Upload
others
View
7
Download
0
Embed Size (px)
Citation preview
MONSON The Saltings, Coast Road, Norman’s Bay, Pevensey, East Sussex
Flood Risk Assessment
Issue A 1 24th April 2016 © Monson Engineering 2016
EXECUTIVE SUMMARY
This report supports a planning application for the re-development of an existing dwelling known as
The Saltings, Coast Road, Norman’s Bay, Pevensey, East Sussex.
All flood risks have been considered but the only risk identified is tidal flooding from the sea due
immediately south of the site.
The modelling undertaken by Rother District Council, as part of its Strategic Flood Risk Assessment,
indicates there is no flooding at the site under breach conditions even for the 1 in 200 year event in
2115 which takes climate change into account. Very shallow flooding is predicted in the event of a
breach for the 1 in 1000 year event with climate change in 2115 and the depth of flood water is so
low that it would not affect the ground floor accommodation. This indicates the site is safe from
flooding for even the most severe of storms.
The re-development proposals retain the same footprint area but two options are being considered.
Option 1:-
The ground floor and first floor structure is retained but the existing spatial layout is re-arranged, the
building services are upgraded, the thermal performance is improved and the building envelope
upgraded. The first floor would be used for the main sleeping accommodation as currently
incorporated in the dwelling whilst a further bedroom is included in the ground floor as part of the
spatial re-arrangement. The existing ground floor is approximately 1.5 metres above the existing
ground levels so will be far more than 600 mm above the predicted flood water levels indicated from
the modelling results.
Option 2:-
Option 2 would result in a completely new dwelling being constructed on the existing base. The re-
arrangement of the spatial layout and upgrade of the building services, thermal performance and
building envelope would all be incorporated as for option 1 but further flood mitigation measures can
be included in the design. These could include the following:-
MONSON The Saltings, Coast Road, Norman’s Bay, Pevensey, East Sussex
Flood Risk Assessment
Issue A 2 24th April 2016 © Monson Engineering 2016
The windows in the first floor which face the sea could be constructed using safety glass to
prevent damage from any shingle flung against the dwelling due to wave and wind action.
Electricity meters and wiring could be installed on the first floor with drop downs to the
ground floor
The ground floor could incorporate tiling rather than carpets to reduce any impact of flooding
should water enter the property.
Waterproof plaster can be uses for the ground floor to again minimise any impact if water
does enter the property.
We would also advocate that the residents connect to the flood warning service so that they
can take the appropriate actions in the event of flood or severe flood warnings.
A further bedroom is proposed on the ground floor but all the modelling results indicate there is no
risk of flooding to this property due to its relative elevation compared to the marsh area to the north.
Therefore, whilst we have advocated the introduction of flood mitigation measures for the design
and construction of Option 2, there is deemed to be far less than a 1 in 1000 chance of the property
being affected by flood water even under a breach scenario in 2115 when the impacts of climate
change have been taken into account.
We would advocate that Option 2 is the preferred solution in terms of flood mitigation as it enables
more flood resilience measures to be introduced in the design and construction of the re-developed
dwelling.
Surface water drainage will be unaffected as the same roof area will be used.
We therefore recommend that no objection is raised to this application as the flood risk to the
property will not increase and will reduce due to the design of the re-development if Option 2 is
adopted.
MONSON The Saltings, Coast Road, Norman’s Bay, Pevensey, East Sussex
Flood Risk Assessment
Issue A 3 24th April 2016 © Monson Engineering 2016
1.0 INTRODUCTION
Monson have been requested to provide a Flood Risk Assessment for the re-development of an
existing dwelling known as The Saltings, Coast Road, Norman’s Bay, Pevensey, East Sussex.
The site is within flood zone 3 so a flood risk assessment is required to accompany any planning
application.
This report will conform to the National Planning Policy Framework and Technical Guidance
published in March 2012.
2.0 DEVELOPMENT DESCRIPTION AND LOCATION
2.1 Development type and location
The proposed development is the redevelopment of the existing dwelling at Norman’s Bay as
indicated on the location plan included in Appendix A.
2.2 Development classification
Household development is classified as “More Vulnerable” as defined in Table 2 of the Technical
Guidance to the National Planning Policy Framework. It is recognised that new development should
be directed to areas of lowest flood risk if possible. This site lies within flood zone 3 which is a high
risk area as indicated on the Environment Agency flood map for planning purposes included in
Appendix B. However, this site is already developed and the works proposed are to improve the
living accommodation within the existing property.
2.3 Sequential Test
The principle of the Sequential Test is to direct development towards areas of lowest flood risk. This
does not apply in this case as the proposed works are to an existing dwelling on this site.
MONSON The Saltings, Coast Road, Norman’s Bay, Pevensey, East Sussex
Flood Risk Assessment
Issue A 4 24th April 2016 © Monson Engineering 2016
2.4 Exception Test
The Exception Test needs to be applied as the site is within flood zone 3 but again as these works
are to an existing dwelling, the Exception Test does not apply.
3.0 DEFINITION OF THE FLOOD HAZARD
3.1 Flood sources
Flooding from the Sea
The site is situated on Coast Road, Norman’s Bay and is protected by the shingle bank running
directly in front of the property which provides a high level of protection. Nevertheless, the risk of
tidal flooding is a significant risk at this location.
Flooding from Rivers
There are a number of watercourses within the marsh areas to the north of the site but the property
is raised compared with the general marsh level beyond so there is no risk of fluvial flooding at this
location.
Flooding from Surface Water Run-Off and Overland Flow
The Environment Agency flood map for surface water, also included in Appendix B, indicates no
surface water flood risk. The area is extremely flat within the marsh area to the north of the property
and surface water is more likely to pond rather than collect at a single point which can lead to deep
surface water flooding. Again due to the elevation of the existing property, the risk of surface water
flooding is negligible.
Flooding from Groundwater
High water tables will occur in this general area due to the low elevation of the marshes and the flat
ground. However, groundwater flooding is normally associated with groundwater emerging from the
MONSON The Saltings, Coast Road, Norman’s Bay, Pevensey, East Sussex
Flood Risk Assessment
Issue A 5 24th April 2016 © Monson Engineering 2016
ground from porous underlying strata and collecting at a low point. This is not the case at this
location as the land is extremely flat.
Ponding of water in the marshes can occur but this would prove no risk to this site as the elevation
is above the general marsh level.
There is no risk of groundwater flooding at this location.
Flooding from Sewers.
There is a 150 mm foul sewer in Coast Road which drains to a pumping station almost opposite The
Saltings. The road and pumping station is below the existing dwelling so if the sewer was
overloaded or blocked, wastewater would flow towards the lower ground to the north of the site.
The sewer records indicate the road level is over 10 m ODN but we believe this must be a mistake
as the Coast Road is approximately 3 m ODN based on ordnance survey point levels along the road.
Flooding from Reservoirs, canals and other artificial sources.
The Environment Agency map for reservoirs shows no risk of flooding and there are no other artificial
sources in the vicinity which pose a risk to this site.
The principal risk to the proposed dwelling is from tidal flooding as indicated from the Environment
Agency’s flood map.
3.2 Surface water drainage
The site is at the back of the shingle bank and the downpipes from the roof discharge to soakaways
which will have excellent soakage characteristics.
The changes to the building will not extend the footprint of the building and therefore there will be
no increase in surface water discharge from the existing situation.
MONSON The Saltings, Coast Road, Norman’s Bay, Pevensey, East Sussex
Flood Risk Assessment
Issue A 6 24th April 2016 © Monson Engineering 2016
4.0 PROBABILITY
4.1 SFRA and other relevant data
The site is situated in flood zone 3 as indicated from the Environment Agency’s flood map (planning)
included in Appendix B. However, the Agency does also provide a tidal and fluvial flood risk map
which takes account of the sea defences and this shows the site to be in flood zone 2/3, which
means the risk lies between the 1 in 100 and 1 in 1000 year return storm event.
Rother District Council has undertaken a detailed Strategic Flood Risk Assessment covering their
whole area and this has included detailed modelling of the impacts of breaches to the sea defences.
One such breach modelled is at Norman’s Bay just east of the site and the results of the breach
analysis are included in Appendix C.
The modelling covered breaches for the existing scenario and also taking into account the impacts
of climate change in 100 years’ time. It is also assumed that no improvement to the sea defences
are undertaken despite the significant rise in sea levels over this period. The results show there is
no risk to the dwellings at this site even under the climate change situation for the 1 in 200 year
storm event. This is because of the raised elevation of the ground compared with the marsh level
behind the defences. It can be seen from the modelling results that the marsh area behind the flood
defences suffers deep flooding should breaches occur.
The modelling also considers the impacts of a breach in the 1 in 1000 year event and again this has
been considered for both the current situation and the climate change situation in 2115. This shows
only a very low level of flooding in the 2115 situation with a low flood hazard. This indicates the risk
of tidal flooding to the property is extremely small even should a breach occur in the flood defences.
The predicted flooding will only occur if there is a breach to the defences and this is unlikely due to
the depth and height of the defences in this location.
Spray from waves and the possible impact of shingle hitting the dwelling also need to be considered
as the dwelling is close to the top of the shingle bank.
MONSON The Saltings, Coast Road, Norman’s Bay, Pevensey, East Sussex
Flood Risk Assessment
Issue A 7 24th April 2016 © Monson Engineering 2016
5.0 CLIMATE CHANGE
The modelling undertaken for the Strategic Flood Risk Assessment has taken climate change into
account.
6.0 DETAILED DEVELOPMENT PROPOSALS
The plans for the proposed dwelling are included in Appendix D and there are two options:
Option 1:-
The ground floor and first floor structure is retained but the existing spatial layout is re-arranged, the
building services are upgraded, the thermal performance is improved and the building envelope
upgraded. The first floor would be used for the main sleeping accommodation as currently
incorporated in the dwelling whilst a further bedroom is included in the ground floor as part of the
spatial re-arrangement. The existing ground floor is approximately 1.5 metres above the existing
ground levels so will be far more than 600 mm above the predicted flood water levels indicated from
the modelling results.
Option 2:-
The superstructure of the existing dwelling is demolished but the base is retained. A new dwelling
will then be constructed on the existing base with the ground floor levels and first floor levels being
at the same height as the current dwelling. This will again enable the existing spatial layout to be
re-arranged and the building services, thermal performance and building envelope to be all
upgraded as for Option 1. One bedroom will also be included in the ground floor accommodation
as for Option 1 which again will be approximately 1.5 metres above existing ground level as in the
current dwelling.
7.0 SAFE ACCESS
Generally safe access can be achieved along Coast Road into the elevated urban areas of
Eastbourne to the west. However, we would advocate that the residents do not stay in the property
MONSON The Saltings, Coast Road, Norman’s Bay, Pevensey, East Sussex
Flood Risk Assessment
Issue A 8 24th April 2016 © Monson Engineering 2016
if a severe flood warning is issued as it would be safer to be away from the area in such
circumstances.
8.0 OFF SITE IMPACTS AND PROPOSED MITIGATION MEASURES
The proposed dwelling will retain the existing footprint area but two options are proposed:-
Option 1 would re-arrange the existing spatial layout and upgrade the building services, thermal
performance and building envelope. There would be no improvement in terms of flood protection
with this option.
Option 2 would result in a completely new dwelling being constructed on the existing base. The re-
arrangement of the spatial layout and upgrade of the building services, thermal performance and
building envelope would all be incorporated as for option 1 but further flood mitigation measures can
be included in the design. These could include the following:-
The windows in the first floor which face the sea could be constructed using safety glass to
prevent damage from any shingle flung against the dwelling due to wave and wind action.
Electricity meters and wiring could be installed on the first floor with drop downs to the
ground floor
The ground floor could incorporate tiling rather than carpets to reduce any impact of flooding
should water enter the property.
Waterproof plaster can be uses for the ground floor to again minimise any impact if water
does enter the property.
We would also advocate that the residents connect to the flood warning service so that they
can take the appropriate actions in the event of flood or severe flood warnings.
A further bedroom is proposed on the ground floor but all the modelling results indicate there is no
risk of flooding to this property due to its relative elevation compared to the marsh area to the north.
Therefore, whilst we have advocated the introduction of flood mitigation measures for the design
and construction of Option 2, there is deemed to be far less than a 1 in 1000 chance of the property
being affected by flood water even under a breach scenario I 2115 when the impacts of climate
change have been taken into account.
MONSON The Saltings, Coast Road, Norman’s Bay, Pevensey, East Sussex
Flood Risk Assessment
Issue A 9 24th April 2016 © Monson Engineering 2016
We would therefore propose that Option 2 is adopted as this does provide an opportunity to reduce
the flood risk through design whilst Option 1 will have a similar flood risk to the existing situation.
9.0 MANAGEMENT OF RESIDUAL RISKS
The flood mitigation proposals have been designed on the basis of the residual risk which is a breach
of the sea defences close to the site.
10.0 CONCLUSION
This report supports a planning application for the re-development of an existing dwelling known as
The Saltings, Coast Road, Norman’s Bay, Pevensey, East Sussex.
All flood risks have been considered but the only risk identified is tidal flooding from the sea due
immediately south of the site.
The modelling undertaken by Rother District Council, as part of its Strategic Flood Risk Assessment,
indicates there is no flooding at the site under breach conditions even for the 1 in 200 year event in
2115 which takes climate change into account. Very shallow flooding is predicted in the event of a
breach for the 1 in 1000 year event with climate change in 2115 and the depth of flood water is so
low that it would not affect the ground floor accommodation. This indicates the site is safe from
flooding for even the most severe of storms.
The re-development proposals retain the same footprint area but two options are being considered.
Option 1:-
The ground floor and first floor structure is retained but the existing spatial layout is re-arranged, the
building services are upgraded, the thermal performance is improved and the building envelope
upgraded. The first floor would be used for the main sleeping accommodation as currently
incorporated in the dwelling whilst a further bedroom is included in the ground floor as part of the
spatial re-arrangement. The existing ground floor is approximately 1.5 metres above the existing
MONSON The Saltings, Coast Road, Norman’s Bay, Pevensey, East Sussex
Flood Risk Assessment
Issue A 10 24th April 2016 © Monson Engineering 2016
ground levels so will be far more than 600 mm above the predicted flood water levels indicated from
the modelling results.
Option 2:-
Option 2 would result in a completely new dwelling being constructed on the existing base. The re-
arrangement of the spatial layout and upgrade of the building services, thermal performance and
building envelope would all be incorporated as for option 1 but further flood mitigation measures can
be included in the design. These could include the following:-
The windows in the first floor which face the sea could be constructed using safety glass to
prevent damage from any shingle flung against the dwelling due to wave and wind action.
Electricity meters and wiring could be installed on the first floor with drop downs to the
ground floor
The ground floor could incorporate tiling rather than carpets to reduce any impact of flooding
should water enter the property.
Waterproof plaster can be uses for the ground floor to again minimise any impact if water
does enter the property.
We would also advocate that the residents connect to the flood warning service so that they
can take the appropriate actions in the event of flood or severe flood warnings.
A further bedroom is proposed on the ground floor but all the modelling results indicate there is no
risk of flooding to this property due to its relative elevation compared to the marsh area to the north.
Therefore, whilst we have advocated the introduction of flood mitigation measures for the design
and construction of Option 2, there is deemed to be far less than a 1 in 1000 chance of the property
being affected by flood water even under a breach scenario in 2115 when the impacts of climate
change have been taken into account.
We would advocate that Option 2 is the preferred solution in terms of flood mitigation as it enables
more flood resilience measures to be introduced in the design and construction of the re-developed
dwelling.
Surface water drainage will be unaffected as the same roof area will be used.
MONSON The Saltings, Coast Road, Norman’s Bay, Pevensey, East Sussex
Flood Risk Assessment
Issue A 11 24th April 2016 © Monson Engineering 2016
We therefore recommend that no objection is raised to this application as the flood risk to the
property will not increase and will reduce due to the design of the re-development if Option 2 is
adopted.
MONSON The Saltings, Coast Road, Norman’s Bay, Pevensey, East Sussex
Flood Risk Assessment
Issue A A 24th April 2016 © Monson Engineering 2016
APPENDIX A - SITE LOCATION
MONSON The Saltings, Coast Road, Norman’s Bay, Pevensey, East Sussex
Flood Risk Assessment
Issue A B 24th April 2016 © Monson Engineering 2016
APPENDIX B - ENVIRONMENT AGENCY MAPS;
FLOOD MAP FOR SEA AND RIVER (PLANNING)
FLOOD MAP FOR SEA AND RIVER
FLOOD MAP FOR SURFACE WATER
FLOOD MAP FOR RESERVOIRS
Environment Agency - What's in your backyard?
http://maps.environment-agency.gov.uk/...floodmap&layer=default&ep=map&layerGroups=default&scale=11&x=567665&y=105391#x=567930&y=105391&lg=1,2,10,&scale=11[24/05/2016 09:39:39]
Other maps Data search Text only versionMap legend
Click on the map to see whatFlood Zone (NationalPlanning Policy Guidancedefinitions) the proposeddevelopment is in.
Flood Map for Planning(Rivers and Sea)
Flood Zone 3
Flood Zone 2
Flood defences(Not all may be shown*)
Areas benefiting fromflood defences(Not all may be shown*)
Main River Line
Main River Line
Other nationalenvironmentalorganisations
Natural ResourcesWales Area ofresponsibility
Scottish EnvironmentProtection Agency Areaof responsibility
Enter a postcode or place name:
Other topics for this area...
Flood Map for Planning (Rivers and Sea)
Flood Map for Planning (Rivers andSea)
X: 567,930;Y: 105,391 at scale 1:10,000
Customers in Wales - From 1 April 2013 Natural Resources Wales (NRW) has taken over the responsibilities of the Environment Agency in Wales.© Environment Agency copyright and database rights 2016. © Ordnance Survey Crown copyright. All rights reserved. Environment Agency, 100026380.
Contains Royal Mail data © Royal Mail copyright and database right 2016.This service is designed to inform members of the public, in line with our terms and conditions. For business or commercial use, please contact us.
More about flooding:
Understanding the Flood Map for Planning (Rivers and Sea)
A more detailed explanation to help you understand the flood map shown above.
Current flood warnings
We provide flood warnings online 24 hours a day. Find out the current flood warning status in your local area.
* Legend Information: Flood defences and the areas benefiting from them are gradually being added throughupdates. Please contact your local environment agency office for further details.
Environment Agency - Risk of Flooding from Rivers and Sea
http://watermaps.environment-agency.gov.uk/...spx?topic=floodmap&scale=11&ep=map&layerGroups=default&lang=_e&y=105391&x=567929#x=567929&y=105391&scale=11[24/05/2016 09:40:52]
Data searchMap legend
Risk of Flooding fromRivers and Sea
High
Medium
Low
Very Low
Other nationalenvironmentalorganisations
Natural Resources WalesArea of responsibility
Scottish EnvironmentProtection Agency Area ofresponsibility
Author: The Environment Agency | [email protected] updated: 24 May 2016
Enter a postcode or place name:
Other topics for this area...
Risk of Flooding from Rivers and Sea
View other Interactive Maps
Risk of Flooding from Rivers and SeaRiver flooding happens when a river cannot cope with the amount of water draining into it from the surrounding land. Sea floodinghappens when there are high tides and stormy conditions.
The shading on the map shows the risk of flooding from rivers and the sea in this particular area.
Click on the map for a more detailed explanation.
Map of X: 567,929; Y: 105,391 at scale 1:10,000
Customers in Wales - From 1 April 2013 Natural Resources Wales (NRW) will take over the responsibilities of the Environment Agency in Wales. © Environment Agency copyright and database rights 2016. © Ordnance Survey Crown copyright. All rights reserved. Environment Agency, 100026380.
Contains Royal Mail data © Royal Mail copyright and database right 2016. This service is designed to inform members of the public, in line with our terms and conditions. For business or commercial use, please contact us.
Follow us: YouTube Twitter Flickr Facebook
Privacy policy | Terms and conditions | Contact us | Cymraeg © Environment Agency 2016
200 m1000 ft
Environment Agency - Risk of Flooding from Surface Water
http://watermaps.environment-agency.gov.uk/wiyby/wiyby.aspx?lang=_e&topic=ufmfsw&layer=default&scale=11&x=567929&y=105391#x=567929&y=105391&scale=11[24/05/2016 09:41:28]
Data searchMap legend
Risk of Flooding fromSurface Water
High
Medium
Low
Very Low
Other nationalenvironmentalorganisations
Natural Resources WalesArea of responsibility
Scottish EnvironmentProtection Agency Area ofresponsibility
Author: The Environment Agency | [email protected] updated: 24 May 2016
Enter a postcode or place name:
Other topics for this area...
Risk of Flooding from Surface Water
View other Interactive Maps
Risk of Flooding from Surface WaterSurface water flooding happens when rainwater does not drain away through the normal drainage systems or soak into theground, but lies on or flows over the ground instead.
The shading on the map shows the risk of flooding from surface water in this particular area.
Click on the map for a more detailed explanation.
Map of X: 567,929; Y: 105,391 at scale 1:10,000
Customers in Wales - From 1 April 2013 Natural Resources Wales (NRW) will take over the responsibilities of the Environment Agency in Wales. © Environment Agency copyright and database rights 2016. © Ordnance Survey Crown copyright. All rights reserved. Environment Agency, 100026380.
Contains Royal Mail data © Royal Mail copyright and database right 2016. This service is designed to inform members of the public, in line with our terms and conditions. For business or commercial use, please contact us.
Follow us: YouTube Twitter Flickr Facebook
Privacy policy | Terms and conditions | Contact us | Cymraeg © Environment Agency 2016
200 m1000 ft
569245, 106142
Environment Agency - Risk of Flooding from Reservoirs
http://watermaps.environment-agency.gov.uk/wiyby/wiyby.aspx?lang=_e&topic=reservoir&layer=default&scale=11&x=567929&y=105391#x=567929&y=105391&scale=11[24/05/2016 09:41:06]
Data searchMap legend
Risk of Flooding fromReservoirs
Maximum extent offlooding
Other nationalenvironmentalorganisations
Natural Resources WalesArea of responsibility
Scottish EnvironmentProtection Agency Area ofresponsibility
Author: The Environment Agency | [email protected] updated: 24 May 2016
Enter a postcode or place name:
Other topics for this area...
Risk of Flooding from Reservoirs
View other Interactive Maps
Risk of Flooding from ReservoirsReservoir flooding is extremely unlikely to happen.
The shading on the map shows the area that could be flooded if a large reservoir were to fail and release the water it holds. Alarge reservoir is one that holds over 25,000 cubic metres of water, equivalent to approximately 10 Olympic sized swimming pools.Since this is a worst case scenario, it’s unlikely that any actual flood would be this large.
Click on the shading to see details of reservoirs that could cause flooding in this area.
Map of X: 567,929; Y: 105,391 at scale 1:10,000
Customers in Wales - From 1 April 2013 Natural Resources Wales (NRW) will take over the responsibilities of the Environment Agency in Wales. © Environment Agency copyright and database rights 2016. © Ordnance Survey Crown copyright. All rights reserved. Environment Agency, 100026380.
Contains Royal Mail data © Royal Mail copyright and database right 2016. This service is designed to inform members of the public, in line with our terms and conditions. For business or commercial use, please contact us.
Follow us: YouTube Twitter Flickr Facebook
Privacy policy | Terms and conditions | Contact us | Cymraeg © Environment Agency 2016
200 m1000 ft
MONSON The Saltings, Coast Road, Norman’s Bay, Pevensey, East Sussex
Flood Risk Assessment
Issue A C 24th April 2016 © Monson Engineering 2016
APPENDIX C – MODELLING OUTPUT FROM ROTHER DISTRICT
COUNCIL’S STRATEGIC FLOOD RISK ASSESSMENT
MONSON The Saltings, Coast Road, Norman’s Bay, Pevensey, East Sussex
Flood Risk Assessment
Issue A D 24th April 2016 © Monson Engineering 2016
APPENDIX D – DEVELOPMENT PROPOSALS