FLOOD RISK – RECENT TRENDS AND POLICY RESPONSES DEVELOPING WESTMINSTER’S LOCAL PLAN

Booklet No. 2 LDF Consultation - CMP Revision November 2013

Westminster is at risk of flooding from a number of sources, including from the River Thames and from surface water flooding resulting from heavy rainfall. Such risks are projected to increase over the coming years as a result of our changing climate. As part of our emerging local plan, which covers the next 15-20 years, the Council is therefore developing a new planning policy to specifically address flood risk management. The policy aims to ensure that flood risk and the impacts of flooding are effectively minimised and managed across the City of Westminster. Implementation of this policy should secure a more resilient City that is less vulnerable to flooding and the negative environmental impacts this brings (e.g. water pollution, damage to property and public realm), thereby protecting the long-term health and wellbeing of residents, visitors and workers and ensuring the sustained success of our businesses. This consultation paper sets out the background to the new policy and recommendations for our policy approach. We are now inviting your comments on our approach and look forward to working with you to ensure that the new planning policy provides an effective means of managing flood risk in the City of Westminster.

INTRODUCTION

CLLR ROBERT DAVIS

Councillor Robert Davis DL Deputy Leader, Westminster City Council Cabinet Member for Built Environment

CONTENTS

Trends 1. Historic Trends 2. Recent Trends

Insights 1. Surface water flood risk 2. River and tidal flood risk 3. What can we do?

Recommendations 1. Flood Risk

This booklet sets out the Council’s proposed approach to flood risk. It focuses on the most significant types of flood risk in Westminster, which are from the river Thames (river and tidal) and surface water flooding. This booklet covers one specific policy: • S32 Flood Risk Whilst all policies will need to be taken into account, some aspects of this topic are included in separate booklets, namely: • Basements Picture credits: Evening Standard (top), Warwick Bambrook (bottom)

TRENDS HISTORIC TRENDS In Westminster the greatest flood risks are from the River Thames and surface water.

Flooding from the Thames In 1928 a tidal surge, at high tide, came up the River Thames resulting in the flood defence walls and embankments being overtopped. Most of the 14 fatalities in Westminster occurred in basement dwellings in Millbank. There was a also major tidal flood in 1953 which led to the construction of the Thames Barrier and associated defence improvements in the 1980s. Today the Thames Barrier, Embankment Wall and associated defences provide a very high level of protection against river and tidal flooding (protection against a tidal flood event with a 0.1% annual probability of occurring).

Surface water flooding In highly developed areas, such as Westminster, surface water flooding occurs when intense rainfall is unable to soak into the ground or enter drainage systems, because of blockages, or breakages in water pipes or where drainage capacity has been exceeded. The City of Westminster has experienced localised surface water flooding in the past (e.g. resulting in the closure of Victoria station). However, the City has not suffered any past floods which had significant harmful consequences registered on a national scale (such as the summer 2007 floods).

Flooding of Pimlico in 1928. Photo: Westminster Archives Centre.

Flooding at Victoria station.

“…developments proposed in flood risk areas should show how they intend to adapt to the effects of climate change, by proposing specific flood risk resistance and resilience measures” Environment Agency

RECENT TRENDS

The latest climate change projections (UKCP09) indicate that winters will be characterised by increased rainfall (an increase of 19% by 2080; see graph on right) in the form of torrential downpours rather than consistent rainfall.

More intense rainfall will cause more surface water runoff, increasing localised flood risk. This is a particular concern for Westminster so the Council is working to understand, communicate and mitigate the risk.

The Government recently consulted on new proposals for home insurance in flood risk areas, an issue for property owners. For further details see the DEFRA website.

Source: Alex Nickson, GLA.

TRENDS

“It is pure luck London has so far escaped the kind of flooding that devastated other parts of the country in 2007, and we know climate change makes severe rainstorms more likely in the future” London Assembly’s Environment Committee

Average Monthly Rainfall: All Scenarios against Baseline

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J F M A M J J A S O N D

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1961-1990 Baseline Rainfall 2020s 2050s 2080s

Rainfall projections for London compared to 1961-1990 baseline

INSIGHTS RIVER AND TIDAL FLOOD RISK Currently there is a low likelihood of tidal flooding and river flooding in Westminster.

Although Westminster benefits from a high degree of protection from the Thames Barrier and the Embankment wall (which together provide for a 1 in 1000 annual probability of flooding), for the purposes of flood risk mapping the Environment Agency assumes a worst case scenario that no flood defences are in place.

Therefore significant parts of Westminster fall into Flood Zone 3, having a 1 in 100 or greater annual chance of river flooding (non-tidal Thames and its tributaries) or a 1 in 200 or greater annual probability of flooding from the sea (the tidal Thames). Flood Zone 3 includes all of the Rapid Inundation Zone shown in blue on the map to the right; this zone represents flooding that would occur in the first hour if the Thames flood defences were breached.

There is also a small section of the City (1%) within Flood Zone 2 which has a medium risk of flooding (0.1%) in any one year. The remainder of the City falls within Flood Zone 1 indicating only a low risk of flooding from the Thames.

Please note that the mapped flood zones are based on no flood defences being in place.

Surface water flooding is the most likely type of flooding in Westminster.

Approximately 22,100 properties are estimated to be at risk from surface water flooding (based on modelling) during a rainfall event with a 1 in 200 annual chance of occurring. The areas at highest risk are identified in dark blue on the indicative map on the right.

Increased torrential rainfall as a result of climate change will increase the risk of surface water flooding. This risk is exacerbated by the dense built urban character of Westminster, with few permeable surfaces to absorb rainfall runoff.

Increased flooding could result in damage to buildings and infrastructure, disruption to transport and business, stress and health problems.

INSIGHTS SURFACE WATER FLOOD RISK

Surface water flood risk map for 1 in 100 event (including permanent water bodies)

Key Depth (m) 0.075 – 0.100 0.101 – 0.200

0.201 – 0.300

0.301 – 0.500

0.501 – 0.750

0.751 – 1.500

> 1.500

WHAT CAN WE DO?

In dense urban areas like Westminster most land identified as being at risk of flooding is already heavily developed. Thus, management of flood risk through the planning process is less about avoiding any development in high risk areas and more about:

• locating the most vulnerable uses outside these areas;

• ensuring that new schemes are designed to reduce flood risk; and

• ensuring they are safe and include suitable flood resistance and resilience measures.

The provision of Sustainable Urban Drainage Systems (SUDs) is increasingly important in reducing surface water flood risk. They do this by reducing the peak water runoff from a site, for example by encouraging water to percolate into the ground, storing water, or slowing down the movement of water. Potential measures include: green roofs, ‘rain gardens’ (planted areas designed to capture runoff water), permeable paving, and rainwater harvesting (see photos).

Highly Vulnerable Uses include police and fire stations, basement dwellings and installations requiring hazardous substances consent. More Vulnerable Uses include hospitals, residential care homes, dwelling houses and hotels.

RECOMMENDATIONS FLOOD RISK

POLICY S32 FLOOD RISK

Highly Vulnerable Uses will not be allowed within Flood Zone 3, and in Flood Zone 2 will be required to pass the Exception Test. Highly Vulnerable Uses should be located outside of Critical Flood Locations.

Proposals for Essential Infrastructure and More Vulnerable Uses within Flood Zone 3 (with the exception of minor development and changes of use) will be required to pass the Exception Test.

Within the Rapid Inundation Zone, new residential units below the tidal breach flood level and extensions to residential at basement level will not be acceptable.

All development proposals should take flood risk into account and new development should reduce the risk of flooding.

Development, particularly redevelopment, should incorporate Sustainable Urban Drainage Systems (SUDS) where relevant and feasible to manage surface water flood risk.

Developments of one hectare or greater in Flood Zone 1 and, where appropriate, developments in Flood Zones 2 and 3 and Critical Flood Locations are required to produce a site specific flood risk assessment. This must demonstrate that where possible the development, particularly redevelopments, will reduce flood risk for the site and beyond through appropriate layout and design, use of flood resistance and resilience measures to reduce the impact of any flood, and ensure safe access to/ egress from the site.

Core Strategy Policy CS29

The National Planning Policy Framework says applications for minor development and changes of use are not required to apply the exception test.

Details of what information should be provided within a site specific flood risk assessment will be outlined in the supporting text to the policy. This will include demonstrating that the development will: be safe for its lifetime (taking climate change and the vulnerability of its users into account), including by considering layout and design and providing safe access/ egress routes and an appropriate evacuation plan; be appropriately resistant and resilient to flooding (e.g. threshold levels designed to minimise the risk of inundation, water resistant materials); not increase flood risk elsewhere, and will where possible reduce flood risk.

In Westminster all areas are already developed and there are no large areas available for development in low flood risk areas. Thus rather than focusing on avoiding development in certain areas which are at higher risk of flooding, the focus is on the ‘exception test’. This requires a development to demonstrate wider sustainability benefits to the community and that it will be safe for its lifetime without increasing flood risk elsewhere.

This means that development must not lead to any increase in run-off from the site to the drainage system. Retrofitting measures to reduce flood risk is more difficult than designing such measures in from the start, hence the higher standard for redevelopments.

As mapped in the Strategic Flood Risk Assessment; these areas will be refined following the completion of enhanced flood modelling.

Details of surface water flooding were not readily available when the Core Strategy was adopted, so this change ensures that high risk development is not located in high risk areas, whether from tidal, riverine or surface flooding.

This will be defined to exclude types of development with no implications for flood risk e.g. satellite dishes.

This booklet is part of the informal consultation for developing the statutory policies in Westminster’s local plan. It builds on previous consultation on the City Management Plan. Further information can be found here.

This booklet only includes the proposed policy. However, Westminster’s local plan will include supporting text. The supporting text will include:

• Introductory text, setting out the background to the topic.

• Policy application: guidance as to how the policy will be applied, including details of how things will be measured or calculated etc.

• Reasoned justification: this is an explanation required by law to accompany a policy, setting out why a policy is applied.

• Glossary definitions: the statutory definitions used for terms that are included in the policies.

If you wish to discuss the issues raised in this booklet with somebody, please telephone 020 7641 2503.

Westminster’s Strategic Flood Risk Assessment - www.westminster.gov.uk/services/environment/planning/ldf/sfra

Westminster’s Preliminary Flood Risk Assessment - www.westminster.gov.uk/services/environment/planning/ldf/sfra/

Environment Agency Flood web page - www.environment-agency.gov.uk/homeandleisure/floods/default.aspx

London Resilience flooding web page -

www.london.gov.uk/mayor-assembly/mayor/london-resilience/risks/flooding

Lloyd’s of London East London Extreme Rainfall Report (2010) - www.lloyds.com

Have Your Say Further Reading To comment on anything in this booklet, please email ldf@westminster.gov.uk or write to us at: City Planning 11th Floor Westminster City Hall 64 Victoria Street London SW1E 6QP Your comments will form part of the statutory record of consultation and will be made available on our website and to the public. Your contact details will not be made available, but we will use them to stay in touch with you about future policy development. If you do not want us to stay in touch, please let us know in your response.