Tandridge District Council Level 2 SFRA Catchment Summary Tables Table of Contents Smallfield ............................................................................................................................................. 2 Caterham on the Hill ........................................................................................................................... 6 Caterham and Whyteleafe ................................................................................................................ 11 1 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. 2 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. 3 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. 4 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