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CH2M was commissioned by the Environment Agency in 2015 to investigate the interaction between the Grand Union Canal and the river Ouzel during high flow events at Leighton Buzzard, Bedfordshire, as local residents and the Regional Flood and Coastal Committee expressed concerns over potential flood risk following overtopping of the canal into the Ouzel.

The project involved the development of a 1D-2D model for the Grand Union Canal and connecting it to an existing hydraulic model of the river Ouzel at Leighton Buzzard. The existing ESTRY-TUFLOW (1D-2D) model included the river Ouzel and tributaries, and allowed for storage from the Grand Union Canal in the floodplain, but no attempt had been made to model the canal as a flooding mechanism.

A review of the model and hydrology was initially carried out to check that the existing files were suitable for the investigation. Following the audit, the model hydrology was re-schematized to meet the needs of the project.

This involved producing flows for heavily urbanized sub-catchments, which could be easily be obtained using the urban subdivision option for ReFH units within Flood Modeller. The urban subdivision option is already available within the ReFH unit and requires simple GIS information that can be gathered using the Flood Modeller interface.

As part of the project, CH2M modelled the 1D network of the Grand Union Canal using Flood Modeller. The ability of the software to use operational rules together with full structure geometry allowed the detailed representation of the complicated system of sluices and culverts along the canal. The canal model was then connected to the existing model of the Ouzel. The software also allows for the use of interpolated and replicated cross sections; this made it much faster to build a good model of the system.

Once the simulations were run, Flood Modeller was used to extract depth/velocity grids and create animations for the depth layer. The user friendly post-processing and automation tools within the software streamlined this process, making the overall project much more efficient.

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