Wednesday Poster Session - Catchment perspective

In the joint project « ZwillE », funded by the Federal Ministry of Research, Technology and Space (BMFTR), a digital twin for the city of Hanover has been developed, providing a virtual image of the drainage system, and, based on this, providing measures and recommendations for action in the case of extreme rain events. We present the elements which constitute the user access platform providing an overview over the current and immediate future situation in the domains of radar-based precipitation, of sewer system, of surface flooding and of natural water bodies, mainly rivers. Consequences of these results are formulated as recommendations to the municipal staff. 

For a long time, the drinking water supply to the Dakar region was provided by the Thiaroye boreholes. But the advance of the salt wedge has led the state authorities to order a halt to these drillings. This disconnection has not only led to a decrease in drinking water production in the area, but it has also encouraged the recurrence of flooding due to the rise of the water table. 

Da Nang, the largest city in central Viet Nam, frequently experiences localized flooding even under moderate rainfall due to inherent limitations in its urban drainage system. While developed countries employ separate sewer networks for wastewater and stormwater, Da Nang, as a developing city, still relies on a combined system. During the dry season, foul odors rising from manholes lead residents to cover street inlets with boards or plastic sheets, inadvertently blocking flow paths when sudden rainfall occurs. Seasonal leaf fall and improper waste disposal further clog inlets and underground conduits, creating debris and sediment accumulation that reduces hydraulic capacity. To investigate these operational malfunctions, this study applies an integrated 1D-2D model to simulate sewer hydraulics and surface inundation in the Thac Gian-Vinh Trung lake area. Multiple malfunction scenarios, including inlet blockage and reduced conduit capacity, are examined alongside real rainfall events. The results reveal critical system bottlenecks and provide scientific evidence to support targeted improvements in stormwater management and urban flood-mitigation planning for Da Nang. 

Design criteria for new drainage systems now consider in several countries that the systems should withstand significant rainfall events without causing unacceptable damage. The dual drainage concept, which considers both the minor and major systems, has been applied successfully for at least thirty years in several regions of Canada as it enables obtaining systems offering an acceptable level of service up to or even exceeding 100 years recurrence. However, for existing systems that had not been designed with these concepts, the level of service without surcharge conditions or surface flooding is often lower than expected and, in many situations, the degree of flood risk is not precisely known. In addition, this risk is also accentuated by poorly controlled urbanization and worsened by the impacts of climate change. When flooding is observed at different sites or simply as part of planning with the objective of increasing the level of service of an existing drainage system, optimal decision-making will require adequate quantification of the risk and vulnerability of the assets. The presentation first discusses dual-drainage concepts for creating resilient drainage networks. The notions of vulnerability and risk are addressed, with a review of approaches to quantify these elements to guide decision-making for the rehabilitation of existing networks. To illustrate the application of these concepts to different regions of Canada, case studies are presented for the City of Calgary (Province of Alberta) and for the Communauté métropolitaine de Montréal (CMM) in Quebec. Created in 2001, the CMM is a planning, coordination and financing organization that brings together 82 municipalities, representing 4.3 million people spread over a territory of more than 4,374 km2. 

This study develops a Decision Support System (DSS) for climate-resilient coastal urban planning by integrating hydrodynamic modelling, machine learning and multicriteria analysis to prioritize urban adaptation strategies under flood and erosion risk. The DSS operates in data-scarce environments, combining physical, environmental and territorial information to generate probabilistic risk maps and strategic zoning layers. Methods include coupled FLOW+SWAN modelling, Random Forest and Convolutional Neural Network CNN-based land cover projections, fuzzy logic normalization, and TOPSIS with Monte Carlo simulations to rank adaptation pathways such as nature-based solutions, soft engineering, built-environment adaptation and planned retreat. Applied to Tumaco (Colombia), results show that omitting physically based modelling overestimates high-risk areas by ~284 ha, while incorporating sea-level-rise scenarios identifies an additional 52 ha requiring long-term intervention. The DSS supports evidence-based land-use regulation, anticipates spatial transformations driven by climate change, and positions water as a central element for strategic urban planning in vulnerable coastal cities. 

This study presents an integrated methodology for identifying and prioritizing suitable areas for Nature-Based Solutions (NBS) in highly urbanized Mediterranean contexts, focusing on the Tondo Gioeni catchment in Catania (Italy). The approach combines hydrological–hydraulic modelling, spatial analysis, and planning-based criteria to address increasing flood risks driven by extreme rainfall events and compact urban development patterns. Flood hazard and risk maps were produced using HEC-RAS simulations for different return periods, highlighting critical zones requiring intervention. These results were overlaid with land-use, morphological, and environmental datasets to identify unbuilt areas where NBS could effectively mitigate peak flows and enhance infiltration. Additional urban determinants, including zoning regulations, planning frameworks, population vulnerability, and land ownership, were incorporated into a multi-criteria evaluation to assess the feasibility and transformability of each site. Preliminary findings reveal significant opportunities for targeted NBS implementation but also emphasize the constraints associated with highly built-up urban settings. The proposed framework supports decision-making processes that integrate engineering, ecological, and planning perspectives for climate-resilient stormwater management in Mediterranean urban environments. 

Urban pluvial flooding is an increasingly critical issue for modern cities, driven by rapid urbanisation, ageing drainage systems, and more frequent intense rainfall events. Since model accuracy depends heavily on input data—especially terrain information controlling overland flow—more research is needed to address a key gap in current practice, where DTMs are often chosen for convenience rather than rigorous evaluation. This study examines how different topographic datasets, varying in resolution and preprocessing, influence the results of a 1D–2D approach for simulating both surface runoff and sewer system dynamics. The analysis focuses on the densely built Sampierdarena district in Genoa (Italy), an area regularly affected by pluvial flooding. Several simulations were performed with IBER model, maintaining the same synthetic 0.5-hour rainfall, based on the Chicago Design Storm (CDS) method. Results show that terrain resolution strongly influences predicted water depths, flow paths, and inundation extent, with coarser DTMs smoothing out key micro-topographic features, shifting flood outlines and potentially misleading risk evaluations. To overcome the limitations of purely 2D modelling, the research progresses toward a coupled 1D–2D IBER–SWMM approach. This integrated method improves the representation of surcharge events, overflow points, and surface-drainage interactions. Ultimately, the work supports a more realistic and reliable urban flood modelling and offers practical guidance for improving resilience in flood-prone urban areas.