Tandridge District Council Level 2 Strategic Flood Risk Assessment

Tandridge District Council Level 2 SFRA Catchment Summary Tables

Table of Contents Smallfield ...... 2 Caterham on the Hill ...... 6 Caterham and Whyteleafe ...... 11

Tandridge District Council Level 2 SFRA Catchment Summary Tables

Catchment Name Smallfield Settlements within catchment Smallfield

OS Grid 532068 143767 reference

Area 531ha Catchment The catchment has the village of Smallfield at its centre with grazing land to the details Current land use north and south. The village is situated in a wide shallow valley with the terrain only varying by Topography ~2m within the village itself (58m in its centre). North of the village the land rises to a height of 121m, and 70m to the south. Weatherhill Stream (a main river) flows through the centre of the village of Smallfield from east to west and is a tributary to the Burstow Stream. This is Existing culverted through the village itself. Outside the village this is fed by an ordinary watercourses watercourse draining farmland to the north east of the village.

The EA Historic Flood Map indicates that fluvial flooding occurred in September 1968, November 1974 and December 2013.

A section 19 report was published in October 2015 covering flooding in the TDC area in the winter of 2013/14. Within this Smallfield was identified as a sub-area. Surface water and sewer flooding was reported resulting in internal property flooding and a number of road closures.

Flood history Flooding from surface water has been recorded along many of the roads in the village, and led to internal property flooding along: Redehall Road, Chapel Road, Plough Road, Weatherhill Road, Wheelers Lane, Broadbridge Lane, Woodside Crescent, Churchill Road, Grangeway, Grange End, William Gardens, Bridgeham Way, Orchard Road, Mead Place, Heather Walk and The Cravens, The Hollies, The Acorns.

External property flooding has also been recorded along: Charlotte Grove and Sources of Kings Mead. flood risk Available modelled data: The site lies within the area covered by the Burstow Stream Modelling study (Environment Agency 2011). Flood characteristics: Flood Zone 3b (functional flood plain) associated with Weatherhill Stream Fluvial Flood covers a large proportion of the centre of Smallfield village, roughly following Risk the course of Weatherhill Road and the lower part of Chapel Road.

Burstow Primary School and Smallfield Evangelical Church are both within Flood Zone 3b as well as a number of local businesses. The extent of Flood Zone 2 covers the majority of the village. This wide floodplain is a result of the of the shallow gradients within the village.

Description of surface water flow paths: The shallow gradients and limited infiltration capacity of the local soils and geology within the village result in large areas within the village that may experience ponding in a 1 in 30-year or greater return period event. Surface Water

Surface water flow paths associated with the ordinary watercourses within the catchment flow into the village from the north east and north.

Tandridge District Council Level 2 SFRA Catchment Summary Tables

Catchment Name Smallfield Settlements within catchment Smallfield

Areas Susceptible to Groundwater Flooding Map class (risk of groundwater emergence) The central and western parts of the village are in an area where there is a risk of groundwater flooding to both surface and subsurface assets. Groundwater may emerge at significant rates and has the capacity to flow overland and/or Groundwater pond in topographic low spots.

The eastern side of the village (from New Road), and the remaining part of the wider catchment are in an area deemed as having a negligible risk from groundwater flooding. Reservoir No part of the catchment lies within an area at risk of reservoir flooding.

Canal No canals are located within the catchment.

Defence Type Standard of Protection Condition Defences The catchment does not receive protection from flood defences. Weatherhill Stream is culverted as it passes through the village. Blockage could cause Culvert / structure significant flooding in the north of the village. Flood risk blockage? management The motorway culvert is also a potential infrastructure blockage risk. Residual risk Impounded water body The catchment is not at risk of inundation in failure? the event of reservoir failure. Breach Zone Defence breach / overtopping? The site is not at risk from breach of defences.

Much of the village is covered by the Ilfield Brook, Upper River Mole, Gatwick Stream, Burstow Stream and Salfords Stream Flood Alert Area. Flood warning Environment Agency flood warnings are now issued to individuals via the Flood Emergency Information Service. planning

Many of the roads running thorugh the catchment have recorded instances of Infrastructure surface water flooding, and some were closed in January 2014.

River Basin District Central Higher Upper Climate change Central End allowances for ‘2080s’ Thames 25% 35% 70% Climate Change Climate change may result in an extension of Flood Zone 3a to cover a wider area of the village in particular to the west of Weatherhill, south of Wheelers Implications for Lane and fill in dry islands within Flood Zone 3a along Chapel Road. the catchment Elsewhere increased rainfall intensity may lead to areas of existing flow and/or ponding of surface water increasing.

Tandridge District Council Level 2 SFRA Catchment Summary Tables

Catchment Name Smallfield Settlements within catchment Smallfield

Bedrock Wealden Group – Mudstone, Siltstone and Sandstone Geology The south west corner of the catchment has superficial river terrace deposits of Superficial sand and gravel. No superficial deposits are known to exist elsewhere in the Geology catchment. The central and eastern part of the village has loamy soils with naturally high Soils groundwater. Elsewhere in the catchment are slowly permeable seasonally wet slightly acid but base-rich loamy and clayey soils with impeded drainage.

SuDS offer opportunities to manage surface water on a development site to reduce the likelihood of a site contributing to flooding elsewhere. They can also offer additional benefits of increasing biodiversity, offering amenity spaces, and the moderation of microclimate. Early design of SuDS is key to maximising those benefits.

Sites close to the centre of Smallfield may be vulnerable to flooding, and so SuDS schemes should be resilient to this. In these cases schemes which include infiltration or storage of surface water will be ineffective during a flood event. Source control schemes such as rainwater harvesting and/or green roofs may be more effective.

Requirement Elsewhere in the catchment the focus should be on minimising the volume of for drainage water leaving each site, reducing the rate of runoff from sites and the volume of control and water that reaches the centre of the village where possible. impact SuDS mitigation The nature of the soils across most of the catchment may limit opportuities for infiltration SuDS schemes, but many other options could be implemented successfully.

All major developments should include provision for sustainable drainage systems (Planning Practice Guidance (PPG) paragraph 051).

Further information on SuDS is available in the CIRA SuDS Manual (2015) and on the Surrey County Council website, including guidance for developers and planners on integrating SuDS as part of master planning.

http://www.susdrain.org/files/resources/other- guidance/water_people_places_guidance_for_master_planning_sustainable_d rainage_into_developments.pdf

Groundwater Source No groundwater source protection zones exist within the catchment. Protection Zone

Historic Landfill There are no sites designated by the Environment Agency as an historic landfill Site within the catchment.

Tandridge District Council Level 2 SFRA Catchment Summary Tables

Catchment Name Smallfield Settlements within catchment Smallfield

The village of Smallfield has a significant flood risk from fluvial, surface water and groundwater sources, as well recorded sewer flooding incidents. New development should ensure that this flood risk is at the very least not added to.

Opportunities for using source control SuDS to manage runoff rates and volumes, contributing to the reduction of flood peaks downstream and existing surface water flow paths leaving the site.

Where development occurs within the flood zone (following the application of the exception test), adequate flood compensation should be provided.

Opportunities for A greenfield development site is likely to increase the impermeable area within flood risk the catchment reducing opportunities for water to infiltrate the ground and betterment increasing the volume and speed that surface water may leave the site, contributing to an increase in flood risk elsewhere.

Under existing guidance major developments (those with 10 or more homes) are expected to integrate SuDS unless demonstrated to be inappropriate.

Small development sites, infill, or windfall sites may not individually contribute a significant volume to runoff, but taken cumulatively, could contribute to an increase in flood risk if not managed appropriately. Therefore, it is recommended that suitable surface water drainage plans are required as part of the planning process in the Smallfield catchment with SuDS designed to suit the smaller sites.

The catchment drains to Weatherhil Stream that is a tributary to Burstow Downstream Stream. An increase in surface runoff within this catchment could increase flood risk flood risk downstream on Burstow Stream or the River Mole. Recommendations for requirements of site-specific Flood Risk Assessment, including guidance for developers Flood risk assessment: • At the planning application stage, a site-specific flood risk assessment (considering all sources of flooding) and surface water drainage strategy should be required for all development. • Consultation with the Lead Local Flood Authority and the Environment Agency should be undertaken at an early stage • Impacts of the development on flood risk to the wider catchment should be assessed for all development. • Safe access and egress should be demonstrated in the 1 in 100 plus climate change event. Recommend-

ations for Local Plan Guidance for site design and making development safe: policy • Development must seek opportunities to reduce overall level of flood risk at the site. • A surface water drainage strategy should be provided for all developments in this catchment and should ensure that the development does not increase flood risk elsewhere. • Discharge from all new developments should be limited to a maximum of greenfield runoff rates. • All development should adopt source control SuDS techniques to reduce the risk of flooding due to post-development runoff. SuDS design should follow current best practice (CIRIA Manual, 2015) and SCC guidance on runoff rates and volumes, to deliver multiple benefits including water quality, biodiversity, amenity, green infrastructure etc. • Drainage designs should ‘design for exceedance’ and accommodate existing surface water flow routes, with development located outside of existing flood risk areas .

Tandridge District Council Level 2 SFRA Catchment Summary Tables

Catchment Name Caterham on the Hill Settlements within catchment Caterham on the Hill

OS Grid 533043 156318 reference

Area 223ha The catchment is predominantly urban with a few limited areas of green space Catchment Current land use (Westway Common, Queens Park, and Caterham School rugby ground in the details south and Coulsdon Common in the north). Caterham on the Hill is situated on a hill which slopes from south (205m) to north (152m). There is also a shallow dry valley running south to north through Topography the area. The western part of Caterham on the Hill drains to the west away from the surface water catchment covering the majority of Caterham on the Hill. Existing No watercourses exist within the catchment. watercourses The EA Historic Flood Map does not record any instances of flooding from fluvial sources.

The catchment has an extensive history of surface water flooding with the majority of roads close to the main topography flow path experiencing internal property flooding, and many of the surrounding roads experiencing highway flooding. Two main recent incidents are recorded, one in the winter of 2013/14 Flood history and one in June 2016. Sources of flood risk The June 2016 flood resulted in an S19 report and documents a flash flood from surface water that affected Caterham on the Hill (and also Caterham Valley, Whyteleafe and Coulsdon Common). 86 reports of internal property flooding and 63 of external floods were recorded.

Available modelled data: No detailed river models are available in this area

Fluvial Flood Risk Flood characteristics:

The catchment is entirely within Flood Zone 1

Tandridge District Council Level 2 SFRA Catchment Summary Tables

Catchment Name Smallfield Settlements within catchment Smallfield

Description of surface water flow paths: A large surface water flow path flows south to north following the natural topography. A second significant flow path joins this from the east at the northern end of Coulsdon Common. Both these flow paths may be present in a 1 in 30-year or greater return period event.

Surface Water Surface water is predicted to continue out of the district area and in to the London Borough of Croydon to the north. A significant flow path continues along Caterham Drive, Coulsdon and Old Lodge Lane to the north.

Other scattered areas of surface water ponding are present in local topographic low spots throughout the catchment in a 1 in 100-year or greater return period event.

Areas Susceptible to Groundwater Flooding Map class (risk of groundwater emergence) Along the topographic low points (corresponding to the main surface water flow paths) there is a risk of flooding to subsurface assets but surface manifestation of groundwater is unlikely. Groundwater The area around Caterham School is in an area where flooding from groundwater is unlikely.

The higher ground to the south and the east and west of the catchment is in an area at negligible risk of flooding from surface water. Reservoir No part of the catchment lies within an area at risk of reservoir flooding.

Canal No canals are located within the catchment.

Tandridge District Council Level 2 SFRA Catchment Summary Tables

Catchment Name Smallfield Settlements within catchment Smallfield

Defence Type Standard of Protection Condition Defences The catchment does not receive protection from flood defences.

The primary drainage route in the catchment is a surface water sewer running south to Flood risk Culvert / structure north. Blockage anywhere along the length management blockage? infrastructure of this sewer would cause surface water to surcharge causing localised flooding. Residual risk Impounded water body The catchment is not at risk of inundation in failure? the event of reservoir failure. Breach Zone Defence breach / overtopping? The site is not at risk from breach of defences. Much of the catchment is covered by the “Groundwater Flooding in South East London” Flood Alert Area. Flood warning Environment Agency flood warnings are now issued to individuals via the Flood Emergency Information Service. planning The majority of roads within the catchment, particularly close to the primary surface water flow routes have experienced surface water flooding, with some Infrastructure being closed during the flash flood in 2016, (Buxton Lane, Court Road, Ninehams Road, and Queens Park Road). River Basin District Central Higher Upper Climate change Central End allowances for ‘2080s’ Thames 25% 35% 70% Climate Change Climate change is highly unlikely to change the Flood Zone classification of the catchment, however higher intensity rainfall may lead to areas of existing flow Implications for and/or ponding of surface water increasing in extent and depth. Surface water the catchment sewers are more likely to be overwhelmed leading to a higher frequency of surcharging.

Tandridge District Council Level 2 SFRA Catchment Summary Tables

Catchment Name Smallfield Settlements within catchment Smallfield

Bedrock White Chalk sub-group Geology

Superficial The catchment contains superficial deposits of Diamicton (Clay with flints). Geology

Slightly acid loamy and clayey soils with impeded drainage throughout most of the catchment. Soils Within Coulsdon Common a region exists of shallow lime-rich soils which are freely draining.

The soils in this area may limit imediate infiltration, however the area is underlain by a highly permeable chalk formation, which has the potential to receive infiltration of surface water. Requirement for drainage Much of the catchment is urbanised, with little space for larger SuDS features. control and Source control schemes such as rainwater harvesting should be employed to impact reduce runoff leaving sites. SuDS mitigation All major developments should include provision for sustainable drainage systems (Planning Practice Guidance (PPG) paragraph 051). It is recommended that this is extended to all development, with discharge limited to a maximum of greenfield runoff rates.

http://www.susdrain.org/files/resources/other- guidance/water_people_places_guidance_for_master_planning_sustainable_d rainage_into_developments.pdf

Groundwater The catchment lies within a groundwater source protection zone (Zone 2 – Source Outer Protection Zone). This should be considered as part of any surface Protection Zone water drainage strategy.

Historic Landfill There are no sites designated by the Environment Agency as an historic landfill Site within the catchment.

Tandridge District Council Level 2 SFRA Catchment Summary Tables

Catchment Name Smallfield Settlements within catchment Smallfield

It was observed in the Caterham on the Hill Surface Water Management Plan (Atkins, 2016) that many properties in the catchment have low thresholds so may be more vulnerable to surface water flooding. New developments must take the surface water flood risk into account when designing freeboard. There may also be opportunities to increase resilience to flooding in existing properties.

Opportunities for using source control SuDS to manage runoff rates and volumes, contributing to the reduction of flood peaks downstream and existing surface water flow paths within the catchment.

Major developments (those with 10 or more homes) are expected to integrate SuDS unless demonstrated to be inappropriate.

Small development sites, infill, or windfall sites may not individually contribute a significant volume to runoff, but taken cumulatively, could contribute to an increase in flood risk if not managed appropriately. Therefore, it is recommended that suitable surface water drainage plans are required as part of the planning process in the Caterham on the Hill catchment with SuDS designed to suit the smaller sites.

Whilst there is no fluvial path downstream, surface water leaving this Downstream catchment will flow through Old Coulsdon and so an increase in surface runoff flood risk could increase flood risk in this area. Recommendations for requirements of site-specific Flood Risk Assessment, including guidance for developers Flood risk assessment: • At the planning application stage, a site-specific flood risk assessment (considering all sources of flooding) and surface water drainage strategy should be required for all development. • Consultation with the Lead Local Flood Authority and the Environment Agency should be undertaken at an early stage • Impacts of the development on flood risk to the wider catchment should assessed for all development. Recommend- • Safe access and egress should be demonstrated in the 1 in 100 plus climate change event. ations for Local Plan Guidance for site design and making development safe: policy • Development must seek opportunities to reduce overall level of flood risk at the site. • A surface water drainage strategy should be provided for all developments in this catchment and should ensure that the development does not increase flood risk elsewhere. • Discharge from all new developments should be limited to a maximum of greenfield runoff rates. • All development should consider source control SuDS techniques to reduce the risk of flooding due to post-development runoff. SuDS design should follow current best practice (CIRIA Manual, 2015) and SCC guidance to deliver multiple benefits including water quality, biodiversity, amenity, green infrastructure etc. • Drainage designs should ‘design for exceedance’ and accommodate existing surface water flow routes, with development located outside of existing flood risk areas.

Tandridge District Council Level 2 SFRA Catchment Summary Tables

Catchment Name Caterham and Whyteleafe Settlements within catchment Caterham, Whyteleafe, West of Warlingham, Woldingham

OS Grid 535915 155921 reference

Area 2590ha

Catchment The catchment is a mix of suburban land (consisting of the settlements of details Current land use Caterham, Whyteleafe, and Woldingham) and green space which is a mix of farmland (grazing), recreational use (golf courses), and woodland. The southern half of the catchment consists of the dip slope of the North Downs with land at the top of the Downs at a height of 212m. Branched trough Topography shaped valleys converge on Whyteleafe in the north of the catchment which is at a height of approximately 88m. The Caterham Bourne is an ephemeral chalk stream, anecdotally reported to Existing be present 1 in 7 years. It rises near Wapses Lodge Roundabout on the A22. watercourses Much of its length is now culverted as it passes through Whyteleafe and into the London Borough of Croydon. The EA Historic Flood Map does not record any instances of flooding from fluvial sources.

Flooding associated with the Caterham Bourne, although classified as a main river, is recorded as flooding from surface water or groundwater.

The catchment has an extensive history of surface water flooding with the flooding recorded in multiple places along the A22 and the roads running through Caterham. Internal property flooding from surface water is recorded on many of roads within Caterham and Whyteleafe. Two main recent incidents are recorded, one in the winter of 2013/14 and one in June 2016.

Flood history In 2013/14 100 properties were impacted by the flooding from the Caterham Bourne and a major incident declared. 11 businesses were also impacted as Sources of well as two schools. flood risk The June 2016 flood resulted in an S19 report and documents a flash flood from surface water that affected Caterham on the Hill to the west of the catchment (and also Caterham Valley, Whyteleafe and Coulsdon Common). 86 reports of internal property flooding and 63 of external floods were recorded.

Earlier records indicate flooding from the Caterham Bourne in the winter of 2000/01, and in 1968.

Available modelled data: No detailed river models are available in this area

Fluvial Flood Flood characteristics: Risk The catchment is predominantly Flood Zone 1, with a small area of Flood Zone 2 and 3 from the Caterham Bourne which runs from Caterham Railway Station along the valley floor close to the railway line to the north.

Tandridge District Council Level 2 SFRA Catchment Summary Tables

Catchment Name Caterham and Whyteleafe Settlements within catchment Caterham, Whyteleafe, West of Warlingham, Woldingham

Description of surface water flow paths: Surface water flow paths follow the natural topography along trough shaped valleys converging on Whyteleafe. Many of these may be present in a 1 in 30- year return period or greater event.

There are several areas of note:

• In Woldingham, south of Uplands Road.

• On Woldingham Road (north west of Woldingham Village), two flow paths from Halliloo Valley and Marden Valley combine. In 2013/14 this resulted in a flow 150mm deep and caused damage to the road. (The road has subsequently been raised which may alter this flow Surface Water path locally).

• In the centre of Caterham, immediately south of the station is a significant area of ponding where two flow paths converge.

• At the Wapses Lodge roundabout on the A22, the flow paths from Caterham and Woldingham converge.

• The course of the Caterham Bourne through Whyteleafe

There is a high degree of connectivity between areas of surface water in this catchment. This increases the risk of surface water flooding towards the district boundary at Whyteleafe. Areas Susceptible to Groundwater Flooding Map class (risk of groundwater emergence)

Groundwater flood risk increases as the land drops in height in the northern part of the catchment, following the course of the Caterham Bourne. Within this Groundwater area there is a risk of groundwater flooding to surface and subsurface assets. There is a possibility of groundwater emerging at the surface locally.

In the south of the catchment, on higher ground, flooding from groundwater is unlikely.

Reservoir No part of the catchment lies within an area at risk of reservoir flooding.

Canal No canals are located within the catchment.

Tandridge District Council Level 2 SFRA Catchment Summary Tables

Catchment Name Caterham and Whyteleafe Settlements within catchment Caterham, Whyteleafe, West of Warlingham, Woldingham

Defence Type Standard of Protection Condition

Defences Following the flooding in the winter of 2013/14, SCC constructed a series of emergency storage areas in the fields adjacent to Woldingham Road. These were subsequently formalised into major attenuation features.

The primary drainage route through Whyteleafe is a culverted section of the Caterham Bourne which acts as a surface water sewer. Blockage anywhere along the length of this would cause surface water to surcharge causing localised flooding.

Flood risk Areas of note are: management infrastructure Culvert / structure blockage? • Succombs Hill where the culvert capacity was exceeded in 2013/14 Residual risk • Well Farm Heights – open culvert section exceeded channel in 2013/14 • Culvert capacity exceeded along Godstone Road • Culverts under the railway line between Church Road and Godstone Road Impounded water body The catchment is not at risk of inundation in failure? the event of reservoir failure. Defence breach / Breach Zone overtopping? Not known at this time Much of the catchment is covered by the “Groundwater Flooding in South East London” Flood Alert Area. Flood warning Environment Agency flood warnings are now issued to individuals via the Flood Information Service. Emergency planning The A22 through Whyteleafe is at risk of flooding from surface water and from the Caterham Bourne. This was closed for an extended period of time in the winter of 2013/14. Infrastructure

The railway line north of Caterham experienced flooding in 2013/14 but did not close. River Basin District Central Higher Upper Climate change Central End allowances for ‘2080s’ Thames 25% 35% 70% Climate Change Climate change is highly unlikely to significantly change the Flood Zone classification of the catchment, however higher intensity rainfall may lead to Implications for areas of existing flow and/or ponding of surface water increasing in extent and the catchment depth. Surface water sewers are more likely to be overwhelmed leading to a higher frequency of surcharging.

Tandridge District Council Level 2 SFRA Catchment Summary Tables

Catchment Name Caterham and Whyteleafe Settlements within catchment Caterham, Whyteleafe, West of Warlingham, Woldingham

Bedrock White Chalk sub-group throughout much of the catchment. The southern Geology central region contains an area underlain by Grey Chalk subgroup. The catchment contains superficial deposits of Diamicton (Clay with flints) in Superficial the area around Warlingham, and in bands running north to south in the Geology southern part of the catchment.

The valleys in the catchment contain shallow lime-rich soils of chalk which are freely draining.

The western part of the catchment, and some of the areas of higher ground in Soils the centre of the catchment contains slightly acid loamy and clayey soils with impeded drainage.

In the south of the catchment following one of the dry valleys is an area of freely draining lime-rich soil.

Requirement for drainage The high groundwater in the northern part of the catchment within Whyteleafe and Caterham, may limit the oportunities for SuDS based on infiltration, where control and soil type allows this may be more appropriate in the southern part of the impact mitigation catchment.

Much of the lower catchment is urbanised, with little space for larger SuDS features. Source control schemes such as rainwater harvesting should be employed to reduce runoff leaving sites in this area, with the potential for larger SuDS schemes in the upper catchment.

All developments within the catchment should include provision for sustainable drainage systems (Planning Practice Guidance (PPG) paragraph 051). It is recommended that this is extended to all development, with discharge limited to a maximum of greenfield runoff rates.

http://www.susdrain.org/files/resources/other- guidance/water_people_places_guidance_for_master_planning_sustainable_d rainage_into_developments.pdf

Groundwater The northern part of the catchment lies within a groundwater source protection Source zone (Zone 1 – Inner Protection Zone), the central part within Zone 2 (Outer Protection Zone Protection zone), and the southern part in Zone 3 (Total Catchment).

Tandridge District Council Level 2 SFRA Catchment Summary Tables

Catchment Name Caterham and Whyteleafe Settlements within catchment Caterham, Whyteleafe, West of Warlingham, Woldingham

A large site designated by the Environment Agency as historic landfill lies to the east of Caterham. This was last used in 1989 and is classified as inert but could influence local drainage. Historic Landfill Site A small historic landfill site exists in Caterham itself off Godstone Road; no information was available on this site.

Other sites exist north east of Woldingham associated with quarry operations.

Opportunities for using source control SuDS to manage runoff rates and volumes, contributing to the reduction of flood peaks downstream and existing surface water flow paths leaving the site.

A catchment based approach could be taken with opportunities taken to hold surface water further up in the catchment. This may be achieved by using Natural Flood Management (NFM) measures in the upper catchment, or developing larger schemes to limit risk within the more developed areas of the catchment

The Working with Natural Processes evidence base published by the EA in 2017, provides high level opportunity mapping for runoff attenuation features which could be used as a starting point.

Opportunities for https://www.gov.uk/government/publications/working-with-natural-processes- flood risk to-reduce-flood-risk betterment A greenfield development site is likely to increase the impermeable area within the catchment reducing opportunities for water to infiltrate the ground and increasing the volume and speed that surface water may leave the site, contributing to an increase in flood risk elsewhere.

Major developments (those with 10 or more homes) are expected to integrate SuDS unless demonstrated to be inappropriate.

Small development sites, infill, or windfall sites may not individually contribute a significant volume to runoff, but taken cumulatively, could contribute to an increase in flood risk if not managed appropriately. Therefore, it is recommended that suitable surface water drainage plans are required as part of the planning process in the Caterham and Whyteleafe catchment with SuDS designed to suit the smaller sites.

From Whyteleafe, the Caterham Bourne flows through Kenley and Purley and discharges to a balancing pond at the Royal Oak Centre. It is culverted for all Downstream of this length. flood risk An increase in surface water leaving the catchment is likely to result in an increase in flood risk in Kenley and Purley. Recommendations for requirements of site-specific Flood Risk Assessment, including guidance for developers Recommend- Flood risk assessment: ations for • At the planning application stage, a site-specific flood risk assessment (considering all Local Plan sources of flooding) and surface water drainage strategy should be required for all policy development. • Consultation with the Lead Local Flood Authority and the Environment Agency should be undertaken at an early stage

Tandridge District Council Level 2 SFRA Catchment Summary Tables

Catchment Name Caterham and Whyteleafe Settlements within catchment Caterham, Whyteleafe, West of Warlingham, Woldingham

• Impacts of the development on flood risk to the wider catchment should assessed for all development. • Safe access and egress should be demonstrated in the 1 in 100 plus climate change event.

Guidance for site design and making development safe: • Development must seek opportunities to reduce overall level of flood risk at the site. • A surface water drainage strategy should be provided for all developments in this catchment and should ensure that the development does not increase flood risk elsewhere. • Discharge from all new developments should be limited to a maximum of greenfield runoff rates. • All development should consider source control SuDS techniques to reduce the risk of flooding due to post-development runoff. SuDS design should follow current best practice (CIRIA Manual, 2015) and SCC guidance to deliver multiple benefits including water quality, biodiversity, amenity, green infrastructure etc. • Drainage designs should ‘design for exceedance’ and accommodate existing surface water flow routes, with development located outside of existing flood risk areas. .