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Water management investigations and application of digital sealing data from official real estate cadastre data

Data on sealed surfaces are the relevant basic information for various water management tasks due to their relevance for precipitation water runoff and the associated consequential effect on the water balance. Despite numerous integral functions, there is neither a uniform methodology for collecting sealing data in NRW nor a central database in which sealing information is kept for water management applications. With the nationwide introduction of the "Official Real Estate Cadastre Information System" (ALKIS), a suitable data basis exists for the first time that can enable the area-wide recording of sealed surfaces.


The aim of the project was to use the ALKIS data to provide the responsible water authorities and other users of data on sealed surfaces with an IT application. With this application, sealed surfaces can be derived for any spatial units in NRW using a scientifically validated, documented and reproducible method. The provision of sealing data for users is to be carried out as a service by the State Office IT.NRW, which will develop a suitable IT solution for this purpose.


In general, paved areas in Alkis can be divided into building and roof areas, traffic areas and access areas, accounting for 1/3 of the paved areas each.In the project "Water Management Investigations and Application of Digital Sealing Data from Official Real Estate Cadastre Data" (WaLKIS), the theoretical foundations and analytical methods for determining paved building and traffic areas from the ALKIS real estate cadastre model were developed, as well as an area-wide analysis for the statistical estimation of paved access areas from the ALKIS data and the verification of the results. This analysis is based on manually digitised sealing polygons from orthophotos as a reference data set, which cover the entire catchment area of the two rivers Emscher and Lippe (EGLV).

Building areas were selected on the basis of ALKIS data covering the entire area and, with the aid of correction values, showed good to very good agreement with the available reference data. The same applies to traffic areas, although the recording of traffic areas in ALKIS is handled very differently by municipalities and the responsible land registry offices. In particular, the completeness and accuracy of the recording of traffic areas and objects that represent traffic areas within settlements differ greatly. In the context of this project, it was also shown for the first time that a statistical estimation of access areas using ALKIS data is possible on the basis of mathematical models. The results of the statistical analysis are suitable for an area-wide application for spatial units, for example catchment areas of medium-sized rainwater basins or comparable technical facilities.

The methods developed and the findings obtained represent a significant, scientifically verifiable and reproducible basis for further analyses and applications in water management.


Philipp Knollmann, M.Sc.
+49 241 80 2 79 78 / E-Mail

Magnus Hoffmann, M.Sc.
+49 241 80 2 66 06 / E-Mail

Rona Michaelis, M.Sc.
+49 241 80 2 68 20 / E-Mail



North Rhine-Westphalia State Agency for Nature, Environment and Consumer Protection (LANUV)