Flood Risk & Climate Change: England Flood Planners must prepare for the worst?

24 Jun 2019

Environmental Planning

Water Services

Flood risk and climate change

Alex Perryman, Delta-Simons Water Services Associate, writes for GRESB (Global Real Estate Sustainability Benchmark) about flood risk and climate change, and how Flood Planners in England must prepare for the worst.

Developers and investors must consider the risk of flooding to the development design, planning and investment process at the earliest opportunity to help inform the decision-making process.  Early engagement with the Environment Agency (EA), local authorities and environmental consultants (such as Delta-Simons who specialize in flood risk and climate change for developers, occupier and investors) will ensure that the masterplan design includes suitable, viable and cost beneficial mitigation measures.  

By not considering climate change during the early stages of design and during the planning process, from a flood risk perspective, the risk of the planning application being objected to or occupiers being unwilling to sign leases increases along with potential delays to timescales due to reworking and spiralling costs. 

Flood plain of river Severn near Worcester with Malvern HillFlooding to developments in the UK is a very real risk both now and in the future, and planners need to prepare for this more frequent eventuality. How have the Government approached this issue and tied it to planning? The updated National Planning Policy Framework (NPPF) in 2019 sets out the Government’s planning policies for England and how these should be applied, the purpose of the framework being to achieve sustainable development: “meeting the needs of the present without compromising the ability of future generations to meet their own needs”. Flood risk is part of just one strategic policy of the development plan which can be crucial to decision making related to planning, a typical output being a Flood Risk Assessment (FRA).

The NPPF sets out how the planning system should help minimise vulnerability and provide resilience to the impacts of climate change, and alongside planning policy guidance demonstrates how flood risk should be managed now and over the lifetime of the development, taking into account climate change.  Consequently, the Environment Agency (EA) has recently updated their climate change guidance in 2016, providing climate change allowances to support the NPPF which is now split by river basin district rather than a blanket percentage increase in river flow.

If the site is outside the floodplain then land raising is not a requirement from a flood risk perspective.  If the site is within a floodplain then the proposed development is typically raised above the flood level.  The exact level of land raising is dependent on the predicted flood levels and the EA allowance for climate change.  However, the displaced floodwaters will need to be compensated for through flood compensatory water storage.  This impacts development as the location of the storage will undoubtedly impact the masterplan as it needs to be located within or on the edge of the floodplain and demonstrated on a level for level basis.  This could also potentially affect the developable area, building design and access. If climate change is not considered, the modelled water levels are likely to be deemed too low and the planning application objected by the EA on flood risk grounds.  

In addition, the EA’s Flood Zones do not take into account climate change so if not formally provided by the EA, hydraulic modelling may be needed to be conducted which can be time and cost prohibitive.

York, United Kingdom –River Ouse overflows following a period of heavy rain and floods the streets of central YorkAside from river flooding, surface water is a key risk as demonstrated in the Pitt Review - the Government’s response to the 2007 summer floods.  The EA climate change guidance applies climate change allowances to peak rainfall to determine runoff rates. This may mean you need larger attenuation storage to protect the proposed development for its lifetime. As per the risk from rivers, the location of surface water attenuation storage or other forms of Sustainable Drainage Systems (SuDS) will impact the masterplan in terms of developable area, building design and access.

In addition to the statutory planning requirements, building occupiers are increasingly aware of the potential for flooding to impact their operations.  As a result, some major occupiers are imposing their own flood risk standards which are more stringent than the planning requirements.  Where an investor is considering an asset that satisfies the statutory requirements, this may not be sufficient to truly consider the potential for re-letting, with some occupiers being unwilling to compromise their own demanding flood standards.

See GRESB Insight article here.

Related article: Climate change: guide for developers and investors