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Flood mapping, England

The major flood events of 2007 not only caused widespread destruction across many towns, villages and rural areas in the UK, but also lead to the Environment Agency refining the country’s Flood Map. Whilst this has highlighted areas that now require better flood management it also brings areas of land into flood risk zones that had no record of previous flooding.

The new flood maps can have a serious impact on the cost of insurance and can hinder new development. However, these flood maps can be challenged and, in the case of Staveley Works near Chesterfield, they were challenged successfully by the environmental consultants Enzygo. This has now led to the local Council adjusting its long term vision for the site, thereby providing a real chance of development in due course.

The starting point for Enzygo was to establish what evidence was provided by the Environment Agency to determine that the majority of the site was at medium risk of flooding. It was quickly discovered that the ruling had been derived from aerial photography, taken of the site following the flooding event in the summer of 2007, although on closer inspection the accuracy of the imagery was deemed to be poor.

More importantly, it was agreed with the Environment Agency that, in principle, most of the site should not be considered to have flooded from the neighbouring River Rother during the summer of 2007 and therefore should not be shown as part of Flood Zone 2 on the Flood Map. However, it was agreed that the Flood Map could only be amended following further hydraulic modelling of the river and submission of digital copies of the site's topographic survey.

Enzygo re-ran the Environment Agency’s 1D hydraulic model of the River Rother, which runs through the area, together with detailed topographic survey information of the site. The outcome confirmed that the majority of the site should now be currently designated within Flood Zone 1.

The Flood Modeller 1D solver allows consultants like Enzygo to carry out fast and accurate modelling of the key elements of river and channel systems. It includes full solution modelling of open channels, floodplains, embankments and hydraulic structures. Any hydrological method can be used and rainfall-runoff simulation enables both event based and conceptual hydrological methods. Our software is particularly beneficial as it features:

  • Proven 1D flow simulation engine with an extensive range of complex structures and operating rules,
  • Unsteady, steady, subcritical, supercritical and transitional flow simulation.
  • Potentially complex logical control rules linked to structure operation, which makes it particularly suited to the optimisation of controlled systems.
  • A range of hydrological methods, including built-in ReFH, FEH and SCS boundary methods to make hydrological analysis easier.
  • Integrated GIS mapping and tools, allowing the user to work with their geo-referenced data sets for model building, results analysis and visualisation.
  • User-friendly productivity tools, including a model health checker and results extractor and analysis.
  • Integrated one and two-dimensional modelling using links between the 1D solver and a range of 2D solvers, including the three Flood Modeller 2D solvers and TUFLOW.
  • ŸŸOpenMI link to allow the user to link it with any other OpenMI-compliant software.
  • An open file system so users can quickly and conveniently see and alter model data files.

The results of the 1D modelling confirmed that only a small area of site would be inundated with water from the River Rother during the 1 in 1000 year flooding event as the majority of the site sits above the water levels. Furthermore, as the ground levels of the site are located above the maximum 1 in 1000 year water levels of the River Rother, only low levels of flooding will be experienced on the site, and mainly along the river corridor, during the 1 in 1000 year event. Flooding of the river corridor, however, will not impact on the overall development of the site since a buffer strip along the River Rother would be required to be provided.

In August 2012 the Environment Agency issued a revised Flood Map for the Staveley Works area as a consequence of the use of our software and the investigation carried out by Enzygo. The map downgraded the flood risk, designating the majority of the site within Flood Zone 1. This then opened the pathway for Chatsworth Estate to facilitate the process of transforming the site. A redevelopment Masterplan for the regeneration of the site has now been published by Chatsworth Estate.

Matt Travis, Director at Enzygo, commented that they used our software "to build upon the Environment Agency's existing 1D model. The software was versatile and enabled rapid amendment and remodelling of the floodplain - it is one of our preferred 1D flood modelling software products”.

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