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Project study Schwetzingen: Design improvements of urban flood prevention measures by accurate drainge simulation
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Topography
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Dimensioning of urban drainage systems makes the simulation of
surface drainage in heavy rainfall events necessary
to derive the annualities of sewage system overloads and surface floodings
from the annualities of rainfalls of different intensity.
The simulation consists of the coupled computation of the drainage on the surface and in
the subsurface sewage system, and the infiltration into the soil and the groundwater.
The programmes RisoDGM and RisoSim perform these tasks
by employing highly-resolved input data, and by creating a
detailed topography description and soil parametrisation of the surface.
Application of these tools are
- accurate modelling of drainage processes,
- proof of conformity with existing regulations and legislative requirements, and
- design of prevention measures on the surface mitigating the effect of flooding events.
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Model of the sub surface sewage network
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Following an extreme rain event in an urban area of the city of Schwetzingen (Germany)
in the summer of 2005,
a new technology has been employed in collaboration with the engineering consultant Pöyri-GKW
(and with the support of the Land Baden-WWürttemberg)
in an area of approximate 1.5 km sidelength.
The sewage system model contained the manholes and the complete set of gullies and house junctions.
For the surface model the circumferences of the buildings, the walls and pavements
were taken into account.
The topography image on the left shows the level of detail by presenting a part of the
computational grid.
In this way we could model drainage processes observed in the rain event
and identify critical regions.
Overloads of the sewage system and flooded streets indicated where improvements
could be developed to provide the flood protection from rain events with annualities stipulated in EN 752.
Additional conduits,
cross section enlargements of existing conduits,
and special constructions together with measures on the surface
(e.g. small retention basins or low barriers on the street)
could be reliably designed using the results of the software tools.
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