with separate sewerage systems, rainwater is drained into water bodies. For every block or block segment area with rainwater drains, the so-called first receiving water body into which the rainwater drain discharges was defined. During the 2017 update, the information on first receiving water bodies was supplemented and checked by sample. For the presentation of this Environmental Atlas map, these first receiving water bodies were combined into water body sections into which they discharge to render the map more comprehensible. So what is shown are the catchment areas of the respective water bodies.
Areas in which rainwater is fed into decentralized percolation facilites (such as basin or trenching systems etc.) were assigned to the sections of the sewerage system or bodies of water, into which they drain via overflows in case of heavy rainfall (such as Karow-Nord).