3 Flood Modelling Results Eastbourne Borough Council

Transcription

Eastbourne Borough Council and Wealden District Council
Level 2 SFRA
3
Flood Modelling Results Eastbourne
Borough Council
3.1.1
EBC has defined 15 discrete neighbourhood areas across their borough, within
which various development types are to be accommodated within the lifetime of the
LDF. This section describes the results of the 2-dimensional modelling for those
neighbourhood areas at risk from tidal flooding. This includes the neighbourhood
areas presented in Table 3-1.
3.1.2
For ease of use, Table 3-1 lists the scenario (breach and overtopping run) and lists
whether the model results show that the neighbourhood floods for that particular
scenario. For example, the neighbourhood of Roselands & Bridgemere floods as a
result of a breach at Princes Park but it does not flood as a result of a breach at
Greytowers in the 5% (1 in 20 year) annual probability event.
Table 3-1: EBC Neighbourhood Areas affected by flooding and relevant model runs
NEIGHBOURHOOD
AREA
PRINCES
PARK 5% (1
IN 20 YEAR)
ANNUAL
GREYTOWERS
5% (1 IN 20
YEAR)
ANNUAL
PEVENSEY
5% (1 IN 20
YEAR)
ANNUAL
PROBABILITY
BREACH
PROBABILITY
BREACH
PROBABILITY
BREACH
0.5% (1 IN
200
YEAR)
ANNUAL
0.1% (1 IN
1000 YEAR)
ANNUAL
PROBABILITY
OVERTOPPING
PROBABILITY
OVERTOPPING
Town Centre
Roselands
&
Bridgemere
Langney Village,
Langney Rise &
West Langney
St Anthonys &
Langney Point
Seaside
Hampden Park,
the Hydneye &
Willingdon
Trees
Shinewater
&
North Langney
Sovereign
Harbour North &
Sovereign
Harbour South
Eastbourne
Park
3.1.3
There are some neighbourhoods that have not been investigated further as they are
considered not to be at risk from tidal flooding. These include Old Town Downside &
Cherry Gardens, Summerdown & Saffrons, Upperton, Meads & Lower Meads,
Ocklynge & Rodmill and Ratton & Willingdon. These neighbourhoods are all located
in Flood Zone 1.
3.1.4
Please note models have been run assuming that coastal defences will be
maintained to ‘hold the line’ to a standard commensurate with the 2115 5% (1 in 20
year) annual probability tidal flood. To represent this in the hydraulic models, the
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Level 2 SFRA
crest levels of costal defences have been raised in the model where they are not
already at or above the 5% (1 in 20 year) annual probability level in 2115.
Legend
Flood Depth
Flood Hazard
High Hazard
Medium Hazard
Low Hazard
3.1.5
NB. Where neighbourhoods have not been affected from a scenario this scenario
has been excluded from individual neighbourhood mapping within this report. For
example the Eastbourne Park area has only been simulated to flood from a breach
at Princes Park so the flooding from a breach at Greytowers and Pevensey has not
been presented.
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Level 2 SFRA
EBC TOWN CENTRE NEIGHBOURHOOD – 0.5% (1 IN 200 YEAR) ANNUAL PROBABILITY OVERTOPPING SCENARIO IN 2115
FLOOD DEPTH
FLOOD HAZARD
DESCRIPTION OF RESULTS
Background: The neighbourhood defined as the Town Centre has an area of 1.1 km², with an approximate coastline of 1000 m; that includes Eastbourne Pier. It has borders with the other neighbourhood areas of Upperton to the north, ,
Seaside to the east, Summerdown & Saffrons to the west and Meads & Lower Meads to the southwest. The Town Centre neighbourhood is completely urbanised with extensive areas of commercial and residential development. The
Level 1 SFRA identified parts of the Town Centre as lying in within Flood Zone 3a in 2115.
Flood Depth and Inundation: In this overtopping scenario the defences around Sovereign Harbour are overtopped first. Flood waters from Sovereign Harbour inundate towards the south west and north east, the larger drains such as
the Horsey and Crumbles Sewer temporarily restrict flood inundation. In the second tidal cycle flood waters overtop the defences near the Redoubt as well as approximately 200 m east of the pier in the south east corner of the Town
Centre neighbourhood. Flood waters from both of these locations (the Redoubt and Sovereign Harbour) combine and encroach further into the Town Centre during the third tidal cycle. The north of the Town Centre experiences flood
depths of 1.5 m; however, the majority of the Town Centre remains dry.
Flood Hazard: Where the modelled results indicate flooding in the Town Centre neighbourhood a low, medium and high flood hazard classification has been defined. The high hazard classification is assigned where the greater flood
depths are experienced which is towards the Roselands & Bridgemere neighbourhood.
Specific Limitations: The Town Centre neighbourhood lies on the fringes of the floodplain for the 2115 0.5% (1 in 200 year) overtopping flood event. Consequently the definition of flood depth and flood hazard is highly dependant on the
available topographic data and mapping technique used and should be refined by further modelling as part of a site specific flood risk assessment.
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Level 2 SFRA
EBC TOWN CENTRE NEIGHBOURHOOD - 0.1% (1 IN 1000 YEAR) ANNUAL PROBABILITY OVERTOPPING SCENARIO IN 2115
FLOOD DEPTH
FLOOD HAZARD
Background: The neighbourhood defined as the Town Centre has an area of 1.1 km², with an approximate coastline of 1000 m; that includes the pier. It has borders with other neighbourhood areas of Upperton to the north, Seaside to
the east, Summerdown & Saffrons to the west and Meads & Lower Meads to the southwest. The Town Centre neighbourhood is completely urbanised with extensive areas of commercial and residential development. The Level 1 SFRA
identified parts of the Town Centre as lying in within Flood Zone 2 in 2115.
the Horsey and Crumbles Sewer temporarily restrict flood inundation. In the second tidal cycle flood waters overtop the defences near the Redoubt as well as approximately 200 m east of the pier in the south east corner of the Town
Centre neighbourhood. Flood waters from both of these locations (the Redoubt and Sovereign Harbour) combine and encroach further into the Town Centre during the third tidal cycle. The railway line restricts the flood waters inundating
the northwest area of the Town Centre. The north of the Town Centre experiences flood depths of 2.0 m; however, the majority of the Town Centre remains dry.
Flood Hazard: Where the modelled results indicate flooding of Town Centre a low, medium and high flood hazard classifications have been defined. The high hazard classification is assigned where there are greater flood depths are
experienced which is towards the Roselands & Bridgemere neighbourhood.
Specific Limitations: The Town Centre neighbourhood lies on the fringes of the floodplain for the 2115 0.1% (1 in 1000 year) overtopping flood event. Consequently the definition of flood depth and flood hazard is highly dependant on
the available topographic data and mapping technique used and should be refined by further modelling as part of a site specific flood risk assessment.
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Level 2 SFRA
EBC EASTBOURNE PARK – 0.5% (1 IN 200 YEAR) ANNUAL PROBABILITY OVERTOPPING SCENARIO IN 2115
FLOOD DEPTH
FLOOD HAZARD
Background: The area defined as the Eastbourne Park has an approximate area of 4.2 km², and has no coastline boundary. It has borders with the neighbourhoods of Hampden Park, Willingdon Trees & The Hydneye and Ocklynge to
the west, Upperton and Roselands & Bridgemere to the south, St Anthonys & Langney Point and Langney Village, Langney Rise and West Langney to the southeast, and, Shinewater & North Langney to the northeast. , The Eastbourne
Park area is primarily parkland that incorporates a golf course and lakes. The Level 1 SFRA identified Eastbourne Park as lying in within Flood Zone 3a in 2115.
the Horsey and Crumbles Sewer temporarily restrict flood inundation. In the second tidal cycle flood waters flood waters firstly inundate onto Eastbourne Park in the southeast from the overtopping at Soveriegn Harbour. Overtopping also
occurs near the Redoubt which rapidly flow northwest and inundate Eastbourne Park from the south near the miniature railway line which holds back some floodwater for a short amount of time. Floodwaters do however also find a route
to the west of the miniature railway line. The eastern area of Eastbourne Park does experience depths up to 3m and the west depths of up to 2.3m.
Flood Hazard: Nearly all of Eastbourne Park has been classified as having a high flood hazard in this scenario.
Specific Limitations: Parts of Eastbourne Park area lies on the fringes of the floodplain for the 2115 0.5% (1 in 200 year) overtopping flood event. Consequently the definition of flood depth and flood hazard is highly dependant on the
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Level 2 SFRA
EBC EASTBOURNE PARK – 0.1% (1 IN 1000 YEAR) ANNUAL PROBABILITY OVERTOPPING SCENARIO IN 2115
FLOOD DEPTH
FLOOD HAZARD
Background: The area defined as the Eastbourne Park has an approximate area of 4.2 km², it has no coastline boundary. It has borders with the neighbourhoods of Hampden Park, Willingdon Trees & The Hydneye and Ocklynge to the
west, Upperton and Roselands & Bridgemere to the south, St Anthonys & Langney Point and Langney Village, Langney Rise and West Langney to the southeast, and, Shinewater & North Langney to the northeast. The Eastbourne Park
area is primarily parkland that incorporates a golf course and lakes. The Level 1 SFRA identified Eastbourne Park as lying in within Flood Zone 3a in 2115.
Flood Depth and Inundation: In this overtopping scenario the defences around Sovereign Harbour are overtopped first followed by near the Redoubt. Flood waters from Sovereign Harbour inundate towards the south west and north
east. Crumbles Sewer, in Princes Park conveys flood water into the Seaside neighbourhood in the first tidal cycle. Flood waters do not retreat from Crumbles Sewer before the onset of the second tidal cycle which then causes flooding in
Eastbourne Park. In the second tidal cycle floodwaters rapidly flood all areas of Eastbourne Park to the east and west of the miniature railway line. The eastern area of Eastbourne Park does experience depths up to 3.5m and the west
depths of up to 3.3m.
Flood Hazard: Nearly all of Eastbourne Park has been classified as having a high flood hazard in this scenario.
Specific Limitations: Parts of Eastbourne Park area lies on the fringes of the floodplain for the 2115 0.1% (1 in 1000 year) overtopping flood event. Consequently the definition of flood depth and flood hazard is highly dependant on the
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Level 2 SFRA
EBC EASTBOURNE PARK – 5% (1 IN 20 YEAR) ANNUAL PROBABILITY AS A RESULT OF A BREACH AT PRINCES PARK IN 2115
FLOOD DEPTH
FLOOD HAZARD
Background: The area defined as the Eastbourne Park has an approximate area of 4.2 km², and has no coastline boundary. It has borders with the neighbourhoods of Hampden Park, Willingdon Trees & The Hydneye and Ocklynge to
the west, Upperton and Roselands & Bridgemere to the south, St Anthonys & Langney Point and Langney Village, Langney Rise and West Langney to the southeast, and, Shinewater & North Langney to the northeast. , The Eastbourne
Park neighbourhood is primarily parkland that incorporates a golf course and lakes. The Level 1 SFRA identified Eastbourne Park as lying in within Flood Zone 3a in 2115.
Flood Depth and Inundation: In this breach scenario flood waters penetrate the breach in the first tidal cycle. Crumbles Sewer, in Princes Park acts as a conduit for flow which means that flood waters are carried further north, through
the Seaside neighbourhood and onto Eastbourne Park. In the second tidal cycle flood waters also flow from the breach in a northwest direction as well as along Crumbles Sewer. These floodwaters are prevented from flooding the east of
Eastbourne Park by the miniature railway line. The floodwaters from the Crumbles Sewer do however, flood the east of Eastbourne Park. The eastern area of Eastbourne Park does experience depths up to 1.3m and the west remains
dry.
Flood Hazard: Of the areas that have been modelled to flood in this scenario all three flood hazard classifications have been assigned. A high flood hazard has been assigned along the Crumbles and Horsey sewer, a medium flood
hazard to the east of Eastbourne Park area and a low flood hazard for the remainder.
Specific Limitations: The margins of the floodplain from a simulated breach at Princes Park are within the Eastbourne Park area. Consequently the definition of flood depth and flood hazard is highly dependant on the available
topographic data and mapping technique used and should be refined by further modelling as part of a site specific flood risk assessment. The propagation of flood water from this breach is heavily influenced by the pond in Princes Park
and the Crumbles Sewer the influence of which should be further investigated in a site-specific FRA.
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Level 2 SFRA
EBC SEASIDE NEIGHBOURHOOD – 5% (1 IN 20 YEAR) ANNUAL PROBABILITY SCENARIO AS A RESULT OF A BREACH AT PRINCES PARK
FLOOD DEPTH
FLOOD HAZARD
Background: The Seaside neighbourhood is situated just to the northeast of the Town Centre it also has borders with Roselands & Bridgemere (northwest), Upperton (northwest) and St Anthonys & Langney Point (north). It has an area
of 1.45 km² with a relatively extensive coastline of approximately 2000 m and includes Princes Park. The Level 1 SFRA identified Seaside as entirely lying within Flood Zone 3a in 2115.
Flood Depth and Inundation: In this breach scenario flood waters penetrate the breach in the first tidal cycle. Flood water flows into the pond in Princes Park as well as the Seaside neighbourhood towards Roselands & Bridgemere.
Crumbles Sewer, in Princes Park acts as a conduit for flow which means that flood waters are carried further north, out of the Seaside neighbourhood. In the second tidal cycle parts of Princes Park become flooded and more flood water
flows into the Seaside neighbourhood. Approximately 50% of Seaside remains dry in this scenario due to the relatively high topography nearer the coastline; to the east of Seaside Road. The park to the west of Seaside Road
experiences depths of up to 1.3 m; Princes Park adjacent to the pond experiences depths up to 1.7 m; the football pitch to the west of Princes Park experiences depths up to 1.2 m; Beach Road remains dry.
Flood Hazard: The breach model hazard mapping shows that area of maximum hazard is nearest the breach; along the fringes of the Princes Park drain and pond; and, on the park to the west of Seaside Road.
Specific Limitations: The margins of the floodplain from a simulated breach at Princes Park are within the Seaside neighbourhood. Consequently the definition of flood depth and flood hazard is highly dependant on the available
topographic data and mapping technique used and should be refined by further modelling as part of a site specific flood risk assessment. The propagation of flood water from this breach is heavily influenced by the pond in Princes Park
and the Crumbles Sewer the influence of which should be further investigated in a site-specific FRA.
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Level 2 SFRA
EBC SEASIDE NEIGHBOURHOOD – 0.5% (1 IN 200 YEAR) ANNUAL PROBABILITY OVERTOPPING SCENARIO IN 2115
FLOOD DEPTH
FLOOD HAZARD
Flood Depth and Inundation: In this overtopping scenario the defences around Sovereign Harbour are overtopped first. From Sovereign Harbour flood waters inundate towards the south west and north east. Crumbles Sewer, in
Princes Park conveys flood water into the Seaside neighbourhood in the first tidal cycle. Flood waters do not retreat from Crumbles Sewer and pond before the onset of the second tidal cycle. During the second tidal cycle flood waters
enter the Seaside neighbourhood from two directions. One of these is directly from Sovereign Harbour were they are directed onto Princes Park. Additionally flood waters overtop the defences near the Redoubt (within the Seaside
neighbourhood) and at a location approximately 200 m east of the pier in the south east corner of the Town Centre neighbourhood. This means that the majority of the seaside neighbourhood is inundated with flood water in both of the
overtopping scenarios modelled. The park to the west of Seaside Road experiences depths of up to 2.3 m; Princes Park adjacent to the pond experiences depths up to 2.2 m; the football pitch to the west of Princes Park experiences
depths up to 2.0 m; Beach Road experiences depths of up to 1.2 m.
Flood Hazard: In the overtopping scenarios the majority of the area flooded has been classified as having a high hazard. It is only the fringes of the flooding that have a lower classification.
Specific Limitations: The margins of the floodplain from a simulated overtopping scenario in the 0.5% (1 in 200 year) annual probability scenario in 2115 within the Seaside neighbourhood. Consequently the definition of flood depth and
flood hazard is highly dependant on the available topographic data and mapping technique used and should be refined by further modelling as part of a site specific flood risk assessment.
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Level 2 SFRA
EBC SEASIDE NEIGHBOURHOOD – 0.1% (1 IN 1000 YEAR) ANNUAL PROBABILITY OVERTOPPING SCENARIO IN 2115
FLOOD DEPTH
FLOOD HAZARD
Flood Depth and Inundation: In this overtopping scenario the defences around Sovereign Harbour are overtopped first. From Sovereign Harbour flood waters inundate towards the south west and north east. Crumbles Sewer, in
Princes Park conveys flood water into the Seaside neighbourhood in the first tidal cycle. Flood waters do not retreat from Crumbles Sewer before the onset of the second tidal cycle. During the second tidal cycle flood waters enter the
Seaside neighbourhood from two directions. One of these is directly from Sovereign Harbour were they are directed into Princes Park. Additionally flood waters overtop the defences near the Redoubt (within the Seaside neighbourhood)
and at a location approximately 200 m east of the pier in the south east corner of the Town Centre neighbourhood. This means that the majority of the seaside neighbourhood is inundated with flood water in both of the overtopping
scenarios modelled. Princes Park to the west of Seaside Road experiences depths of up to 2.8 m; adjacent to the pond depths up to 2.5 m; the football pitch experiences depths up to 2.35 m and Beach Road experiences depths of up to
1.6 m.
Flood Hazard: In this overtopping scenario the majority of the area flooded has been classified as having a high hazard. It is only the fringes of the flooding that have a lower classification.
Specific Limitations: The margins of the floodplain from a simulated overtopping scenario in the 0.1% (1 in 1000 year) annual probability scenario in 2115 within the Seaside neighbourhood. Consequently the definition of flood depth
and flood hazard is highly dependant on the available topographic data and mapping technique used and should be refined by further modelling as part of a site specific flood risk assessment.
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Level 2 SFRA
EBC ROSELANDS & BRIDGEMERE NEIGHBOURHOOD – 5% (1 IN 20 YEAR) ANNUAL PROBABILITY SCENARIO AS A RESULT OF A BREACH AT PRINCES PARK
FLOOD DEPTH
FLOOD HAZARD
Background: The Roselands & Bridgemere neighbourhood is situated just to the northwest of the Seaside neighbourhood; it also has borders with Upperton (southwest) and St Anthonys & Langney Point to the north. It does not have a
coastline border. The Level 1 SFRA identified parts of Roselands & Bridgemere as lying in Flood Zone 3a in 2115.
Flood Depth and Inundation: In this breach scenario flood waters penetrate the breach in the first tidal cycle. Flood water is directed into the pond in Princes Park as well as through the Seaside neighbourhood towards Roselands &
Bridgemere & Bridgemere. Flood waters do not enter the Roselands & Bridgemere neighbourhood until the second tidal cycle. Horsey Sewer which flows through Roselands & Bridgemere temporarily restricts flow to the west but soon
this area becomes inundated. The only area to remain dry is the mound of higher topography in the middle of the neighbourhood. The area just south of Ringwood Road experiences depths up to 1.0 m; Marlow Avenue experiences no
flooding; and the area around Ringwood Avenue experiences depths of up 0.8 m.
Flood Hazard: In the breach scenario at Princes Park it is only the edges of the drain that have been classified as having a high hazard all the other flooded areas are either low or medium.
Specific Limitations: The margins of the floodplain from a simulated breach at Princes Park are within the Roselands & Bridgemere neighbourhood. Consequently the definition of flood depth and flood hazard is highly dependant on the
available topographic data and mapping technique used and should be refined by further modelling as part of a site specific flood risk assessment. The Horsey Sewer influences the propagation of flooding in Roselands & Bridgemere the
influence of which should also be further investigated in a site-specific flood risk assessment.
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Level 2 SFRA
EBC ROSELANDS & BRIDGEMERE NEIGHBOURHOOD – 0.5% (1 IN 200 YEAR) ANNUAL PROBABILITY OVERTOPPING SCENARIO IN 2115
FLOOD DEPTH
FLOOD HAZARD
Background: The Roselands & Bridgemere neighbourhood is situated just to the northwest of the Seaside neighbourhood; it also has borders with Upperton (southwest) and St Anthonys & Langney Point to the north. It does not have a
coastline border. The Level 1 SFRA identified parts of Roselands & Bridgemere as lying in Flood Zone 3a in 2115.
Flood Depth and Inundation: In this overtopping scenario the defences around Sovereign Harbour are overtopped first. Flood waters from here inundate towards the south west and north east. During the second tidal cycle flood waters
enter Roselands & Bridgemere from three directions. One of these is overland directly from Sovereign Harbour and another is from the overtopping at Sovereign Harbour via the Horsey Sewer. Additionally flood waters overtop the
defences near the Redoubt and at a location approximately 200 m east of the pier in the south east corner of the Town Centre, these are directed into Roselands & Bridgemere.
Flood Hazard: The majority of areas that are flooded within Roselands & Bridgemere have been classified as having a high hazard; it is only the fringes of the flooding where low and medium hazard classifications are assigned.
Specific Limitations: The margins of the floodplain from a simulated overtopping scenario for the 0.5% (1 in 200 year) annual probability scenario in 2115 are within the Roselands & Bridgemere neighbourhood. Consequently the
definition of flood depth and flood hazard is highly dependant on the available topographic data and mapping technique used and should be refined by further modelling as part of a site specific flood risk assessment. The Horsey Sewer
also influences the propagation of flooding in Roselands & Bridgemere the influence of which should be further investigated in a site-specific flood risk assessment.
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3 Flood Modelling Results Eastbourne Borough Council

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