We’re looking at what the changes were and how they have been affecting the assessment of flood risk in England.

The National Planning Policy Framework (NPPF) relating to Flood Risk (paragraphs 159 to 173) was updated in July 2021 by the Ministry of Housing, Communities & Local Government. At the same time the Environment Agency released an update to climate change allowances and how these are to be applied when assessing flood risk.

NPPF: Flood Risk and Coastal Change

The changes state that Flood Risk Plans should now take into account all sources of flood risk, and should use opportunities provided by new development to improve green and other infrastructure to reduce the causes and impacts of flooding. The policy goes on to say that natural flood management techniques should be used as much as possible as part of an integrated approach to flood risk management.

By including the reference to ‘all sources of flood risk’ it is increasing the requirement to consider flood risk from sources other than fluvial (river) and surface water. This may mean that a more holistic understanding of flood risk is required when applying this policy, particular in terms of the Sequential and Exception Tests, providing increased weight behind the lesser scrutinised forms of flood risk like groundwater and artificial sources (e.g. reservoirs, canals and sewers).

The use and integration of natural management techniques and green infrastructure as part of a development layout is also being promoted and encouraged further within this update. This approach seems to align itself with the latest movement toward greener and sustainable solutions, and achieving Biodiversity Net Gain on new developments.

Our changing climate, and associated changes in rainfall patterns, is increasing the frequency of flooding in previously unaffected areas. This appears to place emphasis on integrated solutions and use of natural systems, in the form of green infrastructure, for new developments.

3 months on, we are seeing a new mindset emerge from businesses, particularly in the property sector, as they look to sustainably manage the consumption and recycling of water.

Nature-based solutions not only improve the stresses placed on our water environment but positively contribute to human wellbeing and create better places to be.

Naturally absorbing and holding water through green areas, planting and soils also leads to an element of natural cleansing improving water quality whilst financially, nature-based solutions also bring advantages due to a reduction in initial capital expenditure and lower on-going operations expense.

NPPF: Climate Change

The Environment Agency has significantly changed their approach in the way climate change allowances are applied to peak river flow.

Climate change allowances were previously applied on a River Basin District basis. These ten River Basin Districts have now been divided into 92 smaller Catchment Management areas, each with its own set of climate change allowance values.

The updated guidance seeks to simplify how climate change should be applied by type of development, stating that:

• Central Allowance should be applied for most cases, including the assessment of offsite impacts and for floodplain compensation.
• Higher Central Allowance should be applied to essential infrastructure developments.
• Upper End Allowance should be applied to Nationally Significant Infrastructure Projects (NSIPs) new settlements or significant urban extensions. Applying the Upper End allowance should be treated as a ‘sensitivity test’ and will help assess how sensitive development proposals are to changes in the climate for different future scenarios. This will help to ensure proposed infrastructure and significant development can be adapted to large-scale climate change over its lifetime.
• H++ Allowance now only applies to sea level rise and NOT peak river flows.

Surface water (rainfall) and tidal allowances have remained the same since 2016, however these are also expected to be updated in the near future.

Environmental Planning Guidance also states that peak river flow allowances should be applied to developments and allocations where the strategic flood risk assessment shows an increased risk of flooding in the future. This includes locations that are currently in Flood Zone 1 but might be within Flood Zone 2 or 3 in the future.

In simple terms, the new allowances consider the river basin, specific river and geographic location within the catchment when determining climate change requirements.

This could mean that two sites on the same watercourses, in relatively close proximity, could require different climate change allowances to be applied. To assist in identifying allowances for climate change impacts, a new GIS tool ‘Climate change allowances for peak river flow in England’ (arcgis.com) has been launched.

Three months on and there is still no guidance on how to apply the climate change allowance if a site sits between two Catchment Management Areas; however it could be presumed that the higher climate change value is applied as a precautionary approach.

NPPF also suggests that the central climate change allowance is also applied across all flood zones, including Flood Zone 1, for all uses (except Essential Infrastructure).

Climate change continues to be a hot topic for developers, with a need for more scrutiny and in depth assessment on what allowances apply to what watercourses. This approach is certainly giving a more accurate measure watercourse to watercourse, however the knock-on financial implications and delays for developers are having to incorporated.

To discuss the updates to national flood risk policy and climate change allowances further or for advice on the implications of these changes to your site, please contact: [email protected]

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Andrea Nelmes, Principal Flood Risk & Drainage Engineer

Andrea is a chartered Principal Flood Risk & Drainage Engineer with over 16 years’ of experience in the water and land development industry. A technical specialist in flood risk, river restoration, drainage strategies including wastewater modelling and SuDS design. She has worked with and advised LLFAs and the EA on Surface Water Flood Risk and Water Resource Management which has provided her with extensive knowledge of the regulatory framework governing the water industry, enabling her to provide responsive, pragmatic advice to clients on a range of multi-disciplinary projects across the UK.

BSc (Hons) CEnv