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Planning Policy WalesTechnical Advice Note15: DEVELOPMENT ANDFLOOD RISKJuly 2004

This document is one of a series of TechnicalAdvice Notes (TANs) which supplement“Planning Policy Wales”.Further information is available from PlanningDivision 4, The Welsh Assembly Government,Cathays Park, Cardiff, CF10 3NQFurther copies can be obtained free of charge from:Publications CentreAssembly at the PierheadNational Assembly for WalesPierhead Street, Cardiff BayCF99 INATel: 029 2089 8688E-mail: [email protected] is also available on the National Assembly for Wales website:http://www.wales.gov.ukISBN 0 7504 3501 1Designed by Graphics Unit G/136/04-05Satellite image supplied by Infoterraglobal.comJulyINA-15-04-085(7)(130) Crown copyright 2004Typeset by Text Processing Services

TAN15 Text English.qxp16/9/042:05 pmPage 1Planning Policy WalesTechnical Advice Note 15Development and Flood RiskJuly 2004

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TAN15 Text English.qxp16/9/042:05 pmPage m of the TAN3Development advice maps4Nature of development or land use5Justifying the location of built development6Assessing flooding consequences7Surface water run-off from new development8Summary of policy requirements9Action through Development Plans10Development Control11Appendix 1 - Assessing Flooding ConsequencesA.B.C.D.E.Objectives of the AssessmentAssessing Flooding ConsequencesAcceptability Criteria for Flooding ConsequencesAwareness of Flooding ConsequencesTechnical Requirements for Assessing Flooding ConsequencesAppendix 2 - Flooding and Climate ChangeAppendix 3 – The Environment AgencyAppendix 4 – Sustainable Drainage SystemsAppendix 5 – Some Relevant Statutory and Non-Statutory PlansAppendix 6 - Warning Notices/Signs at Caravan and Camping Sites and OtherDevelopment at Risk of Flooding

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TAN15 Text English.qxp116/9/042:05 pmPage 1Introduction1.1This planning advice note should be read in conjunction with PlanningPolicy Wales, 2002. Planning Policy Wales (PPW) and technical advice notes andcirculars should be taken into account by local planning authorities in Wales inthe preparation of development plans. They may be material to decisions onindividual planning applications and will be taken into account by the NationalAssembly for Wales and Inspectors in the determination of appeals and called-inplanning applications.1.2 This TAN provides technical guidance which supplements the policy set outin Planning Policy Wales in relation to development and flooding. It advises ondevelopment and flood risk as this relates to sustainability principles (section 2.2PPW), and provides a framework within which risks arising from both river andcoastal flooding, and from additional run-off from development in any location,can be assessed.1.3 Information on the development advice maps accompanying the TAN willbe available from local planning offices. A hard copy of a relevant map can beviewed at local libraries or obtained from the Welsh Assembly GovernmentPlanning Division.2Background2.1 Flooding of rivers and coastal waters is a natural process which plays animportant role in shaping the environment. However, as a natural phenomenon itis very difficult to predict, and although floods occur relatively infrequently theconsequences can be very significant. Flooding can place lives at risk, causeconsiderable personal trauma, result in extensive damage to property, oftenamounting to millions of pounds, and severely disrupt communications, businessand commerce.2.2 Historically, the topography of Wales has generally resulted in transportinfrastructure and development being concentrated on valley floors, lowlandareas and in the coastal fringes. A large proportion of the Welsh population islocated within urban centres along the coastal plain in North and South Wales,particularly Cardiff, Swansea and Newport and the coastal settlements of NorthWales. The precautionary framework outlined in this TAN allows flooding issuesto be accorded appropriate consideration whilst recognising that developmentwill continue to be necessary in these areas.2.3 Overall, some 140,000 properties in Wales (12% of the total housing stock)are thought to be at risk from flooding by rivers or the sea. During the floodingevents of October and November 2000 more than 1,900 properties were affectedin Wales (Flooding in Wales, Environment Agency Wales, March 2001). Theexperience of recent years suggests that the incidence of problems due toflooding may be increasing, both in frequency and in scale. This arises partly fromchanges in river hydrology and human activity, and also from changes in landmanagement and the increase in development in areas susceptible to flooding.1

TAN15 Text English.qxp16/9/042:05 pmPage 2Even without these factors, the incidence and extent of both river and coastalflooding is expected to increase with time as a consequence of climate change.Therefore, we must plan new development sensitively, and begin to do so now,with climate change in mind.Climate Change2.4 There is mounting evidence that the global climate is changing as a result ofhuman activity. At present there are gaps in our understanding with respect tohow a changing climate will affect areas already vulnerable to flooding, althoughit is expected to increase risk significantly over time.2.5 The latest Climate Change scenarios for the United Kingdom 2002 producedfor the UK Climate Impacts Programme (UKCIP), show how the climate of the UKis already changing, and how this will become more pronounced over the comingdecades. These predict that by the 2080’s winter precipitation may increase byup to 30%. Heavy winter precipitation is likely to become more frequent, withthe precipitation intensities that are currently experienced around once every twoyears becoming possibly between 5% and 20% higher. Relative sea levels willcontinue to rise around most of the UK’s shoreline, and with this extreme sealevels will be experienced more frequently.2.6 Although the future of climate change is not certain, the latest scenariosadd to the already compelling evidence that some degree of climate change isinevitable in the future. As described in the Welsh Assembly Government’s reportClimate Change Wales Learning to Live Differently (2002), the impacts of climatechange will be wide-ranging, particularly those resulting from extreme weatherevents such as floods and droughts, which are often the most damaging andcostly. Planning authorities and developers are directed to the UK ClimateImpacts Programme (UKCIP) for the latest information with regard to climatechange. The Environment Agency will be able to advise planning authorities anddevelopers on the implications of the UKCIP as part of fulfilling the planningrequirements outlined in this TAN. See appendix 2 for background information.2.7 The potential frequency and cost of floods throughout the UK, bothcoastal and inland, has been a concern of the insurance industry for some time.Whilst insurance enables householders and businesses to minimise the cost ofdamage arising out of unforeseen events that may affect property, the industry isconcerned that a number of factors are combining to make floods more frequent,widespread and more costly. This has caused insurers to review their position onthe provision of flood cover to UK property owners. Further details on theposition of the industry can be found on the Association of British Insurerswebsite at www.abi.org.uk.2.8 The affordability of flood cover, and the associated costs of coping withflooding consequences, reinforces the overall principle of avoiding developmentin areas where the consequences of flooding will be unacceptable.2.9 Developers are advised to seek the views of insurers at an early stage, andinsurers themselves may wish to make appropriate representations about2

TAN15 Text English.qxp16/9/042:05 pmPage 3proposals for the location of new development during the preparation ofdevelopment plans. Planning authorities should be aware of the general concernsof insurers and the possible implications. They may wish to consult their owninsurers to ensure that flood defence or mitigation measures are likely to satisfythe requirements of insurers. Generally, the Environment Agency will assist byproviding advice on the detailed flood risk assessment and acceptability offlooding consequences, taking into account the risks to people and property.Sustainable Development2.10 The Assembly has a duty, under section 121 of the Government of WalesAct, to promote sustainable development in the exercise of its functions. Theplanning system has a key role to play in the delivery of sustainable developmentby providing for homes, infrastructure, investment and jobs in a way which isconsistent with sustainable development principles (section 2.2 PPW). In doing soit must provide development which is sustainable in the long term and not createa legacy of problems for future generations.2.11 Managing flooding is an important part of contributing towards achievingsustainable development. Relevant sustainable development considerations fromthe flooding perspective include: Guiding development to locations at little or no risk from river, tidal orcoastal flooding or from run off arising from development in any location; Bearing in mind that government resources for flood and coastal defenceare directed at reducing risks for existing development and are not availableto provide defences in anticipation of future development; Managing the consequences of flooding where development can bejustified and the consequences are considered acceptable in reference tosection 7 and appendix 1; Making provision for future changes in flood risk, for example takingaccount of climate change, where they can be anticipated; Bearing in mind measures within Catchment Flood Management Plans orShoreline Management Plans to restore substantial functionality and/ornatural heritage benefits of flood plains through the removal ofinappropriate existing built development.3Aim of the TAN3.1 The general approach of PPW, supported by the TAN, is to advise caution inrespect of new development in areas at high risk of flooding by setting out aprecautionary framework to guide planning decisions. The overarching aim of theprecautionary framework is, in order of preference, to: Direct new development away from those areas which are at high risk offlooding.3

TAN15 Text English.qxp16/9/042:05 pmPage 4 Where development has to be considered in high risk areas (zone C) onlythose developments which can be justified on the basis of the testsoutlined in section 6 and section 7 are located within such areas.3.2The operation of the precautionary framework is governed by: A development advice map containing three zones (A, B and C withsubdivision into C1 and C2) which should be used to trigger the appropriateplanning tests in relation to sections 6 and 7 and appendix 1. Definitions of vulnerable development and advice on permissible uses inrelation to the location of development and the consequences of flooding.3.3 The precautionary framework should be used for both forward planning anddevelopment control purposes.Roles and responsibilities3.4 The planning authority will need to be satisfied that a proposal is justifiedand that the consequences of flooding are acceptable. Where the risks of, andconsequences of, flooding cannot be managed to an acceptable level thendeveloping in these areas shall be avoided irrespective of justification undersection 6. Developers will need to provide information to demonstrate that theirproposal satisfies the tests contained in the TAN.3.5 The Environment Agency should assist the planning authority in coming totheir decision by providing expert advice on the flooding consequencesassessment and the acceptability of the flooding consequences in terms of therisks to people and property. The Environment Agency should make availabledata and expertise to assist developers in undertaking flood consequencesassessment and, where appropriate, advise on any necessary mitigation measures.(see appendix 3).4Development advice maps4.1 The development advice maps are based on the best available informationconsidered sufficient to determine when flood risk issues need to be taken intoaccount in planning future development. Three development advice zones aredescribed on the maps, to which are attributed different planning actions.4.2 The maps are based on Environment Agency’s extreme flood outlines(zone C) and the British Geological Survey (BGS) drift data (zone B). Figure 1describes the composition and use of these zones to control and managedevelopment.4

TAN15 Text English.qxp16/9/042:05 pmPage 5Figure 1Description of ZoneUse within the precautionaryframeworkConsidered to be at little or no riskof fluvial or tidal/coastal flooding.AUsed to indicate that justificationtest is not applicable and no needto consider flood risk further.Areas known to have been floodedin the past evidenced bysedimentary deposits.BUsed as part of a precautionaryapproach to indicate where sitelevels should be checked againstthe extreme (0.1%) flood level. Ifsite levels are greater than the floodlevels used to define adjacentextreme flood outline there is noneed to consider flood risk further.Based on Environment Agencyextreme flood outline, equal to orgreater than 0.1% (river, tidal orcoastal)CUsed to indicate that floodingissues should be considered as anintegral part of decision making bythe application of the justificationtest including assessment ofconsequences.Areas of the floodplain which aredeveloped and served by significantinfrastructure, including flooddefences.C1Used to indicate that developmentcan take place subject toapplication of justification test,including acceptability ofconsequences.Areas of the floodplain withoutsignificant flood defenceinfrastructure.C2 Used to indicate that only lessvulnerable development should beconsidered subject to application ofjustification test, includingacceptability of consequences.Emergency services and highlyvulnerable development should notbe considered.4.3 While robust for triggering the application of the tests (for both forwardplanning and decision making) at the present time it is inevitable that informationwill be improved and refined over time. It is expected that the developmentadvice maps will remain in place for 3 years, unless the Assembly Government isinformed by the Environment Agency with regard to significant change. Futureversions of the maps would then be issued as numbered and dated copies whichwill supersede earlier versions. It will always be good practice to consult theEnvironment Agency as a first step when considering development in zone C.5

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TAN15 Text English.qxp516/9/042:07 pmPage 7Nature of development or land use5.1 Particular flooding consequences may not be acceptable for particulartypes of development. For example, allowing residential development in areaswhich are subject to high risks of flooding can result in a traumatic impact onpeople’s lives. The precautionary framework identifies the vulnerability ofdifferent land uses to flooding, and for this purpose, development has been subdivided into three categories in figure 2.Figure 2Development categoryTypesEmergency serviceshospitals, ambulance stations, firestations, police stations, coastguardstations, command centres, emergencydepots and buildings used to provideemergency shelter in time of floodHighly vulnerable developmentall residential premises (including hotelsand caravan parks), public buildings (e.g.schools, libraries, leisure centres),especially vulnerable industrialdevelopment (e.g. power stations,chemical plants, incinerators), andwaste disposal sitesLess vulnerable developmentGeneral industrial, employment,commercial and retail development,transport and utilities infrastructure,car parks, mineral extraction sites andassociated processing facilities,excluding waste disposal sites5.2 The Emergency Services category describes facilities which need to beoperational and accessible at all times. Highly vulnerable development describesdevelopment where the ability of occupants to decide on whether they wish toaccept the risks to life and property associated with flooding, or be able tomanage the consequences of such a risk, is limited. It also includes thoseindustrial uses where there would be an attendant risk to the public and thewater environment should the site be inundated. Less vulnerable developmentdescribes development where the ability of occupants to decide on whether theywish to accept such risks is greater than that in the highly vulnerable category.The vulnerability attributed to a mixed use proposal will be defined by the mostvulnerable use.5.3 There are uses which are considered to be exceptions to the general rule,and have not been classified above, because they are required in a fluvial, tidal orcoastal location by virtue of their nature. These include boatyards, marinas,essential works required at mooring basins, and development associated withcanals. They will not be subject to the first part of the justification test insection 6 but will be subject to the acceptability of consequences part of the test7

TAN15 Text English.qxp16/9/042:07 pmPage 8as outlined in section 7 and the requirements of appendix 1. Furtherconsideration is given to minor development in section 11.6Justifying the location of development6.1 Much urban development in Wales has taken place alongside rivers and inthe coastal plain. It is therefore inevitable, despite the overall aim to avoid floodrisk areas, that some existing development will be vulnerable to flooding and fallwithin zone C. Some flexibility is necessary to enable the risks of flooding to beaddressed whilst recognising the negative economic and social consequences ifpolicy were to preclude investment in existing urban areas, and the benefits ofreusing previously developed land. Further development in such areas, whilstpossibly benefiting from some protection, will not be free from risk and could insome cases exacerbate the consequences of a flood event for existingdevelopment and therefore a balanced judgement is required.6.2 New development should be directed away from zone C and towardssuitable land in zone A, otherwise to zone B, where river or coastal flooding willbe less of an issue. In zone C the tests outlined in sections 6 and 7 will be applied,recognising, however, that highly vulnerable development and Emergency Servicesin zone C2 should not be permitted. All other new development should only bepermitted within zones C1 and C2 if determined by the planning authority to bejustified in that location. Development, including transport infrastructure, willonly be justified if it can be demonstrated that:i. Its location in zone C is necessary to assist, or be part of, a local authorityregeneration initiative or a local authority strategy required to sustain anexisting settlement1; or,ii Its location in zone C is necessary to contribute to key employmentobjectives supported by the local authority, and other key partners, tosustain an existing settlement or region;and,iii It concurs with the aims of PPW and meets the definition of previouslydeveloped land (PPW fig 2.1); and,iv The potential consequences of a flooding event for the particular type ofdevelopment have been considered, and in terms of the criteria containedin sections 5 and 7 and appendix 1 found to be acceptable.7Assessing flooding consequences7.1 If a development proposal in zone C1, or in C2 if it is defined as being oflow vulnerability, meets the test outlined in section 6, the justification will be inthe knowledge that those developments will flood and will need to be plannedaccordingly. This section will apply in zone C, and those parts of zone B whereflooding has been identified as a material consideration to allow for localisedproblems.81 Regeneration initiatives will be comprehensive, multi-approach and form part of an integratedsuite of initiatives which have been subject to public consultation. Local authority strategy will bethe development plan for the area (deposit version as minimum).

TAN15 Text English.qxp16/9/042:07 pmPage 97.2 Whether a development should proceed or not will depend upon whetherthe consequences of flooding of that development can be managed down to alevel which is acceptable for the nature/type of development being proposed,including its effects on existing development. It would certainly not be sensiblefor people to live in areas subject to flooding (even in two storey buildings) wheretimely flood warnings cannot be provided and where safe access/egress cannotbe achieved.7.3 Where development is justified the assessment can be used to establishwhether suitable mitigation measures can be incorporated within the design toensure that development is as safe as possible and there is: minimal risk to life; minimal disruption to people living and working in the area, minimal potential damage to property; minimal impact of the proposed development on flood risk generally; and, minimal disruption to natural heritage.7.4 Therefore, before deciding whether a development can take place anassessment, which examines the likely mechanisms that cause the flooding, andthe consequences on the development of those floods, must be undertaken,which is appropriate to the size and scale of the proposed development. Furtheradvice can be found in appendix 1.7.5 Planning authorities should recognise that the presence of protectionmeasures does not eliminate risk completely and that certain developments aremore vulnerable than others. Land protected by defences will be extremelyvulnerable in the event of overtopping or breach because of the speed offlooding in such circumstances. The Environment Agency will advise the planningauthority on the consequences of flooding for the type and nature of proposaland this should enable the planning authority to arrive at a judgement on theacceptability of the flooding consequences. Where development is allowed,developers must put plans/measures in place to manage those consequencesSuch measures must be capable of being implemented at the appropriate stage aspart of the development and, where necessary, long term maintenance must beprovided for.7.6 Planning and building standards have a complementary role in floodmanagement and the use of flood damage resistant and mitigation measures willbe required as part of ensuring that consequences of flooding are acceptable.Simple design features, such as raising floor levels, while ensuring that appropriateaccess is maintained for disabled people, or keeping electrical circuits abovelevels likely to be affected by flooding, can enable buildings to resist and copewith flooding better. In areas where inundation may be rapid, such asimmediately behind sea walls, or in steep river catchments, mitigation of this kindis likely to be more difficult and on its own unlikely to result in acceptableflooding consequences. More information on preparing for flooding can befound in the DTLR document Preparing for Floods (2002) and from thepublications of the Association of British Insurers.9

TAN15 Text English.qxp16/9/042:07 pmPage 107.7 The effect of flooding on water or sewerage infrastructure could havecatastrophic effects on public health and the environment by resulting in thecontamination of potable water, or the mixing of sewerage with flood water.Flood water could enter the public sewerage systems with little control and thecombination of sewerage and flood water would affect properties and theenvironment. The consequences assessment should consider access and egress,for example, if a statutory undertaker is not able to access its apparatus during aflood then this will prolong the time before remediation could occur.7.8 Development proposals on or adjacent to land that may be affected bycontamination can have implications for water quality during times of flood.Where such sites are inundated there is an attendant risk that certaincontaminants may be mobilised and could pose a threat to surface waters orleach into ground waters. In addition, where the development involves, forexample, the storage/use of oils, fuels or chemicals, an industrial process or thestorage or handling of waste materials, there is a risk to the water environmentshould the site be inundated. These factors should be taken into account inreaching a decision by forming part of an assessment required in accordance withsection 7 and appendix 18Surface water run-off from new development8.1 All types of land use change will impact on the natural hydrological cycle inone way or another and flooding is not confined to flood plains, as heavy rainfalling on waterlogged ground can cause localised flooding almost anywhere. Inall zones, development should not increase the risk of flooding elsewhere. Runoff from developments in these areas can, if not properly controlled, result inflooding at other locations and significantly alter the frequency and extent offloods further down the catchment. In many instances this will be determined bylocal knowledge and where such concerns are suspected planning authoritiesshould consult the relevant competent authority on a case by case basis, who willdetermine what, if any, attenuation is to be required.Consultation may be required with one, or more, of the followingorganisations with regard to surface water: Highway Authorities: highway surface water, for example highway culverts,roadside drains, swales Land Drainage Authorities, including IDB’s, Riparian owners or EnvironmentAgency: for example agricultural run-off, ditches, streams and main rivers Sewerage Undertakers: for example roofs and yard water from domesticcurtilage8.2 Built development, such as roads, pavements, and roofing, tends to increasethe surface area of impermeable ground, thus reducing percolation and increasingrapid surface run-off. This has the effect of reducing the time it takes forprecipitation to enter the watercourse and consequently increasing the peakdischarge. SuDs can perform an important role in managing run-off from a siteand should be implemented, wherever they will be effective, in all newdevelopment proposals, irrespective of the zone in which they are located.10

TAN15 Text English.qxp16/9/042:07 pmPage 118.3 Development in one part of a catchment may increase run-off and henceflood risk elsewhere, therefore, the aim should be for new development not tocreate additional run-off when compared with the undeveloped situation, and forredevelopment to reduce run-off where possible. It is accepted that there maybe practical difficulties in achieving this aim.8.4 Sustainable Drainage Systems (SuDs) offer a variety of engineering solutions,both soft and hard, that can be employed to manage surface water run-off. Forexample, a combination of techniques incorporating both wet and dry balancingponds, soakaways and swales can lower flood risk by reducing the quantity ofsurface water run off and delaying its discharge to watercourses. Such systemscan also provide habitat and amenity enhancements and passive treatment toimprove water quality prior to discharge. It should be noted, however, thatoptions which involve increasing infiltration will have limited effectiveness onsites underlain by high groundwater tables and/or very low permeability terrain.8.5 Information with regard to the appropriate mechanisms for consideringSuDs is contained in the ‘Interim Code of Practice for Sustainable DrainageSystems’ (2004) developed by the National Suds Working Group. Planningauthorities may consider imposing a condition requiring developers to examinethe SuDS option and provide the planning authority with details and options. If itis demonstrated that SuDS could work on a site, and subject to the appropriateagreements being in place with regard to adoption, then the planning authoritywould require SuDS to be implemented. Developers will need to give goodreason why SuDS could not be implemented. If a conventional drainage systemdoes not improve the status quo or has a negative impact then this can be a validreason for refusal.8.6 Consideration must also be given to maintaining the effectiveness of anydrainage system, including pipes. Systems must be able to cope with severerainfall/snowmelt events and provision must be made for long term maintenanceand renewal. Where necessary, conditions attached to permissions and /oragreements can be used to secure these objectives. See appendix 4 for furtherinformation.11

12Emergency servicesHighly vulnerabledevelopmentLess vulnerabledevelopmentOtherEmergency servicesAB Acceptable consequences fornature of use Occupiers aware of flood risk Escape/evacuation routespresent Effective flood warning provided Flood emergency plans andprocedures No increase in floodingelsewhere Acceptable consequences fornature of use Occupiers aware of flood risk Escape/evacuation routespresent Effective flood warning provided Flood emergency plans andprocedures Flood resistant design No increase in floodingelsewhere No increase in floodingelsewhere Justification test not applicable Refer to surface waterrequirementsGenerally suitable for most formsof development. Assessments,where required, are unlikely toidentify consequences that cannotbe overcome or managed to anacceptable level. It is unlikely,therefore, that these would resultin a refusal of planning consent onthe grounds of flooding.No constraints relating to river orcoastal flooding, other than toavoid increasing risk elsewhere.Development Advice(Section 5, 6, 7 & Appendix 1)92:07 pm If site levels are greater than theflood levels used to defineadjacent extreme flood outli

3 Aim of the TAN 3.1 The general approach of PPW, supported by the TAN, is to advise caution in respect of new development in areas at high risk of flooding by setting out a precautionary framework to guide planning decisions.