By reference to the types, courses, and slopes of sewerage drains, it was possible mark off catchment areas of combined sewage drains and of separate rain water and sewage drains, respectively. It is not possible to exactly match individual roof and courtyard areas to the catchment areas of rain water sewers by reference to maps of the sewer network. Entire units and subunits 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 parts of a unit drained differently from others under specific circumstances. It is merely stated whether – given the close spatial proximity of a property to a stormwater sewer – it would be possible to provide a connection to this system. There are – in part at least – considerable differences regarding the extent to which properties are actually connected and whether rain water from sealed surfaces is actually discharged into rain water sewers. Data describing this state of affairs was collected when map No 02.13.1 “Surface runoff from precipitation” was prepared.
To some extent, data on the type of sewers cannot be derived from maps and documents available. This is especially true of large-scale industrial and trade areas, where maps of the sewerage networks of the Berliner Wasserbetriebe do not offer any information as to the the type of disposal of rain water. Some of these surfaces are drained directly into water bodies via private canals.
Parts of the city with green areas and open urban spaces which may be considered unconnected to sewers were not included in this analysis. They were not entered onto the map and therefore they are not included in catchment areas.
Rainwater will be drained into water bodies in areas with separate sewers. For every unit or subunit with stormwater drains the water body was defined into which the rain water drain discharges. This is the so-called first receiving water body. For easier reference and for the purposes of this map these first receiving water bodies were combined into water body sections or groups. So what is shown are the catchment areas of the water bodies concerned.
Areas in which rain water is fed into decentralised percolation facilites (such as basin or trenching systems etc.) and which only have a spillway into the sewerage system or into water water bodies, respectively, for situations of heavy rainfall were still matched to these water bodies (such as Karow-Nord).