Establishing appropriate boundary conditions is essential for developing high-accuracy hydrodynamic models. However, this task is particularly challenging in topographically varying urban domains without monotonous slopes due to insufficient boundary information. This study investigates five different boundary conditions and establishes modeling practices of boundary conditions in pluvial urban flood modeling. A numerical test model within the city of Berlin is used, employing the 2D hydrodynamic finite element module of the open-source TELEMAC system. It performs unsteady simulations with nodal rainfall inputs for various precipitation scenarios, excluding infiltration. The results demonstrate that the suitability of boundary conditions is critically dependent on the surrounding topography. For boundary segments with a positive slope, a stage–discharge curve is found to outperform the other boundary conditions investigated in this study. Conversely, for segments with a negative slope, a closed wall boundary condition appears clearly preferable. Additionally, a drainage reservoir boundary condition performs effectively for more complex boundary segments but necessitates extensive preprocessing. Based on these insights, simulations were repeated with segment-tailored boundary conditions. The results indicate that this combined model outperforms the global application of each individual model.

Culverts play a critical role in conveying surface runoff during flash flood events, yet their failure due to blockages can significantly alter local flood dynamics, particularly in small, topographically complex catchments. Despite this, culvert blockages are often neglected in flood modeling. To address such gap, this study presents a comprehensive analysis of culvert blockages using the open-source hydrodynamic model TELEMAC-2D, applied to a flash-flood-prone catchment in central Germany. First, the study assesses recent flood events and evaluates the completeness and accuracy of official culvert datasets, identifying missing culverts. A dynamic culvert blockage module is then implemented, simulating varying degrees and timings of blockage based on water level thresholds at culvert inlets. Through a series of flood scenarios, the study identifies culverts whose blockages have a greater impact on local flood hydrographs and inundation extents, whereas their impact at the catchment scale remain small. Results highlight the importance of accurate culvert representation and present a scenario-based blockage modeling framework that can support the identification of critical infrastructure. This enables the development of targeted mitigation strategies, such as prioritized maintenance or emergency protection, ultimately reducing flood risks. The findings underscore the need to integrate culvert blockages into flash flood modeling and risk assessments and support future research into blockage formation mechanisms and improved field data acquisition.

Urban surface sealing limits infiltration and thus increases the formation of runoff during heavy rain events. Green infrastructure (GI) measures can be used to reduce urban flood risk by promoting decentralized infiltration, water storage and evapotranspiration. With a scenario-based modelling study, we investigate the impact of green infrastructure on urban runoff formation, flood water depths and the resulting damage to buildings; comparing it with the impact of the conventional drainage system. The study area is located in the city of Berlin, in a heavily sealed 3.3 km² urban catchment. Design rain storms with a duration of one hour and totals between 15 and 100 mm are considered. The green infrastructure scenarios include different spatial extents and combinations of bioretention systems, green roofs and pervious pavement. The Storm Water Management Model is used for the urban runoff generation and the 2D-hydrodynamic module of TELEMAC for surface runoff concentration. Building damage is modelled with the Flood Damage Estimation Tool, a recursive partitioning tool developed with survey data representative of building damage caused by pluvial floods. Flood mitigation is investigated regarding absolute and relative reduction and also space efficiency of the GI types. Relative flood mitigation reduces at all modelling steps with increasing rain totals. In contrast, absolute runoff reduction increases with increasing rain totals while the area with maximum water level > 10 cm decreases the most at the 49 mm event and building damage reduces most at 25–30 mm. Bioretention systems achieve the highest spatial efficiency, however, green roofs and pervious pavements do not impede the former land use.

Culverts play a critical role in conveying surface runoff during flash flood events, yet their failure due to blockages can significantly alter flood dynamics, particularly in small, topographically complex catchments. Despite this, culvert blockages are often neglected in flood modeling. To address such gap, this study presents a comprehensive analysis of culvert blockages using the open-source hydrodynamic model TELEMAC-2D, applied to a flash-flood-prone catchment in central Germany. First, the study assesses recent flood events and evaluates the completeness and accuracy of official culvert datasets, identifying missing culverts. A dynamic culvert blockage module is then implemented, simulating varying degrees and timings of blockage based on water level thresholds at culvert inlets. Through a series of flood scenarios, the study identifies culverts whose blockage has a major impact on flood hydrographs and inundation extents. Results highlight the importance of accurate culvert representation and demonstrate how scenario-based modeling of blockages can support the identification of critical infrastructure. This enables the development of targeted mitigation strategies, such as prioritized maintenance or emergency protection, ultimately reducing flood risks. The findings underscore the need to integrate culvert blockages into flash flood modelling and risk assessments and support future research into blockage formation mechanisms and improved field data acquisition.

According to the latest IPCC report, climate change directly impacts the intensity and frequency of floods in urban areas. As a result, Flash floods, characterized by a rapid increase in flood peak during a short duration, are becoming more common. Managing these flash floods is a crucial yet challenging task for water authorities. One important tool supporting the management of flash floods are 2-D hydrodynamic models.In this study, we use the 2-D module of the openTELEMAC-MASCARET software to investigate the effect of the building representation on an urban flash flood. For this, we isolate a sinuous-shaped building group within an artificial study area. The building group itself and the topography in the model are derived from the Moabit district in Berlin. The buildings are cut out from the model as a hole, and the impact on the model results from the vertex distribution around these holes is assessed. We compare different algorithms to resample the vertices of the building. First, we design an algorithm that resamples the vertices of the building edges at an even distance while conserving the overall shape of the building. The resampling distance is set globally but slightly varies for every building edge. This algorithm is then compared with built-in resampling tools from other software: one tool also conserves the shape of the building yet cannot resample the vertices at an even distance (from QGIS), and another tool resamples at an even distance, yet does not conserve the building shape (from SMS). A change in the distribution of vertices causes a change in the mesh distribution around the buildings. Hence, the flow pattern around the buildings also changes. Additionally, we study the numerical stability of the different distributions. With this study, we aim to deepen the understanding of building representation in urban flood modeling and set the path for further investigations within this topic.

Urban surface sealing limits infiltration and thus increases the formation of runoff during heavy rain events. Green infrastructure (GI) measures can be used to reduce urban flood risk by promoting decentralized infiltration, water storage and evapotranspiration. With a scenario-based modelling study, we investigate the impact of green infrastructure on urban runoff formation, flood water depths and the resulting damage to buildings; comparing it with the impact of the conventional drainage system. The study area is located in the city of Berlin, in a heavily sealed 3.3 km² urban catchment. Design rain storms with a duration of one hour and totals between 15 and 100 mm are considered. The green infrastructure scenarios include different spatial extents and combinations of bioretention systems, green roofs and pervious pavement. The Storm Water Management Model is used for the urban runoff generation and the 2D-hydrodynamic module of TELEMAC for surface runoff concentration. Building damage is modelled with the Flood Damage Estimation Tool, a recursive partitioning tool developed with survey data representative of building damage caused by pluvial floods. Flood mitigation is investigated regarding absolute and relative reduction and also space efficiency of the GI types. Relative flood mitigation reduces at all modelling steps with increasing rain totals. In contrast, absolute runoff reduction increases with increasing rain totals while the area with maximum water level > 10 cm decreases the most at the 49 mm event and building damage reduces most at 25–30 mm. Bioretention systems achieve the highest spatial efficiency, however, green roofs and pervious pavements do not impede the former land use.