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London Borough of Southwark Strategic Flood Risk Assessment A Non-Technical Summary Objectives The National Planning Policy Framework (NPPF) and accompanying Planning Practice Guidance emphasise the responsibility of Local Planning Authorities to ensure that flood risk is understood and managed effectively and sustainably throughout all stages of the planning process.

The Strategic Flood Risk Assessment (SFRA) for Southwark aims to facilitate this process by identifying the spatial variation in flood risk across the Borough, allowing an area-wide comparison of future development sites with respect to flood risk considerations.

The overall SFRA should be used to provide an overview of the risk of flooding across the Borough as well as to assist in planning policy formulation, strategic planning, development control and flood risk management. The report additionally contains specific recommendations, for both Southwark Council and local developers with regards to the effective management and mitigation of flood risk, including guidance on the requirements for site specific Flood Risk Assessments and the use of Sustainable Drainage Systems (SuDS).

Sources of Flood Risk The greatest risk to property and life from flooding within the London Borough of Southwark is as a result of tidal activity within the River Thames. However, the Borough is currently protected from combined tidal and fluvial flooding by the River Thames Tidal Defences, up to the 1 in 1000 year event. The risk is therefore of a residual nature, associated with overtopping or breaching of defences. Excepting the River Thames, there are no other watercourses within Southwark known to present a risk of fluvial flooding.

A potential risk of flooding from other (non-river related) sources exists throughout the Borough, including sewer surcharge and surface water flooding as a result of heavy rainfall and/or blocked drainage systems. Southwark plays a key role in managing this risk as a Lead Local Flood Authority, under the Flood and Water Management Act (2010) and the Flood Risk Regulations (2009).

Areas of the Borough are also thought to be susceptible to elevated groundwater levels, which may additionally interact with and exacerbate these other sources of flood risk. It is expected that changing climate patterns will have a substantial impact on the level of flood risk from all sources within Southwark.

Study Outputs This SFRA identifies the tidal floodplains associated with the River Thames and presents Flood Zone Maps that delineate the Flood Zones outlined in the NPPF. Breach modelling has additionally been undertaken to enable a greater understanding of the residual risk associated with breaching of the Tidal Defences. The resulting hazard, depth and velocity mapping contained within this SFRA provide further definition of the spatial variation of flood risk within Flood Zone 3.

Mapping has also been produced to illustrate the understanding of spatial distribution of flood risk from all sources across Southwark, along with other key information in effectively managing flood risk. These maps and associated reporting provide the necessary level of detail to facilitate a risk-based approach to planning, as per the NPPF. This process determines the compatibility of various types of development within each Flood Zone, subject to the application of the Sequential and Exception Tests as needed and a site-specific FRA which clearly demonstrate that the site can be safely developed from a flood risk perspective. Guidance with regards to the process is included within the report.

ConwayAECOM

Key Recommendations A spatial planning solution to flood risk management should be sought wherever possible. As such, flood risk should be an early and primary consideration in strategic planning for developments across the Borough. A sequential approach should be taken to allocating strategic development areas in regions at lowest flood risk, taking into account vulnerability of land use. Consideration should also be given to strategic allocation of open space and preserving and expanding river corridors to create space for flooding to be managed effectively. In consulting on and determining development applications, Southwark Council must ensure that all proposed developments have considered flood risk management from the planning stage, including site specific flood risk assessments where required.

Given the position of the Borough, adjacent to the River Thames, it is highly reliant on flood defences. Ongoing maintenance of these defences is critical, and priority should be given to safeguarding the Standard of Protection (SoP) provided by defences over the lifetime of any development. Additionally, consideration should be given to the specific recommendations of the Environment Agency’s Thames Estuary 2100 (TE2100) plan in requiring reduction of current and future flood risk through raising, maintaining and enhancing flood defences. Existing corridors of land along the river frontage should be safeguarded and opportunities taken to set back development to enable sustainable and cost effective flood risk management, including upgrading of river walls and embankments and landscape, amenity and habitat improvements.

Despite the high SoP provided by the Borough, there is a residual risk through breaching or overtopping of defences. This should be managed through flood resistant and resilient design and protection measures. Flood awareness and robust emergency planning and response will also be critical to sustainable ongoing flood risk management.

In the future, climate change is anticipated to have an impact on all sources of flood risk within the Borough. It is important that planning decisions recognise the potential risk that increased runoff poses to property and plan development accordingly so that future sustainability can be assured. Robust surface water management, including the use of Sustainable Drainage Systems (SuDS), will be critical to ensuring sustainability. It is recommended that runoff rates from new development be restricted to greenfield runoff rates, wherever possible, and managed in line with the SuDS hierarchy.

Next Steps

This Level 1 SFRA report will be complemented by further detailed assessment of the allocated development sites within the Borough, during the Level 2 SFRA.

In order for this SFRA to serve as a practical planning tool now and in the future, it is important that the report is adopted as a ‘living document’ and is reviewed periodically in light of emerging policy directives and an improving understanding of flood risk within the Borough.

London Borough of Southwark Strategic Flood Risk Assessment

SuDS Design Amenity

• Maximise multi-functionality • Enhance visual character • Deliver safe surface water management • Support site resilience and adaptability • Maximise legibility • Support community environmental learning

Biodiversity • Support and protect natural local habitats and

species • Contribute to the delivery of local biodiversity

objectives • Contribute to local habitat connectivity • Create diverse, self-sustaining and resilient

ecosystems

Water Quantity • Use surface water runoff as a resource • Support the management of flood risk in

receiving surface waters • Preserve natural hydrological systems • Design system flexibility and adaptability • Drain the site effectively • Manage on-site flood risk

Water Quality • Support the management of water quality in

the receiving surface waters and groundwater • Design system resilience to cope with future

change

Guidance for SuDS in Southwark Introduction

Sustainable Drainage Systems (SuDS) are designed to maximise the opportunities and benefits of surface water management. This is particularly important in increasingly urban areas where there is less permeable ground available for natural infiltration and evapotranspiration, leading to increased rainfall runoff from impermeable surfaces which contribute to flooding, pollution and erosion. SuDS can counteract these impacts on the water cycle and additionally enhance urban spaces by making them more vibrant, attractive, sustainable and resilient, with improved air and water quality, microclimate and amenity.

There are four main categories of benefits which can be achieved through high quality SuDS design, as summarised below:

The installation of high quality and multi-functional SuDS is most likely to be achieved through early and multi-disciplinary consideration of surface water management. Ideally this should be integrated within the overall site planning and design, including early consultation with relevant stakeholders and consideration of ongoing operational and maintenance responsibilities.


SuDS design should be based around the general principles of: • Harnessing surface water runoff as a resource; • Managing rainfall close to where it falls; • Managing runoff on the surface; • Promoting infiltration of rainwater into the ground; • Encouraging evapotranspiration; • Attenuating runoff to mimic natural flow characteristics; • Reducing contamination of runoff through pollution prevention and controlling the runoff at source; and • Treating runoff to reduce the risk of urban contaminants causing environmental pollution.

The following sections provide an overview of common types of SuDS measures, which may be suitable for installation within the Borough. Generally, SuDS should not be thought of as isolated features, but delivered as an interconnected sequential train of surface water management and treatment. Further information on the philosophy of SuDS and detailed guidance on design, installation and maintenance, is provided in the CIRIA SuDS Manual (2015) and other sources described at the end of this document.


Swale Swales are vegetated shallow depressions designed to convey and filter water. These can be ‘wet’ where water gathers above the surface, or ‘dry’ where water gathers in a gravel layer beneath the ground level. They have the ability to remove pollutants and can be used to channel surface water to the next stage of a treatment train. Check dams can be constructed along their route to control flow velocities, and promote infiltration and sediment deposition.

Advantages Disadvantages • Encourages evapotranspiration

and infiltration of runoff • Provides attenuation to reduce

peak run-off rates • Relatively simple to incorporate

into landscaping • Effective removal of urban

pollutants • Minimal maintenance

requirements • Aesthetically pleasing • Good community acceptability

• Careful consideration of location and design is required to reduce potential health and safety hazards

• May limit opportunities to use trees in landscaping

• Blockages can occur in connecting pipework

• Retrofitting opportunities are limited

Effective Locations Ineffective Locations • Residential and commercial areas • Contaminated sites • Sites above vulnerable

groundwater • Alongside roadways • Linear street garden areas • Field boundaries

• High density areas • Steeply sloping areas

Performance Criteria Rating Ecological Advantages Medium Peak Flow Reduction Medium

Amenity Potential Medium Water Quality Treatment Potential High Surface Water Volume Reduction Medium

In the Community Design Example Swales can be used to replace conventional drainage systems and are particularly effective when installed adjacent to roadsides or transport links, to capture and re-route surface water. They are also suitable for residential and commercial areas and may be integrated with areas of open space and landscaping, or used to create informal barriers.


Filter Strip or Drain Filter strips and drains can be used to manage runoff from impermeable areas, providing conveyance and filtration. Filter Strips allow water to flow across grass or dense vegetation; whereas filter drains are hardscape systems where runoff is temporarily stored in a shallow trench filled with stone or gravel.

Advantages Disadvantages • Simple to design and can be

incorporated into site landscaping for aesthetic benefit

• Minimal public safety risks • Encourages evaporation and

infiltration • Important hydraulic and water

quality benefits can be achieved • Can be retrofitted into a site with

ease • Low construction cost

• Vegetation must be light and can get damaged

• Loose gravel can be removed • Drains relatively small

catchments • High cost to replace filter

materials

Effective Locations Ineffective Location • Residential and commercial areas • Between hard standing surfaces

and grassland • High density areas • Contaminated sites • Sites above vulnerable ground

water

• Steeply sloping areas

Performance Criteria Rating Ecological Advantages Low Peak Flow Reduction Medium

Amenity Potential Low Water Quality Treatment Potential High Surface Water Volume Reduction Low

In the Community Design Example Filter strips or filter drains are a suitable retrofitting option for heavily trafficked or spatially constrained areas as they cause no safety hazards and can be implemented into small spaces with ease. They can be simply implemented along the edges of pathways or pavements or integrated within site landscaping.


Bio-Retention Areas or Rain Gardens Bio-retention areas or rain gardens are vegetated depressions with gravel and sand layers below, designed to collect, channel, filter and cleanse water vertically. Water can infiltrate into the ground or enter a piped drainage system. These systems can be integrated with site landscaping, including tree pits, planter areas or gardens. Treatment performance can be improved through engineered soils and enhanced vegetation.

Advantages Disadvantages • Provides initial water treatment • Aesthetically pleasing • Provides ecological benefits • Capability to be retrofitted in

heavily paved areas or existing vegetation

• Effective pollutant removal • Minimal ground take with

spatially flexible layout

• May be susceptible to clogging or blockage due to surrounding landscape

• Regular inspection and maintenance is required to maintain effectiveness

Effective Locations Ineffective Locations • Residential and Commercial areas • Contaminated sites • Sites above vulnerable

groundwater • Seating areas • Impermeable areas • High density areas

• Steeply sloping areas

Performance Criteria Rating Ecological Advantages Medium Peak Flow Reduction Medium

Amenity Potential Good Water Quality Treatment Potential High Surface Water Volume Reduction Medium

In the Community Design Example Rain gardens and bio-retention systems can be planned as aesthetically pleasing landscaped features, providing critical green space within the urban areas. These measures can be retro-fitted around existing street infrastructure, such as seating areas, and incorporated within both paved and vegetated areas.


Rainwater Harvesting Rainwater harvesting involves capturing rainwater and reusing it for purposes such as irrigation or toilet flushing. Rainwater is collected from building rooftops or other paved surfaces and stored in tanks for treatment and reuse locally.

Advantages Disadvantages

• Water can be used for variety of non-potable uses, such as toilet flushing and irrigation

• Reduces potable water demand • Provides source control of storm-

water run-off • Rooftop or underground tanks can

minimise land take and visual impact

• Can be retrofitted to existing buildings

• Potentially complex installation and high capital cost, particularly for retrofit

• Ongoing energy requirement for pumping, if below ground storage is used

• Careful management required to manage any health risks associated with water reuse

• Above ground storage can be visually intrusive

• Regular maintenance is required

Effective Locations Ineffective Locations

• Residential and Commercial areas • High density areas • Contaminated sites • Sites above vulnerable

groundwater

• Fields or large open space

Performance Criteria Rating Ecological Advantages Low Peak Flow Reduction High

Amenity Potential Low Water Quality Treatment Potential Low

Surface Water Volume Reduction High

In the Community Design Example Rain-water harvesting can be implemented on a variety of scales; however, is particularly suitable for implementation in buildings with large rooftop areas, significant water consumption and defined ownership and maintenance responsibilities. Installation is generally easier when integrated into the design of new buildings; however, water butts can provide a simple means of retrofit.


Ponds and Basins Ponds or Basins can be used to store and to treat water. ‘Wet’ (retention) ponds have a constant body of water and run-off water is additional to this, whilst ‘dry’ (detention) ponds are empty during periods without rainfall. Ponds can be designed to allow infiltration through its base to ground or to store water for a period of time, before it is discharged via a soakaway to ground. They can support emergent and submerged vegetation, enhancing both treatment and biodiversity.


• Pollutant removal through sedimentation and biological treatment mechanisms

• Effective accommodate of large storm events

• Good community acceptability • Potential for biodiversity

improvement • Relatively simple construction • Has the potential for supply of

irrigation to other amenities • Aesthetically pleasing • Potential recreational benefit

• Requires infiltration to achieve significant reduction in surface water runoff volumes

• Significant spatial requirements • Requires control measures to

prevent migration of invasive species

• Consideration of public safety may require control measures in certain settings

• Careful design is required to manage undesirable impacts associated with eutrophication and fluctuating water levels


• Residential and Commercial areas • Fields • Parks or areas of open space • Areas with feature requirements

• High density areas • Locations with vulnerable

people

Performance Criteria Rating Ecological Advantages High Peak Flow Reduction High

Amenity Potential High Water Quality Treatment Potential High

Surface Water Volume Reduction Low

In the Community Design Example Ponds can be aesthetically pleasing, and can be used to support urban amenity, recreation and ecology. They can provide central features within areas of community space. However, careful design consideration is required to ensure they do not pose a health and safety risk to the public.


Soakaway Soakaways and other infiltration systems collect and store runoff, allowing it to rapidly soak into permeable layers of soil. During construction, an underground pit is dug and filled with gravel and rubble or specially designed material. Surface water can be directed into a soakaway using a number of above or below ground methods, with overlying vegetation and underlying soils providing treatment benefits.


• Minimal land take • Provides recharge of natural

ground water levels • Good storm volume reduction and

peak flow attenuation • Simple operation and

maintenance • Relatively simple to construct • Effective retrofitting solution • Good community acceptability

• Not always practicable near to structural foundations

• Long term performance is uncertain and difficult to guarantee if property owner is responsible for maintenance

• Requires good subsurface drainage

• Infiltration rates need to be investigated


• Residential and commercial areas • High density areas • Fields • Small grassed/planted areas

• Contaminated sites • Sites above vulnerable

groundwater • Sites with shallow

groundwater • Sites underlain by

impermeable ground


Amenity Potential Low Water Quality Treatment Potential Medium


In the Community Design Example Soakaways are effective in areas with good infiltration potential and where the water table is relatively low. Soakaways can be covered over by suitable permeable materials and be used for a variety of purposes at ground level. Caution should be taken when implementing these techniques in tightly constrained areas as they should not be built within a close proximity to structural foundations.


Living Roofs A planted soil layer is constructed on the roof of a building to create a living medium. Following rainfall, water is stored in the soil layer and absorbed by planted vegetation. They may be designed to be accessible and landscaped to provide biodiversity and amenity benefit. Blue roofs can also be used to store water, without the use of vegetation.


• High potential to reduce surface run off

• Suitable for high density development

• Can deliver building insulation and sound proofing

• Inaccessible to general public • Can provide biodiversity benefits

to the local area • Improved air quality • Assists in amelioration of the

urban heat island effect • Can be retrofitted

• Additional structural loading to roof (compared with most traditional rooftops)

• Irrigation may be required during drought

• Replacement and maintenance of plants is required on a regular basis


• Residential and Commercial areas • High density areas • Contaminated sites • Sports centres

• Roofs with inadequate access • Steep pitched roofs • Rooftops with inadequate

structural support

Performance Criteria Rating Ecological Advantages High Peak Flow Reduction Medium

Amenity Potential High Water Quality Treatment Potential High

Surface Water Volume Reduction Medium

In the Community Design Example Living roofs provide an opportunity to attenuate and store rainwater in spatially constrained areas, while providing potential benefits for local biodiversity, air quality, microclimate and amenity. They have controlled access, which means the associated risk of misuse or vandalism is low.


Permeable / Porous Paving This is paving which allows water to soak into the underlying ground. It can be in the form of paving blocks with gaps in between or porous mediums where water filters through the paving itself. Water can be stored in the sub-base beneath or be allowed to infiltrate into the ground below.


• Good potential for water quality treatment

• High potential for surface water run off

• Very efficient • Good community acceptability • Requires minimal maintenance • Effectively requires no space, as it

allows for a dual usage • It can remove the need for

manholes or gully pots

• Requires closure of surfaced areas whilst SuDS are constructed

• Cannot be used where high sediment loads are likely to be washed across the surface

• Requires vegetation maintenance • Regular inspection of the surfaces

required to ensure effectiveness • Can deflect if subject to heavy

vehicular loads


• Residential and Commercial areas • Car Parks • Low speed roads (below 30 mph) • Pathways • Residential pavements • Hard courts

• High speed roads


Amenity Potential Low Water Quality Treatment Potential High


In the Community Design Example Permeable surfaces offer effective drainage solutions that integrate within residential environments. Porous paving is effective at managing runoff from paved surfaces, and this low maintenance method is particularly useful in built up environments, including city centres. Replacing hard standing with permeable surfaces could improve drainage across a site whilst creating more aesthetically pleasing environments.


References For detailed information on the design and delivery of SuDS, reference should be made to the CIRIA SuDS Manual (2015), which is freely available online at www.ciria.org.

A range of further resources on SuDS, including case studies, videos, presentations, fact sheets and links to research can be found on the Susdrain website at http://www.susdrain.org.

Additional supporting information is available from DEFRA (www.defra.gov.uk) and the Environment Agency (www.environment-agency.gov.uk). Developers within Southwark should also refer to the London Borough of Southwark publication Developers’ Guide for Surface Water Management, for detailed guidance on drainage strategies submitted with planning submissions.

http://www.ciria.org/

http://www.susdrain.org/

http://www.defra.gov.uk/

http://www.environment-agency.gov.uk/


Mapping and Dataset Summary A series of maps, and a geodatabase have been produced to accompany this study and assist the assessment of sites by London Borough of Southwark as part of their decision making process. A GIS based mapping system using the software package ‘ArcGIS’ was implemented to enable this.

Throughout this study, a range of datasets have been requested and obtained. Each of these datasets has been analysed in conjunction with key stakeholders to agree the most updated and relevant information to be included in the SFRA and additional or modified datasets created where necessary. A summary of the maps created and the GIS layers used for each of the maps is included in the Table C1 below.

Table C1 - Summary of Maps Created

Map Number Map Title Layers Used

Map A1 River Network

• Ordnance Survey Base-mapping (25k)* • Borough Boundary* • Main River* • Ordinary Watercourse* • Culvert* • Hidden Watercourses; • Docks • Reservoirs • Quays

Map A2 Flood History

• Historical Groundwater Flooding • Historical Surface Water Flooding • Recorded Flood Outlines - From River and

Sea • Properties Flooded From Overloaded Sewers

Map A3 Flood Risk From Rivers And Sea • Flood Zone 2 • Flood Zone 3a • Flood Zone 3b

Map A4 Flood Map for Surface Water

• Flood Map for Surface Water 30 year extent • Flood Map for Surface Water 100 year extent • Flood Map for Surface Water 1000 year extent • Critical Drainage Areas

Map A5 Areas at Risk of Flooding from Groundwater • Susceptibility to Groundwater Flooding

Map A6 Flood Risk From Reservoirs • Flood Risk From Reservoirs • Reservoirs

Map A7 Flood Risk Management Infrastructure • Areas Benefiting From Defences • Flood Defences - Earth Embankment • Flood Defences - Rail Embankment

Map A8.1

Breach Mapping - Maximum Predicted Flood Extents

• Maximum Flood Extent - MLWL2014 • Maximum Flood Extent - MLWL2065 • Maximum Flood Extent - MLWL2100


Map Series A8.2

Breach Mapping - Flood Depth (Per Individual Breach Location)

• Detailed River Network Breach Locations Flood Depth For (2014, 2065 and 2100)

Map Series A8.3

Breach Mapping - Flood Hazard (Per Individual Breach Location)

• Detailed River Network Breach Locations Flood Hazard (for 2014, 2065 and 2100)

Map Series A8.4

Breach Mapping - Flood Velocity (Per Individual Breach Location)

• Detailed River Network Breach Locations Flood Velocity (for 2014, 2065 and 2100)

Map A9 Flood Warning Areas • Flood Alert Area • Flood Warning Area

Map A10.1 Vulnerable Sites – Flood Risk from Rivers And The Sea

• Vulnerable Sites (Medical Facilities, Ambulance Stations, Fire Station, Police Stations, Public Transport Stations, Education Sites, Aged Care, Scheduled Ancient Monuments, SSSI, World Heritage Site)

• Flood Zone 2 • Flood Zone 3a • Flood Zone 3b

Map A10.2 Vulnerable Sites – Flood Risk from Surface Water

• Vulnerable Sites (as above) • Flood Zone 2 • Flood Zone 3a • Flood Zone 3b

Map A10.3 Vulnerable Sites – Flood Risk from Groundwater

• Vulnerable Sites (as above) • Flood Risk from Groundwater

Map A11 SuDS Infiltration Suitability • SuDS Summary Map

Map A12 Topography • Lidar (Elevation Data)

Note: *Included in all maps

ArcGIS uses multiple datasets with associated attribution to present geo-located features from multiple sources. An overview of the information provided for mapping purposes by the various key stakeholders is shown below.

All of the datasets used in this SFRA update have been newly obtained from stakeholders, to ensure the latest available understanding of flood risk. The date each dataset was obtained has been included for ease in establishing the need for any subsequent update.


Table C2 - Description of GIS Layers used to inform the assessment

Dataset Source Format Layer Description Date Received

Fluv

ial a

nd T

idal

Detailed River Network Environment Agency GIS shapefile Identification of the river network including main rivers and ordinary watercourses. 27/08/2015

Flood Map for Planning (Rivers and Sea) Flood Zones 2 and 3 Environment Agency GIS shapefile Shows areas at varying risk of flooding from rivers and the sea. 27/08/2015

Historic Flood Map Environment Agency GIS shapefile Single GIS layer showing the extent of fluvial historic flood events. 27/08/2015

Asset Information Management System (AIMS)

Environment Agency GIS shapefile Shows where there are existing defences, structures, heights, type and design standard. However many fields contain default values. 27/08/2015

Areas Benefitting from Defences Environment Agency GIS shapefile Indicates the areas within the Borough that are under the protection

of flood defences. 27/08/2015

Flood Defences Environment Agency GIS shapefile Location of flood defences within the Borough. 27/08/2015

Flood Warning Area Environment Agency Geostore GIS shapefile Shows areas benefitting from fluvial flood warning schemes in the Borough. 27/08/2015

Thames Tidal Breach Modelling Study

Environment Agency GIS ascii and shapefiles and PDF

Reports and GIS outputs summarising the breach modelling of the TTD, completed in 2014.

09/09/2015

Flood Alert Area Environment Agency Geostore GIS shapefile Shows areas benefitting from flood alert schemes in the Borough. 27/08/2016



Hidden Watercourses London Borough of Southwark (updated by AECOM) GIS shapefile

Shows indicative location of the ‘hidden’ culverted watercourses within the Borough, based on historic maps. The location is approximate only.

11/11/2015

Pluv

ial

Updated Flood Map for Surface Water Environment Agency Geostore GIS shapefile

Provides an indication of the broad areas likely to be at risk of surface water flooding during a 1 in 30 year, 1 in 100 year and 1 in 1000 year return period event.

27/08/2015

Recorded Flood Outline London Borough of Southwark (from SWMP) GIS shapefile Indicates the extent of historic surface water flood events. 12/10/2015

Flood Defences London Borough of Southwark (from SWMP)

GIS shapefile Indicates informal flood defences, including railway and earth embankments, identified during the Surface Water Management Plan.

12/10/2015

Critical Drainage Areas London Borough of Southwark (from SWMP) GIS shapefile Location of designated critical drainage areas within the Borough. 27/08/2015

Historic Flooded Properties London Borough of Southwark (from SWMP) GIS shapefile Location and descriptions of surface water flooding events

recorded within the Borough. 12/10/2015

Gro

undw

ater

Geology London Borough of Southwark GIS shapefile Illustrates bedrock and superficial geology across the Borough. 27/08/2015

Aquifer Designation Map Environment Agency GIS shapefile Broadly shows extents of aquifers in the Borough. 27/08/2015

Infiltration SuDS Summary Map British Geological Society GIS shapefile Dataset produced by BGS illustrating the likely suitability of the

utilisation of infiltration SuDS techniques across the Borough. 10/11/2016



Susceptibility to Groundwater Flooding British Geological Society GIS shapefile Broad scale assessment of areas likely to be susceptible to

groundwater flooding based on geological indicators. 10/08/2016

Source Protection Zones Environment Agency GIS shapefile Shows areas which are Groundwater Source Protection Zones. 27/08/2015

Res

ervo

ir

Area Deemed at of Risk of Flooding from Reservoirs Environment Agency GIS shapefile Identifies areas which are at risk of flooding in the event of a

reservoir breach. 12/10/2015

Sew

er Sewer Network Thames Water GIS shapefile Details of the combined sewer assets across the Borough. 12/10/2015

DG5 Register of sewer flooding incidents, by post code area

Thames Water MS Word Indicates post code areas that may be prone to flooding as have experienced flooding in the last 10 years.

08/10/2015

O

ther

Administrative boundary London Borough of Southwark GIS shapefile Defines the administrative area of the Borough for mapping purposes. 27/08/2015

Post Code Boundaries London Borough of Southwark GIS shapefile Delineates Post Code Boundaries for the Borough, enabling mapping of Thames Water datasets. 27/08/2015

National Receptor Database Environment Agency GIS shapefile A comprehensive register of land uses across the Borough, used to identify vulnerable sites and water management infrastructure. 24/09/2015

Ordnance Survey 25k Background

Purchased from Emapsite Contractor Link

Raster file (.tiff)

Provides background mapping and indicates important features and street names in detail. 16/09/2015

LiDAR Data Environment Agency Raster file (.tiff)

Provides a useful basis for understanding local topography and the surface water flood risk in the area. 09/12/2015


SFRA Management Guide NPPF highlights the importance of maintaining Strategic Flood Risk Assessments current to ensure the decision making process by the Local Planning Authorities is based on the most up to date information and understanding of flood risk within the Borough. A summary of the key aspects to be considered to ensure that the SFRA is kept up-to-date and maintained is provided in the table below.

Table D1 - Summary of main aspects to be considered during maintenance of the SFRA

Area Covered Source of Information Provider Comments Next Review

Flood Zones

Hydraulic modelling of main rivers and the sea (Tidal Thames)

EA Should new Flood Zone information become available, the data should be digitised and georeferenced within the GIS system.

When further modelling is carried out and/or outlines reviewed by EA.

Climate Change Scenarios

Environment Agency Guidance and Modelling

EA

The climate change scenarios in this report are based on best practice and the latest predictions and modelling published at the time of this study. However, climate change predictions are constantly being updated and refined, and it is expected that current modelling will be updated to reflect. New predictions can have a significant effect on flood zones and therefore the SFRA. When a review of the SFRA is undertaken, it is recommended that, in liaison with the Environment Agency, the climate change scenarios are reviewed to ensure that the SFRA is still relevant to best practise and the latest available knowledge.

When new information becomes available, and during the next general review of the SFRA.



Flood Defences, Critical Water Management Structures and Areas Benefiting

EA Database and Southwark SWMP EA, LBS

If any new local flood defences or management structures are installed within Southwark these should be added as a new point to the relevant GIS layer, including metadata. EA datasets should be updated in their entirety to replace superseded layers.

When new relevant information becomes available.

Flooding History Stakeholders records EA,LBS When new flooding incidents are reported, these should be added as

a new point to the relevant GIS layer, including metadata. Next general review of the SFRA.

Local Plan Information

New Southwark Plan LBS

The New Southwark Plan was in preparation at the time of publishing this SFRA. It is intended that detailed assessment of the proposed allocated development sites is undertaken as a further phase of this SFRA, once this plan and proposed development sites are finalised.

Finalisation of Local Plan and allocated development sites.

Groundwater Flood Risk

Geology and Groundwater Vulnerability

EA

The groundwater flood risk dataset used for this SFRA is a high level map indicating the proportion of land that is considered susceptible to groundwater flood emergence, within a 1 km square grid. As such it is of limited site specific relevance and an update is recommended when suitable information becomes available.

Next general review of SFRA.

Surface Water Flood Outlines EA Dataset EA

It is understood that the EA surface water flood maps are due to be updated to take account of site specific modelling undertaken by local Boroughs.

When new relevant information becomes available.

Sewer Flood Risk Thames Water TW Very limited information on areas at risk of sewer flooding was provided during this study.

When information is available.



OS Background Mapping Ordinance Survey LBS

The SFRA has made use of OS 1:25,000 digital mapping. Periodically these maps are updated. Updated maps are unlikely to alter the findings of the SFRA but should be reviewed as part of the SFRA maintenance.

Next General review of SFRA.

Flood Risk Policy NPPF and NPPG

This SFRA was created using guidance that was current in February 2016, principally the NPPF and the accompanying Technical Guidance. Should new flooding policy be adopted nationally, regionally or locally, the SFRA should be checked to ensure it is still relevant and updates made if necessary.

When changes to relevant planning policy are adopted.

It should be noted that, prior to any data being updated within the SFRA, it is important that the licensing information is also updated to ensure that the data used is not in breach of copyright. The principal licensing bodies relevant to the SFRA at the time of publishing were the Environment Agency (Thames Region), Ordnance Survey and Thames Water. Updated or new data may be based on datasets from other licensing authorities and may require additional licenses. Generally, when updating the GIS information associated with this SFRA, it is important that the meta-data is updated in the process. This is the additional information that lies behind the GIS polygons, lines and points.

It is recommended that an interim review of the SFRA is undertaken on an annual basis, in liaison with the Environment Agency, to assess any maintenance or update work required. In particular, this would include incorporation of any major changes in terms of flood management infrastructure and any recorded flooding incidents. An overall general review of the SFRA is recommended every 3 years, to re-evaluate flood risk and planning policies according to latest legislation and best practice.

Should LBS decide any significant changes are necessary; the SFRA should be updated and re-issued. It is essential that any reviews and updates of the SFRA are recorded in a structured manner. To facilitate this task, the following register has been created:


STRATEGIC FLOOD RISK ASSESSMENT REVIEW

Type of Review Scheduled ☐ Interim ☐ Date of Review:

Reviewer Name: Organisation:

Area Reviewed Source of Information Provider Maps Modified Comments


Historic Flooding Records Date

Attributed Source of Flooding

Location Description and Comments Reference

6th January 1928

Tidal flooding associated with the River Thames

Thames Frontage

Severe flooding affected the borough of Southwark on 6th January 1928 when the defences along the River Thames were breached. Amongst other disaster locations, failure of a 25 metre stretch of embankment near Lambeth Bridge resulted in the death by drowning of fourteen people within basements. Four thousand people were made homeless as a direct result of this flooding event.

2008 SFRA

8th November 2000 Groundwater Peckham Waterlogging. EA groundwater flooding

records

13th November 2000

Groundwater Peckham district Rise of water table. EA groundwater flooding records

5th April 2001 Groundwater East Dulwich 1 foot of water in basement. Probable blockage of drainage. EA groundwater flooding records

6tt April 2001 Groundwater Dulwich district Flooding in basement. EA groundwater flooding records

18th April 2001 Groundwater Dulwich Waterlogged garden. EA groundwater flooding records

April 2001 Surface water flooding Dulwich

Minor flooding occurred in Dulwich area caused primarily by run off from large areas of open spaces and recreational land including Dulwich, Belair and Brockwell Parks (Ref: Floods in Southwark Report March 2005).

Southwark SWMP

7th January 2002 Groundwater South Eastern

Head district Water seeping into basement flat. Considered unlikely to be groundwater flooding as no problem was observed the previous winter.

EA groundwater flooding records

4th April 2002 Groundwater Camberwell district Possible spring in basement. EA groundwater flooding records


20th August 2002 Groundwater Camberwell district Water appeared in cellar, fluctuates daily and rises after rain. No spring line,

incident likely to be related to near-surface drainage. EA groundwater flooding records

27th April 2004

Surface water flooding

Dulwich, East Dulwich and Herne Hill

Intense periods of rainfall in the south of the Borough caused extensive surface water flooding which inflicted damage on residents and their homes, public services and private businesses in the Dulwich, East Dulwich and Herne Hill. A reported 60 mm of rain fell in just under one hour. Residential properties flooded (some residents could not return to their properties for 6 months). Commercial properties flooded (some commercial properties remained closed for 3 months). Local schools were closed including Chester School in Dulwich which was closed on Wednesday 28th April. Severe traffic disruptions were reported, particularly on East Dulwich Road and Lordship Lane where the majority of the flooding occurred. Drivers in Dulwich Village had to abandon their cars as roads became rivers deeper than 300mm. Fire engines had to pump out water from flooded cellars and basements. Costs of flooding in 2004 have been put at a minimum of £1 million pounds (according to Floods in Southwark Report March 2005 as referenced in Southwark LCLIP Report).

Southwark SWMP

10th December 2005

Tidal Flooding associated with River Thames

River Thames frontage

The Thames Barrier which normally protects the London Borough of Southwark from tidal flooding, was not shut, and sufficient warning was not provided to local residents close to the floodgates prior to the onset of flooding, causing flooding along the Southwark frontage and into some basements to a depth of between 4 and 6 inches (according to Report on Planning 188 Southwark Council March 2009 as referenced in Southwark LCLIP Report).

Southwark SWMP

10th May 2006 Surface water flooding

Blackfriars Road, junction with Boundary Row

Footway flooding at dropped kerb. SWMP GIS dataset


Blackfriars, Cathedral Extensive carriage flooding due to blocked drain. SWMP GIS dataset


Outside 104 Street George Road Blocked drain. SWMP GIS dataset

25th May 2006 Groundwater Peckham district Flooded road, possibly groundwater related. EA groundwater flooding records


12th June 2006 Surface water flooding New Kent Road Dampness causing power to trip. SWMP GIS dataset

14th June 2006 Surface water flooding Various

Heavy rainfall (40mm in an hour) caused surface water flooding in some parts of the Borough and the closure of Rotherhithe Station (Source: Southwark LCLIP report).

Southwark SWMP

19th June 2006 Surface water flooding

The Salsa Restaurant, Walworth Road

Waste water running over footway. SWMP GIS dataset

29th June 2006 Surface water flooding Old Kent Road Hilly valley causing deep waters when it rained. SWMP GIS dataset

16th August 2006


Outside St. Marys Church, Kennington Park Road

Broken drain resulting in localised ponding. SWMP GIS dataset

19th September 2006


881-883 Old Kent Road Blocked gully resulting in localised ponding. SWMP GIS dataset

2nd October 2006


186-188 Tooley Street Basement flooding due to blocked drain in road. SWMP GIS dataset

3rd October 2006


Junction of Street Thomas Street and London Bridge

Localised ponding. SWMP GIS dataset

4th October 2006


Corner of Melon and Peckham Road Localised Ponding. SWMP GIS dataset

24th October 2006


Elephant and Castle Subway flooded. SWMP GIS dataset

25th October 2006


190 Peckham High Street Broken drain resulting in basement flooding. SWMP GIS dataset

14th November 2006

Surface water flooding New Kent Road Subway Flooded. SWMP GIS dataset


16th November 2006


Elephant and Castle Subway flooded. SWMP GIS dataset

20th November 2006


Camberwell New Road Blocked gully resulting in localised ponding. SWMP GIS dataset

07th December 2006


32-34 Camberwell Church Street Blocked gully resulting in localised ponding. SWMP GIS dataset

29th January 2007


199 Tower Bridge Road Blocked gully resulting in localised ponding. SWMP GIS dataset

19th February 2007


32-34 Camberwell Church Street Blocked gully resulting in localised ponding. SWMP GIS dataset

27th February 2007


Outside Street Marys Church, Kennington Park Road

Broken drain resulting in localised ponding. SWMP GIS dataset

19th March 2007


Jamaica Road, outside Bermondsey Tube station

Flooding. SWMP GIS dataset

06th March 2007


Blackfriars Road near Union Street Water leakage evident from ground. SWMP GIS dataset

26th March 2007


97-101 Blackfriars Road Flooding. SWMP GIS dataset

08th March 2007

Surface water flooding 1-4 Tooley Street Water leakage evident from ceiling. SWMP GIS dataset

20th July 2007 Surface water flooding

Surrey Quays railway station

Heavy rainfall caused Surrey Quays railway station to be closed for 3 hours due to flooding on 20th July 2007 (Source: Network Rail). Southwark SWMP

30th August 2006


Corner of Melon and Peckham Road Localised Ponding. SWMP GIS dataset


22nd May 2008 Groundwater Rotherhithe district Recurring Water in basement. EA groundwater flooding records

10th February 2009 Groundwater South Eastern

Head district Water in lower basement. EA groundwater flooding records

03rd December 2009 Groundwater East Dulwich Water in basement for three months since September 2009. EA groundwater flooding

records

29th July 2010 Groundwater Rotherhithe Water seeping into garage. EA groundwater flooding records

20 September 2010 Groundwater Camberwell Flooded basement March/April 2010.

EA groundwater flooding records

14th August 2014

Surface water flooding Peckham Flash flooding as a result of Hurricane Bertha. LBS records

23rd June 2016 Surface water flooding Hendre Road SE1 Multiple flood incidents London Fire Brigade

23rd June 2016 Surface water flooding

Meeting House Lane SE15 Multiple flood incidents London Fire Brigade


Kinglake Street SE17 Flood incident London Fire Brigade


Oscar Court, Rotherhithe Street SE16

Flood incident London Fire Brigade


Walworth Road SE17 Multiple flood incidents London Fire Brigade


Rotherhithe New Road SE16 Flood incident London Fire Brigade

23rd June 2016 Surface water flooding Sandell Street SE1 Flood incident London Fire Brigade



Kennington Road SE11 Flood incident London Fire Brigade

23rd June 2016 Surface water flooding Maude Road SE5 Flood incident London Fire Brigade

23rd June 2016 Surface water flooding Chapter Road SE17 Flood incident London Fire Brigade

23rd June 2016 Surface water flooding Boyson Road SE17 Flood incident London Fire Brigade


Camberwell New Road SE5 Flood incident London Fire Brigade


Russell Court, Heaton Road SE15 Incident flagged to SHU Management London Fire Brigade


Devon Mansions SE1 Flood incident London Fire Brigade


Bolton Crescent SE5 Flood incident London Fire Brigade

23rd June 2016 Surface water flooding Friary Estate SE15 Flood incident London Fire Brigade


Camberwell Road SE5 Flood incident London Fire Brigade


Walworth Road SE17 Multiple flood incidents London Fire Brigade

23rd June 2016 Surface water flooding Lower Road SE16 Multiple flood incidents London Fire Brigade


Elephant Road SE17 construction basement flooding London Fire Brigade


Street Josephs Primary School, Flood incident London Fire Brigade


Gomm Rd, SE16

23rd June 2016 Surface water flooding Orange Place SE16 Flood incident London Fire Brigade


7 Islands Leisure Centre, Lower Road SE16


23rd June 2016 Surface water flooding Dunton Road SE16 Flood incident London Fire Brigade


Sumner Road, Galleria Court SE15 Multiple flood incidents London Fire Brigade


Metro Central Heights, Newington Causeway SE1



Surrey Square, SE17 Flood incident London Fire Brigade


Southampton Way SE5 Multiple flood incidents London Fire Brigade

23rd June 2016 Surface water flooding Hopton Street SE1 Flood incident London Fire Brigade


Webster Road SE16 Flood incident London Fire Brigade

23rd June 2016 Surface water flooding Old Kent Road SE1 Multiple flood incidents London Fire Brigade

23rd June 2016 Surface water flooding Brook Drive SE11 Flood incident London Fire Brigade


Strathnairn Street SE1 Flood incident London Fire Brigade


23rd June 2016 Surface water flooding Elim Estate SE1 Multiple flood incidents London Fire Brigade

23rd June 2016 Surface water flooding East Street SE17 Multiple flood incidents London Fire Brigade


Kinglake Street SE17 Flood incident London Fire Brigade


Old Vic, The Cut SE1 Flood incident London Fire Brigade

23rd June 2016 Surface water flooding Sandell Street SE1 Flood incident London Fire Brigade


Southwark Street SE1 Flood incident London Fire Brigade


Southwark Park Road SE16 Multiple flood incidents London Fire Brigade


Meeting House Lane SE15 Flood incident London Fire Brigade


191-209 Kennington Lane SE11 5QS

Multiple flood incidents London Fire Brigade

London Borough of Southwark Strategic Flood Risk Assessment › assets › attach › 12166 ›...

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