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managingflood risk

River Ouse CatchmentFlood Management PlanSummary Report December 2009

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Environment Agency River Ouse Catchment Flood Management Plan 3

Introduction

The Ouse CFMP is one of 77 CFMPs for England andWales. Through the CFMPs, we have assessed inlandflood risk across all of England and Wales for the firsttime. The CFMP considers all types of inland flooding,from rivers, groundwater, surface water and tidalflooding, but not flooding directly from the sea (coastalflooding), which is covered by Shoreline ManagementPlans (SMPs). Our coverage of surface andgroundwater is however limited due to a lack ofavailable information.

The role of CFMPs is to establish flood riskmanagement policies which will deliver sustainableflood risk management for the long term. This isessential if we are to make the right investmentdecisions for the future and to help prepare ourselveseffectively for the impact of climate change. We willuse CFMPs to help us target our limited resourceswhere the risks are greatest.

This CFMP identifies flood risk management policies toassist all key decision makers in the catchment. It wasproduced through a wide consultation and appraisalprocess, however it is only the first step towards anintegrated approach to flood risk management. As weall work together to achieve our objectives, we mustmonitor and listen to each others progress, discusswhat has been achieved and consider where we mayneed to review parts of the CFMP.

The main source of flood risk in the Ouse CFMP area isfrom both localised river flooding, which is made worseby the influence of the tide, and some surface waterflooding. The risk is mainly located in Lewes, Newhavenand Uckfield.

We cannot reduce flood risk on our own, we willtherefore work closely with all our partners to improvethe co-ordination of flood risk activities and agree themost effective way to management flood risk in thefuture. The key partners we have worked with areNatural England, Southern Water, East Sussex CountyCouncil, Lewes District Council, Mid Sussex DistrictCouncil, South East Water, Sussex Ouse ConservationSociety, Wealden District Council.

This is a summary of the main CFMP document, if youneed to see the full document an electronic versioncan be obtained by emailing enquiries@environment-agency. gov.uk oralternatively paper copies can be viewed at any of ouroffices in Southern Region.

Toby WillisonRegional Director, Southern Region

I am pleased to introduce our summary of the OuseCatchment Flood Management Plan (CFMP). ThisCFMP gives an overview of the flood risk in theOuse catchment and sets out our preferred plan forsustainable flood risk management over the next50 to 100 years.

4 Environment Agency River Ouse Catchment Flood Management Plan

Contents

The purpose of a CFMP in managing flood risk 5

Catchment overview 6

Current and future flood risk 8

Future direction for flood risk management 11

Sub-areas

1 High Weald and Middle Ouse 13

2 Haywards Heath 14

3 Uckfield 15

4 Ouse Low Weald (East and West) 17

5 Lewes 18

6 The Brooks and Lower Ouse 20

7 Newhaven 21

8 South Downs (East and West)/Saltdean and Peacehaven 22

9 Seaford 23

Map of CFMP policies 24


The purpose of a CFMP in managing flood risk

CFMPs help us to understand thescale and extent of flooding nowand in the future, and set policiesfor managing flood risk within thecatchment. CFMPs should be usedto inform planning and decisionmaking by key stakeholders such as:

• The Environment Agency, who willuse the plan to guide decisionson investment in further plans, projects or actions;

• Regional planning bodies and local authorities who can use the plan to inform spatial planning activities and emergency planning;

• IDBs, water companies and other utilities to help plan their activities in the wider contextof the catchment;

• Transportation planners;

• Land owners, farmers and land managers that manage and operate land for agriculture, conservation and amenity purposes;

• The public and businesses to enhance their understanding of flood risk and how it willbe managed.

CFMPs aim to promote moresustainable approaches to managingflood risk. The policies identified inthe CFMP will be delivered through acombination of different approaches.Together with our partners, we will implement these approachesthrough a range of delivery plans,projects and actions.

The relationship between the CFMP,delivery plans, strategies, projectsand actions is shown in figure 1.

Policy delivery plans (see note)• Influence spatial planning to reduce risk

and restore floodplains.

• Prepare for and manage floods(including local flood warning plans).

• Managing assets.

• Water level management plans.

• Land management and habitat creation.

• Surface water management plans.

Projects and actions• Make sure our spending delivers the best

possible outcomes.

• Focus on risk based targets, for examplenumbers of households at risk.

Figure 1. The relationship between CFMPs, delivery plans, projects and actions.

Policy planning• CFMPs and Shoreline Management Plans.

• Action plans define requirement for deliveryplans, projects and actions.

Note: Some plans may not be led by us – we mayidentify the need and encourage their development.


Catchment overview

The River Ouse CFMP covers an areaof approximately 605 squarekilometres and is home to around165,000 people. The main urbancentres are located either on thecoastal plain, in towns such asNewhaven and Seaford, or in inlandtowns such as Lewes, Uckfield andHaywards Heath. Its uniquelandscape and natural beauty makeit an important recreational andtourist destination. A significant areaof the catchment is designated asArea of Outstanding Natural Beauty(AONB) including the High Wealdand South Downs AONBs. The SouthDowns AONB is also within the area

of the South Downs National Park.The area is particularlyenvironmentally rich and includesone Special Protection Area (SPA),three Special Areas of Conservation(SACs), two National NatureReserves (NNRs) and 24 Sites ofSpecial Scientific Interest (SSSIs).Many of these sites supportimportant wetland habitats andspecies sensitive to changes inwater level, flow and quantity.

The River Uck is one of the maintributaries of the River Ouse.Relatively steep slopes and channelgradient can produce relatively rapid

run-off causing the river to respondquickly to heavy rainfall events. Theupper parts of the River Ouse incomparison are not as steep andthe river flows through gentlyundulating countryside. Below theconfluence with the River Uck, theRiver Ouse is characterised by abroad floodplain through which theriver meanders down to Lewes. AtLewes the River Ouse flows througha narrow gap in the chalk hills of theSouth Downs, emerging onto thelow lying Lewes Brooks where theriver becomes tidal as it approachesthe coast at Newhaven.

View of the River Ouse from LewesRailway Land Local Nature Reserve.

‘Many protected areas support important wetlandhabitats and species sensitive to changes in water level,flow and quantity.’

➜


Map 1. Overview map of the Ouse catchment.

‘The River Uck catchment has relatively steep slopesand channel gradient, which results in rapid run-offcausing the river to respond quickly to heavy rainfallevents. The upper parts of the River Ouse incomparison are not as steep, flowing through gentlyundulating countryside.’


Flood risk is the combination of thelikelihood of a flood occurring andthe consequences when it does. Wehave assessed flood risk across theCFMP area using broad-scalecomputer modelling, thoughmaking best use of existingknowledge and models whereappropriate. Flood risk figures takeinto account current flood defences.Around 880 properties (residentialand commercial) are at risk offlooding from the rivers during a 1% annual probability flood event.The impact of flooding to theenvironmentally designated sites isgenerally positive with benefits tomany habitats, such as floodplain

grazing marsh, which support awide diversity of invertebrate andamphibious species. Floodingoccurs from a number of sourcesincluding rivers (fluvial and tidalflooding), urban surface water run-off exacerbated by inadequate localdrainage, run-off from fields andgroundwater flooding. Known andpotential flood prone areas includeLewes, Newhaven, Seaford, Uckfield,Haywards Heath and Lindfield.

There have been a number of majorflooding events over the last century,including the 1960, 1979, 1987,1993 and 2000 events that affectedthe urban areas of Uckfield, Lewes,

Haywards Heath and Lindfield. TheRiver Ouse is tidally influenced fromBarcombe Mills to Newhaven, whichexacerbates river floodingparticularly in Lewes and Newhaven.

Overview of the current flood risk

➜ Barcombe Mills floodwaters - February 2006.

Where is the risk?

The map on page 10 illustrates theconsequences of a 1% annualprobability event (1 in 100 year)occurring in the CFMP area.

The areas with the highestconcentration of properties at riskfrom river flooding are tabulated onpage 9.

Current and future flood risk


• Strategic planning to plan long term investment.

• Environmental improvements.

How we currentlymanage the riskFlood risk management in the Ousecatchment has historically relied onembankments and walls acting todefend areas at risk and we aretherefore looking for opportunitiesto revert the catchment back to itsnatural state. Our activity isprioritised on a risk basis and ourmain activities include:

• The maintenance of existing and the construction of new or replacement flood defences and structures such as the raised embankments along the tidalreach of the River Ouse from the mouth of the river at Newhaven up to Barcombe Mills. The embankments primarily protectagricultural land, however, approximately 2,000 propertiesare also currently protected bythese structures downstream ofBarcombe Mills.

• Flood forecasting and warnings, which are currently sent to approximately 60% of the properties at risk of flooding and aim to give at least two hour lead time ahead of river flooding.

• Development control to influence spatial planning so that new developments are sited away from flood risk areas or take appropriate mitigation measures and do not make flooding worse for anyone else.

• Flood risk mapping.

3 emergency services, 6 electricity sub stations, 2 sewage/watertreatment works

Table 2. Critical infrastructure at risk:

Number of properties at risk Locations

>1000 None

500 to 1000 None

100 to 500 Lewes, Newhaven

50 to 100 Uckfield

25 to 50 Haywards Heath

Table 1. Locations of towns and villages with 25 or more properties at riskin a 1% annual probability river flood.

0

250

500

750

1000

1250

Uckfield

Current

Num

ber o

f pro

pert

ies

at fl

ood

risk

Lewes NewhavenHaywardsHeath

Future

Figure 2. Current and future (2100) flood risk to property from a 1% annualprobability river flood, taking into account current flood defences.


The effect that flooding will have inthe future is influenced by a rangeof issues such as climate change,changes in land use such asdevelopment, and changes in howland is managed.

Predictions of future change arebased on understanding the existingcondition of the catchment, anextrapolation of trends over the longterm (up to 100 years), and a highlevel review of likely future changebased on research findings andknowledge. Although the catchmentis largely rural, developmentpressures to meet demand for housingwithin the South East will inevitablyresult in some urban growth, however,the predicted increase in urbangrowth relative to the River Ousecatchment area is small and as a

whole the catchment is notparticularly sensitive to this level ofchange in urbanisation. There is someevidence to support the likelihoodof an very small increase in run-offdue to change in land managementpractices, however, changes to landuse and land use management havevery little impact on flood risk andare also unlikely to occur on acatchment scale. The broadscalemodelling did show that the RiverOuse CFMP catchment was sensitiveto both increased flow and sea levelrise. The scenario which has thegreatest effect on future flood risk isclimate change with up to 20%increase in peak flood flows. Thisscenario is used to assess likelyimpacts in the catchment. In the Ousecatchment the future flood risk is

likely to be from river flooding andsome surface water flooding. Ourappraisal of the future risk in thecatchment reveals the number ofproperties at risk to the 1% annualprobability event will increase from858 to 1872 properties by the year2100. The majority of theseproperties are located in Lewes,Newhaven and Uckfield.

The key trends are:

• More frequent and intense stormscausing more widespread and regular flooding from drainage systems and some rivers.

• More rain in winter, increasing the likelihood of large scale flood events.

The impact of climate change and future flood risk

Map 2. Flood risk to property in a 1% annual probability river flood, taking into account current flood defences.


We have divided the River Ouse catchment into nine distinct sub-areaswhich have similar physical characteristics, sources of flooding and level ofrisk. We have identified the most appropriate approach to managing floodrisk for each of the sub-areas and allocated one of six generic flood riskmanagement policies, shown in Table 3.

To select the most appropriate policy, the plan has considered how social,economic and environmental objectives are affected by flood riskmanagement activities under each policy option.

Future direction for flood risk management

Approaches in each sub-area

Map 3. Sub-areas and flood risk management policies.


➜ Policy 1Areas of little or no flood risk where we will continue to monitor and advise

This policy will tend to be applied in those areas where there are very few properties at risk of flooding. It reflects acommitment to work with the natural flood processes as far as possible.

➜ Policy 2Areas of low to moderate flood risk where we can generally reduce existing flood risk management actions

This policy will tend to be applied where the overall level of risk to people and property is low to moderate. It mayno longer be value for money to focus on continuing current levels of maintenance of existing defences if we canuse resources to reduce risk where there are more people at higher risk. We would therefore review the flood riskmanagement actions being taken so that they are proportionate to the level of risk.

➜ Policy 3

Areas of low to moderate flood risk where we are generally managing existing flood risk effectively

This policy will tend to be applied where the risks are currently appropriately managed and where the risk offlooding is not expected to increase significantly in the future. However, we keep our approach under review,looking for improvements and responding to new challenges or information as they emerge. We may review ourapproach to managing flood defences and other flood risk management actions, to ensure that we are managingefficiently and taking the best approach to managing flood risk in the longer term.

➜ Policy 4Areas of low, moderate or high flood risk where we are already managing the flood risk effectively but where wemay need to take further actions to keep pace with climate change

This policy will tend to be applied where the risks are currently deemed to be appropriately-managed, but wherethe risk of flooding is expected to significantly rise in the future. In this case we would need to do more in thefuture to contain what would otherwise be increasing risk. Taking further action to reduce risk will require furtherappraisal to assess whether there are socially and environmentally sustainable, technically viable andeconomically justified options.

➜ Policy 5Areas of moderate to high flood risk where we can generally take further action to reduce flood risk

This policy will tend to be applied to those areas where the case for further action to reduce flood risk is mostcompelling, for example where there are many people at high risk, or where changes in the environment havealready increased risk. Taking further action to reduce risk will require additional appraisal to assess whether thereare socially and environmentally sustainable, technically viable and economically justified options.

➜ Policy 6

Areas of low to moderate flood risk where we will take action with others to store water or manage run-off in locations that provide overall flood risk reduction or environmental benefits

This policy will tend to be applied where there may be opportunities in some locations to reduce flood risk locallyor more widely in a catchment by storing water or managing run-off. The policy has been applied to an area (wherethe potential to apply the policy exists), but would only be implemented in specific locations within the area, aftermore detailed appraisal and consultation.

Table 3. Policy options.


High Weald and Middle Ouse

Sub-area 1

Our key partners are:

Mid Sussex District Council and Wealden District Council

Natural England

National Farmers Union

Farming and Wildlife Advisory Group

High Weald Joint Advisory Committee

The issues in thissub-areaA small extent of the OffhamMarshes Sites of Special ScientificInterest (SSSI) is prone to floodingfrom the 1% annual probabilityflood event, however periodicflooding is a natural element of thehabitat. The key risk in this sub-areais localised river flooding from theRiver Ouse tributaries in extremeconditions. Defences includemaintained and culverted channelsand raised defences.

• Natural England’s agri-environmentand woodland schemes grantsshould be explored to help fund the change of land use and land use management to increase the water retention in the catchment.

• Carry out a Sussex Landcare Project focusing on improving land management.

• Undertake a pre-feasibility studyto focus on river restoration from the Sloop Inn to Fletching, including Sheffield Park.

• A pre-feasibility study should be undertaken focusing on opportunities for flood storage and increased floodplain inundation to provide benefits toLewes. Habitat creation and restoration benefits should also be investigated.

• Develop the Offham MarshesWater Level Management Plan.

Impact of a 1% annual probability flood event

Today Future (2100)

Number of properties at risk 24 24

The vision and preferred policy

Policy Option 6 – areas of low tomoderate flood risk where we willtake action with others to storewater or manage run-off in locationsthat provide overall flood riskreduction or environmental benefits.

The key messagesThis policy can deliver benefits forpeople and the environment locallyor in other parts of the CFMP area. It sets a framework that activelysupports increased inundation ofareas that naturally benefit frombeing wetter and will help keepwater on the land for longer. Anincrease in flood storage couldreduce flood risk to properties inUckfield and Lewes into the future.

Proposed actions toimplement the preferredapproach:• Develop a System Asset

Management Plan (SAMP) to review maintenance regimes andaim to restore more sustainable river functions.

• Work with the AONB Joint AdvisoryCommittee to achieve the targetsset in the AONB Management Plan.

• Increase the number of whole farm plans under the Sustainable Agriculture and Rivers Project in the upper River Ouse and Uckcatchments.

• Investigate removal of structuresto restore rivers and floodplainsto a naturally functioning state.

Flood waters at New Weir in BarcombeMills, 2004.➜


Sub-area 2

Haywards Heath


Mid Sussex District Council

Lewes District Council

Southern Water

The issues in thissub-areaLocalised flooding may occur fromthe Scrase Bridge Stream and WestCommon Stream as a result ofsurface water overwhelming urbandrainage systems. There is urbandevelopment proposed in this sub-area which will have an impact onflood risk into the future.


Today Future (2100)


Proposed actions to implement the preferredapproach:• Develop a System Asset Management Plan (SAMP) to review

maintenance regimes.

• Develop a Surface Water Management Plan (SWMP) for Haywards Heath.

• Put in place policies within the local development frameworks that worktowards long-term protection and re-creation of the Scrase Bridge Stream and West Common Stream.

• Provide development control advice to ensure no increase in run-offfrom developments.

• Increase the coverage of the Floodline Warnings Direct in HaywardsHeath and Lindfield.

• Install level gauges on the streams within Lindfield to increase the efficiency of Floodline Warnings Direct.


Policy Option 4 – areas of low,moderate or high flood risk wherewe are already managing the floodrisk effectively but where we mayneed to take further actions to keeppace with climate change.

The key messagesIt will ensure appropriate urbangrowth is identified for the sub-areain the South East Plan. There arealso opportunities to extend and re-create habitats, such as wetwoodland, in order to enhance thenature conservation value orexisting river systems.


Sub-area 3

Uckfield


Wealden District Council

East Sussex County Council(Highways)

Southern Water

The issues in thissub-areaThere is currently a significant riskfrom fluvial flooding from the RiverUck. Flooding in the area can occurrelatively frequently and during theless frequent, more severe floodevents a significant number ofpeople and property are at risk offlooding. The catchment respondsrapidly to rainfall and run-off arrives


Today Future (2100)



Policy Option 5 – areas of moderateto high flood risk where we cangenerally take further action toreduce flood risk.

The key messagesA policy to take further action applieswhere the current flood risk isdemonstrated to be unacceptablyhigh. There is currently a risk fromflooding in Uckfield due to the rapidonset of flooding, the high velocitiesof floodwater and the associateddepth of the water. Flood riskmanagement activities need torespond to the current high levels offlood risk.

➜ Uckfield Mills Weir at high flow, February 2007.

in the main river very quickly.Surface water flooding and urbandrainage flooding is alsoexperienced in this sub-area.


Proposed actions to implement the preferred approach:• Encourage the uptake of Defra’s flood resistance and resilience pilot project.

• Seek out funding and partnership opportunities in connection with new developments and consider options forredevelopment of more open river corridors through Uckfield, to reduce the number of properties in the floodplain and therefore reduce the number of properties at risk of flooding.

• Put in place policies within the local development frameworks that work towards long-term protection and reinstatement of a functioning floodplain through Uckfield through sustainable land management.

• Develop a Surface Water Management Plan (SWMP).

• Consider options to increase the coverage of the Floodline Warnings Direct service in Uckfield.

• Investigate the potential for improving the current defences to reduce the cost of flood damages in Uckfield .

• Provide development control advice to ensure no increase in run-off from the new developments proposed in the South East Plan and seek opportunities to reduce current run-off rates, where possible.

• Carry out a study to investigate the potential for an upstream flood storage area. The flood storage area would be provided upstream of Uckfield in the High Weald sub-area.

• Install water level gauges further upstream of Uckfield town centre to increase the efficiency of Floodline Warnings Direct and reduce the risk of flooding to people in Uckfield.

• Develop a System Asset Management Plan (SAMP) to review maintenance regimes with an aim to reduce flood risk.

• Undertake Flood Alleviation Scheme at Uckfield as recommended in the Sussex Ouse Flood Management Strategy.

Uckfield Rail Station.➜


Sub-area 4

Ouse Low Weald (East and West)


Mid Sussex District Council


The issues in thissub-areaThis sub-area is mostly managedgrassland and arable land withisolated properties and smallsettlements. The current flood risk isconsidered to be low with smallareas of localised fluvial floodingassociated with the tributaries ofthe River Ouse, and surface waterflooding in Wivelsfield Green,Plumpton Green and Ringmer. Floodrisk is not expected to increase inthe future due to climate change.


Today Future (2100)


Proposed actions toimplement the preferredapproach:• Understanding of flood risk in this

sub-area should be enhanced through a pre-feasibility study. This should concentrate on the present flood risk at Plumpton Green and Ringmer.

• Maintain existing level ofmaintenance within the communities of Ringmer, Plumpton Green and Wivelsfield Green, looking for efficiencies and improvements to ensure the existing flood risk to these communities does not get worse in the future.

• Undertake a System AssetManagement Plan (SAMP) to investigate options to better target the available funds for flood risk management.

• Encourage the take up of flood resistance and resilience measures by people at risk ofsurface water flooding.

The vision and preferred policyPolicy Option 2 – areas of low tomoderate flood risk where we cangenerally reduce existing flood riskmanagement actions.

The key messagesThis policy applies where thecurrent level of flood risk is low andflood risk is not expected tosignificantly increase in the future. It will allow a controlled reduction in flood risk managementmaintenance costs to a moreappropriate level for the level offlood risk in the sub-area, whilefocusing flood risk managementactions within the communities athigher risk of flooding from localfluvial and surface water sources.

It is recognised that flood risk willchange in the future, andmanagement actions may change in time to gain efficiencies orimprove effectiveness.

View from Clearwater Lane, Scaynes Hill.➜


Sub-area 5

Lewes



Southern Water


Natural England

The issues in thissub-areaThis sub-area is largely urban,including the main town of Lewes.There is significant flood riskassociated with the River Ouse,which flows through the towncentre, and surface water, urbandrainage and groundwater flooding.The town is classed as anarchaeologically sensitive area withat least ten Scheduled Monumentsand additionally there are six Sitesof Special Scientific Interest (SSSI)that fully or partly lie in the sub-area(including Lewes Brooks andOffham Marshes). This sub-areaincludes the Malling at Lewes,Winterbourne Stream at Lewes andthe majority of the Lewescommunity flood warning areas.Flood risk in this sub-area has beenassessed as high with a likelihoodof increased flood risk in the future.


Today Future (2100)


View downstream of Lewes town centre.➜


Policy Option 5 – areas of moderateto high flood risk where we cangenerally take further action toreduce flood risk.

high. Flood risk managementactivities need to respond to thecurrent level of flood risk taking intoaccount any potential futureincreases in flood risk.

The current flood defences alongthe River Ouse through Lewesprovide a degree of protection forthe more frequently occurring floodevents. This policy will reduce floodrisk in Lewes either by improvingdefences or by taking alternativeactions, such as improved floodwarning or greater flood resilience.

The key messagesA policy to take further actionapplies where the current flood riskis considered to be unacceptably


Proposed actions to implement the preferred approach:• Seek funding to carry out flood resistance and resilience in Lewes to make vulnerable homes more resilient to

the threat of flooding and thus reduce the cost of flood damages to properties.

• Put in place policies within the local development frameworks that work towards long-term protection and re-creation of the River Ouse corridor through sustainable land management. This should look at opportunitiesto enhance the biodiversity and reduce the number of properties affected by flooding in Lewes.

• Deliver the outcomes of the Surface Water Management Plan (SWMP) for Lewes looking at all sources offlooding (groundwater, surface water, urban drainage and fluvial flooding).

• Increase the coverage of the Floodline Warnings Direct service in Lewes to reduce the flood risk to people in Lewes and surrounding areas.

• Investigate the potential for installing demountable and the preliminary deployment of temporary defences in advance of permanent solutions through the town centre of Lewes to reduce the cost of flood damages.

• Develop the Offham Marshes Water Level Management Plan to identify water level management that meets the need of flood risk management and the enhancement of the wetland habitat – in conjunction with Middle Ouse sub-area.

• Develop a flood warning system for groundwater flooding. This should focus on the Winterbourne Stream to thewest of Lewes to reduce the number of people at risk from groundwater flooding.

• Provide development control advice to ensure no increase in run-off from new developments and seekopportunities to reduce current run-off rates, where possible.

• Take forward Flood Alleviation Schemes at Lewes as recommended in the Sussex Ouse Flood ManagementStrategy.

• Install water level gauges upstream on the Malling Brooks tributary to increase the efficiency of Floodline Warnings Direct and reduce the flood risk to people in Lewes and surrounding areas.

• Develop a System Asset Management Plan (SAMP) to review maintenance regimes with an aim to reduce flood risk.


Sub-area 6

The Brooks and Lower Ouse



Natural England

The issues in thissub-areaThis sub-area is mainly rural withisolated settlements within the lowlying valley of the River Ouse. Thefrequency of flooding is likely toincrease in this area in the future asa result of sea level rise, the impactof the additional flooding will beminimal. There are no proposedmajor urban developments in thissub-area.


Today Future (2100)


Proposed actions toimplement the preferredapproach:• Develop the Lewes Brooks Water

Level Management Plan to identify water level managementthat meets the need of flood riskmanagement and the enhancement of the wetland habitat.

• A pre-feasibility study should be undertaken to identifyrealignment options to increase flood storage and inundation ofareas to reduce flood risk and benefit the environment.

• Implement schemes to increase floodplain inundation downstream of Lewes and upstream of Newhaven.

• Develop a System AssetManagement Plan (SAMP) to review maintenance regimes.


Policy Option 6 – areas of low tomoderate flood risk where we willtake action with others to store wateror manage run-off in locations thatprovide overall flood risk reductionor environmental benefits.

The key messagesThe chosen policy can deliverbenefits for people and theenvironment locally or in other sub-areas. By increasing flooding locallyin this sub-area, flood risk in Lewescan be reduced. Increasingfrequency of inundation is likely toimprove wetland biodiversity, asflooding is an essential part offloodplain ecosystems. There ispotential to increase the area ofexisting Lewes Brooks Site ofSpecial Scientific Interest (SSSI)wetland habitat; identified withinambition five of The South DownsManagement Plan (Draft June 2006).

➜Lower Ouse and Lewes Brooks SSSI.


Newhaven



Southern Water


The issues in thissub-areaThis sub-area is mainly at risk fromtidal flooding as a result of high sealevels entering the river mouth andovertopping the riverembankments. The current risk offlooding is low, however climatechange is expected to significantlyincrease the flood risk from tidalflooding. Surface water run-off andurban drainage flooding are alsoexpected to increase over time dueto climate change and from plannednew development.


Today Future (2100)

Number of properties at risk 361 1,223

Sub-area 7

The key messagesThere are opportunities to reduce flood risk and improve the existing waterquality by promoting and encouraging the use of Sustainable urbanDrainage Systems (SuDS) within the new housing developments. Due tothe coastal location of the sub-area any actions will have to be undertakenin accordance with the relevant Shoreline Management Plan (SMP) andcoastal defence strategies.


Policy Option 4 – areas of low,moderate or high flood risk wherewe are already managing the floodrisk effectively but where we mayneed to take further actions to keeppace with climate change.

➜Newhaven Harbour at low tide.

Proposed actions to implement the preferredapproach:• Develop a Surface Water Management Plan (SWMP) for Newhaven. This

should concentrate on understanding the complexities and linksbetween the various forms of flooding in Newhaven.

• Provide development control advice to ensure no increase in run-offfrom the new developments, where possible.

• Carry out a more detailed study to investigate the future fluvial and surface water flood risks to Newhaven and surrounding areas as a resultof predicted sea level rise.

• Increase the coverage of the Floodline Warnings Direct service in Newhaven.

• Develop a System Asset Management Plan (SAMP) to review maintenance regimes.


South Downs (East and West)/Saltdean and Peacehaven



Brighton and Hove City Council

Proposed actions toimplement the preferredapproach:• Continue to monitor and advise.


Today Future (2100)


Sub-area 8


Policy Option 1 – areas of little orno flood risk where we will continueto monitor and advise.

The issues in thissub-areaThe current level of flood risk fromriver, surface water, sewer andgroundwater flooding is assessedas low with no increase expected inthe future. Flood risk from the sea isdealt with in the Beachy Head toSelsey Bill Shoreline ManagementPlan (SMP). The South Downs ishighly rural with only a very smallrisk of fluvial flooding from theGlynde Reach. There are raised man-made flood defences, with a designstandard for the 3.3% annualprobability flood event along partsof the Glynde Reach.

The key messagesThe chosen policy promotes activemonitoring and providing advice butdoes not support any flood riskmanagement actions within thesub-area. For a very small area ofthis sub-area, maintenanceassociated with the existing raisedman-made defences along theGlynde Reach will continue. Thispolicy also encourages a shifttowards best practice in landmanagement. By working withlandowners and government thiscould reduce disruption from

surface water flooding to locallyimportant transport links, such asthe railway. The southern part ofthis sub-area is coastal. Any actionsin this coastal area will have to beundertaken in accordance with theBeachy Head to Selsey BillShoreline Management Plan (SMP).


Seaford



Southern water

Sussex Police and other emergencyservices

The issues in thissub-areaThis sub-area is largely urban,including the main town of Seaford.There is currently low to mediumrisk of flooding as a result of surfacewater running off the South Downsalong the dry river valleys andoverwhelming urban drainagesystems. There are no formal fluvialflood defences or community floodwarning areas and no rivermaintenance is undertaken in thissub-area. Flood risk is not expectedto increase significantly in the futuredue to climate change or urbandevelopment.

Seaford is included within theSeahaven Flood Plan (Draft) October2007. This document sets out theco-ordinated and inter-agencywarning mechanism and responseto flooding incidents in the Seafordarea.

Sub-area 9


Today Future (2100)


Proposed actions toimplement the preferredapproach:• Continued practice and

development of the emergencyresponse plan.

• Develop a Surface Water Management Plan (SWMP) for Seaford with a start date of 2018.The study will review surface water drainage, the implications of tidelocking and climate change.


Policy Option 1 – areas of low tomoderate flood risk where we aregenerally managing existing floodrisk effectively.

The key messagesThe chosen policy applies where thecurrent level of flood risk isdemonstrated to be acceptable andthe level of flood risk managementappropriate to the level of risk. Thecurrent flood risk managementactivities carried out in this sub-areafor the surface water urban drainageflooding problems are consideredappropriate for the level of floodrisk. It is recognised that flood riskmanagement actions may need tochange in time to gain efficienciesor improve effectiveness.

There are opportunities to supportlocal schemes and studies alreadyin place to reduce the surface waterurban drainage flooding problemsin the urban area.

Due to the coastal location of thesub-area any actions will have to beundertaken in accordance with theBeachy Head to Selsey BillShoreline Management Plan (SMP).


Map of CFMP policies

Map of the policies in the River Ouse catchment.

GESO1008BOWG-E-E

Environment first: Viewing this on screen? Please consider theenvironment and only print if absolutely necessary. If you’re reading a paper copy, please don’t forget to reuse and recycle.

Would you like to find out more about us,or about your environment?

Then call us on 08708 506 506 (Mon-Fri 8-6)

[email protected]

or visit our website www.environment-agency.gov.uk

incident hotline 0800 80 70 60 (24hrs)

floodline 0845 988 1188

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summary report december 2009 managing flood risk · 2014-03-19 · regional director, southern...

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