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Cotswold Canal Modelling, England

The Flood Modeller 1D solver was used to support a four-mile canal restoration project on the Cotswold Canals through Stroud. The software was primarily applied to the section of canal between Wallbridge and Ebley due to the complexities within the channel as it is designated 'main river' and has three significant feeder streams, all of which are important ecological habitats.

Significant challenges were present due to the conflicting requirements of future navigation and flood risk management, as the watercourses could create large fluctuations in water levels within the canal.

The same section of canal also contained two locks which fell into disrepair with gates having been removed and replaced with fixed concrete weirs. This section also combined a new flood bypass channel with incorporated fish and eel passage as well as the infrastructure for future power generation via a mini-hydro scheme.

The project required an integrated flood risk management approach which was based upon detailed topographic surveys blended with LiDAR topographic data leading to the generation of a linked 1D-2D model with the TUFLOW 2D solver. This predicted how the two water bodies would interact under all flow conditions.

Overview of flood modelling approach

An overall model of the Lower Frome area was provided by Stroud District Council. This was the uncalibrated strategic flood risk assessment model for the Stroud Valley based on ESTRY-TUFLOW.

The Ebley to Wallbridge section of the model was rebuilt as a detailed 1D-2D model with new survey data to represent accurately the complex interaction between the canal and River Frome which run parallel to each other along the valley floor. This model was calibrated to the 2007 flood events based on gauged data at the Ebley Weir and detailed wrack mark levels.

The Flood Modeller 1D solver and TUFLOW were selected over the previous solution so that the restored canal system could easily be incorporated into the model and accurately represent the behaviour of the locks, bypasses and fish passes which were to be built on the canal. Our 1D solver also accurately represented arch bridges as a bridge unit which provided improved accuracy for the large number of traditional arched canal bridges on the system.

The flexibility of the model and streamlined results processing software provided quick and detailed options, to trial different types of structures and optimise weir sizes and levels for the full range of flows by quickly comparing results from a large number of model runs. Our 1D solver was particularly beneficial as it also has the ability to simulate and optimise automated control structures and replicate moveable gates through the use of control rules.

Through this optimisation process, a flood relief system was developed for the canal which met all parties’ requirements for water level management at both high flows and low flows. This ensured that sufficient water was available for navigation in the canal at all times and flood flows could pass though the system. This also delivered flood defence benefits to specific areas along the canal.

The detailed model enabled individual flood risk assessments for each structure to be quickly developed, optimised and approved.

Flood events on the Frome since the construction of the scheme have proved the capability of the system. All of the individual components have behaved as predicted by the modelling results produced by the Flood Modeller 1D solver and TUFLOW.

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