Designing a Flood Risk Management Scheme for Rochdale, England
- oliverashton3
- Oct 13
- 4 min read
“ Flood Modeller has been central to the development of the Flood Risk Management Scheme in Rochdale. From optimisation of orifice sizes for the flood storage area outlet structures, to calibrating the hydraulic model with observed results, the software has played a big part in the development of the project over its lifetime”
Georgina Palmer, Hydraulic Modeller, Jacobs
Key Facts
Phase 2 of the Littleborough and Rochdale Flood Risk Management Scheme (FRMS) aims to achieve a Standard of Protection of 1.33% Annual Exceedance Probability (AEP) for fluvial flooding.
The scheme design includes two flood storage areas (FSA) in addition to linear defences along sections of the River Roch and Buckley Brook.
Flood Modeller was utilised to assist in the design of the flood storage area outlet structures, using orifice units of different sizes to understand changes in pass-forward flow.
Residual Uncertainty Analysis was also undertaken and global edit tools in Flood
Modeller were used to bring efficiencies to the process.
Use of Flood Platform throughout the project ensured model results were available at key milestones.
The Flood Modeller-TUFLOW hydraulic model will be used in future to further refine Phase 2 design, so confidence in the software and its outputs is key.
Jacobs were commissioned by the Environment Agency to design a Flood Risk Management Scheme (FRMS) for the towns of Littleborough and Rochdale in Greater Manchester. The scheme will be delivered in two phases; Littleborough (Phase 1) and Rochdale (Phase 2). Phase 2 of the scheme aims to achieve a Standard of Protection of 1.33% Annual Exceedance Probability (AEP) for fluvial flooding.
A hydraulic model of Littleborough and Rochdale, which is a dynamically linked 1D-2D Flood Modeller-TUFLOW model, has been developed and refined over a number of project phases. The 1D model component covers approximately 14km of the River Roch and a number of tributaries, including 5km of Buckley Brook. The 2D model component covers an area of approximately 125km2. The model represents a complex system; there are several reservoirs within the study area and many different structures.
Phase 2 of the FRMS includes two Flood Storage Areas (FSAs), in addition to linear defences along sections of the River Roch and Buckley Brook. The FSAs have outlet structures designed specifically to limit pass-forward flow, reducing peak water levels through central Rochdale during a storm event. The design of the outlet structures was refined during testing using Flood Modeller. The hydraulic model was run using orifice units with different opening sizes, and also with modified calibration factors to examine how changes to these parameters affected pass-forward flow. The latest design is based on an opening size which allowed an acceptable amount of flow forward without leading to overtopping of the embankment of the FSA in the design event.
Residual Uncertainty Analysis (RUA), now a mandatory requirement for flood risk management schemes in England, was undertaken to assess uncertainty in design of the linear defences. This included testing a range of selected variables across four confidence intervals. Flood Modeller's global edit tools were helpful in the process of setting up the different networks for the RUA modelling. For example, the global edit tool was used to adjust hydraulic roughness across the channel, completing the task in seconds - compared to the hours it would have taken to manually update values in such a large model. It also streamlined the process of uplifting inflows for a separate set of RUA runs, significantly improving efficiency.
Flood Platform was utilised throughout the project to maximise efficiency and reduce the amount of time required to run the model when compared to running on internal servers. This proved especially valuable given the high volume of model runs needed throughout the project. Flood Platform provided confidence that critical results would be delivered on time, supporting key project milestones with reliability and speed.
Model outputs were used to generate a suite of deliverables for the Environment Agency, including flood maps that compare baseline flood extents with those resulting from the proposed scheme. These visualisations clearly demonstrate the benefits of the latest design and serve as valuable tools for stakeholder engagement. They also provide a critical source of information to support ongoing project development and decision-making.
Further work is required to refine the design before Phase 2 construction can begin. The hydraulic model will remain a key tool for design teams going forward, so having confidence in the software and the outputs produced is crucial. The Flood Modeller–TUFLOW model has effectively demonstrated the scheme’s impact on flood risk in Rochdale. With ongoing software enhancements and the introduction of new utilities in Flood Modeller 8.0, its value is expected to grow even further in supporting the next phase of the project.
Georgina Palmer
Georgina is a Hydraulic Modeller at Jacobs with over 3 years’ experience using Flood Modeller. In her role she works across a range of projects including flood alleviation schemes, reservoir flood studies and surface water flood mapping. She has built and worked with a variety of hydraulic models, including fluvial 1D and 1D/2D linked models. Georgina also delivers 'Introduction to 1D River Modelling' training for Flood Modeller.
