Climate Change Risk Assessment and the Future Flood Explorer
Horritt Consulting has been involved with the Climate Change
Risk Assessment since 2015. Working as part of consortiums
undertaking a UK wide flood risk assessment, this has involved
bringing together national data sets across the UK and
projecting forward in time to give a national picture of flood
risk and how this changes in response to climate and population
change.
Perhaps the most exciting and challenging aspect of the project
is the development of a "Future Flood Explorer" (FFE) which
allows a wide range of users to investigate the impact of
adaptation measures on future risk, and help guide future
policy. The FFE represents a significant advance in how we do
national risk assessment - we can use a simple desktop
application to explore risk and adaptation strategies at UK
scale.
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| Risk reduction from
traditional defences, NFM and property level
protection in Carlisle (inset) and the wider Eden
valley. |
NaFRA2
The Environment Agency's NaFRA2 project is a pioneering new
flood risk assessment for England. Matt is technical lead for
assessing uncertainty in NaFRA2 outputs, developing an
innovative new method which can track uncertainty through the
NaFRA2 system and deliver confidence information for hazard maps
and risk outputs. Many previous uncertainty analyses either
needed to make assumptions about uncertainties (e.g. limited to
normal distributions) and model sensitivities (e.g. linear
response), or used computationally intensive Monte Carlo methods
which limit the scope of application. NaFRA2's uncertainty
method uses a pragmatic set of simplifications for uncertainties
that are less important, concentrating computational resources
on the uncertainties that matter. The result is a method that
can deliver a probability distribution expressing the
uncertainty for each 2m cell and individual property in England.
The method is being used to inform confidence information for
NaFRA2 outputs, and to plan future model and data improvements.
Thame Catchment Restoration
Horritt Consulting are involved in a number of projects for river and landscape restoration in the Thame catchment in Oxfordshire and Buckinghamshire. The Stadhampton Mill Fish Pass project delivered by the River Thame Conservation Trust has opened up a 3.25 km length of chalk stream habitat to migratory fish. Horritt Consulting worked closely with the trust in the design of this scheme, using hydrological and hydraulic modelling to ensure the scheme offered the best potential for fish passage and show there is no impact on flood risk. We are also involved in design and flood risk assessment at Dorchester, where the weirs feeding Overy Mill are a barrier to fish migration. Our hydrological and hydraulics expertise have been used to optimise the design and again demonstrate the scheme will not adversely affect flood risk nearby or elsewhere in the catchment.
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Stadhampton fish passage
scheme under construction |
We are also working with South Oxfordshire District Council to develop natural flood management options for Watlington. This is a hydrologically complex site, with properties at risk from a combination of surface water, fluvial and groundwater flooding, in an ungauged catchment. We are modelling the potential for NFM measures to reduce risk through plausible rainfall scenarios which reflect the real complexity of catchment response and importance of antecedent conditions in a way that standard design events cannot.
Chesterfield Canal Water Resources
Horritt Consulting delivered a project in 2020 to model water resources and undertake a Water Framework Directive assessment for restoration of the Chesterfield canal, for the Chesterfield Canal Trust. This involved hydrological analysis to generate a time series of daily flows in the River Rother (the main source of water for the upper pounds of the canal) and using these to feed a hydraulic model of the restored canal and its proposed extension beyond Staveley. The model allowed the trust to explore options for management of water resources in the canal, balancing abstraction from the river against keeping the canal in water and available for boat traffic. We have continued to support the trust and Derbyshire County Council with advice on water management and abstraction licensing for the Chesterfield and Cromford canals.
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| Restored
canal on the approach to Chesterfield |
Schematic of hydraulic
model used to assess water resources requirement |
Chesterfield Canal Water Resources