This paper presents a novel use of 1D-1D hydraulic modelling methodology to represent both below ground sewer networks and above ground overland flow pathways, to assess the impact of linear infrastructure projects on existing drainage patterns in an urbanized area. Using a Light Rail Transit (LRT) project in the Greater Toronto Area (GTA) as an example, the study explains how a 1D model is developed to include overland flow channels and the sewer system. Inlet structures are included as a physical component in the model to control the transfer of rainfall-runoff from surface to sewer, while weirs are added at potential spill routes.
This study illustrates how 1D models can be used to assess overland flows and surface ponding results from high-intensity rainfall events, which in most cases may exceed the capacity of inlet structures to capture runoff and discharge to sewers. The approach can be adapted to integrate proposed linear infrastructure along roadways with the existing drainage system; which is critical in the case study where the LRT line acts as a barrier to disrupt existing drainage patterns such as ponding locations and pluvial flooding.
This 1D-1D hydraulic modelling methodology has the potential to provide a more accurate representation of the impact of linear infrastructure on both overland flow patterns and sewer network performance than traditional 1D models with a singular overland flow conduit. The 1D-1D methodology also allows for a more rapid assessment than full 1D-2D models, which often require more input data, are complex to build, difficult to calibrate and need more computing power to run. Finally, the paper discusses some advantages and limitations of the approach, as well as data requirements and potential sources of error or uncertainty which need to be considered when analysing the model outputs.