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Gregory Gray Associates
The latest Defra Review on the UK’s flood defences has underlined that more than a short term fix is required with flood management for people and property – yet this is what it is proposing right now.
The Review underlines already well understood predictions of greater, more frequent flood events. It incorporates a new Met Office 20-30% uplift in rainfall and flood extent scenarios over next 25 years, to which they have a 90% confidence that these levels will not be exceeded.
The Review only examined river and coastal risk and is specifically focussed on measures that will protect critical infrastructure. In fact, the target is some 530 identified property assets within what is described as the “Extreme Flood Outline”. These have annually a 0.1% chance of severe flooding occurring that would severely compromise these assets, including electricity stations, telecoms facilities and hospitals.
In response, the government has proposed £12.5M of investment on temporary flood defences for these assets. They will provide some degree of protection, but they are of little value on their own and will do nothing against other types of flooding, crucially missed from the Review – groundwater, surface and sewer flooding.
The Scientific Advisory Group supporting the Review highlighted that there was scope to more fully integrated modelling of weather and rainfall scenarios and how this translates to likely flood events and depths on a local and national scale. There remains plenty of uncertainty on long term views on flood events, as existing records only go back 30-40 years. The Review acknowledged the work of the Flood Forecasting Centre partnership between the Met office and the Environment Agency (EA).
It was again disappointing to note that groundwater was largely omitted as a consideration in the Review. It provides a signature to many flood events but remains little understood, partly due to fragmented regulatory structure. The high profile 2014 flooding in the Thames basin was a good example of how groundwater multiplies flood risk. Flooding occurred at excessive levels, and yet it would have been a normal flood event, had it not been driven by already high levels of groundwater flooding in the catchment.
The role of groundwater in contributing to flooding and its impacts at the property level remain largely forgotten. There is an understandable focus on potential loss of life as a priority, but groundwater significantly prolongs flood damage to infrastructure and property.
It is only when looking further ahead, beyond 2021, that the Review notes that natural flood management must be more widely implemented at the catchment level with “catchment leaders” coordinating planning and land management in order to “slow the flow”.
The Review also acknowledges the role of Sustainable Drainage Systems (SuDS) in stemming the impact of surface water flooding. It made clear refer reference to the Planning Review in Spring next year which will assess the positive contribution of SuDS and whether legislation should be further strengthened for future property development.
In response to the Review, Stuart Pearce, Managing Director at GeoSmart said:
“The Review has focused on short term resilience measures for critical infrastructure, in recognition of the overwhelming evidence of more frequent, larger flood events.
While the Government clearly notes this is just part of the solution, all flood risks must be considered to provide holistic solutions. We look forward to working with regulators, authorities and industry to bring groundwater flood risk into the heart of enhanced modelling, so these are better understood. Our groundwater flood risk map is already proving vital in completing the picture for our clients.
We welcome the Review’s reference to the review of planning policy on natural flood management and Sustainable Drainage Systems (SuDS). This will create a greater impetus for these to be implemented across developments and communities for the longer term.”