Summary Report December 2009 managing flood risk...Lymington and New Milton. Its unique landscape and natural beauty make it an important recreational and tourist destination. The

managingflood risk

New Forest CatchmentFlood Management PlanSummary Report December 2009

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Environment Agency New Forest Catchment Flood Management Plan 3

Introduction

The New Forest CFMP is one of 77 CFMPs for Englandand Wales. Through the CFMPs, we have assessedinland flood risk across all of England and Wales forthe first time. The CFMP considers all types of inlandflooding, from rivers, groundwater, surface water andtidal flooding, but not flooding directly from the sea(coastal flooding), which is covered by ShorelineManagement Plans (SMPs). Our coverage of surfaceand groundwater 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 New Forest CFMP isfrom river flooding and the increasing effect of the tidedue to sea-level rise. Flood risk is concentrated withinthe urban areas such as Brockenhurst, Lymington and Totton.

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. Our partners we have worked with to carry outthe actions to reduce flood risk include New ForestDistrict Council, Natural England, Southern Water,Forestry Commission and the National Farmers Union.

This is a summary of the main CFMP document, if youneed to see the full document an electronic versioncan be obtained by emailing [email protected] or alternatively 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 NewForest Catchment Flood Management Plan (CFMP).This CFMP gives an overview of the flood risk in theNew Forest catchment and sets out our preferredplan for sustainable flood risk management overthe next 50 to 100 years.

4 Environment Agency New Forest 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 Milton/Milford 13

2 Lyndhurst 15

3 Brokenhurst 16

4 Lymington 18

5 Hythe/Fawley 19

6 Totton 20

7 New Forest 21

Map of CFMP policies 23


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 New Forest CFMP area covers317 square kilometres and is hometo nearly 169,000 people, withurban centres around the coastincluding Totton, Hythe, Fawley,Lymington and New Milton. Itsunique landscape and naturalbeauty make it an importantrecreational and tourist destination.The majority of the catchment isincluded in the New Forest NationalPark. The area is environmentallyrich, with protected areas coveringaround half of the catchment,including two Ramsar Sites and

Special Protection Areas (SPA),three Special Areas of Conservation(SAC) and 14 Sites of SpecialScientific Interest (SSSI). Many ofthese sites support importantwetland habitats and speciessensitive to changes in water level,flow and quantity.

The New Forest watercourses draininto either the Solent orSouthampton Water. The two largestwatercourses are the LymingtonRiver and the Beaulieu River, whichboth flow through largely forestedareas. Other watercourses of note

are the largely forested Avon Water,the mixed character Bartley Waterand the relatively urbanised Danes Stream.

Due to the geology and overlyingsoils, the catchments of the NewForest are considered relativelyimpermeable, which generallyleads to a quick response to rainfalland large fluctuations in river flows.The Danes Stream is thewatercourse that responds mostquickly to rainfall.

Lymington River near Brockenhurst.Forested streams such as this are typicalof the upper catchment.

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

➜


Map1. Overview map of the New Forest catchment.

‘The catchments of the New Forest are relativelyimpermeable, which leads to a quick response torainfall and large fluctuations in river flows.’


Flood risk is the combination of thelikelihood of a flood occurring andthe consequences when it does.Serious flooding does not occurvery often in the New Forest CFMParea, and extreme flooding is veryrare. In many parts of the catchment,flooding brings environmentalbenefits to habitats such as wetwoodland and reed bed.

The main source of flooding in theNew Forest CFMP area is from riverswith significant influence from tidalconditions. Risks are most significantin Brockenhurst, Milford on Sea,Lymington, Totton and Keyhaven.

There have been several largeevents over the last century,particularly on the Danes Stream.

Bartley Water and Lymington Rivercatchments. The Calmore Canalpassing through Totton exacerbatessurface water flooding after heavyrain because culvert restrictionscause high water levels reducingthe efficiency of the road drainage network.

Overview of the current flood risk Where is the risk?

The map on page 10 illustrates thedistribution of the flood riskconsequences in the New ForestCFMP area.

The areas with the highestconcentration of properties at riskfrom river flooding are tabulatedopposite.

Current and future flood risk

➜ This environmentally rich catchment offers a unique landscape and natural beauty.


Number of properties at risk Locations

>1000 None

500 to 1000 None

100 to 500 Brockenhurst, Totton, Lymington

50 to 100 Milton/Milford, New Forest

25 to 50 Hythe and Fawley

How we currentlymanage the riskFlooding from fluvial sources doesnot pose a significant risk to most ofthe New Forest catchment and we aretherefore looking for opportunitiesto revert the catchment back to itsnatural state. Our activity isprioritised on a risk basis and ourmain activities include:

• Maintenance of existing and commission of new flood defences and structures such asthe flood storage reservoir on the Danes Stream which protectsMilford-on- Sea and the recentlycompleted Flood Alleviation Scheme for Lymington.

• Flood forecasting and warnings, which are currently sent to approximately 840 propertiesand aim to give at least two hourslead time ahead of river flooding.

• Development control to influencespatial planning so that new developments are sited awayfrom flood risk areas, or take appropriate mitigation measures.

• Flood risk mapping.

• Strategic planning to plan long term investment.

• Environmental improvements.

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

1 emergency service, 11* electricity sub stations, 1 sewage/water treatment works

Table 2. Critical infrastructure at risk:

* Considered to be tidal flooding, except for 1 site in Lymington

New Forest RAMSAR, SAC, SPA

Table 3. Designated sites at risk:

* Considered to be tidal flooding, except for 1 site in Lymington

0

50

100

150

200

250

300

350

400

450

500

Brockenhurst

Current

Num

ber o

f pro

pert

ies

at fl

ood

risk

Lymington TottonMilton/Milford

Future

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


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

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

Predictions of future change are basedon 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. Present urbandevelopment plans within the CFMParea are limited, with the majorconstraint to development being thatthe majority of the catchment is nowa National Park. Therefore the effect

on flood risk at a catchment scale islikely to be minimal. The land usechange projections increase floodpeak flows on the upper catchmentsand on the Lymington River, but lessso on the Avon Water and in all casesthey are significantly less than thevalues resulting from increased flowsdue to climate change. We have foundthat whilst land use change is likelyto have an impact on flood risklocally, this is not significant on acatchment scale. We have thereforedecided not to include land usechange further in our scenarios. Thescenario which has the greatest effecton future flood risk is climate changewith up to 20% increase in peak floodflows. This scenario is used to assesslikely impacts in the catchment. In

the New Forest catchment the futureflood risk is likely to be from riverflooding. Our appraisal of the futurerisk in the catchment reveals thenumber of properties at risk to the 1%annual probability event will increasefrom 897 to 1299 properties by theyear 2100. The majority of theseproperties are located inBrockenhurst, Lymington and Totton.

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


We have divided the New Forest catchment into seven 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 4.

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 of the New Forest Catchment.


➜ 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 4. Policy options.


Milton/Milford

Sub-area 1

Our key partners are:

New Forest District Council

Natural England

The issues in thissub-areaThe key risk in this sub-area is fromriver flooding in the Sway, Keyhavenand Milford-on-Sea. A floodattenuation scheme on DanesStream offers protection to Milford-on-Sea. Near the coast river floodingmay be affected by high tide levels,which will get worse with predictedfuture sea level rise. Only modestdevelopment is planned within thepolicy unit, however any newdevelopment could act as anadditional source and/or receptor of flooding.

Impact of a 1% annual probability flood event

Today Future (2100)

Number of properties at risk 77 244

The vision and preferred policy

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.

Flood attenuation dam upstream of Milford-on-Sea.➜

The key messagesThis policy applies where thecurrent risk is acceptable but futurechanges are expected to have asignificant impact. Flood riskmanagement activities need torespond to the potential increasesin flood risk.

Any actions will have to beundertaken in accordance with thePennington and Keyhaven WaterLevel Management Plan (WLMP) anddue to the proximity of the unit tothe coast be in accordance with theNorth Solent Shoreline ManagementPlan (SMP).


Proposed actions to implement the preferred approach:• Undertake System Asset Management Plans (SAMPs) to review maintenance regimes, to assess future

investment needs and to maintain current level of risk.

• Review the Pennington and Keyhaven Water Level Management Plan (WLMP) to identify and agree water levelmanagement that meets the need of flood risk management and the enhancement of wetland habitat.

• Investigate opportunities to work with developers to implement local drainage improvements providing part ofa strategic solution, or to obtain contributions to wider flood mitigation schemes, as well as implementing Sustainable urban Drainage Systems (SuDS).

Danes Stream,Milford-on-Sea.

➜


Sub-area 2

Lyndhurst



The issues in thissub-areaThere is a relatively low risk offluvial flooding to areas in the northand south of Lyndhurst. Surfacewater flooding occurs in some urbanareas due to the capacity of drainsbeing exceeded. Only modest urbandevelopment is planned.


Today Future (2100)



Policy Option 3 – areas of low tomoderate flood risk where we aregenerally managing existing floodrisk effectively.

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

maintenance regimes, and to maintain the current assets. Links need to be made with upstream attenuation on the New Forest.

New Forest Life Project.➜

The key messagesThe chosen policy supportseconomic and social sustainabilityby prioritising significant gainselsewhere with the acceptance forsome potential for future minorlosses within the sub-area.


Sub-area 3

Brockenhurst



The issues in thissub-areaThe Lymington River catchmentupstream of Brockenhurst isresponsive to rainfall with threeupstream tributary catchments.High flood levels in the LymingtonRiver may affect levels in The Weir.Floodwater flows from the Weirs canhave a high velocity and the limitedchannel capacity causes flooding.


Today Future (2100)


A tributary of theLymington Rivernear Brockenhurst.

➜

Policy Option 4 – areas of low,moderate or high flood risk wherewe are already managing the flood

risk effectively but where we mayneed to take further actions to keeppace with climate change.



The key messagesThis policy applies where the current risk is acceptable but future changes are expected to have an impact. Floodrisk management activities need to respond to the potential increases in flood risk.

Where possible, any response should seek to extend floodplain storage creating wetland habitat, and providingecological enhancements such as improving the condition of the Lymington River SSSI.

Proposed actions to implement the preferred approach:• Undertake System Asset Management Plans (SAMPs) to review maintenance regimes, to assess future

investment needs and to maintain current level of risk.

• Links need to be made with upstream attenuation on the New Forest. Any necessary works will be subject to a habitats regulations assessment to ensure compatibility with the interest features of the European designatedsites and that there is no net loss of habitat.

New Forest LIFE project.➜


Sub-area 4

Lymington



Natural England

The issues in thissub-areaLymington lies at the downstreamtidal end of the Lymington River.There are also drainage channelswith small urban catchments in theLymington and Pennington urbanareas. Flooding in Lymington maybe affected by high tide levels andrisk will increase with predictedfuture sea level rise. New flooddefences were completed in 2008.

The impact on flooding of newdevelopment depends on theimplementation of Sustainable urbanDrainage Systems (SuDS), which isof particular importance as surfacewater flooding due to overloadeddrainage, is already a problem.

Proposed actions toimplement the preferredapproach:• Develop the Lymington Water

Level Management Plan to identify and agree water levelmanagement that meets the needof flood risk management and theenhancement of wetland habitat.

• Undertake System AssetManagement Plans (SAMPs) to review maintenance regimes, to assess future investment needsand to maintain current levelof risk.


Today Future (2100)


Flood alleviation scheme at Lymington,completed in 2008.➜

High tide at Keyhaven➜



The key messagesThis policy applies where thecurrent risk is acceptable but futurechanges are expected to have animpact. Flood risk managementactivities need to respond to thepotential increases in flood risk.

Any actions will have to beundertaken in accordance with theLymington Reed Beds Water LevelManagement Plan and due to theproximity of the sub-area to thecoast must also be in accordance tothe North Solent ShorelineManagement Plan (SMP).


Sub-area 5

Hythe/Fawley



Partnership for Urban South Hampshire

The issues in thissub-areaThis sub-area is relatively urban andresponsive to rainfall. Near thecoast, river flooding may be affectedby high tide levels, which preventflood waters form discharging intothe sea. This is predicted to worsenwith future sea level rise. Hytheurban drainage is currently pumpedduring high tides.


Today Future (2100)




Culverts under road to Hythe VillageMarina.➜

Proposed actions toimplement the preferredapproach:• Undertake System Asset

Management Plans (SAMPs) to review maintenance regimes, to assess future investment needsand to maintain current levelof risk.

• Work in partnership with New Forest District Council and the Partnership for Urban South Hampshire to encourage localplanning authorities to applyPPS25, avoiding inappropriate development in the floodplain, and influence local developmentframeworks to effectivelymanage flood risk.

Outfall at Hythe.➜

The key messagesThis policy applies where thecurrent risk is acceptable but futurechanges are expected to have animpact. Flood risk managementactivities need to respond to thepotential increases in flood risk.

Planning guidance should beapplied to the new development inthe sub-area to ensure this isdirected away from the higher riskareas and storm water is effectivelymanaged.

Opportunities need to be sought tominimise catchment run-off and use developer contributions tomitigate flood risk both now and in the future.


Sub-area 6

Totton



Partnership for Urban South Hampshire

Hampshire County Council

Southern Water

Natural England

The issues in thissub-areaFor Totton and Ashurst, theupstream river catchment includesthe relatively small and responsiveBartley Water (mainly rural) uppercatchment as well as the urbanlower catchment. The watercoursesin Marchwood have small mainlyurban catchments. Near the coastriver flooding may be affected byhigh tide levels, which will getworse with predicted future sealevel rise. Surface water flooding isalso present in this sub-area andthere is significant urbandevelopment planned in Totton and Marchwood.


Today Future (2100)


• Undertake System AssetManagement Plans (SAMPs) to review maintenance regimes, to assess future investment needsand to maintain current levelof risk.

• Undertake flood forecasting modelling on Bartley Water to increase lead times and improve the flood warning service.

• We will need to work in partnership with New ForestDistrict Council, Partnership for Urban South Hampshire and Southern Water to develop a collaborative Surface Water Management Plan (SWMP) to address current and future pressures on the drainage network. This plan should be linked to the Surface Water Management Plan (SWMP) for Southampton in the Test and Itchen CFMP.

Ealing Tide Mill.➜



The key messagesThis policy applies where thecurrent risk is acceptable but futurechanges are expected to have asignificant impact. Flood riskmanagement activities need torespond to the potential increasesin flood risk.

Proposed actions toimplement the preferredapproach:• We will need to work in

partnership with New ForestDistrict Council and the Partnership for Urban South Hampshire to encourage localplanning authorities to applyPPS25, avoiding inappropriate development in the floodplain, and influence local developmentframeworks to effectivelymanage flood risk.


Sub-area 7

New Forest



Forestry Commission

Natural England

England Catchment sensitive Farming Delivery Initiative

National Farmers Union

The issues in thissub-areaThe New Forest sub-area includesthe Beaulieu urban area at thedownstream end of the BeaulieuRiver, and some smallersettlements. Downstream urbanareas of this sub-area can be affectedby high flows. Near the coast, riverflooding may be affected by hightide levels and risk will increasewith predicted future sea level rise.


Today Future (2100)


➜ New Forest pony.

Lymington River at Brockenhurst.➜


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 environmentalbenefits.


The key messagesThe chosen policy supports economic and social sustainability by providing the possibility for what are estimatedto be significant environmental gains and flood risk reduction.

Any losses incurred by implementing this policy would be minimised by careful choice of location and design.

The implementation of this policy will assist in controlling or reducing flood risk in the downstream urban areassuch as Brockenhurst, Lyndhurst, Sway, and Totton. The duration and severity of impacts upon transport,infrastructure, public assets and amenities, as well as historically and culturally significant sites, within thedownstream policy units would also be reduced.

Proposed actions to implement the preferred approach:• Monitor existing initiatives, such as the Life3 project, ensuring that these schemes inform the habitat creation

action and help to minimise the flood risk to communities within the New Forest and downstream. This should include hydrological monitoring as well as habitat surveys.

• Work in partnership with Forestry Commission, Natural England and landowners to create wetland habitat. These opportunities must consider joint flood risk management benefits such as reducing run-off from the forest and increasing upstream attenuation.

• Undertake a System Asset Management Plan (SAMP) to review maintenance regime, maximising attenuation onthe forest and restoring sustainable, natural river functions.

• Work in partnership with England Catchment sensitive Farming Delivery Initiative, Natural England, NationalFarmers Union and the Forestry Commission to develop a land management plan to explore the potential for land use and management practices throughout the New Forest.

• Review the Pennington and Keyhaven Water Level Management Plan to identify and agree water levelmanagement that meets the need of flood risk management and the enhancement of wetland habitat.


Map of CFMP policies

Map of the policies in the New Forest catchment.

GESO1008BOWA-E-E

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Summary Report December 2009 managing flood risk...Lymington and New Milton. Its unique landscape and natural beauty make it an important recreational and tourist destination. The