Comparative Assessment for 1D and 2D Modelling Approaches of Stormwater Systems

Municipalities are increasingly dependent on hydraulic modelling tools to design, manage and diagnose urban stormwater systems. For any model application, the accuracy and adequacy of a specific modelling approach, or the lack thereof, define the design solution provided to manage existing problems in the system. Based on model simulation results, municipal planners and engineers take responsibility for funding capital projects to address existing concerns in their stormwater systems, including flooding problems or operability. A deficient model basis would result in projects that do not sufficiently address the storm networks’ real issues and risk the misuse of public resources. Currently, two main hydraulic modelling approaches are applied in the most widely used storm modelling software packages: 1D dual-drainage models and 2D direct rainfall models. With varying model prediction accuracy, level of effort and resource requirements, selecting the right model approach for a specific model application becomes critical. The objective of this study is to inform municipalities and other stormwater utility operators about the conditions and limitations of different modelling approaches, which form the basis upon which investment decisions for future stormwater infrastructure projects are made. In the present study, a real stormwater system in the City of St. Albert, Alberta, was selected as a case study. The system was modelled employing the three stormwater modelling approaches using MIKE+ 2022 software package by DHI. The model build of the different approaches was compared in terms of person-hour, data needs, representativity of the real system behaviour and scalability. In addition, model results were compared and examined against system observations and known issues. Comparison of the output from different model approaches showed that the 2D model was more accurate in simulating the performance of the storm system, especially looking at grid-level surface flows in areas where the pipe system cannot naturally surcharge. The dual-drainage model adequately simulated flows in gutters and ditches, which makes it more suited for the design of these features as an alternative to the rational method.