Urban Stormwater Management Using 1D-2D Hydrodynamic Flood Modelling

Abstract

Requirements imposed on municipalities, together with increasing floods due to climate change, have intensified the need for more effective stormwater management. A wide range of modelling approaches has been developed, and their purposeful utilization, which considers both the required level of detail and accuracy of results as well as time efficiency, supports addressing this need. Among the approaches, hydrodynamic modelling is widely used for the assessment of floods and related risks. However, its implementation in the practical design and optimization of stormwater management has remained more limited due to its computational complexity. This thesis examines the 1D-2D hydrodynamic flood modelling utilized in flood assessment and design of stormwater management. The key objective is to evaluate how hydrodynamic modelling can be applied to quantitative evaluation and selection of stormwater management practices. Moreover the principles of stormwater management, theoretical framework of stormwater modelling and different modelling approaches are reviewed. To examine these perspectives, this thesis developed a 1D-2D hydrodynamic flood model for the Houkanoja area in Tampere. The flood model was developed using the Core+ DynamicFlood add-on in SCALGO Live. The modelling process included data collection and pre-processing, selection of boundary conditions, specification of model settings and parameters, and model calibration and validation. The developed flood model was then utilized to evaluate flood conditions in the focus area, identify the key problem areas and the underlying causes as well as to evaluate the efficiency of the selected stormwater management practices. The validation of the developed model indicated best performance for high-intensity rainfall events, whereas the model tended to underestimate both water depths and flows during low-intensity events. Validation was supported by using Percent Bias (PBIAS) and Nash-Sutcliffe Efficiency (NSE). For water depths, acceptable PBIAS values were achieved for the majority of the simulations, whereas NSE values met acceptable levels in half of the simulations. The results during current conditions indicated significant flood risks within the focus area, particularly at Houkanojanraitti and Solkimäenkatu. Further, Solkimäenkatu was identified as a critical bottleneck, with maximum simulated water depths ranging from 2 cm to 62 cm. Among the modeled stormwater management scenarios, street elevation increase and ditch maintenance were recognized as the most effective solutions. The results indicated that combination of these could decrease the flooding at Solkimäenkatu as well as shorten flood duration and decrease water depth levels in surrounding areas. However, during the climate change adjusted design scenario, the maximum water depths were approximately 50% higher than during design scenarios with current climate conditions. This highlighted the importance of considering climate change in stormwater management design. The findings of this thesis demonstrate the potential of utilizing hydrodynamic modelling in stormwater management. The developed model provided a detailed tool for evaluating the time-dependent development of floods, flow paths, and critical flood locations. In addition, the combined 1D-2D model enabled simultaneous analysis of surface flow and drainage network within the same simulations. The incorporation of the drainage network into the model was identified as a key factor in the realistic representation of urban flow paths.