Urban flash floods
Due to extreme precipitation, the simulation of the sewer network loses importance in favour of the simulation of surface runoff. We reduce our requirements to what is feasible and, when calculating urban flash floods, we are looking for minimum drainage comfort - which also works under extreme conditions. Suitable measures and methods must be used to create flood protection and its function must be proven as early as the planning phase.
The decoupled simulation of flash floods is the suitable method if the (extreme) precipitation (runoff formation and runoff concentration) is to be mapped in a 2D-HN surface runoff model - without the sewer network playing a role. All N-A processes therefore take place in the 2D model. Flood area, water depth, flow velocity at each node, flow paths and sink volumes as well as discharge quantities are the simulation results. It is irrelevant whether a road or a receiving watercourse is to be modelled and the discharge behaviour investigated. The model technique is the same. Basis are the depth averaged shallow water equations in their original form.
The coupled 1D/2D simulation has the highest value in the DWA-M119. Their application is recommended for particularly endangered areas.
Coupled 1D/2D models (sewer network/2D model) allow a realistic calculation of the flooding processes. The use of coupled models appears to be particularly useful in cases where a rough analysis has identified flooding focal points (hotspots), the hazards of which are subsequently to be subjected to closer examination, or where action is already required as a result of damage events in the past. During the runtime of the programmes, the water quantities are exchanged bidirectionally between the sewer network model and the 2D model at shafts and road drains.
With the programs GraPS (graphics system for sewer networks), HYKAS (hydrodynamic sewer network calculation) and FLUSS-2D (2D surface discharge models) as well as HYKAS-2D we offer the appropriate software to meet the requirements of the DWA-M119. The programs are the ideal tool for a graduated approach: from the rough analysis to the sophisticated 2D model, perfectly coordinated and proven in practice.