NOTE TO FILE JBA Project Code 2016s5367 Contract Lancaster City Council Level 1 SFRA Client Lancaster City Council Day, Date and Time 5 June 2017 Author Tasmin Fletcher Subject Functional Floodplain Delineation 1 Functional Floodplain Definition 1.1 Flood Risk and Coastal Change PPG – Table 1, Paragraph 065 These Flood Zones refer to the probability of river and sea flooding, ignoring the presence of defences. They are shown on the Environment Agency’s Flood Map for Planning (Rivers and Sea), available on the Environment Agency’s web site, as indicated in the table below. Flood Zone Definition Zone 1 Land having a less than 1 in 1,000 (0.1%) annual probability of river or sea flooding. Low (Shown as ‘clear’ on the Flood Map – all land outside Zones 2 and 3) Probability Zone 2 Land having between a 1 in 100 (1%) and 1 in 1,000 annual probability of river Medium flooding; or Probability Land having between a 1 in 200 (0.5%) and 1 in 1,000 annual probability of sea flooding. (Land shown in light blue on the Flood Map) Zone 3a Land having a 1 in 100 or greater annual probability of river flooding; or High Land having a 1 in 200 or greater annual probability of sea flooding. Probability (Land shown in dark blue on the Flood Map) Zone 3b This zone comprises land where water has to flow or be stored in times of flood. The Local planning authorities should identify in their Strategic Flood Risk Assessments Functional areas of functional floodplain and its boundaries accordingly, in agreement with the Floodplain Environment Agency. (Not separately distinguished from Zone 3a on the Flood Map) Note: The Flood Zones shown on the Environment Agency’s Flood Map for Planning (Rivers and Sea) do not take account of the possible impacts of climate change and consequent changes in the future probability of flooding. Reference should therefore also be made to the Strategic Flood Risk Assessment when considering location and potential future flood risks to developments and land uses. 1.2 Flood Risk and Coastal Change PPG – Paragraph 015 The definition of Flood Zone 3b in Table 1 explains that local planning authorities should identify areas of functional floodplain in their Strategic Flood Risk Assessments in discussion with the Environment Agency and the lead local flood authority. The identification of functional floodplain should take account of local circumstances and not be defined solely on rigid probability parameters. However, land which would naturally flood with an annual probability of 1 in 20 (5%) or greater in any year, or is designed to flood (such as a flood attenuation scheme) in an extreme (0.1% annual probability) flood, should provide a starting point for consideration and discussions to identify the functional floodplain. A functional floodplain is a very important planning tool in making space for flood waters when flooding occurs. Generally, development should be directed away from these areas using the Environment Agency’s www.jbaconsulting.com www.jbarisk.com Page 1 of 5 www.jbaenergy.com NOTE TO FILE JBA Project Code 2016s5367 Contract Lancaster City Council Level 1 SFRA Client Lancaster City Council Day, Date and Time 5 June 2017 Author Tasmin Fletcher Subject Functional Floodplain Delineation catchment flood management plans, shoreline management plans and local flood risk management strategies produced by lead local flood authorities. The area identified as functional floodplain should take into account the effects of defences and other flood risk management infrastructure. Areas which would naturally flood, but which are prevented from doing so by existing defences and infrastructure or solid buildings, will not normally be identified as functional floodplain. If an area is intended to flood, e.g. an upstream flood storage area designed to protect communities further downstream, then this should be safeguarded from development and identified as functional floodplain, even though it might not flood very often. 2 2007 Functional Floodplain Text taken from the 2007 Level 1 SFRA: Areas subject to flooding up to (and including) once in every 20 years on average have been delineated. These areas have been sub-delineated on the basis of current land use, i.e. open space or currently undeveloped areas (i.e ‘Zone 3b Functional Floodplain (Undeveloped)’) vs areas that are ‘previously developed’ (i.e. ‘Zone 3b Functional Floodplain (Developed)’). Within the context of the SFRA, ‘previously developed’ areas are solely existing buildings that are impermeable to floodwaters. The land surrounding these buildings are important flow paths and/or flood storage areas that must be retained. 3 Functional Floodplain Delineation Based on the above guidance and definitions provided in the FRCC-PPG, the following models and modelled flood outlines (MFO) were provided by the EA.: Watercourse Extent Data Source Included in Functional Floodplain delineation (Yes/No) River Lune Forge Bank Weir to River Lune Flood Zones Yes – 4% AEP defended MFO Sunderland Point and ABD Mapping Study (2011) River Keer A6/A601 road junction to Lune 2 Tributaries Flood Yes – 4% AEP undefended estuary mouth Risk Mapping Study MFO* (2007) River Conder M6 motorway to south of Lune 2 Tributaries Flood Yes – 4% AEP undefended Galgate village near Risk Mapping Study MFO* Lancaster Canal (2007) Ou Beck Shearset Bridge to Lune 2 Tributaries Flood Yes – 4% AEP undefended confluence with River Risk Mapping Study MFO Conder (2007) Whitley Beck M6 motorway near Lune 2 Tributaries Flood Yes – 4% AEP undefended Smith Green to Risk Mapping Study MFO confluence with River (2007) Conder Back Lane East of Carnforth to Lune 2 Tributaries Flood Yes – 4% AEP undefended Watercourse confluence with River Risk Mapping Study MFO (inc. Nether Keer (2007) Beck) River Wenning Four reaches have Lune 2 Tributaries Flood Yes – 4% AEP undefended MFOs: Risk Mapping Study MFO* High Bentham (2007) Low Bentham Wennington Hornby www.jbaconsulting.com www.jbarisk.com Page 2 of 5 www.jbaenergy.com NOTE TO FILE JBA Project Code 2016s5367 Contract Lancaster City Council Level 1 SFRA Client Lancaster City Council Day, Date and Time 5 June 2017 Author Tasmin Fletcher Subject Functional Floodplain Delineation *Although the 2007 study modelled these areas with defences, defended outlines for the 4% AEP event were not available for use in functional floodplain delineation. Further datasets interrogated: Functional Floodplain from previous SFRA (2007) EA Flood Storage Areas (FSA) – none present EA Areas Benefitting from Defences (ABD) EA Historic Flood Map (HFM) Urban areas - OSOpenMapLocal_Raster (to remove developed areas from functional floodplain) 3.1 GIS Methodology The 2007 functional floodplain provided the starting point (FZ3b_1.shp) and was compared to the current Flood Zone 3 of the Flood Map for Planning (version February 2017) to ascertain whether the Flood Map may have been updated since the 2007 FZ3b was finalised. No changes were made where the outlines were consistent with each other (i.e. from the same model), which was the case only for the 2007 Back Lane 4% AEP event MFO. In many locations the current EA FZ3 is different to the 2007 FZ3b outline, indicating that more recent modelling has been carried out since the 2007 FZ3b was produced. The following MFO were merged with the 2007 FZ3b outline (FZ3b_2.shp): o The 2011 River Lune 4% AEP defended outline was used to update the functional floodplain for parts of fluvial River Lune (see table below for locations) o The 2007 River Keer 4% AEP undefended outline was used to update the functional floodplain for parts of the River Keer (see table below for locations) o The 2007 River Conder 4% AEP undefended outline was used to update the functional floodplain for parts of the River Conder, Ou Beck and Whitley Beck (see table below for locations) o The 2007 River Wenning 4% AEP undefended outline was used to update the functional floodplain for parts of the River Wenning (see table below for locations) o The 2007 Back Lane Watercourse 4% AEP undefended outline was used to update the functional floodplain for parts of the Back Lane Watercourse (see table below for locations) Areas where no modelled flood outlines were available have been updated using Flood Zone 3 (FZ3b_3.shp) The HFM layer was added but only for fluvial areas and where MFOs were not provided (FZ3b_4.shp) As defended flood outlines were not available for the Rivers Wenning, Keer and Conder, the ADB dataset was used to removed areas which would be defended against flooding and therefore should not be defined as functional floodplain (FZ3b_5.shp) The OS Open Data OSOpenMapLocal_Raster dataset was used to identify urban areas, waterbodies and transport infrastructure to be removed from the functional floodplain (FZ3b_6.shp). Watercourse Extent Data Source Forge Bank Weir to Sunderland River Lune Flood Zones and ABD River Lune Point Mapping Study (2011) River Lune Upstream of Forge Bank Weir Flood Zone 3 (February 2017 version) A6/A601 road junction to estuary Lune 2 Tributaries Flood Risk Mapping River Keer mouth Study (2007) River Keer Upstream of A6/A601 road junction Flood Zone 3 (February 2017 version) M6 motorway to south of Galgate Lune 2 Tributaries Flood Risk Mapping River Conder village near Lancaster Canal Study (2007) Upstream of M6 River Conder motorway/Southwest of Galgate Flood Zone 3 (February 2017 version) village www.jbaconsulting.com www.jbarisk.com Page 3 of 5 www.jbaenergy.com NOTE TO FILE JBA Project Code 2016s5367 Contract Lancaster City Council