5 Understanding Flood Risk In

Home , Brislington Brook, Cheddar Reservoir, Cheddar Yeo, Chilcompton, Congresbury Yeo, Frome Rural District

5 Understanding flood risk in MDC One of the key purposes of this SFRA is to identify the influential local flood risk issues and to summarise recorded local flood incidents and predicted flood risk to the area. Flood risk can arise from a variety of different sources, as described within this section. Often however, flooding originates from a combination of courses as flood mechanisms are integrated.

5.1 How flood risk is assessed A flood is now formally defined in the Flood and Water Management Act (2010) as “any case where land not normally covered by water becomes covered by water”. The Act also states that a flood, as defined above, can be caused by: • Heavy rainfall • A river overflowing, or its banks being breached • A dam overflowing or being breaches • Tidal waters • Groundwater • Anything else (including a combination of factors) In the context of the FWMA (2010) a flood does not include: • A flood from any part of a sewerage system, unless wholly or partly caused by an increase in the volume of rainwater (including snow and other precipitation) entering or otherwise affecting the system • A flood caused by a burst water main (within the meaning given by section 219 of the Water Industry Act 1991) The FWMA (2010) states that flood risk “means a risk in respect of flood”, where risk is “assessed and expressed (as for insurance and scientific purposes) as combination of the probability of the occurrence with its potential consequences”. Thus, it is possible to define and express flood risk as:

Consequences Flood Flood Receptor Receptor = Probability X Hazard X presence X Vulnerability Risk Magnitude

5.2 Historical flooding Mendip District has a history of documented flood events with the main sources being from fluvial flooding, with surface water flooding also significant. There are small areas of documented reservoir flooding and sewer flooding too. Several different data sources have been used to understand the historic flood risk in Mendip District, including from the previous SFRA, as well as the EA, SCC, Wessex Water and Mendip District flood incident databases. Events from the flood incident databases are outlined in Table 5-1, Table 5-2 and Table 5-3.

5.2.1 Previously reported flood incidents in the Mendip District Level 1 SFRA (2008) Fluvial flooding The areas around Glastonbury and Street were recorded in the 2008 SFRA as being affected the most from fluvial flooding, referring to the EA’s Recorded Flood Outlines

Dataset. Other incidents of fluvial flooding were recorded along the River Frome at Frome, particularly alongside Rodden Road on the right bank. This resulted in the Devon & Somerset Fire and Rescue Service being called out almost 20 times between 2005 and 2008 to help assist with the removal of water from properties. Shepton Mallet is also a location of known flood risk with incidents of flooding of the River Sheppey. Many historic flooding incidents have been recorded at Shepton Mallet, involving 14 Fire & Rescue Service call-outs between 2005-2008. The SFRA also noted that in North Wootton the River Redlake regularly floods following extreme rainfall. This has previously resulted in difficulties in crossing the bridges in Stock Lane and Northtown. Older incidents of historic fluvial flooding have been recorded in the 2008 SFRA under the historic flooding section. These records have been obtained from Parish Councillors, SCC and drainage boards, and combined with the EA Flood Reconnaissance Information System (FRIS). Particularly large events are noted below:

9th-25th August 1954 The event involved an overflowing of the River Brue on the 9th and 13th of August resulting in serious flooding in Butt Moor and areas of Barton Moor. This overflowing also caused the South Drain to overflow below Sharpham Bridge causing flooding in Street Heath, Walton Heath and Sharpham. The flooded areas were not completely free of water until the 25th August.

10th July 1968: During this event, nine properties flooded in and around Mells due to the overflowing of the Mells Stream. The degree of property flooding varied greatly with ceiling to floor flooding affecting some properties. In addition to this, five properties were also flooded in Nunney and an unknown number flooded in Frome.

19th August 2006: Intense rainfall on the 19th August resulted in flooding to Oakhill High Street. Roads received much of the runoff that overwhelmed and blocked highway drainage systems, with several properties suffering internal flooding. EA rain gauge measurements estimate a return period of 1 in 200 years for this event. Other significant historic fluvial events recorded in the 2008 SFRA include the 11th January 2008 and 28th August 1960. Full details of these events can be found in section 3.3 of the MDC Level 1 SFRA (2008).

Groundwater flooding The EA flood incident dataset (FRIS) used in the previous SFRA (2008) identified two locations of ground water flooding; one at Glastonbury and one at King’s Sedgemoor to the north of Henley. No other incidents of groundwater flooding were highlighted during the data collection exercise.

Surface water flooding The SFRA highlighted that there have been several serious floods in Westbury-sub- Mendip recorded, all caused by surface water runoff. Stoke St. Michael Parish has similar surface water flooding problems, with drains regularly blocked.

In addition to this, numerous surface water flooding incidents have been reported in Nunney as far back as 1960, with more recent and frequent events occurring from the early 2000s onwards.

Sewer flooding The previous SFRA (2008) states that the EA flood incident dataset (FRIS) did not contain any records of sewer flooding at the time of writing. Therefore, the primary source of data used to inform historical sewer flooding was supplied by Wessex Water. The majority of historic sewer flooding recorded by Wessex Water was located in Frome, with the information provided only representative of the situation as of November 2007. It was noted in the report that Wessex Water were currently undertaking extensive work to eliminate the majority of foul sewage flooding incidents by 2010, therefore they would expect to see most, or all of the locations removed by 2010.

Reservoir flooding Whilst there is an acknowledgement of the location of reservoirs in and around the MDC area and the level of flood risk posed by reservoirs in the previous Level 1 SFRA, there is no mention of any recorded reservoir flood incidents.

5.2.2 Previous documents and reports describing flood incidents SCC’s website provides a summary of previous flood investigation reports. Reports relevant to the study area include: • Parsonage Lane, The Street, Church Lane, Broadway and Greenditch Close, Chilcompton Flood Investigation Report 2016 • Croscombe, Shepton Mallet Flood Investigation Report 2012 A summary of these are provided below:

Parsonage Lane, The Street, Church Lane, Broadway and Greenditch Close, Chilcompton flooding incident June 2016 During the incident on the 17th June surface run-off water from the catchment area travelled via the B3139 to the lowest point on The Street, Chilcompton. Heavy rainfall was witnessed in the 6 days prior to the event followed by 44.6mm rainfall between 15:00 and 17:00 on the 17th June. The consequential high volumes of surface water run-off from the large catchment, increased the water volume in the River Somer. This resulted in the river overtopping its banks opposite a public footpath known as The Pitching. The large volume of water also overwhelmed the highway drainage system. Probable causes of the flooding were due to exceptional levels of rainfall at almost 10 times greater than the average daily rainfall for June. Existing drainage systems and watercourses were unable to cope with the high volume of water in the short duration of the event. Further actions and investigations were undertaken and a large obstruction in the watercourse was moved. Previous flooding evidence and historical data identifies that the properties suffering internal flooding are in a Flood Zone 3 area. Therefore, these properties have a high probability of flooding identified by the EA’s Flood Map for Planning. This investigation concluded that the highway drainage system had been maintained appropriately and was only a contributory factor. The system was overwhelmed by an increased volume of water outside the highways design capabilities and curtilage. The LLFA’s Civil Contingencies Unit worked with the Parish Council and community to put in place a Flood Action Plan. Inspections of the watercourse showed no areas of

concern related to the ordinary watercourse maintenance. There was however one small section that required the removal of a build-up of stones and debris caused by the flood event. It was found that there may be an opportunity for the LLFA to carry out Property Flood Resilience (PFR) assessments of the properties that suffered internal flooding.

Croscombe, Shepton Mallet flooding incident July 2012 On the 11th July, intense rainfall led to large amounts of surface water runoff from the steep catchment to the south of the village of Croscombe. The runoff flowed down roads and accumulated on Long Street (A371), where it was unable to enter the river. This affected eight properties. Most of this surface water flowed down Old Street Lane and Jack’s Lane. In addition, there were also reports of overflow from foul manholes located close to Townend Bridge. Probable causes of the flooding were the high volumes of surface water runoff from locally intense rainfall, with flooding the most severe experienced in the last 20 years. The steepness of the catchment resulted in the highway drainage either being bypassed or blocked with debris washed down from upstream. SCC are due to undertake an appraisal of alleviation options for mitigating with surface water flood risk in consultation with local stakeholders.

5.2.3 MDC Flood Incidents Database The Mendip District Flood Incidents Database holds all records of flooding known to the council since 1925. The information has been collected from several sources including historic maps, public records and reports from members of the public. Most significant flood incidents outlined in the database are from fluvial flooding, with surface water flood events also frequent. The largest number of concurrent reports recorded for a single flood incident was for a surface water flood event on the 10th July 1968. Incident reports have regularly been recorded for Glastonbury and Shepton Mallet, with both areas affected by surface water and fluvial flooding. A surge in flood incident reports has been seen since 2008.

Table 5-1: Key flood events in the Mendip District based on the council's Flood Incident Database and additional information

Date Number Location of reports Source of flooding of reports 28/10/1960 1 Glastonbury Unknown

01/12/1959 2 Dye House Lane, Glastonbury Fluvial

01/06/1968 1 Pensford and Glenthorne, Great Elm Fluvial

10/07/1968 14 Egford Bridge and Elm Lane, Surface water runoff Nunney, Jeffries Mill

30/05/1979 2 Mells Fluvial

2001 1 Old Nunney Fluvial- Urban drainage overwhelms River Sheppey

19/08/2006 1 A37 between Ashwick and Oakhill Surface Water- Blocked highway drainage

2007 2 Shepton Mallet, High Street Ashwick Surface Water

25/01/2008 2 Stock’s Lane, North Wootton Surface water

11/01/2008 3 Shepton Mallet Fluvial- too much water for balancing ponds Note: Based on data supplied by MDC on 15/07/2019.

5.2.4 SCC Flood Incident Database The SCC’s Flood Incidents Database holds all records of flooding known to the council since 1825. The information has been collected from several sources including historic maps, public records and reports from members of the public. The database shows that most historic flood incidents are from combined fluvial and surface water flooding. There is also a high number of drainage related flooding incidents. Hotspots for flood incident reports include Alhampton, Glastonbury and Nunney.

Table 5-2: Key historic flood events in Mendip District based on SCC’s Flood Incident Database

Date Number Location Type of Source of of Flooding Flooding Reports 09/08/1954 1 Glastonbury Fluvial River Brue

03/08/1965 4 Alhampton, Nunney, Fluvial, River Alham, Prestleigh, Batcombe Surface water Nunney Brook

10/07/1968 19 Batcombe, Buckland Fluvial/surface River Alham, Dinham, Coleford, Buckland Cranmore, Downhead, Brook, Edford, Frome, Kilmersden, River Frome/ Mells, Nunney, Oakhill, Surface Wanstrow, West Pennard, West Woodlands, Wookey, Westbury Sub- Mendip 2000 1 Coxley Fluvial and River Surface Sheppey/ Surface

Date Number Location Type of Source of of Flooding Flooding Reports 28/05/2008 7 Alhampton, Nunney, Wells Surface and River Alham Fluvial and Nunney Brook 13/12/2008 1 Glastonbury Surface Surface

07/08/2012 2 Axbridge, Street Drainage Drainage

21/11/2012 26 Axbridge, Baltonsborough, Surface, Surface, Coxley, Emborough, Frome, drainage unidentified Glastonbury, Hornblotton, stream, River Leigh upon Mendip, North Sheppey Wootton, Norton St Philip, Nunney, Polsham, Rode, Rodney Stoke, Shepton Mallet, Stoke St Michael, Street, Walton, Wanstrow, Wells, West Horrington, West Pennard, Wookey

02/01/2014 6 Alhampton, Frome, Surface water Surface water Glastonbury, Norton St and Drainage Philip, Pilton, Stoke St Michael

5.2.5 EA Recorded Flood Outline dataset The EA Recorded Flood Outline dataset provides details of all recorded flood incidents by the EA from rivers, sea, groundwater and surface water. This data set is provided using aerial photography, data from local authorities, surveys carried out by the EA and consultancies and visual accounts. The dataset provides details of 162 flood incidents dating back to 1894. Data for the study area are shown in Appendix C and are outlined in Table 5-3. It is important to note the few incidents of fluvial flooding attributed to overtopping of defences in 2012 and 2014 as they may be an indication of necessary alterations to existing flood defences. The dataset shows large areas of recorded floods in the southwest of the district, surrounding Glastonbury, Meare and Street, with additional floods recorded following the watercourse of the River Frome between Farleigh and Upton Noble. Smaller areas of recorded floods were also seen along the Mells River and through the town of Shepton Mallet. The recorded flood events were mostly a result of fluvial flooding a few surface water incidents reported for Nunney.

Table 5-3: Key flood events identified in the EA's Recorded Flood Outlines data

Date Location of reports Source of flooding 31/01/1925 Frome Fluvial- Channel Capacity exceeded (no raised defences) 30/12/1955 Glastonbury, Lower Godney, Upper Godney, Fluvial- Channel Capacity exceeded (no raised defences) Meare 27/10/1960 Frome Fluvial- Channel Capacity exceeded (no raised defences)

28/10/1960 Glastonbury, Street, Meare, Butleigh, Lower Fluvial- Channel Capacity exceeded (no raised defences) Godney 04/12/1960 Witham Hall Farm Fluvial- Channel Capacity exceeded (no raised defences) 04/12/1960 Nunney Local drainage- surface water 05/12/1960 Rodden, Wallbridge, Witham Friary, Fluvial- Channel Capacity exceeded (no raised defences) Beckington, Oldford, Farleigh, Hungerford 18/12/1965 Freshford, Witham Friary, Beckington, Oldford Fluvial- Channel Capacity exceeded (no raised defences) 05/11/1966 Waterloo, Frome Fluvial- Channel Capacity exceeded (no raised defences)

11/06/1968 Nunney, Whatley, Wanstrow, Great Elm Fluvial- Channel Capacity exceeded (no raised defences)

10/07/1968 Farleigh, Hungerford, Tellisford Fluvial- Channel Capacity exceeded (no raised defences)

10/07/1968 Witham Friary Fluvial- Channel Capacity exceeded (no raised defences)

11/07/1968 Vobster, Coleford, Great Elm Fluvial- Channel Capacity exceeded (no raised defences)

02/12/1972 Waterloo, Frome Fluvial- Channel Capacity exceeded (no raised defences) 02/12/1972 Nunney Local Drainage- Surface water 30/05/1979 Godney, Southway, Glastonbury, Fluvial- Channel Capacity exceeded (no raised defences) Baltonsborough, Butleigh, frome, Shawford 31/01/1983 Eden Vale, Frome Fluvial- Channel Capacity exceeded (no raised defences) 28/01/1986 Lullington, Frome, Farleigh, Hungerford Fluvial- Channel Capacity exceeded (no raised defences) 13/10/1993 Vobster Local Drainage- surface water 37

Date Location of reports Source of flooding 31/10/1998 Alhampton Fluvial- Channel Capacity exceeded (no raised defences) 04/11/1998 Glastonbury, Street Fluvial- Overtopping of defences 20/10/2006 Shepton Mallet Fluvial- Channel Capacity exceeded (no raised defences)

29/05/2008 Shepton Mallet Fluvial- Channel Capacity exceeded (no raised defences)

13/12/2008 Glastonbury, Baltonsborough, West Pennard Local Drainage- surface water

13/12/2008 Wallbridge, Frome Overtopping of defences

10/02/2010 Wallbridge, Frome, Rodden Mill Fluvial- Channel Capacity exceeded (no raised defences) 26/03/2009 East/West Lydford, Meare Overtopping of defences 09/07/12 Shepton Mallet, Bowlish, Croscombe Local Drainage- surface water

04/11/2012 Croscombe Fluvial- Channel Capacity exceeded (no raised defences)

20/11/2012 King’s Sedge Moor, Southway, Wookey Hole, Overtopping of defences Mudgeley, Upper Godney, Glastonbury, Street, Meare, Edgarley 20/11/2012 Butleigh Fluvial- Channel Capacity exceeded (no raised defences)

20/11/2012 Binegar Other

21/11/12 Lower Godney Fluvial- Channel Capacity exceeded (no raised defences)

24/12/2013 Mells Fluvial- Channel Capacity exceeded (no raised defences)

04/01/2014 Lullington Fluvial- Channel Capacity exceeded (no raised defences) 09/01/2014 Westhay, Mudgeley, Street, Glastonbury, King’s Overtopping of defences Sedge Moor, Southway, Upper Godney, Lower Godney, Glastonbury 06/02/2014 Mells unknown 17/06/2016 Chilcompton Fluvial- Channel Capacity exceeded (no raised defences)

5.2.6 Wessex Water Sewage Incident Report File (SIRF) dataset for Mendip District Historical incidents of flooding are detailed by Wessex Water in their Sewage Incident Report File (SIRF). This database records incidents of flooding relating to public foul, combined or surface water sewers and identifies which properties suffered flooding. The flooding incidents are coded to indicate where investigations into the flooding have been raised, are underway or where schemes have been completed. Wessex Water work in partnership with other risk management authorities to investigate issues where flood risk is apparent from a number of sources. For confidentially reasons, this data has been supplied on a postcode basis. The data from the SIRF is summarised in Table 5-3. The SIRF indicates a total of 148 recorded flood incidents in Wessex. The more frequently flooded postcodes are BA11 (48 incidents), BA6 (34 incidents) and BA4 (26 incidents). It is important to recognise the SIRF does not contain information about properties and areas at risk of sewer flooding caused by operational issues such as blockages. Also, the SIRF represents a snap shot in time and will become be in need of updating with properties being added to the register following rainfall events, whilst risk will be reduced in some locations by capital investment to increase the capacity of the network. As such the SIRF is not a comprehensive ‘at risk register’. Mapping of sewer flood incidents since 2005 is shown in Appendix D. Frome, Glastonbury and Street are areas with the highest density of flood incidents. There have been sewer flooding incidents in Beckington. The data highlights that in Beckington, there is a scheme in appraisal in partnership with SCC and MDC. A number of schemes have been completed across the district, including in Wanstrow, Edford, Shepton Mallet, Butleigh and Frome.

Table 5-4: Wessex Water Recorded flood incidents within Mendip District

Postcode Recorded flood incidents

BA11 48 BA16 8 BA2 1 BA3 15 BA4 26 BA5 15 BA6 34 TA11 1 Total: 148 Note: Based on data supplied on 03/09/2019

5.2.7 Mendip Priority Sub Catchments The SRA funded two projects within Mendip during the year 2019/20. These projects were looking at enhanced maintenance of culverts and watercourses within the district. To enable sites to be prioritised for inspection and review, a detailed review of the catchment data was undertaken using GIS mapping software. The district was divided up into sub-catchments and each sub catchment analysed against various data sets, such as records of flooding and flood risk maps, and prioritised according

to regularity and severity of flooding. The top priority sites were visited first (priority 1 and 2) and the inspection reports were shared with the partners (County Highways, Somerset County Council and Wessex Water) to identify opportunities for collaboration and co-ordination of projects within the same sub-catchment. This will enable multi-agency works to be carried out at one time, provide a more joined up approach to flood resilience work and enable additional opportunities and enhancements to schemes to be realised for each site. Highest priority sub-catchments identified within Mendip district include Frome, Shepton Mallet, Wells and Street. These rankings are now being used to form the basis for ground truthing and investigative surveys. These sub-catchments are mapped in Appendix E.

5.2.8 Summary of historic flood incidents Using the Wessex Water, SCC and Mendip District Flood Incident datasets, a table of counts of incidents per ward has been produced ( Table 5-5). This table also summaries the number of incidents per flood source and shows the importance of sewer flooding and drainage incidents. The number of flood incidents per ward is also displayed in Appendix F.

Table 5-5: Summary of flood incidents per ward for each flooding source using the combined datasets of Mendip Council, SCC and Wessex Water

Ward Total Fluvial Groundwater Sewer Surface Water No Flooding Unknown Ammerdown Ward 43 3 27 13 Ashwick, 42 4 38 Chilcompton and Stratton Ward Beckington and 44 12 28 4 Selwood Ward Butleigh and 43 10 29 4- possible Baltonsborough drainage Ward problems Chewton Mendip 28 27- drainage issues 1 and Ston Easton Ward Coleford and 50 11 39 Holcombe Ward Cranmore, Doulting 34 5 20 9 and Nunney Ward Creech Ward 8 1 5 2- pond flooding Croscombe and 36 18 14 4- following heavy rainfall Pilton Ward Frome Berkley 11 2 8-blocked drain 1 Down Ward Frome College 4 4-blocked drain Ward Frome Keyford 31 20 10 Ward 1 Frome Market Ward 19 5 11 3 Frome Oakfield 4 1 Ward Frome Park Ward 10 2 5 3 Glastonbury St. 19 2 10- drainage 7 Benedict's Ward Glastonbury St. 15 15-drainage Edmund's Ward Glastonbury St. 11 3 8- drainage John's Ward Glastonbury St. 9 9-drainage Mary's Ward Moor Ward 47 23 24-blocked culvert suspected Postlebury Ward 39 9 27- drainage issues 3- surface runoff from hills Rode and Norton 27 1 24- drainage issues 2- flood prevention through balancing St. Philip Ward ponds Rodney and 18 15 1 2

Ward Total Fluvial Groundwater Sewer Surface Water No Flooding Unknown Westbury Ward Shepton East Ward 22 6- flash floods 16 Shepton West Ward 14 6 8- drainage St. Cuthbert Out 17 1 16- drainage North Ward Street North Ward 17 3 14- drainage Street South Ward 12 2 9- drainage issues caused by road resurfacing works Possible surface water flooding exacerbated by drainage issues but not confirmed Street West Ward 1 1 The Pennards and 21 1 20-drainage Ditcheat Ward Wells Central Ward 9 1 8 Wells St. Cuthbert's 8 7 1 Ward Wells St. Thomas' 14 1 11- insufficient drainage Ward Surface runoff made worse by retaining wall Wookey and St. 40 5 34- blocked drains caused 6 inch surface flooding 1 Cuthbert Out West Ward

5.3 Topography, geology and soils The topography, geology and soil are all important in influencing the way the catchment responds to a rainfall event. The degree to which a material allows water to percolate through it, the permeability, affects the extent of overland flow and therefore the amount of run-off reaching the watercourse. Steep slopes or clay rich (low permeability) soils will promote rapid surface runoff, whereas more permeable rock such as limestone and sandstone may result in a more subdued response.

5.3.1 Topography The topography of Mendip District is shown in Appendix G. The Mendip platform rises steeply from the Somerset Levels and Moors to the South and provides a great contrast to the low elevations of the Bristol and Avon Valleys. Black Down in the North West corner of Mendip District is the highest area of land at 325mAOD and the topography of the plateau slopes gently in a south easterly direction towards Shepton Mallet. The land around Shepton Mallet is fairly steep and on the south side drops down to the River Alham. In the north of the district, the land slopes down from the Mendip platform to the River Somer, north of Midsomer Norton. The eastern end of the Mendip Hills merges gradually with the southern end of the Cotswolds and the Yeovil Scarplands. The elevation loss around Priddie and Cheddar Gorge, on the southern boundary of the Mendip Hills is much greater than on the northern edge. The lowest lying area of land is situated around Glastonbury and slopes gently in a westward direction towards Burnham-on-Sea at the Severn Estuary. This analysis has been based on LiDAR (Light Detecting and Ranging) data.

5.3.2 Geology and soils Appendix H and Appendix I show the geology within Mendip District. The areas to the west of the Mendip District are underlain by Dinantian rocks composed of limestone, mudstone, siltstone and sandstone, with Lias on the southern boundary. The east of the district mostly consists of Inferior Oolite, Great Oolite, and Cornbash Clay Valves (composed of varying compositions of limestone, sandstone, siltstone and mudstone), extending up to the Frome floodplains. The areas of high elevation dominated by the Mendip Hills are covered with freely draining, base rich, loamy soils. Shallow, lime-rich soils over limestone dominate at the Mendip Platform edges. Smaller areas of slowly permeable, seasonally wet acid loamy and clayey soils can be found in the Holcombe area. At the north of the Mendip District there are narrow regions of lime-rich loamy and clayey soils with impeded drainage. The soils covering the limestone ridge of the Northern Mendips consist of slightly acid but base rich soils which are freely draining. This area has a low risk of flooding due to the topography of the land and freely draining soils. The lower lying areas of the Somerset levels near to Glastonbury are underlain by the Lias Group composed of varying compositions of mudstone, siltstone, limestone and sandstone. The soils here are mostly loamy and clayey floodplain soils with high groundwater. Nearby areas of the Somerset levels are overlain by fen peat soils and raised bog peat soils. In a low-lying area with a mixture of both impermeable and semi-permeable geology, only a reduced amount of water can penetrate the underlying geology and therefore, there is a higher risk of surface water flooding. The combination of low-lying ground, soils with slightly impeded drainage and a semi-permeable underlying geology can lead to surface water flooding.

The town of Midsomer Norton is situated near the source of the Wellow Brook at the top of the Cam Valley. The soils consist of acid loamy and clayey soils which are slowly permeable with impeded drainage in the higher reaches of the stream.

5.4 Hydrology There are a number of watercourses that flow through the study area. These include main rivers and ordinary watercourses. Appendix J shows the location of Main Rivers and ordinary watercourses in Mendip District. An outline summary of the principal watercourses in the SFRA study area is provided in Table 5-6. Table 5-6: Main watercourses in the study area

Watercourse Classification Description River Sheppey Main river The source of the River Sheppey is in the high land around Shepton Mallet. The Sheppey is a tributary of the River Brue. It runs along the A371 south of Wells to the flat elevations of the Somerset Levels where it merges into the James Wear River. River Brue Main river The source of the River Brue is in the Parish of Brewham (South Somerset), approximately thirty-one miles from where it reaches the Severn Estuary at Burnham-on-Sea. The river enters Mendip District from the south by the A37 at East Lydford and travels in a North-westerly direction through Street towards Meare. River Frome Main river The River Frome is approximately twenty-one miles long, rising in North Brewham (South Somerset) and flowing in a northerly direction to Avoncliff, near Bath where it enters the River Avon as a tributary. The river has many weir structures and therefore water levels are maintained longer than many other local rivers. River Alham Main river The River Alham is formed by springs which rise north of Higher Alham. The River flows for approximately ten miles before joining the

Watercourse Classification Description River Brue. The River Alham is joined by several unnamed tributary streams. The first rises in the hills above Batcome, joining the Alham near Rockwells Farm. At Arthur’s Bridge the Alham is joined by a stream which originates on Easton Hill. River Axe5 Main river The River Axe rises from the ground at Wookey Hole Caves. Water drains from the high elevations of the Mendips forming the source of the river. The river flows west through the village of Wookey before it splits into two channels. The Lower River Axe runs past the south of the village towards Henton and onto Panborough Moor where it joins a series of rhynes and drains. The 2 channels meet again at the boundary between Knowle and Panborough Moors. Mells River Main river Mells River is a tributary of the River Frome, rising on Blacker’s Hill above Benter and Nettlebridge. It flows in an easterly direction through Mells and Vallis Vale where it is joined by the Nunney Brook, joining the River Frome just north of Frome Town. Whitelake Water Main river Whitelake Water rises between 2 limestone ridges on the southern edge of the Mendip Hills. The confluence of two small streams which make up Whitelake Water, are on the site of the Glastonbury Festival on Worthy Farm. Whitelake Water flows west for approximately 6 miles —————————————————————————————————————————————

5 Somerset Rivers (2019): http://www.somersetrivers.co.uk/index.php?module=Content&func=view&pid=46

Watercourse Classification Description until it joins the River Brue at Westhay. Fodbury Water Main river Fodbury Water rises in the Mendip Hills, near Cranmore, where it occupies a narrow valley. It flows in a north-easterly direction for approximately 4 miles until its confluence with Mells River in Great Elm. Egford Brook Main river Egford Brook starts at the head of the Wanstrow valley and travels through the grounds of Nunney Castle. The confluence of Egford Brook with Mells River is at Great Elm. Nunney Brook Main river Nunney Brook is a tributary of the Egford Brook rising in Nunney, adjacent to the south-easterly end of the Mendip Hills. North Drain Main river North Drain flows for approximately 6.5 miles in a westerly direction from Hurn Sluice on the River Sheppey to the North Drain Pumping station at the confluence with the River Brue. The river passes through various moors including Westhay Moor and Aller Moor and is crossed by several droves. White’s River Main river A short river of approximately 0.9 miles. It is an extension of the Division Rhine and is joined by the James Wear River and the Decoy Rhine before flowing into the River Brue. Division Rhine Main river The Division Rhine is a short river most commonly known as White’s River beyond Hartlake Farm on the A39 north of Glastonbury. The Division Rhine turns westerly through Crannel Moor, passing south of Godney where it joins with White’s

Watercourse Classification Description River which flows into the River Brue.6

5.4.1 Main rivers These tend to be larger streams and rivers, though some of them are smaller watercourses of local significance. The EA has permissive powers to carry out maintenance, improvement or construction work on Main Rivers to manage flood risk. Consultation with the EA will be required for any development projects within 20m of a Main River or flood defence.

5.4.2 Ordinary watercourses These are all watercourses not designated as Main Rivers or IDB watercourses. An ordinary watercourse is any river, stream, ditch, drain, dyke etc. which is not classified as a Main River. As LLFA, SCC are required to develop a strategy to tackle local flood risks involving flooding from ordinary watercourses. The local authority or IDB has permissive powers to maintain them, but the responsibility lies with the riparian owner.

5.5 Fluvial flood risk Fluvial flood risk occurs when water levels rise higher than the bank levels within a river channel, causing floodwater to spill onto adjacent land (floodplain). The main reasons for this to occur are: • Intense and long duration rainfall causing runoff and flow to increase in rivers resulting in flows exceeding the capacity of the river channel. This can be further exacerbated by wet antecedent conditions or where there are significant contributions of groundwater • Constrictions within the river channel resulting in flood water backing upstream. • Blockage of structures or within the river channel itself causing flood water to back up upstream. • High water levels and/or flood gates prevention discharge out the outlet of the watercourse. Fluvial flooding is significant within Mendip and is prevalent across most areas of the district. Significant rivers and their tributaries within the district that contribute towards flood risk include but are not limited to the: • River Frome • River Brue • Mells River • River Sheppey Mapping of fluvial flood risk can be found on the EA’s Flood Map for Planning website. Fluvial flood risk within the study area has been mapped in Appendix B.

5.6 Surface water flood risk Surface water runoff occurs when rainfall fails to infiltrate to the ground or enter the drainage system, causing water to pond or flow over the ground surface. The likelihood of flooding is dependent on the rate of runoff and the condition of the surface water drainage system. ————————————————————————————————————————————— 6 Somerset Rivers (2019): http://www.somersetrivers.co.uk/index.php?module=Content&func=view&pid=46

The Risk of Flooding from Surface Water (RoFSW) dataset shows that surface water predominately follows topographical flow paths of existing watercourses or dry valleys with some isolated ponding in low lying areas. Areas at risk from surface water flooding within MDC is shown in Appendix A. Mendip District has a relatively high risk of surface water flooding. Naturally, the area affected by risk of surface water flooding increases with return period. The area most at risk of surface water flooding occurs to the South-West of the district, located around Street and Glastonbury and the lower elevations of the Mendip District. The east of the district, in the vicinity of the River Frome and its tributaries, are also shown to be at risk of surface water flooding. The higher elevations of the Mendip Hills are at lower risk of surface water flooding. The Mendip plateau traverses the district in a diagonal. There is a lower risk of surface water flooding on the higher areas of the plateau surrounding Westbury-sub-Mendip, however there is still a risk of surface water flooding along topographic flow paths, and there are small areas of ponding.

5.7 Groundwater flood risk Groundwater flooding is the term used to describe flooding caused by unusually high groundwater levels. It occurs as excess water emerging at the ground surface or within manmade underground structures such as basements. Groundwater flooding tends to be more persistent than surface water flooding, in some cases lasting for weeks or months, and it can result in significant damage to property. In comparison to fluvial flooding, current understanding of the risks posed by groundwater flooding is limited and mapping of flood risk from groundwater sources is in its infancy. Under the Flood and Water Management Act (2010), LLFAs have powers to undertake risk management functions in relation to groundwater flood risk. Groundwater level monitoring records are available for areas on Major Aquifers. However, for lower lying valley areas, which can be susceptible to groundwater flooding caused by a high groundwater levels in mudstones, clays and superficial alluvial deposits, very few records are available. Additionally, there is increased risk of groundwater flooding where long reaches of watercourse are culverted as a result of elevated groundwater levels not being able to naturally pass into watercourses and be conveyed to less susceptible areas. As part of the SFRA deliverables, mapping of Mendip District has been provided and shows the susceptibility to groundwater flooding provided by the BGS dataset. Details of the dataset are provided in Section 4.4. This information is provided in Appendix K. The BGS dataset shows that most of the study area has a limited potential for groundwater flooding to occur and also contains large areas which are not considered to be prone to groundwater flooding. The potential for groundwater flooding to occur at the surface is generally restricted to valleys and low-lying areas with permeable geology.

5.8 Tidal flood risk Flooding from the sea occurs when water levels in the sea rise above ground levels of the coast. This can occur during normal tides, extreme atmospheric events and wind driven action causes water levels of the sea to rise. Mendip District is land locked and the assessment performed for the previous Level 1 SFRA for MDC (2008) found that there is no tidal flood risk to Mendip District. The only tidal river that flows into Mendip District is the River Brue. However, the tidal limit of the river is at Highbridge, which is located in Sedgemoor District. Tidal flooding should however be considered for present and the future due to predicted increases in sea level. The greatest concern rises from the potential threat of a combined tidal and extreme fluvial event. The probability of this occurring is significantly less than both

events occurring independently. Developers should therefore consider tidal flood risk when making land use planning decisions in respect to the design life of developments.

5.9 Artificial sources

5.9.1 Flooding from canals Canals may pose a flood risk if they overtop or breach, but impacts will depend on the topography. There are no canals which run through the study area and therefore there is no flood risk from canals to the study area.

5.9.2 Flooding from reservoirs Reservoirs with an impounded volume greater than 25,000 cubic metres are governed by the Reservoir Act 1975 and are listed on a register held by the EA. The level and standard of inspection and maintenance required under the Act means that the risk of flooding from reservoirs is relatively low. Recent changes to legislation under the Flood and Water Management Act require the EA to designate the risk of flooding from these reservoirs. The EA is currently progressing a ‘Risk Designation’ process so that the risk is formally determined. Reservoir flooding is very different from other forms of flooding. It may happen with little or no warning and evacuation will need to happen immediately. The likelihood of such flooding is difficult to estimate, but it is less likely than flooding from rivers or surface water. It may not be possible to seek refuge upstairs from floodwater as buildings could be unsafe or unstable due to the force of water from the reservoir breach or failure. The EA maps represent a credible worst-case scenario. In these circumstances, it is the time to inundation, the depth of inundation, the duration of flooding and the velocity of flood flows that will be most influential. The risk to development from reservoirs is residual but developers should consider reservoir flooding during the planning stage. • Developers should seek to contact the reservoir owner to obtain information which may include: • reservoir characteristics: type, dam height at outlet, area/volume, overflow location; • operation: discharge rates / maximum discharge; • discharge during emergency drawdown; and • inspection / maintenance regime. • Developers should apply the sequential approach to locating development within the site. The following questions should be considered: • can risk be avoided through substituting less vulnerable uses or by amending the site lay-out? • can it be demonstrated that less vulnerable uses for the site have been considered and reasonably discounted? and • can layout be varied to reduce the number of people or flood risk vulnerability or building units located in higher risk parts of the site? • Consult with relevant authorities regarding emergency plans in case of reservoir breach • In addition to the risk of inundation those considering development in areas affected by breach events should also assess the potential hydraulic forces imposed

by the rapid flood event and check that the proposed infrastructure fabric can withstand the loads imposed on the structures by a breach event. The EA Reservoir Flood Outline (Extent) layer was used to assess risk of flooding from reservoirs to Mendip District. There are 5 reservoirs located within the Mendip District boundary and the district is also at risk of flooding from reservoirs located just outside the district boundary. The largest area of the district with modelled reservoir flooding occurs in Frome and follows the course of the River Frome from Farleigh and Hungerford in the north-east of the district to Tytherington and also in a westerly direction through Mells. This flooding is from the Marston Pond and Mells Park Upper Lake Reservoirs. A significant area impacted by reservoir flooding is located at the north-west of Mendip District in the area surrounding Rodney Stoke and Cocklake. The areas affected are predominately rural, but the modelled flooding could affect road networks and residential properties. This flooding originates from the Cheddar reservoir located approximately 2.5 miles from the north-west district boundary. Another area of modelled reservoir flooding is located to the south of the district in the area surrounding Lydford and Butleigh from flooding of the Bruton Dam Flood Storage Reservoir in South Somerset (this has a design standard of protection up to the 1 in 100 year event). The areas affected here are more urban in nature. A final area of potential maximum reservoir flooding within the district occurs in a small area to the north of Litton. The modelled flooding is located within close proximity of the B3111.

5.9.3 Flooding from sewers Sewers are the underground network of pipes which remove waste-water from properties. They are categorised by the type of waste-water they remove. The categories include: • Foul sewer • Surface Water sewer • Combined sewer • Treated effluent Foul sewers and treated effluent both convey waste-water. Surface water sewers convey collected surface runoff and combined sewers convey a mixture of both foul water and surface water. Rainwater frequently drains into surface water sewers or sewers both containing surface and waste-water – these are known as combined sewers. These sewers can become overwhelmed during storm events and become blocked or are not designed to have adequate capacity, resulting in flooding of the surrounding area until the water can be drained away. This is a particular issue for combined sewers because it runs the high risk of contaminated water flooding a property internally. Wessex Water is responsible for the Public sewer networks in this area. Wessex Water are represented on MDC Strategic Flood Board and work in partnership with other risk management authorities to investigate issues where flood risk is apparent from a number of sources. Any allocated or new development will need to address the impact on the existing capacity of the sewer system, any associated sewage treatment works and ensure close liaison with Wessex Water to agree the phasing of improvement works. Surface water strategy must follow the Sustainable Drainage Systems (SuDS) hierarchy. Wessex Water pursue a policy of reducing surface water flows to combined sewers and preventing surface water connections to sewers designed for foul flows only. Wessex Water has provided a list of sewer flooding incidents for the MD area for the last 12 years. These records include sewer flooding attributable to surface water.

Wessex Water provided the postcode locations for 148 occurrences of sewer flooding (Table 5-4).

5.10 Summary of flood risk by location A high-level review of the flood risk to five different settlements has been undertaken. These were agreed on in consultation with MDC and are Frome, Glastonbury, Shepton Mallet, Street and Wells. Table 5-7 summaries the flood risk to the five settlements. The summary review draws on mapping and risk information in the SFRA and reference should be made to the previous sections in this chapter for interpretation of the comments with respect to the uncertainty and assumptions associated with the mapping.

Table 5-7: Summary of flood risk to key settlements in the district

1 - Frome

Flood risk summary Frome has several recorded flood incidents evidenced in the EA’s Recorded Flood Outline and MDC’s historic flooding database. Many of these are located close to the River Frome. The SCC database has Flood history several recorded incidents of surface water flooding in the early 2000s. There are also records of incidents of fluvial flooding from the Mells Stream and Rodden Brook.

1 - Frome

Frome is at risk of flooding from the River Frome and Fluvial flood risk from the Mells Stream. There are properties at risk of flooding in the vicinity of the River Frome.

Tidal flood risk There is no tidal flood risk in this area. Frome is at risk of surface water flooding. The town is at risk from even low return period flooding along roads and topographic flow routes towards the River Frome. Surface water flood risk Many properties are affected particularly in the 0.1% AEP event. The greatest risk is found adjacent to the River Frome. Isolated ponding occurs in open spaces and gardens. Large areas of Frome are not considered to be prone to groundwater flooding according to the BGS dataset. However, a small linear area that crosses through the Groundwater flood risk centre of Frome has potential for groundwater flooding to occur at the surface. To the north of the town there are small areas with limited potential for groundwater flooding to occur. Frome is affected by sewer flooding and has twenty- Other sources of flood risk nine recorded historic sewer flooding incidents. Strategic flood risk considerations

Development should preferably be located outside of areas shown to be at current or future risk of flooding where possible. If there is a need to locate development in areas at risk, it is likely that a Level 2 SFRA study will be required to provide evidence for the Exception Test for development that could be affected by flood risk.

Potential for use of Sustainable Drainage Systems

In areas that are at risk of flooding from surface water, development could provide opportunity to reduce this risk through reduction in impermeable surfaces and use of SuDS. The settlement is not located within a Groundwater Source Protection Zone and no EA designated historic landfill lie within the boundary of the town.

2 – Shepton Mallet

Flood risk summary

Shepton Mallet has many recorded flood events as seen in the EA Recorded Flood Outline dataset. These incidents are confined to the River Sheppey. There are also many records of historic flooding outlined in the Mendip district Flooding Incident Flood history database. Whilst 5 of these lie along the River Sheppey, there are incidents of flooding in areas of the town away from the river. The SCC database confirms the severity of fluvial flooding from the River Sheppey with eight incidents arising from fluvial flooding.

Shepton Mallet is at risk of fluvial flooding from the River Sheppey. Small areas of the town sit within the EA’s Flood Zone 3, mainly parts of the Wells Road Fluvial flood risk and Town Lane. Both of these flood zones follow the River Sheppey and do not extend into the centre of town, with the exception of land to the South of Charlton Road.

Tidal flood risk There is no tidal flood risk in this area.

2 – Shepton Mallet

Shepton Mallet is at risk from surface water flooding. Most of the town is affected by 0.1% AEP event, yet there are still large areas of the road system that Surface water flood risk flood in the lower return periods, mostly the 1% AEP event. Small areas of surface water flooding from 3.3% AEP event can be seen in West Shepton and the fields to the south of Charlton Road.

Shepton Mallet has an almost entirely limited potential for groundwater flooding to occur, with Groundwater flood risk exception to small areas along the Wells Road (A371).

Sewer flooding does pose a risk to Shepton Mallet and there have been 4 historic incidents of sewer Other sources of flood risk flooding, all of which have involved external flooding to sewer assets. Shepton Mallet has no risk from reservoir flooding. Strategic flood risk considerations

Potential for use of Sustainable Drainage Systems In areas that are at risk of flooding from surface water, development could provide opportunity to reduce this risk through reduction in impermeable surfaces and use of SuDS. The settlement is partially located within a Groundwater Source Protection Zone to the east of Shepton Mallet. No Groundwater Source Protection Zones exists within the main urban area of Shepton Mallet. There is a historic landfill site in the outskirts of Shepton Mallet in Charlton. Source control techniques are likely to be suitable for the west area of the town.

3 – Glastonbury

Flood risk summary

There are large areas to the north, west and south of the town which are covered by the EA recorded flood outline but there are no recorded flood incidents affecting the urban area of Glastonbury. There are however 7 recorded historic flood incidents Flood history in Glastonbury according to MDC’s flood incident database. The SCC database has eighteen recorded flood incidents in Glastonbury. Most of these are surface water flooding events except for several fluvial flooding incidents from the River Brue and the nearby Rhynes.

No part of the urban area of Glastonbury lies within Flood Zone 3 with exception to a small area surrounding Beckery and to the East of the A39. Fluvial flood risk Glastonbury is at risk from the Mill Stream and the River Brue, as well as small branches of the Rhyne such as the Division Rhyne.

Tidal flood risk Tidal flood risk is negligible in Glastonbury.

3 – Glastonbury Glastonbury is mostly at risk of surface water flooding from 0.1% AEP Events, with small areas at risk from 1% AEP events. Very small areas of Surface water flood risk Glastonbury, particularly those around Beckery are at risk from surface water flooding from 3.3% AEP events.

The majority of Glastonbury has limited potential for groundwater flooding to occur with exception to the south-eastern boundary of the town close to Groundwater flood risk Glastonbury Tor where there is the potential for groundwater flooding of property situated below ground level.

The wider Glastonbury area has 5 recorded incidents of sewer flooding, of which 4 involved external Other sources of flood risk flooding of the asset. Glastonbury is not at risk from reservoir flooding.

Strategic flood risk considerations

Development should preferably be located outside of areas shown to be at current or future risk of flooding where possible. If there is a need to locate development in areas at risk it is likely that a Level 2 SFRA study will be required to provide evidence for the Exception Test for development that could be affected by flood risk.

Potential for use of Sustainable Drainage Systems In areas that are at risk of flooding from surface water, development could provide opportunity to reduce this risk through reduction in impermeable surfaces and use of SuDS. The settlement is not located within a Groundwater Source Protection Zone. However, there is an EA designated historic landfill site which underlies the area between the A39 and Dyehouse Lane. It must be noted that this site is small and is located outside of the main urban area of Glastonbury. Source control techniques therefore could be suitable for this site.

4 – Street

Flood risk summary Very few areas of Street are covered by the EA Recorded Flood outline. MDC’s database shows there are few recorded historical flood incidents in Street. The Mendip Council record details a surface Flood history water flood caused by torrential rain on 01/01/2008 at the junction of Oriel Road and Merriman Road. The SCC’s database indicates a large number of historic surface water flooding incidents in Street.

Street has a small fluvial flood risk from the Rhynes situated to the north of the settlement. There is a Fluvial flood risk small area of the town close to Portway which is in EA Flood Zone 3. The rest of the town is not located in Flood Zone 2 or 3.

There is a negligible tidal risk to the settlement of Tidal flood risk Street. Street has several small areas at risk from surface water flooding from a 3.3% AEP event. A large concentration of these areas lie along the A39 as it Surface water flood risk passes by Street. Many of the residential roads in Street are also affected by 1% AEP events and so Street can be classified as at ‘medium to high risk’ or surface water flooding.

4 – Street The entire urban area of Street has limited potential for groundwater flooding to occur. More rural areas Groundwater flood risk to the north of the town, between Glastonbury and Street have the potential for groundwater flooding to occur at the surface. Street is not at risk from Reservoir flooding but does have flood risk from sewer flooding. Wessex Water Other sources of flood risk have recorded 4 sewer flooding incidents in their historic database 75% of which involved external flooding of assets. Strategic flood risk considerations Development should preferably be located outside of areas shown to be at current or future risk of flooding where possible. If there is a need to locate development in areas at risk it is likely that a Level 2 SFRA study will be required to provide evidence for the Exception Test for development that could be affected by flood risk. Potential for use of Sustainable Drainage Systems

In areas that are at risk of flooding from surface water, development could provide opportunity to reduce this risk through reduction in impermeable surfaces and use of SuDS. The settlement is not located within a Groundwater Source Protection Zone and there are only two very small EA designated historic landfill sites in the southern outskirts of Street. Source control techniques are likely to be suitable for this site.

5 – Wells

Flood risk summary There are no historic incidents recorded for Wells within the MDC’s historic flood database or the EA Recorded Flood Outline. However, there are sixty- nine incidents recorded within the SCC’s database. Almost all of these incidents are from fluvial and Flood history surface water flooding with significant events and flooding to properties recorded on the 28/05/2008 and on 09/02/2009. Repeated surface water incidents have been recorded on St Cuthberts Street on 1999, 2002, 2007, 2008 and 2011. Wells has a fluvial flood risk from the St Andrew’s Stream and Keward Brook. Historical records show regular flooding to the town from St Andrew’s Fluvial flood risk stream. Large areas of the town including those in St Andrew and south of the A39 are in Flood Zone 3. The centre of the urban area of Wells is mostly in Flood Zone 2.

Tidal flood risk Tidal risk to Wells is considered to be negligible.

5 – Wells Areas close to St Andrew’s Stream in St Andrew have a 3.3% AEP risk of surface water flooding. Smaller Surface water flood risk more linear zones on impermeable areas in Wells are at risk from 1% AEP events. Most of the immediate Wells area is not considered prone to groundwater flooding based on the data used. Groundwater flood risk The outskirts of the town however, near to South Horrington and Wookey Hole do have potential for groundwater flooding of property situated below ground. Wells has relatively low risk of flooding from sewers with 3 recorded historic flooding incidents detailed in Other sources of flood risk the Wessex Water register. Wells has no risk from reservoir flooding. Strategic flood risk considerations

Development should preferably be located outside of areas shown to be at current or future risk of flooding where possible. If there is a need to locate development in areas at risk it is likely that a Level 2 SFRA study will be required to provide evidence for the Exception Test for development that could be affected by flood risk.

Potential for use of Sustainable Drainage Systems In areas that are at risk of flooding from surface water, development could provide opportunity to reduce this risk through reduction in impermeable surfaces and use of SuDS. The settlement is not located within a Groundwater Source Protection Zone and no EA designated historic landfill sites are underlying the site. Source control techniques are likely to be suitable for this site.

6 Flood warning and emergency planning

6.1 Emergency planning Emergency planning is an option to help manage flood related incidents. From a flood risk perspective, emergency planning can be broadly split into three phases: before, during and after a flood. The measures involve developing and maintaining arrangements to reduce, control or mitigate the impact and consequences of flooding and to improve the ability of people and property to absorb, respond to and recover from flooding.

6.2 NPPF In development planning, a number of emergency planning activities are already integrated in national building control and planning policies, for example the NPPF Flood Risk Vulnerability and Flood Zone ‘Compatibility’ table seeks to avoid inappropriate development in areas at risk from all sources of flooding. However; safety is a key consideration for any new development and includes residual risk of flooding, the availability of adequate flood warning systems for the development, safe access and egress routes and evacuation procedures. The NPPF Planning Practice Guidance outlines how developers can ensure safe access and egress to and from development to demonstrate that development satisfies the second part of the Exception Test. As part of an FRA, the developer should review the acceptability of the proposed access in consultation with MDC (where appropriate) and the EA. There are circumstances where a flood warning and evacuation plan7 is required and / or advised: • It is a requirement under the NPPF that a flood warning and evacuation plan is prepared for sites at risk of flooding used for holiday or short-let caravans and camping and are important at any site that has transient occupants (e.g. hostels and hotels) and for essential ancillary sleeping or residential accommodation for staff required by uses in this category [water-compatible development], subject to a specific warning and evacuation plan. • The EA and DEFRAs standing advice for undertaking flood risk assessments for planning applications states that details of emergency escape plans will be required for any parts of the building that are below the estimate flood level. It is recommended that Emergency Planners at MDC (where appropriate) are consulted prior to the production of any emergency flood plan. In addition to the flood warning and evacuation plan considerations listed in the NPPF / PPG, it is advisable that developers also acknowledge the following: • How to manage the consequences of events that are un-foreseen or for which no warnings can be provided e.g. managing the residual risk of a breach. • Proposed new development that places additional burden on the existing response capacity of the Councils will not normally be considered to be appropriate. • Developers should encourage those owning or occupying developments, where flood warnings can be provided, to sign up to receive them. This applies even if the development is defended to a high standard. • The vulnerability of site occupants.

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7 Flood warning and evacuation plans may also be referred to as an emergency flood plan or flood response plan.

• Situations may arise where occupants cannot be evacuated (e.g. prisons) or where it is safer to remain “in-situ” and / or move to a higher floor or safe refuge area (e.g. at risk of a breach). These allocations should be assessed against the outputs of the SFRA and where applicable, a site-specific Flood Risk Assessment to help develop emergency plans. Further emergency planning information links: • 2004 Civil Contingencies Act • DEFRA (2014) National Flood Emergency Framework for England • How to register with the EA’s Flood Warnings Direct service • National Flood Forum • GOV.UK Make a Flood Plan guidance and templates

6.3 Flood warnings Flood warnings can be established for particular locations and, along with evacuation plans, can inform emergency flood plans or flood response plans. The EA is the lead organisation for providing warnings of fluvial flooding (for watercourses classed as Main Rivers) and coastal flooding in England. Flood Warnings are supplied via the Flood Line Warnings Directive (FWD) service, to homes and business within Flood Zones 2 and 3. The different levels of warning are shown in Table 6-1.

Table 6-1: EA Warnings explained

Flood Warning What it means What to do Symbol Flood Alerts are used to warn • Be prepared to act on your people of the possibility of flood plan flooding and encourage them • Prepare a flood kit of essential to be alert, stay vigilant and items make early preparations. It is • Monitor local water levels and issued earlier than a flood the flood forecast on the EA warning, to give customers website advance notice of the • Stay tuned to local radio or TV possibility of flooding, but • Alert your neighbours before there is full confidence • Check pets and livestock that flooding in Flood Warning • Reconsider travel plans Areas is expected. • Move family, pets and valuables to a safe place • Turn off gas, electricity and Flood Warnings warn people of water supplies if safe to do so expected flooding and • Seal up ventilation system if encourage them to take action safe to do so to protect themselves and • Put flood protection equipment their property. in place • Be ready should you need to

evacuate from your home • ‘Go In, Stay In, Tune In’

Flood Warning What it means What to do Symbol

• Stay in a safe place with a Severe Flood Warnings warn means of escape people of expected severe • Co-operate with the emergency flooding where there is a services and local authorities significant threat to life. • Call 999 if you are in immediate danger

Informs people that river or sea conditions begin to return • Be careful. Flood water may to normal and no further still be around for several days

flooding is expected in the • If you've been flooded, ring Warnings no area. People should remain your insurance company as longer in force careful as flood water may still soon as possible be around for several days.

It is the responsibility of individuals to sign-up to this service to receive the flood warnings via FWD. Registration and the service is free and publicly available. It is recommended that any household considered at risk of flooding signs-up. Developers should also encourage those owning or occupying developments, where flood warnings can be provided, to sign up to receive them. This applies even if the development is defended to a high standard. There are currently 11 Flood Warning Areas (FWA) and 8 Flood Alert Areas (FAAs) in Mendip District. The locations of these are displayed in Appendix L. A list of the FWA is shown in Table 6-2 and a list of FAAs is shown in Table 6-3.

Table 6-2: Flood Warning Areas within Mendip District

Flood Warning Code Flood Warning Name Description Watercourse

River Brue (upper) from 112FWFBRU10A Gants Mill, Cole, Ansford Bridge and Alford River Brue Bruton Dam to Lovington

Somerset coast at Burnham- West Huntspill, Highbridge, Burnham-on-Sea and 112FWTBUR03 on-Sea, Huntspill, Highbridge Berrow to the west to Mark in the east including East Bristol Channel and Berrow Huntspill, Edithmead, East Brent and Rooksbridge

River Mells including Edford, Ham Bridge, Coleford, River Mells and Whatley 112FWFMEL10A Lower Vobster, Mells, Great Elm and Spring Gardens River Mells Brook and the Whatley Brook

112FWFNUN10A Nunney Brook Nunney Brook including Wanstrow, Holwell, Nunney and Egford and the Sharpshaw Watercourse Nunney Brook Shepton Mallet to Lower Godney including Garston Street, Leg Square, Lower Lane, Longbridge and 112FWFSHE10A River Sheppey Draycott Road in Shepton Mallet and properties in River Sheppey Bowlish, Darshill, Croscombe, Dulcote, Coxley, Fenny Castle, Wookey, Upper Godney and Lower Godney River Brue and Glastonbury Tootle Bridge, Catsham, Church Moor at Millstream from Lovington to 112FWFBRU30A Baltonsborough, Street Drove, the B3151 Glastonbury River Brue Highbridge, low lying to Meare road, Westhay Bridge and Tadham Moor properties Spring Gardens to Freshford including Oldford, Somerset Frome from Frome 112FWFSFR30A Lullington Weir, Shawford, Rode, Farleigh Hungerford, River Frome to Freshford Iford Bridge and Friary Willow Vale, King Street, Saxonvale, Market Place, The 112FWFSFR20A Somerset Frome at Frome Bridge, Bridge Street, Westway, Scott Road, Justice Somerset Frome Lane, Welshmill Road and Welshmill Lane East Lydford, West Lydford, Tuckers Lane at 112FWFBRU30B River Brue and Glastonbury River Brue Baltonsborough, Street Drove, the A39 between Street Millstream from Lovington to and Glastonbury, Cradle Bridge, Glastonbury Heath and Glastonbury Highbridge Street Heath Millstream Witham Friary to Wallbridge including Harris Close, Somerset Frome from 112FWFSFR10A Tucker Close, Waters Edge, River Walk, Ellworthy Court Somerset Frome Witham Friary to Frome and the A362 at Wallbridge

Tidal River Parrett at Bridgwater to Langport to the south including Stathe, Bristol Channel 112FWTBRI03 Bridgwater, Moorland, Burrowbridge, Athelney, Moorland, Middlezoy and Burrowbridge and Stathe Westonzoyland River Parett

Table 6-3: Flood Alert Areas within Mendip District

Flood Alert Code Flood Alert Name Description Watercourse Rivers in North Somerset including Congresbury Yeo, Cheddar Yeo, 112WAFTNSA North Somerset Area Congresbury Yeo, Cheddar Yeo, Axe River Axe, River Banwell and tributaries River Yeo from Yeovil to Langport, the River Parrett from Langport to River Yeo and River Parrett, Lower River Parrett, River Yeo, River Cary, 112WAFRYP Bridgwater, the Rivers Cary and Reaches River Sowy, Kings Sedgemoor Drain Sowy, the Kings Sedgemoor Drain and their tributaries River Biss and tributaries between 112WAFTRBC River Biss catchment River Biss Westbury and Trowbridge

Midford Brook catchment River Cam, Wellow and Midford River Cam, Wellow Brook, Midford 112WAFTMBC Brooks and tributaries Brook

Boscombe, Cholderton, Collingbourne Ducis, Hanging Langford, Hindon, Hurdcott, Groundwater flooding in the Idmiston, Newton Tony, Orcheston, 111FAGSPGW Groundwater Salisbury Plain area Porton, Salisbury, Shipton Bellinger, Shrewton, Stratford Sub Castle, Tidworth, Tilshead, Tisbury, Wilton, Winterbourne Stoke and Woodford Mid River Avon and tributaries 112WAFTMBA Mid Bristol Avon Area including Melksham and Bradford on Bristol River Avon Avon

Somerset coast at Minehead, Coastal and tidal areas at Minehead, Bridgwater, Burnham-on-Sea and Combwich, Bridgwater, Burnham-on- 112WATSOM3 Uphill to Kingston Seymour Sea, Uphill, Weston-super-Mare, Bristol Channel Kewstoke, Sand Bay and Kingston Seymour

Upper Stour and tributaries Tributaries between Gillingham and River Stour, River Lodden, River 111WAFSTOU Sturminster Newton Shreen

111WAFWYLE River Wylye and tributaries Tributaries between Norton Ferris Wylye and Wilton

Lower River Avon, River Boyd, By 112WAFTLBA Lower Bristol Avon Area Bristol River Avon, River Boyd, By and Brislington Brooks and Brook, Brislington Brook tributaries River Chew from Chew Stoke to 112WAFTRCC River Chew, Chew Stoke Stream, River Chew Catchment Keynsham, Chew Stoke Stream Winford Brook and Winford Brook Rivers Brue, Sheppey, River Brue, River Sheppey, North 112WAFTESR East Somerset Rivers Glastonbury Millstream and North Drain, South Drain and South Drains River Frome and Mells, and the Somerset Frome Area Somerset Frome, River Mells, 112WAFTSFA Whatley and Nunney Brooks and Whatley Brook, Nunney Brook tributaries

6.4 Local arrangements for managing flood risk The Mendip Council’s website provides advice on reporting flooding, flood alerts, health advice and advice for protecting property during a flood event. SCC website also provides advice on planning, flooding and drainage. Members of the public can report property flooding using the FORT(SWIM) tool.

6.5 Emergency planning and development

6.5.1 NPPF The NPPF Flood Risk Vulnerability and Flood Zone ‘Compatibility’ table seeks to avoid inappropriate development in areas at risk from all sources of flooding. It is essential that any development which will be required to remain operational during a flood event is located in the lowest flood risk zones so that, in an emergency, operations are not impacted on by flood water or that such infrastructure is resistant to the effects of flooding such that it remains serviceable/operational during ‘upper end’ events, as defined in the EA’s Climate Change allowances (February 2016). For example, the NPPF classifies police, ambulance and fire stations and command centres that are required to be operational during flooding as Highly Vulnerable development, which is not permitted in Flood Zones 3a and 3b and only permitted in Flood Zone 2 providing the Exception Test is passed. Essential infrastructure located in Flood Zone 3a or 3b must be operational during a flood event to assist in the emergency evacuation process. All flood sources such as fluvial, surface, groundwater, sewers and artificial sources (such as canals and reservoirs) should be considered. In particular sites should be considered in relation to the areas of drainage critical problems highlighted in the SWMP. The outputs of this SFRA should be compared and reviewed against any emergency plans and continuity arrangements. This includes the nominated rest and reception centres (and perspective ones), so that evacuees are outside of the high-risk Flood Zones and will be safe during a flood event.

6.5.2 Safe access and egress The NPPF Planning Practice Guidance outlines how developers can secure safe access and egress to and from development in order to demonstrate that development satisfies the second part of the Exception Test. Access considerations should include the voluntary and free movement of people during a ‘design flood’ as well as for the potential of evacuation before a more extreme flood. The access and egress must be functional for changing circumstances over the lifetime of the development. The NPPF Planning Practice Guidance sets out that: • Access routes should allow occupants to safely access and exit their dwellings in design flood conditions. In addition, vehicular access for emergency services to safely reach development in design flood conditions is normally required; and • Where possible, safe access routes should be located above design flood levels and avoid flow paths including those caused by exceedance and blockage. Where this is unavoidable, limited depths of flooding may be acceptable providing the proposed access is designed with appropriate signage etc. to make it safe. The acceptable flood depth for safe access will vary as this will be dependent on flood velocities and risk of debris in the flood water. Even low levels of flooding can pose a risk to people in situ (because of, for example, the presence of unseen hazards and contaminants in floodwater, or the risk that people remaining may require medical attention).

The depth, velocity and hazard mapping from hydraulic modelling should help inform the provision of safe access and egress routes. As part of an FRA, the developer should review the acceptability of the proposed access in consultation with MDC and the EA. Site and plot specific velocity and depth of flows should be assessed against standard hazard criteria to ensure safe access and egress can be achieved. The EA and Association of Directors of Environment, Economy, Planning and Transport (ADEPT) have produced some joint guidance on Flood Risk Emergency Plans for New Development.

6.5.3 Potential evacuations During flood incidents, evacuation may be considered necessary. The NPPF Planning Guidance states practicality of safe evacuation from an area will depend on8. 1. the type of flood risk present, and the extent to which advance warning can be given in a flood event; 2. the number of people that would require evacuation from the area potentially at risk; 3. the adequacy of both evacuation routes and identified places that people could be evacuated to (and taking into account the length of time that the evacuation may need to last); and 4. sufficiently detailed and up to date evacuation plans being in place for the locality that address these and related issues. The vulnerability of the occupants is also a key consideration. The NPPF and application of the Sequential Test aims to avoid inappropriate development in flood risk areas. However, developments may contain proposals for mixed use on the same site. In this instance, the NPPF Planning Practice Guidance states that layouts should be designed so that the most vulnerable uses are restricted to higher ground at lower risk of flooding, with development which has a lower vulnerability (parking, open space etc.) in the highest risk areas, unless there are overriding reasons to prefer a different location9. Where the overriding reasons cannot be avoided, safe and practical evacuation routes must be identified. The EA and DEFRA provide standing advice for undertaking FRAs for planning applications. Please refer to the government website for the criteria on when to following the standing advice. Under these criteria, details must be provided of emergency escape plans for parts of the building that are below the estimated flood level. The plans should show: • single storey buildings or ground floors that do not have access to higher floors can access a space above the estimated flood level, e.g. higher ground nearby; • basement rooms have clear internal access to an upper level, e.g. a staircase; and • occupants can leave the building if there is a flood and there is enough time for them to leave after flood warnings10. Situations may arise where occupants cannot be evacuated (e.g. prisons) or where it is safer to remain “in-situ” and / or move to a higher floor or safe refuge area (e.g. developments located immediately behind a defence and at risk of a breach). These allocations should be assessed against the outputs of the SFRA and where appropriate, a site-specific Flood Risk Assessment to help develop appropriate emergency plans. —————————————————————————————————————————————

8 NPPF Planning Practice Guidance: Flood Risk and Coastal Change (paragraph 057, Reference ID: 7-057-20140306) March 2014 9 NPPF Planning Practice Guidance, Flood Risk and Coastal Change (Paragraph: 053 Reference ID: 7-053-20140306) March 2015 10 EA and DEFRA (2012) Flood Risk Assessment: Standing Advice

6.5.4 Flood warning and evacuation plans Flood warning and evacuation plans are potentially mitigation measures to manage the residual risk, as stated in the NPPF Planning Practice Guidance. A flood warning and evacuation plan should detail arrangements for site occupants on what to do before, during and after a flood as this will help to lessen its impact, improve flood response and speed up the recovery process. The EA provides practical advice and templates on how to prepare a flood plan for individuals, communities and businesses (see text box for useful links). It is recommended that emergency planners at MDC are consulted prior to the production of any emergency flood plan. The council will provide guidance to help local communities to protect their home and valuables and understand what to do before, during and after a flood. Once the emergency flood plan is prepared, it is recommended that it is distributed to emergency planners at MDC and the emergency services. When developing a flood warning and evacuation plan, it is recommended that it links in with any existing parish / community level plan.

Guidance documents for preparation of flood response plans • EA (2012) Flooding – minimising the risk, flood plan guidance for communities and groups • EA (2014) Community Flood Plan template • EA Personal flood plans • Flood Plan UK ‘Dry Run’ - A Community Flood Planning Guide

6.5.5 Other sources of information As well as being a statutory consultee for new development at risk of flooding, the EA can offer independent technical advice. The EA website contains a breadth of information on flood risk and there are numerous publications and guidance available. For example, the “flooding from groundwater” guide has been produced by the EA and Local Government Association to offer practice advice to reduce the impact of flooding from

groundwater.

The Met Office provides a National Severe Weather Warning Service about rain, snow, wind, fog and ice. The severity of warning is dependent upon the combination of the likelihood of the event happening and the impact the conditions may have. In simplistic terms, the warnings mean: Yellow: Be Aware, Amber: Be Prepared, Red: Take Action. This service does not provide flood warnings. The Met Office provide many other services and products. For further information, please visit their website.

The National Flood Forum (NFF) is a national charity, set up in 2002 to support those at risk and affected by flooding. The NFF helps people to prepare and recover from flooding as well as campaigning on behalf of flood risk communities, including providing advice on matters such as insurance. The ‘Flood Re’ reinsurance scheme, as agreed between the Government and insurance companies, was launched in April 2016. Flood Re is designed to provide homeowners at risk of flooding with access to affordable flood protection cover. Further information is available from http://www.floodre.co.uk. It should be noted that new developments do not qualify for Flood Re. Individual property flood resilience (PFR) measures are designed to help protect homes and businesses from flooding. These include a combination of flood resistance measures - trying to prevent water ingress – and flood resilience measures - trying to limit the damage and reduce the impact of flooding, should water enter the building. It is important that any measures have the BSI Kitemark. This shows that the measure has been tested and ensures that it meets industry standards. Please visit the Government website: “Prepare for flooding” for more information.

7 Climate change

7.1 Climate Change and the NPPF The 2019 NPPF sets out how the planning system should help minimise vulnerability and provide resilience to the impacts of climate change. NPPF and NPPG describe how FRAs should demonstrate how flood risk will be managed over the lifetime of the development, taking climate change into account. The updated 2019 NPPF also states that the ‘sequential approach should be used in areas known to be at risk now or in the future from any form of flooding’ (para 158).

7.2 Climate change guidance and allowances The Environment Agency published updated climate change allowance on 19 February 2016 (further updated on 15 February 2019), providing information on how climate change should be accounted for when considering development, specifically how allowances for climate change should be included with FRAs. The 2016 climate change guidance includes climate change predictions of anticipated change for peak river flow, sea level rise and peak rainfall intensity. By making an allowance for these climate change predictions it will help reduce the vulnerability of the development and provide resilience to flooding in the future. These allowances are based on climate change projections and different scenarios of carbon dioxide emissions to the atmosphere. However, at the time of preparing the 2020 SFRA this guidance is being revised in line with the UK Climate Projections 2018 (UKCP18). The UKCP18 projections replace the UK Climate Change Projections 2009 (UKCP09) projections and are the official source of information on how the climate of the UK may change over the rest of this century. The Environment Agency have confirmed that this may result in changes to the climate change allowances in the future. Please contact the Environment Agency for interim guidance if you are preparing a Flood Risk Assessment for a development. For the purposes of the 2020 Level 1 SFRA the 2016 allowances have been considered. Any changes which impact on this SFRA will be added as an addendum after the release of the updated predictions. If a Level 2 SFRA is required, any changes to the climate change allowances will be considered at that stage.

7.3 Using climate change allowances To help decide which allowances to use to inform the flood levels that the flood risk management strategy will be based on for a development or development plan allocation, the following should be considered: • likely depth, speed and extent of flooding for each allowance of climate change over time considering the allowances for the relevant epoch (2020s, 2050s and 2080s) • vulnerability of the proposed development types or land use allocations to flooding • ‘built in’ resilience measures used, for example, raised floor levels • capacity or space in the development to include additional resilience measures in the future, using a ‘managed adaptive’ approach Flood Risk Assessments (FRAs) are required to demonstrate future implications of climate change have been considered, and risks managed where possible, for the lifetime of the proposed development. This may include for instance: • Consideration of the vulnerability of the proposed development types or land use allocations of flooding and directing the more vulnerable away from areas at higher risk due to climate change,

• Use of ‘built in’ resilience measures. For example, raised flood levels, • Capacity or space in the development to include additional resilience measures in the future, using a ‘managed adaptive’ approach. The last consideration acknowledges that there may be instances where some flood risk management measures are not necessarily needed now but may be in the future. The latest guidance on climate change allowances for FRA released by the EA 11 provides predictions of anticipated change. The elements to be considered in FRAs for developments in MDC’s authoritative area are: • Peak rainfall intensity; • Peak river flow • Sea level rise The EA provides peak rainfall intensity climate change allowances to be considered in FRAs. The guidelines which should be used in FRAs are outlined in the following sections.

7.4 Peak river flows Climate change is expected to increase the frequency, extent and impact of flooding, reflected in peak river flows. Wetter winters and more intense rainfall may increase fluvial flooding and surface water runoff and there may be increased storm intensity in summer. Rising river levels may also increase flood risk. The peak river flow allowances provided in the guidance show the anticipated changes to peak flow for the river basin district within which the subject watercourse is located. Once the river basin district has been identified, guidance on uplift in peak flows are provided for three allowance categories, Central, Higher Central and Upper End which are based on the 50th, 70th and 90th percentiles respectively. The allowance category to be used is based on the vulnerability classification of the development and the flood zones within which it is located. These allowances (increases) are provided, in the form of figures for the total potential changed anticipated, for three climate change periods: • The ‘2020s’ (2015 to 2039) • The ‘2050s’ (2040 to 2069) • The ‘2080s’ (2070 to 2115) The time period used in the assessment depends upon the expected lifetime of the proposed development. Residential development should be considered for a minimum of 100 years, whilst the lifetime of a non-residential development depends upon the characteristics of that development. Further information on what is considered to be the lifetime of development is provided in the NPPG. Mendip District is located in two River Basin Districts, and therefore the peak river flow allowances should be chosen for the river basin district within which the subject watercourse is located. The allowances for the Severn River Basin District are provided in Table 7-1 and for South West River Basin are provided in Table 7-3.

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11 https://www.gov.uk/guidance/flood-risk-assessments-climate-change-allowances

Table 7-1: Peak river flow allowances for the Severn River Basin District

Total potential Total potential Total potential Allowance change anticipated change anticipated change anticipated category for ‘2020s’ (2015 for ‘2050s’ (2040 for ‘2080s’ (2070 to 39) to 2069) to 2115) Upper end 25% 40% 70% Higher central 15% 25% 35% Central 10% 20% 25%

Table 7-2: Peak river flow allowances for the South West River Basin

7.4.1 High++ allowances High++ allowances only apply in assessments for developments that are very sensitive to flood risk, for example large scale energy generating infrastructure, and that have lifetimes beyond the end of the century. H++ estimates represent the upper limit of plausible climate projections and would not normally be expected for schemes of plans to be designed to or incorporate resilience for the H++ estimate. Further information is provided in the EA publication, Adapting to Climate Change: Advice for Flood and Coastal Erosion Risk Management Authorities.

7.4.2 Which peak river flow allowance to use? The flood zone and flood risk vulnerability classification should be considered when deciding which allowances apply to the development or the plan. Vulnerability classifications are found in the NPPG. The guidance states the following:

Flood Zone 2

Vulnerability classification Central Higher Central Upper end

Essential infrastructure ✓ ✓ Highly vulnerable ✓ ✓ More vulnerable ✓ ✓ Less vulnerable ✓ Water compatible None

Flood Zone 3a

Vulnerability classification Central Higher Central Upper end

Essential infrastructure ✓ Highly vulnerable Development not permitted More vulnerable ✓ ✓ Less vulnerable ✓ ✓ Water compatible ✓

Flood Zone 3b

Vulnerability classification Central Higher Central Upper end

Essential infrastructure ✓ Highly vulnerable More vulnerable Development not permitted Less vulnerable Water compatible ✓

7.5 Peak rainfall intensities Climate change is predicted to result in wetter winters and increased summer storm intensity in the future. This increased rainfall intensity will affect land and urban drainage systems, resulting in surface water flooding, due to the increased volume of water entering the systems. The table below shows anticipated changes in extreme rainfall intensity in small and urban catchments. These allowances should be used for small catchments and urban drainage sites. For catchments, larger than 5km2, the guidance suggests the peak river flow allowances should be used. For flood risk assessments, both the central and upper end allowances should be assessed to understand the range of impact.

Table 7-3: Peak rainfall intensity allowance in small and urban catchments

Applies across Total potential Total potential Total potential all of England change anticipated change anticipated change anticipated for 2010 to 2039 for 2040 to 2059 for 2060 to 2115

Upper end 10% 20% 40%

Central 5% 10% 20%

7.6 Groundwater The effect of climate change on groundwater flooding problems, and those watercourses where groundwater has a large influence on winter flood flows, is more uncertain. Milder wetter winters may increase the frequency of groundwater flooding incidents in areas that are already susceptible, but warmer drier summers may

counteract this effect by drawing down groundwater levels to a greater extent during the summer months. The western, lower lying area of Mendip District located near to Glastonbury and Street has the potential for groundwater flooding to occur at the surface. Watercourse valleys such as the Frome also have the potential for surface groundwater flooding. The remainder of the district largely has a limited potential for groundwater flooding to occur with many large areas not prone to any groundwater flooding.

7.7 Tidal flood risk There is no tidal risk within Mendip District due to the landlocked geography of the district. There are tidal rivers which enter the district however the tidal limit of these rivers has been checked and are outside of the study area.

7.7.1 The UK Climate Projection 2009 (UKCP09)

The UK Climate Projection 2009 predict the following climatic changes to the study area: South West England • Increased summer temperatures of 5.1°C by 2050. • Increased winter temperatures of 3.5°C by 2050. • Reduced summer rainfall of 16% by 2050 making summers much drier. • Increased winter rainfall of 41% by 2050. UKCP09 has been superseded by UKCP18. UKCP18 provides a number of future projections for different variables across the UK.

7.8 Adapting to climate change NPPG Climate Change contains information and guidance for how to identify suitable mitigation and adaptation measures in the planning process to address the impacts of climate change. Examples of adapting to climate change include: • Considering future climate risks when allocating development sites to ensure risks are understood over the development’s lifetime • Considering the impact of and promoting design responses to flood risk and coastal change for the lifetime of the development • Considering availability of water and water infrastructure for the lifetime of the development and design responses to promote water efficiency and protect water quality • Promoting adaptation approaches in design policies for developments and the public realm for example by building in flexibility to allow future adaptation if needed, such as setting new development back from watercourses • Identifying no or low-cost responses to climate risks that also deliver other benefits, such as green infrastructure that improve adaptation, biodiversity and amenity, for example by leaving areas shown to be at risk of flooding as public open space.

7.9 Modelling outputs The EA models of Wells (2012) and Shepton Mallett (2013) have been re-run to consider climate change for the 1% AEP event with 40% and 85% increases. Results of this are displayed in Figure 7-1 and Figure 7-2.

For the rest of the district it has been assumed that Present Flood Zone 2 represents Future Flood Zone 3 Extent. Future Flood Zone 2 has not been considered as part of the Level 1 SFRA and should be considered as part of the Level 2 SFRA or by developers through more detailed modelling.

Figure 7-1: Climate change future Flood Zone 3 modelling outputs – Shepton Mallet and Croscombe

Figure 7-2: Climate change future Flood Zone 3 modelling outputs – Wells

8 Flood defences A high-level review of formal flood defences was carried out for this SFRA interrogating existing information that gives their condition and standard of protection. Details of the flood defence locations and condition were provided by the EA for preparing this assessment. The assessment has considered man-made defences and not natural defences which may arise for instance due to the presence of naturally high ground adjacent to a settlement. The formal defences and their location are summarised in the following sections.

8.1 Defence standard of protection and residual risk One of the main aims of the SFRA is to outline the present risk of flooding across Mendip District including consideration of the effect of flood risk management measures (including flood banks and defences). The modelling that informs understanding of flood risk within the district is typically of a catchment-wide nature, suitable for preparing evidence on possible site options for development. In cases where a specific site risk assessment is required, more detailed studies should be performed to seek to refine the current understanding of flood risk from all sources. Consideration of the residual risk behind flood defences has been undertaken as part of this study. The residual risk of flooding in a flood event or from failure of defences should also be carefully considered. Developers should also consider the standard of protection provided by defences and residual risk as part of a detailed Flood Risk Assessment (FRA).

8.2 EA defence condition Formal structural defences are given a rating based on a grading system for their condition12. A summary of the grading system used by the EA for condition is provided in Table 8-1. This detail, in addition to descriptions and standard of protection for each, were provided by the EA for the purpose of preparing this SFRA which reports on the standard of protection using this information. Table 8-1: Defence asset condition rating

Grade Rating Description 1 Very Good Cosmetic defects that will have no effect on performance. Minor defects that will not reduce the overall performance of 2 Good the asset. 3 Fair Defects that could reduce the performance of the asset. Defects that would significantly reduce the performance of the 4 Poor asset. Further investigation required. 5 Very Poor Severe defects resulting in complete performance failure. Source: Condition Assessment Manual – EA 2006 The condition of existing flood defences and whether they will continue to be maintained and/or improved in the future requires consideration as part of the risk based sequential approach and, considering this, whether possible site options for development are appropriate and sustainable. In addition, detailed FRAs will need to thoroughly explore the condition of defences, especially where these defences are

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12 Condition Assessment Manual, EA (2006)

informal and demonstrate a wide variation of condition grades. It is important that all these assets are maintained to a good condition and their function remains unimpaired. A review of key defences across Mendip District, their condition and standard of protection is included in the following sections. Formal flood defences within Mendip District have been derived from the EA Spatial Flood Defences dataset. The type of flood defences in the district have been determined from the asset type field. This SFRA has not considered natural defences (i.e. naturally high ground).

8.3 Standard of protection The standard of protection of flood defence structures should also be considered.

Standard of protection Flood defences are designed to give a specific standard of protection, reducing the risk of flooding to people and property in flood prone areas. For example, a flood defence with a 1% AEP standard of protection means that the flood risk in the defended area is reduced to a 1% chance of flooding in any given year.

Although flood defences are designed to a standard or protection it should be noted that, over time, the actual standard of protection provided by the defence may decrease, for example due to deterioration in condition or increases in flood risk due to climate change

For the purpose of this study, structures which are categorised to be natural banks and have a standard of protection higher than 10% AEP (i.e. a lower return period) have not been included within analysis. The EA manage flood defences as group structures, rather than as individual assets. These are termed ‘management units’ and are managed through System Asset Management Plans (SAMPS).

8.4 Mendip District flood defence structures review Figure 8-1, Figure 8-2, Figure 8-3, Figure 8-4 and Table 8-2 provide a summary of the defence type, data source, standard of flood protection and condition within Mendip District. Data provided is based on the EA’s Spatial Flood Defence dataset. This is the most up to date information available at the time of writing. The Flood Defences within Mendip District largely consist of hard engineering structures; concrete lined banks or masonry lined banks. The condition of these structures is mostly 2 or 3, with 1 masonry wall being a category 4. Descriptions of the defence condition categories are outlined in Table 8-1. Defences within Mendip District mostly have a 100 to 150-year standard of protection. There are both council and EA defences.

Figure 8-1: Flood defence structures located within Frome

Figure 8-2: Flood defence structures located within Shepton Mallet

Figure 8-3: Flood defence structures located within Wells

Figure 8-4: Flood defences located within Glastonbury

Table 8-2: EA's Flood defences within Mendip District

Defence ID Asset Type Standard of Protection Condition 451 Walled Bank 100 3 497 Sheet Piled Bank 100 3 583 Concrete Lined Bank 100 2 583 Walled bank 100 3 599 Masonry Lined Bank 100 3 600 Stone Lined Bank 100 2 613 Walled Bank 100 2 625 Gabion Walled Bank 100 3 696 Walled Bank 100 3 706 Concrete Lined Bank 100 2 707 Concrete Lined Bank 100 2 731 Masonry Wall 100 3 732 Walled Bank 100 2 1148 Masonry Wall 100 3 1209 Masonry Lined Bank 100 3 1317 Masonry Wall 100 4 119 Natural Bank 50 3 317 Natural Bank 50 3 787 Natural Bank 50 3 123 Natural Bank 50 3 351 Natural Bank 100 3 377 Natural Bank 100 3 390 Natural Bank 100 2 404 Natural Bank 100 2 476 Natural Bank 100 2 484 Natural Bank 100 3 520 Natural Bank 100 2 681 Natural Bank 100 3 782 Natural Bank 100 2 828 Natural Bank 100 3 85

Defence ID Asset Type Standard of Protection Condition 829 Natural Bank 100 2 846 Natural Bank 100 4 848 Natural Bank 100 3 850 Natural Bank 100 3 851 Natural Bank 100 2 860 Natural Bank 100 3 892 Natural Bank 100 2 929 Natural Bank 100 2 1046 Natural Bank 100 3 1020 Natural Bank 100 3

8.5 Areas benefitting from defences The EA has a dataset called “Areas Benefiting from Defences”. This dataset for England shows those areas that benefit from the presence of defences in a 1 in 100 (1%) chance of flooding each year from rivers; or 1 in 200 (0.5 %) chance of flooding each year from the sea. There are two small areas in Mendip District that are identified by the EA to benefit from flood defences. Both areas are located in the south west of the district, in relative proximity to Glastonbury and Street. These areas are detailed in Appendix B. It is important to note that the EA “Areas Benefiting from Defences” does not show all areas that benefit from defences.

8.6 Flood risk assessment considerations Flood Risk Assessments (FRAs) will need to thoroughly explore the condition of defences, especially where any defences are informal and demonstrate a wide variation of condition grades. It is important that all these assets are maintained to a good condition and their function remains unimpaired.