Theme: Catchment perspective
Thursday, July 2
From peak flow reduction to economic feasibility: A multi-scenario evaluation of LID strategies
Unplanned urban expansion has intensified flood risk in Brazilian cities by increasing impermeable surfaces and overloading stormwater systems. Low Impact Development (LID) practices offer an opportunity to mitigate runoff, but their application requires evaluating hydrological benefits and economic feasibility—particularly in ungauged catchments where data scarcity challenges conventional modeling. This study integrates hydrological modeling (SWMM) and hydrodynamic simulation (HEC-RAS) to assess the performance of three LID techniques—green roofs, micro-reservoirs, and roof disconnection—applied at viable locations in the Esperança Stream sub-basin (São Lourenço, Brazil). Three scenarios were analyzed: current conditions (C0), full implementation of LIDs (C1), and partial implementation (50%, C2). Results show reductions of 20–40% in peak flows, 13–38% in flood extent, and up to 5% in flood heights. Cost-benefit analysis demonstrates that LIDs are economically viable in higher-income residential sectors but less favorable in commercial and low-income areas. The methodology proves suitable for data-poor environments and offers a replicable framework for integrating sustainable drainage into urban planning.
Integrating nature-based solutions for climate adaptation: Lessons from Dutch case studies on urban transitions
Nature-based solutions are increasingly being recognised for their benefits in numerous urban transitions, particularly climate adaptation, being rigorously incorporated into national and local policy. But as different urban transitions occur simultaneously in the same urban environment, interactions between urban sectors become inevitable, resulting in trade-offs and synergies to be addressed throughout the planning process. This calls for the integration of climate adaptive blue-green infrastructure with other urban transitions, such as energy, mobility, and circular economy. While targets and policies present clear intentions, the implementation of climate adaptation measures is often limited in practice. Recent research at the Technische Universiteit Delft (TU Delft) identified factors contributing to this issue, particularly competition for space and poor cross-sectoral collaboration. Drawing on knowledge from these research projects, this study aims to understand the technical conflicts and organisational shortcomings throughout the transition processes.
Evaluation of large-scale de-paving potential
The Alter-rain® project has enabled the design, development and marketing of an innovative solution to meet the needs of regions adapting to the challenges of climate change. The solution is aimed at local authorities wishing to commit to a urban soil unsealing strategy. The Alter-Rain® solution uses descriptive data about the area and objective criteria to identify the areas within their territory where soil unsealing operations will deliver maximum local environmental, technical, social and economic combined benefits. The Eurométropole de Strasbourg (67) served as the test area for this project. By providing local data superimposed on OpenData and workshops for selecting objective criteria, the solution's processing algorithms made it possible to produce territorial data identifying where soil unsealing best serves the Eurometropolis' objectives.
Prioritizing sustainable urban drainage systems to mitigate combined sewer overflows in Girona (Spain)
Combined Sewer Overflows (CSOs) remain a major environmental issue in European cities with combined sewer networks. This study applies a hydrological–hydraulic model to assess the potential of Sustainable Urban Drainage Systems (SUDS) to reduce CSOs in the city of Girona (Spain). A synthetic 12-hour storm with a 50-year return period was simulated to evaluate 22 candidate sites for bioretention cells, selected according to their contribution to overflow volumes and availability of public open space. Each scenario represents the implementation of one SUDS, and results were compared to the current baseline. The simulations show that individual SUDS can reduce overflow volumes by up to 9.4 million litres, while implementing all 22 candidates simultaneously would reduce total discharges by 35 million litres (≈5%) for the extreme rainfall event. The most effective locations correspond to subcatchments draining toward the Ter and Onyar rivers. Co-benefits include slight improvements in green space accessibility and air quality through enhanced vegetation cover. The study demonstrates how hydrodynamic modelling combined with spatial indicators can guide the prioritization of SUDS in dense urban environments. This integrated approach supports evidence-based planning for climate adaptation and water quality improvement in Mediterranean cities.