Appendix V3-B: Code of Practice 2 Flood Resilience and ......B2.2 Flood Warning and Enhancement of...

Appendix V3-B:

Code of Practice 2 Flood Resilience and Adaptation Measures

EU Interreg IVB FloodResilienCity Project

Final Report – Dublin

Volume Three: Pluvial Flood Risk Management

Volume Three; Appendix V3-B Code of Practice 2: Flood Resilience and Adaptation Measures

CONTENTS

B1 STRUCTURE OF CODE OF PRACTICE 1

B2 GENERIC AND EARLY WIN MEASURES 3 B2.1 Planning and Building Control 3 B2.2 Flood Warning and Enhancement of Flood Emergency Management 3 B2.3 Development Policy and Urban Land-use Management (see also B2.1) 4 B2.4 Basement and Ground Level Access Protection 5 B2.5 Enhanced Maintenance 6 B2.6 Green Roofs 7 B2.7 Aggregated Micro-Storage 8 B2.8 Other Generic SuDS Measures (see also B4.3 – B4.7) 9 B2.9 Rain Gardens 10 B2.10 Gulley Enhancement 10 B2.11 Vegetation Management 11 B2.12 Summary of Generic and Early Win Measures 12

B3 COMMUNITY FLOOD RESILIENCE MEASURES 16 B3.1 Awareness Raising and Education 16 B3.2 Specific Basement Measures 17 B3.3 External Resistance Measures 18 B3.4 Internal Resilience Measures 19 B3.5 Rainwater Harvesting 20 B3.6 Domestic Rain Gardens 22 B3.7 Summary of Community Resilience Measures 23

B4 SITE SPECIFIC MEASURES 25 B4.1 Fringe Interception / Storage and Land Management 25 B4.2 Enhance Existing Storage 25 B4.3 SuDS Storage 25 B4.4 GreenWaterSpace Storage 26 B4.5 SuDS Infiltration 27 B4.6 Surface Conveyance - Streets-as-Streams / Roads-as-Rivers 27 B4.7 BioSwales 29 B4.8 Below-ground Conveyance 29 B4.9 Separation of Foul and surface Water Sewers 30 B4.10 Temporary and Demountable Defences (non-domestic) 30 B4.11 Summary of Site Specific Measures 32

B5 CASE STUDY EXAMPLES 35 B5.1 Generic Measures 35 B5.2 Community Flood Resilience Measures 36 B5.3 Site Specific Measures 36 B5.4 Highlighted Examples - Community Flood Resilience 38


B6 TEMPLATE AND GUIDANCE FOR BUILDING RESISTANCE AND RESILIENCE MEASURES 42

B6.1 External Measures - Resistance 42 B6.2 Internal Measures - Resilience 45 B6.3 Assessment Template 49


EU IVB FloodResilienCity Project Final Report – Dublin V3-B1

B1 STRUCTURE OF CODE OF PRACTICE

In the following sections (B2 – B4) , guidance on individual measures relevant to both new and retrofit properties is grouped according to the following categories:

• Generic and Early Win Measures – those which can be applied universally across the whole of the Dublin administrative area and aim to raise the overall level of resilience to pluvial flood risk. They apply to areas of high risk and lesser risk and therefore cover areas where the level of risk does not justify investment in Site Specific measures. Those measures which are low cost or easy to implement and yet achieve a significant benefit may be categorised as Early Wins.

• Community Flood Resilience Measures require engagement and participation at community or householder level. Specific actions may be required to implement building resistance and resilience measures and ownership of that responsibility will be an important element of effective resilience raising – this will usually lie with the householder and/or community group. A draft outline template to provide broad guidance to community groups and householders on the type of measure that may be appropriate for a particular type of property is provided in Section B6. Means to review and report on the level of consistency achieved in compliance with guidance and in application and operation are also considered.

• Site Specific Measures are normally applicable only in areas of identified high risk. They are likely to involve capital investment and there may be an ongoing maintenance commitment.

The matrix shown in Figure B1.1 overleaf illustrates how the primary responsibility for the implementation of the above noted measures is shared between Government agencies / Municipality, developers and the community. The measures in each of the above main groupings are described in the following sections (Sections B2, B3 and B4). An extract of the matrix presented in Figure B1.1 is included as an introduction to these sections, and a summary table is provided at the end of each section to indicate the scope of application of each measure as well as the relative advantages and risks, indicative and relative costs, likely level of maintenance required and which stakeholder body is likely to have responsibility for implementation. The effectiveness of any one measure depends on the particular circumstances for the location where application of the measure is being considered. Thus for any location, an initial evaluation of likely effectiveness is undertaken at the technical screening stage by applying the evaluation matrix approach described in Section 2.3.3 in the Volume Three Main Report. This is then refined during more detailed assessment of the measures which emerge for futher evaluation. Examples of the application of this approach are provided in Volume Four Detailed Pluvial Flood Risk Assessment of Pilot Areas. Given the number of basement properties in Dublin, ‘Basement and Ground Level Access Protection’ (Generic Measures) and ‘Basement Specific Measures’ (Community Flood Resilience Measures) should be given particular attention.



* Indicates potential innovative solution X* Can share responsibility when applied in community-wide schemes

Figure B1.1: Matrix of Measures and Implementation Responsibility Case Studies to illustrate a number of these measures are provided in Section B5 . Section B6 builds on the guidance provided in Sections B2-B4 by outlining further guidance for property owners / occupants to consider household-level flood protection. This includes a broad indication of which measures are likely to be suitable for different circumstances.



B2 GENERIC AND EARLY WIN MEASURES

Figure B2.1: Matrix of Generic and Early Win Measur es and Implementation Responsibility

B2.1 Planning and Building Control

Spatial planning must recognise and plan for the risk presented by pluvial flooding. Effective planning and building control can be one of the most cost-effective and sustainable means of mitigating the risk from this type of flooding when taken into consideration with other types of flooding and acknowledging the interactions between them. Planning policy is a powerful tool which Dublin City Council can use to steer new development away from known surface water flood risk areas or, if necessary, to control their development. Specific flood management measures can be implemented through planning or building control. Basements should be given particular consideration. Policies should also aim to control or limit urban creep. In general terms, planning control aims to pursue opportunities for development to respect the natural passage of water and provide mutual benefits of management of flooding and water resources, social and environmental improvement and adaptation to climate change. Building control aims to pursue opportunities for future development to respect natural landform (e.g. ensure sufficiently high property thresholds) and rectify existing drainage problems (which although are linked with this Code of Practice, are not specifically addressed here).

In view of the importance of this measure, guidance is provided in Code of Practice 1: Spatial Planning and Building Regulations (Volume Three, Appendix V3-A), which should be read in conjunction with the guidance in Code of Practice 2 with regard to Planning and Building Control measures.

B2.2 Flood Warning and Enhancement of Flood Emergen cy Management

Flood Warning can provide people in areas at risk of flooding with more time to protect themselves and their homes from the effects of flooding. Given knowledge of areas most susceptible to pluvial flooding, flood alerts can be used to target responsive action. Any warning service relies on a rapid and effective response from professionals



and those at risk and therefore a programme of awareness raising and pre-planning should also be considered in parallel. Flood forecasting and warning is considered in much more detail under other elements of the Dublin FRC project. This also considers a fully integrated system with forecasting and warning for tidal, fluvial, drainage and dam-breach flood risk. Warnings are often based on a combination of likelihood of occurrence and potential impact, as indicated in the Figure B2.2 below, with the most effective flood warnings generally in cases where both the likelihood and the potential impact is considered to be high.

Figure B2.2: Flood Risk Matrix example

Some potential wider benefits to Dublin City Council from an integrated flood warning service involving pluvial flooding include:

• impacts on the road network, local transport and associated services may be minimised;

• staff and resources may be deployed and managed more effectively;

• equipment, such as that for temporary flood protection, can be mobilised and deployed in advance; and

• communication teams are better informed and prepared to handle media and public response.

Flood emergency management seeks to incorporate knowledge of likely high risk areas susceptible to pluvial flooding into Emergency Flood Plans, designation of rest centres, safe access routes avoiding deep or fast flowing water etc. This will be an important use of the pluvial flood risk mapping prepared under the Dublin FRC project. Further information on the application of flood warning as part of the Dublin FRC project is provided in Volume One Rainfall and Forecasting and in Volume Five Pluvial Flood Alerting and Warning System Integration.

B2.3 Development Policy and Urban Land-use Manageme nt (see also B2.1)

Development policy should aim to integrate urban planning with measures which will mitigate pluvial flood risk through use of urban green space for flood storage where possible and green corridors where practical to route floodwater to these storage areas. Further information on specific measures to create an urban environment where surface floodwater management is an accepted and integral part of the urban environment and forward planning is provided in subsequent sections. ‘Urban creep’, typically characterised by the paving over of front gardens to provide car parking space and by extension of roofed area by the construction of conservatories,



can have a significant adverse effect on surface water flood risk by increasing surface water runoff and the rate at which it enters the below-ground drainage system. Planning and building control policy should therefore seek to limit urban creep and mitigate adverse impacts by encouraging or specifying the use of permeable surfaces and at source storage (waterbutts or rainwater harvesting) or soakaways where rooftop area is being increased.

B2.4 Basement and Ground Level Access Protection

Doorway and access threshold levels are an important factor in determining the susceptibility of domestic and commercial properties and below ground infrastructure to pluvial flooding. This can be especially important in flat areas where although the depth of ponding may be relatively shallow it can be extensive and potentially affect many properties if doorway and access thresholds are close to street level or even below street level. For low doorway accesses to domestic properties raising of the threshold step may be practical in some instances but not always – in such circumstances temporary door-guards should be considered but these will require advance warning for installation ( see also Property Resistance and Resilience Measures). Doorway accesses to public, commercial and retail properties are often at ground level to facilitate access. Shallow ramping may be sufficient to keep pluvial floodwater out of the building. Vehicular accesses may also ramp down to underground car parks or basement loading areas for example. Again raised ramping across the entrance may be sufficient to mitigate the risk. Drainage augmentation across entrances may assist but in itself may not be sufficient to deal with surface flows arising from high intensity rainfall Particular care should be taken where there are street level accesses to below-ground infrastructure such as underground or low-level transportation systems – in such circumstances rapid inundation could pose a threat to life as well as potentially causing major disruption and damage. Access protection should be considered as a potential ‘early win’ particularly for one-off situations where shallow ramping is feasible and relatively inexpensive to install. If the number of properties with low thresholds is extensive then provision of financial incentives to support property resistance measures can be considered but this is less likely to be an ‘early win’.



B2.5 Enhanced Maintenance

Maintenance, desilting and removal of obstructions can aim to ensure that drainage infrastructure (particularly road gullies) and small local watercourses are operating to their full potential. In the case of surface water features (e.g. ponds, swales etc) this also provides improved amenity and aesthetic value. This can be taken as the ‘do minimum’ scenario although it is recognised that maintenance alone will provide no adaptation to the likely impacts of climate change so that, in real terms, flood risk is likely to increase. Enhancement of exiting maintenance practices wherever this is practical should therefore be considered. Surface water management in Dublin may benefit from improved/more targeted maintenance of the following:

• Road gullies and drains

• SuDS features

• Small local watercourses in open channel

• Culverted sections of small local watercourses Although maintenance of sewers is outside the scope of this Code of Practice ongoing maintenance of combined elements of the system to maintain surface drainage capacity is directly related to surface water management. If a satisfactory level of cleaning and clearance activities is not maintained this could have an adverse impact on surface water flood risk. Furthermore any remedial works which may be required could be considered as opportunities to increase sewer capacity which may in turn benefit surface water flood risk.

Any impairment in the capacity of the road gulley network is likely have an immediate adverse impact on surface water flood risk. It is therefore important that current maintenance procedures are at least maintained and that they are examined to see where enhancement may be possible or where maintenance should be prioritised. It is suggested that future maintenance of Dublin’s gulley drainage infrastructure focus on those identified flow routes and areas most at risk of pluvial flooding.

Sustainable Drainage System (SuDS) features are already being established and integrated as part of the existing surface drainage system in Dublin. SuDS features are an important group of measures in mitigating pluvial flood risk and further SuDS features are likely to be installed. Maintenance requirements of SuDS likely to be most suitable in Dublin can be summarised as:

• Medium: ponds, detention basins, swales and green roofs; and

• Low: pervious pavements and soakaways It is important to at least maintain and where possible improve the capacity of open channel and culverted sections of the existing network of small



urban watercourses in Dublin. This is likely to involve maintenance and clearance of screens, removal of obstructions and blockages and possibly desilting of certain sections. Weed cutting may also be required as well as trimming of overhanging tree limbs and large shrubs that may break away and fall into the watercourse (see B2.11). Enhanced maintenance is often viewed as an ‘early win’ measure as enhancements may be relatively easy to introduce at modest cost within a short timescale. Existing maintenance practices should therefore be reviewed as a potential early action in progressing improved surface water management.

B2.6 Green Roofs

Green roofs1 covered with vegetation can intercept and retain precipitation to reduce the volume of runoff and attenuate peak rainfall. Large flat or gently sloping roofs (e.g. commercial buildings, schools and hospitals) are particularly suited and cost-effective. Green roofs are an increasingly common feature on buildings. They typically take the form of a carpet of plants supported by a lightweight growing medium and overlying a drainage layer. For most types of roofs, they may provide a range of benefits:

• Surface water source control (with respect to water quantity and quality)

• Improved durability of the roof

• Aesthetic and amenity value (where accessible) and enhancement of biodiversity

• Promotion of evaporative cooling and reduction of urban heat island effect Due to the extra thermal insulation and protection to the underlying roof structure provided by the green roof, the whole life cost of a green roof may well be less when compared with a standard flat roof. Green roofs may therefore help to improve surface water management in urban areas, particularly those in city centre areas with little open space for attenuation on the ground. Green roofs can potentially have a significant benefit in reducing surface runoff, compared to traditional roofs, although seasonal effects can be significant. Some studies have indicated that in terms of stormwater attenuation effectiveness, 25% or more of rainfall runoff can be intercepted. However, this depends on the nature of the rainfall and prevailing conditions. The actual runoff from a green roof during storm conditions is largely dependent on the depth of the green roof (in particular the substrate depth), the antecedent weather conditions (e.g. the number of dry days before a storm and the temperature that influence soil moisture content) and the total storm rainfall depth. However, the concept is to replace the rapid runoff of a hard roof with one that

1 Further information on this measure and its application can be found in page 2 of “Small scale SuDs for Individual Buildings” from www.Irishsuds.com. Available from: http://www.irishsuds.com/information/Small_Scale_SuDS.pdf



replicates or betters the original greenfield runoff rate, with reductions of between 50% and 80%. Water can be stored and discharged at a controlled rate like a detention system or it can be harvested for use in the building. Green roof is a principle not a material, roofs are rarely grass, more often Sedum succulents which can survive short drought periods but equally, gravel or other surfaces can be used provided voids are available to store water and a control to discharge is put in place. Retrofitting green roofs is feasible on many buildings providing spare load capacity is available. Although the capital cost of retrofitting a green roof will typically be greater than simply replacing a traditional flat roof, the whole life cost of the green roof may well be less, and could be considered if the existing roof is in need of replacement. Green roof systems are often resisted because the building structures may need to be strengthened to carry additional loads. However, this is often only true for lightweight frame structures of typical single storey industrial warehouses, which are unlikely to have spare capacity for retrofitting green roofs.

B2.7 Aggregated Micro-Storage

The concept of Aggregated Micro-Storage (AMS) is based on the fact that in urban areas there may be many small areas of potential surface water flood storage (small car parks, hardstandings or roof areas) which individually may only provide a relatively small volume of storage but in combination provide sufficient storage to have an appreciable benefit in terms of pluvial flood risk mitigation. Emerging technology in pluvial flood forecasting capabilities and communications and hardware technology offers the possibility of control of this storage in a coordinated way at the onset and during a pluvial flood event to optimise the benefit of this ‘ aggregated storage’. Hard open-space surfaces such as car parks can rapidly generate significant volumes of runoff which may otherwise flow directly into the sewer. An alternative approach to infiltration is to provide temporary storage for storm water on the surface of the car park or other large area of hard-standing, using simple ramping and kerb design, to maintain maximum depths of between 150 - 200mm which would be unlikely to significantly impact most vehicles. The water could then be drained off site via swales to provide some improvement in water quality or by piped drainage. Through ‘smart control’ and linking to a forecasting system for heavy rainfall, filling and draining could be controlled via a remotely actuated flap gate or valve. Shallow floodwater storage may render parts of the car park out of service for a time. Otherwise, the water depths are unlikely to cause damage to cars already in the park. Water on the ground surface remains easier to manage and the system will be easier to maintain. Discharge should be passed through an interceptor to remove hydrocarbons etc. A similar concept can be considered for flat roofed areas as ‘Rooftop Reservoirs’ instead of or as well as Green Roofs.



B2.8 Other Generic SuDS Measures (see also B4.3 – B 4.7)

Pervious pavements2 are suitable for pedestrian and vehicular traffic and allow rainwater to infiltrate through the surface where it can be temporarily stored, reused or released into a drainage system once the peak has passed. Construction can use porous material which permits infiltration across the entire surface or material which is impervious to water but which is laid with void spaces to permit infiltration. The sub-base of the pavement may use geocellular block systems which provide high storage capacity. However, although the pervious pavement surface and the geocellular base can in theory have relatively low maintenance burdens, use of sand as a filter as part of the design could have a much higher maintenance burden, especially in situations where there is a high silt load which can clog the system. Filter drains3 / filtration trenches4 are shallow excavations filled with permeable material (rubble, stone or other void forming media that creates temporary sub surface storage). Surface water from the edge of paved areas flows into the trenches, is filtered and conveyed to other parts of the site. Infiltration treats run of by filtration through the soil, reduces runoff rates and volumes. A slotted or perforated pipe may be built into the base of the trench to collect and convey the water. Geocellular products can be used as alternative to stone for infiltration or conveyance systems. They have a higher void ratio but limited treatment capacity, and are often used to provide additional storage zones for higher order events in conjunction with other treatment components. Rainwater from roofs and hard surfaces can be stored and used5. If designed appropriately the systems can also be used to reduce the rates and volumes of runoffs. Collected water can be used for range of non-potable purposes, such as flushing toilets, washing machines or cooling (which may require adaptation) and irrigation. Typically the water is held in off-line storage tanks and supplied to the applications via submersible water pump. Rainwater harvesting facilities should ideally be sited at or close to their catchment area and close to the place of the intended rainwater use. Technically they can be located almost anywhere in urban areas, for example on roofs, at the end of the down pipes, under parking areas, beneath buildings, and as extra storage volume in ornamental ponds. Ideally the tank should be located in a place that will moderate water temperature, reducing bacterial growth in summer and frost damage in winter (e.g. underground). See also B3.5.

Further information on this measure and its application can be found in the: 2 “Permeable Pavements” document from www.Irishsuds.com. Available from: http://www.irishsuds.com/information/Permeable_Pavements.pdf 3 ”Filter Drains” document from www.Irishsuds.com. Available from: http://www.irishsuds.com/information/Filter_Drains.pdf 4 “Infiltration Trenches & Soak-Aways” document from www.Irishsuds.com. Available from: http://www.irishsuds.com/information/Infiltration_Trenches_Soakaways.pdf 5 “Small scale SuDs for Individual Buildings” document from www.Irishsuds.com. Available from: http://www.irishsuds.com/information/Small_Scale_SuDS.pdf



B2.9 Rain Gardens

The concept of ‘Green Streets’ uses attractive kerbside planted Rain Gardens into which surface water on the road is directed. The plants provide some cleaning of the water, attenuation of peak flows and, given suitable ground conditions, infiltration of the stored water (see B2.10). Rain gardens can be described as shallow landscaped depressions which mainly rely on the engineered soils and enhanced vegetation and filtration to remove pollution and reduce runoff downstream. They are aimed at managing runoff from frequent rainfall events. Part of the runoff volume will be removed through evaporation and plant transpiration. Trees and large shrubs can be included as they intercept precipitation and allow for larger quantities of water to evaporate, dissipate rainfall - runoff energy, and facilitate groundwater recharge. Suitable flow routes or overflows are required to convey water in excess of the design volumes to appropriate receiving drainage systems safely. Rain gardens or bio-retention6 areas are suitable for numerous situations including residential plots, car parks, along roads and roads, within larger landscaped pervious areas and as landscaped islands draining impervious areas. They should be generally applied to small catchments, although larger sites can be divided into several smaller parcels with multiple and/or linked bio-retention zones. They are designed for intermittent flow and must be designed to be drained and re-aerated between rainfall events. They should not be used on sites with a continuous groundwater flow.

B2.10 Gulley Enhancement

In addition to enhanced gulley maintenance (see B2.5) consideration should also be given to the provision of ‘Gulley-Gardens’ where space permits adjacent to gulleys. These are small vegetated rain gardens which provide some attenuation and water quality enhancement.

Consideration can also be given to the use of over-sized gulley-pots to increase the amount of at source storage and attenuation. Some form of outlet flow control might

6 Further information on this measure and its application can be found in the “Bio - Retention” document from www.Irishsuds.com. Available from: http://www.irishsuds.com/information/Bio-retention.pdf



also be considered although there may be less scope for introducing remote control linked to flood forecasting (in a similar way to Aggregated Micro-Storage) unless drainage from groups of gulleys can be controlled. Some form of simple automatic flow control device might be possible.

B2.11 Vegetation Management

As discussed under B2.5 weed-cutting may be necessary along small urban watercourses as part of maintenance procedures in order to maintain capacity. Trimming of overhanging tree limbs and large shrubs that may break away and fall into the watercourse should also be considered.


EU IVB FloodResilienCity Project Final Report – Dublin V3-B 12

B2.12 Summary of Generic and Early Win Measures

Indicative Cost Generic Measure

Scope of Application Key Advantages Risks Relative Cost

Range (€)

Unit

Maintenance Level

Responsibility for Implementation

Planning and Building Control

Future developments, changes/alterations to existing development.

Relatively inexpensive and simple to implement.

Potentially highly effective in reducing future flood risks.

Benefits may not be fully realised for some years.

Low - Strategic Low Local Authorities

Flood Warning and Enhancement of Flood Emergency Management

Applicable to all stakeholders: Local Authorities, emergency services, other services (transportation, water and waste water treatment facilities, other utilities), commercial businesses, communities.

Improved emergency response to extreme rainfall events. Reduced impact on road network, local transport and associated services. Effective management of resources (staff and equipment). Effective communication.

Requires significant community education and engagement to ensure full take up of warning services and appropriate response.

Moderate - Strategic Required resources for hardware and software management, for related training and community awareness campaigns.

Local Authorities in partnership with Met Eireann and OPW.

Development Policy and Urban Land-use Management

Future developments, changes/alterations to existing development, future infrastructure, future development plans.

Improved sustainability and reduced flood risk to future developments. Avoids any worsening of flood risk to existing properties arising from future developments.

Benefits may not be fully realised for some years. Require political buy in.

Low - Strategic Low Department of Environment, Community and Local Government





Range (€)

Unit

Maintenance Level


Basement and Ground Level Access Protection

Residential and commercial properties and below-ground infrastructure with access at or close to street level or below street level.

In many cases can be relatively inexpensive and quick to apply.

Not suitable to all properties. Not effective against deeper flooding.

Low 50 Per m Low Owners/occupants of properties. Local Authority to support wider implementation.

Enhanced Maintenance

Road gullies and drains, SuDS features, small local watercourses in open channels, culverted sections of small watercourses, sewers. Targeted high risk locations, known flooding hot spots.

Potential quick win measure.

May result in an increase in existing flows in the below ground systems and exacerbate any weaknesses in these systems.

Low to Moderate

Variable

**

Per m Required resources for regular upkeep.

Local Authority

Green Roofs New development, existing developments with flat roofs (where structural check confirms acceptable for additional loading). More scope for large roof commercial/industrial buildings including schools, hospitals, shopping centres and other developments with relatively large roof areas.

Minimises runoff through potentially useful volume of surface water storage available. Potentially significant amenity value. Potential improvements in water quality.

Expensive to retrofit. Cannot be fitted to light framed buildings despite large roof area (warehouses). Could require amendments to planning regulations to encourage take up.

Moderate 150 - 200 Per m2 High Owners/occupants of properties. Local authority for planning consents. Department of Environment, Community and Local Government for changes in regulations.





Range (€)

Unit

Maintenance Level


Aggregated Micro-Storage*

(kerb raising)

Hard standing areas in built up areas - car parks, roof areas, sports facilities.

Potential to maximise benefit from many relatively small storage areas and optimise the control of this storage in real time.

May result in some areas temporarily out of service. Dependent on forecasting system and smart control.

Low to Moderate

20 - 50 Per m3 Moderate to upkeep the smart control.

Local Authority but privately owned storage areas may be utilised with consent.

Other Generic SuDS

Applicable to new developments and upgrades of existing infrastructure.

Reduces run off volumes from large paved areas, enhances water quality when appropriately designed. Can be used as pathway measures alongside roads.

Structural and environmental aspects should be considered in design.

Moderate 60 - 120 Per m2 Potentially high Developers, National Roads Authority, Local Authority, property owners (e.g. using pervious paving for gardens)

Rain Gardens Urban roads infrastructure, schools, hospitals, shopping centres and other developments with relatively large paved areas. Residential and commercial properties.

Reduces run off volumes, enhances water quality. Relatively easily and cheaply implemented. Additional amenity value. Can be installed in public and private places.

Only suitable for permeable ground conditions. Requires ongoing framework for adoption and maintenance.

Low 50 - 100 Per m2 Potentially high Developers, Local Authority

Gulley Enhancement and ‘Gulley Gardens’*

Urban roads infrastructure

Reduces run off volumes, enhances water quality. Easily and cheaply implemented.

Gulley Gardens only suitable for permeable ground conditions. Requires ongoing framework for adoption and maintenance.

Low - Moderate

100 - 500 Per m2 Potentially high Local Authority





Range (€)

Unit

Maintenance Level


Vegetation Management

Urban watercourses. Increases capacity in conveying flood waters. Potential quick win solution.

Should be treated as supplementary measure, used alone may not mitigate long term climate change effects.

Low Variable

**

Per m2 Moderate Local Authority

* Indicates potentially innovative solution.

** Cost will be dependent on the type of maintenance as well as the manpower and machinery required. For Vegetation Management, costs will also vary each season.



B3 COMMUNITY FLOOD RESILIENCE MEASURES

The local community and individual property owners/occupiers have a key role to play in raising the overall level of resilience to pluvial flooding. Protection of individual properties and timely deployment of building resistance / resilience measures is the specific responsibility of the owner/occupier but community groups can provide an important supporting role in helping to gather and pass on warnings (particularly important for basement properties), acting as a conduit for advice on flood resilience and ensuring consistency in deployment of flood mitigation measures. Dublin City Council may also be able to provide supporting advice and promote overall awareness-raising. Developers also have a responsibility to implement flood resistance and resistance measures as part of the ‘new build’ where properties are constructed in areas that may be vulnerable to pluvial flooding. The various measures which are appropriate to consider at ‘community’ level are summarised in the Figure B3.1 below.

Figure B3.1: Matrix of Community Flood Resilience M easures and Implementation Responsibility

B3.1 Awareness Raising and Education

Raising Awareness of surface water flood risk within the council, partner organisations and with the public should be a first step in encouraging community groups and property owners to consider property level resistance and resilience and other measures, and encouraging reporting and recording of flooding. The latter will facilitate the gathering of evidence of a problem, which could be used to target resourcing and funding in the future. Awareness raising would be an essential precursor to effective flood warning and response. The planning and implementation of awareness raising and education in flood risk and flood risk management should be undertaken through preparation of a Communications and Engagement Plan. Means to raise awareness could include information provision through a dedicated website (possibly a section within the Dublin City Council website) supported by guidance leaflets. General public awareness: careful education of the public about the possibility of flooding from surface water as a risk distinct from flooding from the rivers or the sea will be



beneficial and could be linked to encouraging property owners to consider property level resistance and resilience measures and ‘at source’ storage. Also to discourage paving over property curtilage, or blocking natural drainage routes. It is also important that property owners understand that reporting flooding enables evidence of a problem to be gathered which can improve future flood risk management. Specific public awareness: any future schemes to manage pluvial flooding could be accompanied by explanations that the council is seeking multiple benefits through managing flood risk. Appropriate health and safety notices (e.g. for unexpected deep or fast flowing water) should be considered.

B3.2 Specific Basement Measures

There are estimated to be around 18,000 basement properties in Dublin. This is a major pluvial flood risk – flooding of basements during a pluvial flood event could occur rapidly and flood to a considerable depth. This could therefore pose a potential threat to life. Basement properties within surface water ponding areas or adjacent to surface water flowpaths may be particularly vulnerable. Flooding may be exacerbated by backflow through drainage systems or by groundwater flooding. During site visits, many basement properties were observed to have low access thresholds at the entrance to steps down into basements. However this is not consistently the case and situations were observed where one property has a high step (providing a significant level of protection against pluvial flooding) and an adjacent property has no raised step or the step has been purposely removed. Dublin City Council should promote a generic policy to raise thresholds at the entrance to basement properties. This could be through awareness raising and education and the provision of incentives to community groups and individual householders to raise entrance steps. Where raising is not practical property owners / residents could consider temporary guard boards installed when a flood warning is provided. However this could not be guaranteed to provide reliable protection and flooding of one property could affect adjacent ‘protected’ properties. Some form of self-actuating ‘Riser-Step’ could therefore be considered – this could either be a self-tipping rising flap or a floating step both of which would rise with rising flood water levels. Some leakage could be tolerated which might be dealt with by a simple sump pump.



Some form of automated audible and visible alarm system (similar to a fire alarm system) should also be considered. This could be linked to a flood warning system but should also be capable of operating independently if floodwater in the basement is detected. This would be particularly important during the night when residents may be sleeping

Other measures to be considered could include:

• Backflow valves on drainage systems;

• Ensuring safe means of rapid egress for occupants;

• Automated sump pumps; and

• Other property resistance and resilience measures as discussed above.

B3.3 External Resistance Measures

Property owners / occupants can fit resistance measures can to prevent surface water entering buildings. Measures can be fitted to new properties or retrofitted to existing properties. Retail and other premises which must permit disabled access can consider gentle ramping, although sufficient space must be available (see also B2.4) Implementation of resistance measures that are only deployed upon receipt of a flood warning is dependent on implementation of an effective pluvial flood warning system. In the UK, grant assistance is provided to encourage property owners to install such devices but currently there is not such provision in Ireland. Installing flood resistance (and resilience) measures can:

• Yield long-term financial savings to properties in flood risk areas;

• Significantly reduce the disruption caused by flooding and provide homeowners with an increased peace of mind;

• Potentially increase the value of properties in flood-prone areas; and

• Potentially make homes easier to insure, with a greater likelihood of securing better terms from insurers than would otherwise be the case.

A Research and Development study by Defra and the Environment Agency in the UK has indicated that temporary flood resistant measures (flood guards, air brick covers) can reduce damage costs by up to 50% if properly deployed before flooding. Installation of flood resistant and resilient measures as part of refurbishment to a flood-damaged property was found to be only marginally more expensive than refurbishing a property ‘normally’, although this is often not done. If properties in Dublin are flooded, Dublin



City Council could consider funding the additional cost of installing flood resistance and resilience measures over and above standard repairs as a means of encouraging their uptake. Potential flooding of properties through airbricks also needs to be considered where a surface water flood risk has been identified – this could involve temporary or permanent measures. Backflow flooding via domestic drainage systems should also to be considered and whether the installation of backflow values may be possible. From various pilot schemes, it is apparent that property owners are unsure what the correct property-level measures to use are. Dublin City Council could consider raising awareness of which products are recognised and approved. As a possible early action, council web-pages could link to examples of good practice possibly including the following examples in the UK in addition to guidance provided by OPW’s ‘flooding.ie’ website:

• The National Flood Forum’s Blue Pages (www.bluepages.org.uk) which provide an independent directory of flood protection products and services;

• The Association of British Insurers Consumer Guide: A Guide to Resistant and Resilient Repair After a Flood;

• Defra (2007) Flood resistance and resistance solutions: an independent R&D scoping study. R&D Technical Report. May 2007; and

• Defra (2008) Developing the evidence base for flood resistance and resilience, R&D Summary Report FD2607/TR1. June 2008.

Further information and guidance is provided in Section B6.

B3.4 Internal Resilience Measures

If a property is vulnerable to repeated flooding, it is important to limit damage that might be associated with rapid drying to allow early re-occupation by making the inside of the home resilient to floodwater. This can involve ensuring that the walls, floors, and fixtures will not be damaged by water, and also re-organising the house so that valuable and costly items (including service meters and the boiler) are above the level of the flood. Making the property flood resilient is more affordable during the normal course of renovation of a property, or during repairs after a previous flood. A number of measures can be progressively implemented by property owners inside their homes to limit damage to the building fabric and possessions. This can be supported by advice and information developed by Dublin City Council, property insurers and other stakeholders. These measures include:

• Raised electrical sockets, TV points etc;

• Flood resilient kitchens (plastic, stainless steel, free standing removable units);



• Raising of white goods, kitchen units or other vulnerable items;

• Storage of vulnerable items off the floor or in upstairs locations;

• Changes to internal walls to speed recovery after a flood (e.g. different rendering; dry-lining; horizontal use of plasterboard);

• Flood resilient skirting; and

• Internal doors that can easily be removed during a flood to permit free passage of any floodwater.

Further information and guidance is provided in Section B6.

B3.5 Rainwater Harvesting

Rainwater harvesting aims to reduce the runoff rate and reuse stored water. Property owners should consider this in conjunction with green roofs or other ‘property-specific’ measures. Water butts are commonly used to collect rainwater from individual properties for outside use, although modifications are generally required to make them effective to control stormwater runoff. Modifications could include:

• A throttled overflow so that excess water is directed to a soakaway or other attenuation area.

• Linking two or more butts in series so that at least one retains storage capacity and one retains water for external use.

• The ‘Leaky-Butt’ concept which aims to retain storage capacity which is only utilised during heavy rainfall events.

The effectiveness of this type of unit depends on local rainfall conditions as well as the storage volume potential of the butt or series of butts. These are usually most effective in capturing rainfall during the early stages of an event.

By way of example, the 10% Annual Exceedance Probability (1 in 10 year annual chance) 1 hour duration rainfall depth across Dublin is approximately 20mm. If this rainfall fell over a residential property with a roof (plan) area of 50m2, the total rainfall on the roof would be 1m3. If the property had two typical water butts of 200 litres each (similar to that shown in the photo above), and the water butts were empty at the start of the event they would be able to capture 40% of the rainfall total, or if they were half full at the start of the event, they would capture 20% of the rainfall total.

The ‘leaky butt’ concept, which makes use of storage capacity in water butts is described below.



Alternatively, downpipes which discharge directly into the surface water sewer network can be disconnected and be routed instead away from the property across a grassed area or through a domestic Rain Garden or other attenuation feature.

Full ‘rainwater harvesting’ more generally collects rainwater for non-potable reuse both internally and externally. Rainwater can be collected, stored, possibly mixed with ‘grey’ water and, after filtration and cleaning, made available for a variety of domestic purposes as ‘green water’. Although systems can be complex and expensive to install, with careful design they can provide storm water attenuation (through retention of the water at source) during the early stages of an event as well as substantially reducing mains water demand. Use of rainwater harvesting systems on larger non-residential properties will therefore have multiple benefits.

Disconnected d own pipe discharging into a small pond or domestic Rain Garden

Infiltration planter for downpipe disconnection



B3.6 Domestic Rain Gardens

Any shallow garden depression implemented to capture and retain rain water within the property garden area can be considered a domestic rain garden, particularly if vegetation is maintained and the function and role of the rain garden recognised. Rain gardens can be of any size or shape. This is mainly dependent on the underlying soils / clay – in sandy free draining soils the rain garden is usually about 20-30% of the size of the drained area – in heaver clay soils the rain garden would normally be larger. Residential rain gardens are usually between 10 and 30m2 and located down slope from any buildings. It may be easier to create two separate rain gardens. Typical mixture of the rain garden soil mix is 50-60% sand, 20-30% top soil, 20-30% compost.



B3.7 Summary of Community Resilience Measures

Indicative Cost Community Flood Resilience Measure


Range (€)

Unit

Maintenance Level


Awareness Raising and Education

Residential and business communities in areas historically and potentially affected by flooding.

Potential widespread benefit. May result in raising Local Authority profile and reputation. Enhances community preparedness and resilience to flooding.

May be difficult to manage expectations which might result in bad press. Requires resources and regular liaison.

Low - - Requires designated resources (community liaison officer).

Local Authority in dialogue with Community and Business Groups.

Specific Basement Measures including Riser-Steps*, leak detection, alarm system

Residential and commercial and properties occupying lower ground floor and basement premises. Use in conjunction with resistance and resilience measures. Ensure means of safe egress in conjunction with alarm systems.

Provides protection to highly vulnerable properties.

Risk that may not always be effective. Some measures require an effective warning system. Neighbouring properties may still be susceptible to flooding if adjacent property does not install or implement.

Low to Moderate

500 - 8000

Per unit (property)

Moderate Developers, occupiers, Local Authority for financial assistance.

External Resistance Measures

Residential and commercial properties.

Can be applied for individual property flood proofing where larger engineering works are not practical.

Dependent on effective warning system. Require installation works. Neighbouring properties may still be susceptible to flooding if adjacent property does not install or implement. Require management and maintenance plans if applied to community areas.

Low to Moderate

1500 – 5000

Per unit (property)

Moderate. Require management and maintenance plans if applied to community areas.

Developers, owners/occupiers of properties, Local Authority.



Indicative Cost Community Flood Resilience Measure


Range (€)

Unit

Maintenance Level


Internal Resilience Measures

Residential and commercial properties in areas historically and/or potentially affected by flooding. Use in conjunction with resistance measures.

Limits damage and speeds up drying-reoccupation time. Provides “peace of mind” to occupiers. Can reduce internal structural damage.

Could be relatively expensive for residents if no grant/assistance programme is provided.

Moderate to High for individual occupiers unless grant assistance provided.

2000 - 8000

Per unit (property)

Moderate. Developers, occupiers, Local Authority for financial assistance.

Rainwater Harvesting including Leaky-Butts*

Residential and commercial properties.

Effective in capturing and diverting potentially significant volumes of run off at source. Sustainable solution minimising overall water use. Easily applicable to new developments. Potential for re-use of waste plastics for manufacture.

Likely to require amendments to planning regulations and/or public engagement programme to encourage take up. Larger harvesting measures may be more difficult to retrofit.

Low 100-200 Per unit Low to Moderate

Householders, Developers, Department of Environment, Community and Local Government for changes in regulations.

Domestic Rain Gardens

Residential properties. Reduces run off volumes, enhances water quality. Relatively easily and cheaply implemented. Additional amenity value.

Only suitable for permeable ground conditions. Likely to require amendments to planning regulations and/or public engagement programme to encourage take up.

Low 50-100 Per m2 Low Householders, Developers, support by Local Authority.

* Indicates potentially innovative solution



B4 SITE SPECIFIC MEASURES

Figure B4.1: Matrix of Site Specific Measures and I mplementation Responsibility

B4.1 Fringe Interception / Storage and Land Managem ent

Fringe Interception of runoff from the urban/rural fringe can reduce the volume of water entering the urban area via overland flow or in local watercourses. Runoff can be attenuated in detention basins or through alternative land management practices (e.g. contour ditching or forestation).

B4.2 Enhance Existing Storage

Enhancement of the flood storage capacity that may be available in existing reservoirs, ponds and wetlands to further attenuate surface water runoff may be feasible in some cases. It is possible that some treatment of the runoff may be required so that any contaminants that might be present in the surface water runoff do not disturb the existing ecology. For reservoirs any enhancement would require consideration of reservoir inspection and regulatory regimes.

B4.3 SuDS Storage

Control of surface water runoff near to its source can be achieved through the use of ponds, wetlands, detention basins and swales. The flood risk management purpose of these features is to detain surface water in a safe place until the flood peak has passed. Although they provide good removal of pollutants and can have high ecological, aesthetic and amenity benefits, they can sometimes require large areas which may not be available in the highly developed central urban area of Dublin. However, existing open water bodies in Dublin at various locations, including parkland areas such as St Stephens Green, provide a precedent for these features. Strategic redevelopment



opportunities for installing such features may also exist. Detention basins 7 are surface water storage areas which provide flow control and reduction through attenuation. They are normally dry and therefore could be used as car parks recreational or sports facilities for much of the time. In these situations, appropriate signage to warn of potentially deep water is required. It may be possible to reuse the stored water on site (e.g. irrigation or aquifer recharge) depending on storage arrangements. In areas of vulnerable groundwater (i.e. Source Protection Zones), detention basins may need to be lined. Ponds 8 and wetlands 9 are designed to be areas of permanent standing water which can provide attenuation of flows and a certain degree of treatment. In doing so they can provide some improvement in water quality as well as providing ecological, aesthetic and amenity benefits. If land around the permanent pond is designed to flood and store high flows then there will be shallow water depths around the perimeter and deep water towards the centre. This health and safety risk must be properly addressed through signage and awareness raising.

B4.4 GreenWaterSpace Storage

Parkland and other green space areas provide opportunities for ponds, detention basins and wetlands. Surface water can be conveyed to these areas and the areas linked by ‘green corridors’ (or ‘grey corridors’) where the conveyance may be by swales, the natural topography or by some other ‘designated flow path’. This linked system of green storage areas and green conveyance routes can be termed ‘GreenWaterSpace’ storage. In addition to surface floodwater attenuation, GreenWaterSpace systems can provide added amenity and environmental enhancement with increased biodiversity. Two landscaped green swales and retention areas have already been constructed by Dublin City Council at Glendhu Park and these have proved successful in attenuating stormwater as a pluvial flood mitigation measure.

Further information on this measure and its application can be found in the: 7 “Detention Basins” document from www.Irishsuds.com. Available from: http://www.irishsuds.com/information/Detention_Basins.pdf 8 “Retention Ponds” document from www.Irishsuds.com. Available from: http://www.irishsuds.com/information/Retention_Ponds.pdf 9 “Stormwater Wetlands” document from www.Irishsuds.com. Available from: http://www.irishsuds.com/information/Stormwater_Wetlands.pdf



GreenWaterSpace systems also provide the potential for carbon sequestration whereby carbon absorption by specific material used to line storage areas and connecting swales may be possible. This has yet to be trialled but if successful could offer an attractive additional benefit. The extent to which lining material would need to be replaced / re-used has still to be determined. Pluvial Meadows are area where shallow periodic inundation of GreenWaterSpace areas by surface water may be feasible. This would effectively form a wetland area or alternatively enhanced storage in an existing wetland area may be feasible.

B4.5 SuDS Infiltration

SuDS infiltration can be considered where the underlying geology permits. Special consideration has to be given as to whether the carriageway subsurface could be weakened by implementing such measures. Pervious pavements 10 can be suitable for pedestrian and vehicular traffic areas or car parks and allow rainwater to infiltrate through the surface where it can be temporarily stored, reused or released into a drainage system. Construction can use porous material which permits infiltration across the entire surface or material which is impervious to water but which is laid with void spaces to permit infiltration. The sub-base of the pavement may use geocellular block systems which increase storage capacity. Soakaways are filled excavations which store runoff from individual or grouped properties or larger developments and also roads and allow infiltration into the surrounding soil. They are only feasible in freely draining soils and where the groundwater does not pose a flood risk itself. They may be particularly applicable where there is no existing road drainage system.

B4.6 Surface Conveyance - Streets-as-Streams / Road s-as-Rivers

Roads and other features of the urban fabric can be designed to manage overland flow and direct it safely through the urban environment, such that floodwater is less likely to enter a building or other structures. This is the Streets-as-Streams / Roads-as-Rivers concept. This links closely with the GreenWaterSpace concept – see B4.4. Such an approach is sometimes termed ‘Designing for exceedance’ and recognises that flows that exceed the below ground drainage capacity are always possible but can be managed to some degree by creating designated flow routes which may also involve threshold raising at access points. These measures may be particularly suitable for Dublin when integrated with designated storage

10 Further information on this measure and its application can be found in the: “Permeable Pavements” document from www.Irishsuds.com. Available from: http://www.irishsuds.com/information/Permeable_Pavements.pdf



areas or directed to points on major watercourses where the added flow would be unlikely to exacerbate fluvial flood risk. At steep gradient locations potentially high flow velocities will require careful coordination with emergency planners and other relevant authorities to maintain public safety. Designated surface flow routes, formalised through road profiling, kerb heights, speed bumps etc, can be used to safely route exceedance flows through urban areas. Specific actions may be as simple as removing speed ramps so as not to obstruct flow or even placing them to steer flow. Road profiles can potentially be shaped to direct flow into drains and safely away to storage or a suitable discharge point. Designing for exceedance can bring important social and environmental benefits. Maintenance of features for managing surface flow will typically be easier and less expensive than maintenance of underground infrastructure. It should be noted that routing could involve a significant number of specific measures such as kerb raising, profiling etc and also potential disruption – careful assessment of requirements along each potential route would be required. Street shaping, or ‘reprofiling’ opportunities can be planned to occur whenever re-surfacing is planned as part of ongoing road maintenance programmes so as to keep cost to a minimum.

Other aspects which should be considered include:

• The practicality of altering street profiles without considerable disruption and cost, and in accordance with road design policy and guidelines;

• The potential for high kerbs or roadside open channels and any safety risks;

• Traffic management when streets are used as flowpaths and requirements for any signage;

• The need for sufficient early warning of pluvial events to bring designated flow routes ’into operation’; and

• The possibility of stray motorists and pedestrians using designated flow routes whilst in operation.

Outside of the built environment, surface runoff will follow the natural topography. Before this surface water reaches any recognised watercourse, it could be viewed as runoff which has exceeded the natural infiltration capacity. Therefore, in the same way as for built environments, future development should be designed to accommodate exceedance flows along these natural drainage routes. To encourage implementation in new development areas, a map showing the likely natural drainage routes, as well as topographic depressions where water could pond can be prepared for likely development areas. Thought should be given to ‘Shared Space’ in an urban setting so that kerbs, channels and street furniture direct flow without obstructing access to wheelchairs, pedestrians and cars which could share the same space. Stakeholder engagement



will be integral to the process of Shared Space and designing for exceedance and key stakeholders will be the relevant departments within Dublin City Council, residents associations to discuss concerns about increased flood risk to properties, and Dublin City Council emergency planning. In relation to small watercourse conveyance , widening and/or deepening of the small local watercourse channels and opening up of culverted sections have the potential to improve the capacity of local small watercourses to receive and convey flood flows. Where rapidly passing peak flows could cause flooding downstream, any local improvement in conveyance should be offset with increased storage to attenuate the peak. Any deepening or re-grading or other alterations to the channel profile should consider any requirement for mitigation measures to counter possible adverse effects on the stream geomorphology, water quality or ecology.

B4.7 BioSwales

Swales11 are shallow linear vegetated drainage features which can store and convey surface water. As part of an engineered flowpath they can pass water from one storage area to the next or to a suitable discharge point; and provide infiltration where underground conditions are suitable. Swales can be designed to be permanently wet or generally dry and are often located next to roads, car parks or other open spaces. In linking storage area they can be used as part of GreenWaterSpace systems (see B4.4) and in doing so provide environmental and biodiversity enhancement – the term ‘BioSwales’ is therefore appropriate. There is also the possibility that BioSwales could be used for carbon sequestration as discussed under B4.4.

Other potential benefits include:

• Enhancement of visual amenity; and

• Water quality improvement. B4.8 Below-ground Conveyance

Increasing the capacity of the current drainage network may be possible through enlarging existing sewers or adding new sewers (which can be oversized to provide additional storage). Increased network capacity could reduce the likelihood of flooding and the discharge of potentially polluted floodwater through Combined Sewer Overflows.

11 Further information on this measure and its application can be found in the: “Swales” document from www.Irishsuds.com. Available from: http://www.irishsuds.com/information/Swales.pdf



In general, managing surface water on the land surface (a) is more cost-effective and easier to maintain (b) permits attenuation of peak flows to reduce risk downstream and (c) provides opportunities for social and environmental benefits. However, in some situations, particularly in densely developed areas, adding storage and/or increasing the capacity of the sewer network may have to be considered to limit overland flow and flooding and the discharge of potentially polluted floodwater through misconnections with the foul sewer and through Combined Sewer Overflows. Sometimes there may be a need to move surface flood water from a high risk area to a safe storage area but there is no suitable surface flow route. A new below-ground drain could collect excess surface water and convey it safely to a point where it can either break to the surface within an open detention pond or to an underground storage tank. In general the cost of below ground sewerage and drainage capacity enhancement is likely to be prohibitive unless capacity increase is required to meet other needs. Focus is therefore normally placed on relatively minor works or on benefiting from capital improvement schemes that may be planned or under way for other reasons.

Increasing sewer capacity could be possible through:

• Including on-line or off-line storage tanks in the sewer (surface water or combined);

• Adding new sewers which can be oversized to provide additional storage (surface water or combined); and

• Enlarging existing sewers during maintenance work (surface water or combined).

B4.9 Separation of Foul and surface Water Sewers

Greenfield development opportunities usually have separate foul and surface water drainage systems and such opportunities should be maximised. Brownfield development opportunities are generally as for Greenfield but the existing drainage system may be combined. In such cases opportunities should be taken to convert to a separate surface water piped system where practical. This can however be a very expensive option unless justified for other reasons. Misconnections between the surface water and foul systems should be rectified as opportunities arise. This can reduce pollution associated with surface water flooding.

B4.10 Temporary and Demountable Defences

(non-domestic)

Temporary and Demountable Defences are normally considered as fluvial flood defence measure. However they can be erected in areas more vulnerable to surface water flooding to reduce the consequences of flooding, and to route flood water to a safe location. They can also be



deployed to manage surface water for Streets-as-Streams / Roads-as-Rivers designated flowpath routing (see B4.6). Temporary or demountable flood defences should be used in conjunction with improved flood warning, so that the flood defences can be installed in a timely manner, prior to flood incidents occurring. Demountable community flood defences are structures that have permanent and temporary elements. They normally have permanent foundations with guides or sockets to install barriers when there is a risk of flooding. The barriers are then removed when there is no risk of flooding. There are many proprietary systems available including:

• Slot in flood barriers;

• Pivot barriers; and

• Flip up flood barriers. These systems require detailed design by qualified engineers and usually involve heavy engineering works. They can be an effective option where traditional, permanent defences are not appropriate or cost effective. Some locations may be sensitive conservation areas. Demountable barriers can provide protection without being permanently intrusive. Careful detailing may be needed where permanent base plates are installed. Management plans for storage, maintenance and deployment involve cooperation between local authorities, emergency services and local community groups. By contrast, a temporary flood defence is a system that can be installed during a pluvial flood event and then completely removed when no longer required. Sandbags are the most common form of temporary flood defence. Free standing barriers are designed to be rapidly deployed and are generally used where flood depths are less than 1m but are often capable of more. They often require associated pumping arrangements to remove seepage water. They can be applied as large scale community and critical infrastructure defences.



B4.11 Summary of Site Specific Measures

Indicative Cost Site Specific Measure

Scope of Application

Key Advantages Risks Relative Cost Range

(€) Unit

Maintenance Level


Fringe Interception / Storage (SuDs storage); Land Management

Urban/rural fringe areas where surface runoff potentially enters urban areas.

Reduce pressure on urban drainage. Open space to implement.

May require extensive land management plan.

Low to Moderate

50 – 100

500 - 2000

Per m3

Per Hectare

Moderate

Local authority (Planning departments), Forestry, Landowners

Enhance Existing Storage

Existing reservoirs, attenuation ponds and wetlands.

New land intake not required.

Potentially some treatment of the run -off required to avoid disturbing existing ecology. Compliance with regulatory requirements for reservoirs.

Low to Moderate

30 – 80 Per m3

Moderate Local authority. Reservoir owner.

SuDs storage Applicable to new developments and upgrades of existing infrastructure.

Reduces run off volumes from large paved areas, enhances water quality when appropriately designed.

Requires health and safety risks to be assessed and addressed in design.

Low to Moderate

50 – 100

Per m3

Potentially high.

Developers. Local Authority.

GreenWaterSpace Storage*

Existing green areas and urban parks systems.

Utilisation of existing green areas to minimise runoff. Potential for carbon sequestration.*

Trialling of carbon sequestration techniques.

Low to Moderate

50 – 150

Per m3

Moderate to potentially high.

Local Authority. Park management bodies.

SuDs Infiltration Pedestrian, low volume vehicular traffic areas, car parks. Applicable to new developments or upgrades of existing infrastructure.

Reduces run off volumes from large paved areas.

Infiltration capacity depends on permeability underlying soil.

Low to moderate

50 - 100 Per m2

Low to Moderate

Developers. National Roads Authority, Local Authority






(€) Unit

Maintenance Level


Surface Conveyance (Streets as Streams Roads as Rivers)

Urban road system and drainage paths.

Allows for surface water to be routed to attenuation areas or other suitable discharge point reducing risk to residential and commercial properties.

Requires coordination with forecasting system, signage and communication with roads authorities and local communities in relation to temporary affected routes.

Moderate to High

100 – 200

**

Per m Low to Moderate

Local Authority. Roads Authorities.

Bio Swales Urban roads infrastructure, schools, hospitals, shopping centres and other developments with relatively large paved areas.

Reduces run off volumes, enhances water quality. Additional amenity value. Can be used to link GreenWaterSpace areas. Potential for carbon sequestration.*

Requires sufficient space to construct. If use for infiltration requires permeable ground conditions. Trialling of carbon sequestration techniques.

Low to Moderate

50 – 200

Per m2 Moderate Local Authority. Roads Authorities. Developers.

Below Ground Conveyance

In areas where managing surface water on the land surface in limited for various reasons.

Can take advantage if combined with other underground sewer network works.

High cost, extensive works and less sustainable method.

High to Very High

500 – 1000

Per m Moderate Local Authority

Separation of Foul and Surface water sewers

Greenfield development and brownfield where opportunities arise. Otherwise ongoing rectification of misconnections whenever feasible.

Reduces risks of sewers overflowing, reduces pressure on waste water treatment facilities.

Potentially high cost and extensive works required unless opportunistic rectification of misconnections.

Very High

5000 – 10000

***

-

***

Moderate Local Authority.






(€) Unit

Maintenance Level


Temporary and Demountable Defences

Community areas where traditional resistance measures are not effective. As part of Streets as Streams / Roads as Rivers flowpath designation.

Effective where traditional resistance measures are not effective.

Dependent on effective warning system. Requires storage and staff available for deployment. Some measures may require engineering works. Require management and maintenance plans if applied to community areas.

Moderate to High

2500 - 3500

Per 5m Moderate. Require management and maintenance plans if applied to community areas.

Local authority. Community groups (liaison).

* Indicates potentially innovative solution ** Indicative costs includes for kerb raising on both sides of the road with minor re-profiling. External resistant measures for properties along

flow routes may also be required, but these are not included in the cost range for this item. Potential costs associated with major road re-profiling or re-surfacing are also excluded.

*** Costs associated with management of mis-connections



B5 CASE STUDY EXAMPLES

B5.1 Generic Measures

Drainage Inlet Controls USA: Properties in the village of Skokie, Chicago, experienced regular basement flooding due to excess storm water entering the combined system. Traditional solutions to resolve the problem such as sewer separation and installation of larger sewers to carry away the storm water were too expensive to implement. To alleviate the flooding, flow regulators were installed at inlet controls along roads and streets. This prevented excess surface water runoff entering the sewer during peak rainfall, which alleviated basement flooding, and instead surface water was designed to ‘pond’ in the streets, and drain into the combined sewer when there was available capacity in the system. A key factor identified in ensuring the success of this programme was public engagement and interaction to outline the benefits of this scheme, and it has achieved widespread public acceptance. http://web.sbe.hw.ac.uk/staffprofiles/bdgsa/11th_International_Conference_on_Urban_Drainage_CD/ICUD08/pdfs/198.pdf Mapping for future SuDs incorporation UK: The Lower Irwell ‘IUD pilot’ developed a SuDS map based on the geology of the catchment, to identify which type of SuDS would be suitable in the catchment. The SuDS map indicated whether an area was suitable for storage-based (grey areas on map) or infiltration-based (orange areas on map) SuDS solutions, or both (green areas on map). This can be a useful tool for planners and others in determining the type of SuDS which are appropriate. http://archive.defra.gov.uk/environment/flooding/documents/manage/surfacewater/lowirwellabce.pdf Maintenance UK: The Poringland Integrated Urban Drainage Pilot (‘IUD pilot’) identified blocked drainage ditches as a significant source of local flood risk, which were cleaned out as part of the study. Additionally, West Garforth reduced flood risk in the area through a range of ‘early win’ measures including desilting culverted watercourses and removal of flow obstacles. http://archive.defra.gov.uk/environment/flooding/documents/manage/surfacewater/poringappend.pdf Alignment with other local investment activities UK: The East and South East Leeds (EASEL) regeneration project involves major regeneration of the area and the provision of up to 10,000 new homes. The regeneration will occur upstream of an area at high surface water flood risk and therefore the development offers a unique opportunity to reduce flood risk through co-ordinated redevelopment. The Leeds first edition SWMP focussed on a sub-catchment in East Leeds and demonstrated that creation of green infrastructure as part of the redevelopment would not only reduce downstream flood risk by reducing surface water runoff, but also create biodiversity and amenity benefits. http://www.leeds.gov.uk/Page.aspx?pageIdentifier=1b91a511-8ef2-4749-9aef-c1cee7017b77



B5.2 Community Flood Resilience Measures

Community Measures in General Germany: The development of the areas adjacent to the Rhine has become a new focus of attention in Mainz. The City of Mainz and its municipal utility company, Stadtwerke Mainz AG, are converting the customs harbour area of Mainz ("Zollhafen") into an attractive quarter for living, working and leisure activities. The Zollhafen area is located in the flood plain of the Rhine. As the Zollhafen project is intended to serve as a model for life along the Rhine, flood-adapted buildings will be constructed according to the latest knowledge and planners will rely on advanced methods of flood prevention. Under the Interreg IVb FloodResilienCity project guidance has been prepared for people who will live or work in the new Zollhafen development area to raise awareness and increase the overall level of resilience of the Zollhafen community to flooding. This takes the form of a brochure which answers 10 central questions about the flood risk and its management. This includes specific advice on how to protect or adapt domestic power and water supplies, communication systems and sewerage systems; how to protect moveable equipment: how flood warnings will be provided; how to prepare for an approaching flood; and actions to take during a flood. Redevelopment of the Zollhafen Mainz as Flood Resilient Development, Heinrich Webler, IAHR European Congress Edinburgh (2010) UK: Engagement through existing local action groups during the first edition SWMP in Thatcham, the public were engaged throughout the process. At all project steering group meetings, the public were represented through representatives from the Thatcham Flood Forum and Cold Ash Community Group. In addition, the SWMP study was included as an article in the newsletter for Thatcham Town Council, and a member of the steering group gave presentations at council meetings. The Thatcham Flood Forum website was also used as a method to provide information on the SWMP study, and the project steering group has planned to hold a full consultation in due course to communicate the outputs from the study and the proposed way forward. http://archive.defra.gov.uk/environment/flooding/.../swmp1-thatcham .pdf

B5.3 Site Specific Measures

Green Infrastructure - Malmo, Sweden Sweden: A new storm water management system has been installed because the former sewage and water management system was outdated and heavy rain would cause flooding, leading to vehicle and property damage. The new system collects runoff from the rooftops and impervious surfaces and channels it through canals, ditches, holding ponds and wetlands before it enters the traditional closed sub-surface storm water system. This helps to slow the volume of water that enters the storm water system and prevent flooding (CABE, 2009). http://www.forestresearch.gov.uk/pdf/urgp_case_study_015_Malmo.pdf/$FILE/urgp_case_study_015_Malmo.pdf Green Infrastructure- rain gardens and swales - Por tland school USA: In areas with enough space rain gardens can be complimented by swales planted with native vegetation species. This solution increases surface water retention, as the action of the plant roots, leaves and soil biomass increases soil infiltration capacity. During the growing season transpiration by the plants replenishes water storage absorption capacity. http://cfpub.epa.gov/npdes/greeninfrastructure/gicasestudies_specific.cfm?case_id=66



Location of attenuation areas outside the city UK: Hartlepool IUD pilot study examined the possibility of creating surface water storage on the urban periphery to alleviate downstream urban flooding. The study proposed to divert flows from the watercourse into a surface water storage pond to alleviate flooding in the downstream urban area. http://archive.defra.gov.uk/environment/flooding/documents/manage/surfacewater/hartlepoolreport.pdf



B5.4 Highlighted Examples - Community Flood Resilie nce

Two case study examples are provided in the following pages. 1. Morpeth (UK) Flood Action Group This case study demonstrates how the establishment of Flood Wardens and development of Flood Plans at community level can support the community not just during and after a flood event, but also in preparation for such events to help minimise flood risk if possible, i.e. monitor the area for potential contributing factors which may increase the flood risk or ease evacuation. 2. Moffat (UK) Flood Action Group The Moffat case study highlights the benefit that a national support agency (Scottish Flood Forum in this case) can provide in helping a community to recover following a significant flood event, providing access to relevant information, assisting in the formation of a local flood action group and, overall, raising the level of community resilience to flooding.



B6 TEMPLATE AND GUIDANCE FOR BUILDING RESISTANCE AN D RESILIENCE MEASURES

The objective of building flood resistance and resilience measures is to promote the use of household-level flood protection in cases where flooding occurs frequently and other flood management solutions are not economically, environmentally or technically viable. Such information should be accessible by community groups and individual householders. Information on a broad range of flood mitigation products currently available in Ireland and the UK can be accessed on the OPW’s brochure ‘Making a home flood resistant’: www.flooding.ie and on the UK National Flood Forum's Blue Pages directory: www.bluepages .org.uk and www.floodforum.org.uk. In the UK building flood resistance and resilience products are expected to meet the PAS test specification that underpins the BSI Kitemark for flood protection products. The following standards apply:

• PAS 1188-1 - Flood protection products. Building apertures;

• PAS1188-2 - Temporary and demountable flood protection products;

• PAS 1188-3 - Flood protection products for buildings & building skirt systems. Product suppliers should be expected to provide evidence of appropriate testing with their tenders for the work. In the UK the Flood Protection Association represents manufacturers and designers of flood defence products. See www.floodprotectionassoc.co.uk. Similar evidence should be sought for products purchased within Ireland.

B6.1 External Measures - Resistance

Resistance measures are installed to prevent floodwater from reaching or entering a property. Permanent options are normally of the form of walls which surround properties or communities, or are applications or additions to the fabric of the building. Temporary options are typically designed to cover building apertures, i.e. doors, airbricks. Where the appearance of a building is changed by the measures it may be necessary, particularly in a conservation area, to consult with a local conservation/heritage officer or planning department for consent.

The following external measures can be applied to protect the property: Low bunds or walls around a property A low earth bund or periphery wall may provide an effective local flood defence to floodwater around a property or group of properties where practical and acceptable to the planning authority and the relevant flood management authority. There may be a need to provide pumping arrangements to remove localised rainwater or floodwater seepage. Access will be required so bunds or walls will be either tied into high ground or incorporate flood resistant gates.



Boundary walls and fencing can be aesthetically designed to create flood resistant barriers. Options also include solid gates with discreet waterproof seals and where possible, integral drains, or fencing where the lower elements are constructed to be more resistant to flooding. Low walls must be sealed and may need below ground work to prevent seepage. Bunds or walls require expert engineering design to design against breaching or overtopping failure and check that flood risk would not be increased elsewhere as a consequence. Substantial groundwork may be involved. Measures may be required to guard against flooding via the sewerage and drainage system The raising of thresholds Where flood duration is short and flood depth is low (less than 300mm) it may be practical and cost effective to raise the threshold into a property above predicted flood level. This may be achieved by adding a step and raising an entrance door where practical. Ramps may need to be considered for disabled access. The construction of storm porches If a raised threshold is not practical then it may be possible to build a storm porch, where the porch entrance is raised above property entrance/exit door level. This measure is generally only suitable for flood depths less than 300mm. UPVC flood resistant entrance doors can be used in combination with storm porches. Water resistant materials should be used for construction e.g. engineering bricks/facing. Good workmanship is required to ensure seals between the porch and existing walls are fully water resistant. Outside wall renders and facings, including veneer walling An effective method to minimise floodwater entering a property through external walls is to apply water resistant render or an additional layer or veneer of water resistant materials (e.g. engineering bricks) to the external walls. In order to maintain the appearance of a property pressed facing bricks may be added as a final resilient layer to match or compliment the existing appearance. Mortar joints must be thoroughly filled to reduce the risk of water penetration. An extra thickness of brickwork at low level is unlikely to be unobtrusive but planners or conservation bodies may need to be consulted for larger applications. External renders are effective barriers to water penetration and should be used with blocks (or bricks) at least up to the predicted flood level plus the equivalent of a course of bricks as freeboard. Structural checks may be necessary to ensure stability, because of the external water pressures that could occur for design flood depths above 600mm. External cement renders with lime content (in addition to cement) can induce faster



surface drying. Render application or a damp proof membrane must be applied below ground to the foundations to retain a seal. A layer of impermeable external insulation behind the additional bricks on cavity walls, where appropriate, can also improve flood resistance. Where a protective veneer of masonry is applied it is appropriate to install a layer of thermal installation to further improve flood resistance. This method is generally appropriate for flood depths up to 600mm and where flood duration can be relatively long i.e. of the order of days. Products needing deployment such as demountable bar riers, flood skirts, free-standing barriers, door boards and airbrick covers. These are designed to be deployed to prevent floodwaters reaching or entering a property or a group of properties following sufficient, advance flood warning. Demountable barriers , whilst being temporary, are usually considered semi-permanent because permanent below-ground work is often necessary. These systems require detailed design by qualified engineers and may involve significant engineering works. They can be an effective option where traditional, permanent defences are not appropriate or cost effective. Free standing barriers are designed to be rapidly deployed and are generally used where flood depths are less than 1m. They often require associated pumping arrangements to remove seepage water. For both demountable and free standing barriers, suitable nearby store and the availability of personnel to erect the system are important considerations. Aperture covers/flood guards are designed to cover the openings to a building i.e. doors, windows, airbricks, entrances, garages etc. Ancillary products , such as a pump and sump or anti-flood valves , are often supplied with the guards where necessary. In general flood guards are designed to withstand flood depths less than 1m. Again the means of storage and deployment (usually by the occupant) must be considered. Flood skirt systems are bespoke and are designed following comprehensive ground and property surveys. Initially, a property is sealed from foundations up to ground level and around service entry points and non-return valves installed on sewer and vent pipes. A flexible, sectioned membrane (skirt) is housed in an underground duct surrounding the property walls and is manually raised and attached to the property in advance of a flood. Skirt sections are connected with air seals which are manually inflated at the sides of each section to form a continuous barrier. The occupant is responsible for deployment so it is essential that contingency plans for deployment are in place with this type of barrier if the occupant is not available.



Air Brick Covers : Many of the manufacturers of accredited aperture guards also market airbrick covers of similar design and material to the guards. Homeowners are not always happy with cover frames permanently attached to the building fabric. However, one manufacturer provides an inexpensive but effective airbrick cover made of a thin, adhesive membrane which is simply compression sealed manually. This type is single use only and ideally must be applied when the surface is dry. Anti flood valves (non return valves / “check” valv es) In order to prevent contaminated floodwater entering a property, anti-flood valves can be installed in pipework. Also drainage inspection covers can be bolted down where if sewer system is likely to be overloaded by surface water runoff. Flap gates, gate valves or ball valves are fitted within specially constructed inspection chambers, which facilitate maintenance.

All these measures can be used for relatively short duration floods of perhaps several hours. A check should be made that flood risk to neighbours is not increased.

B6.2 Internal Measures - Resilience

Resilience measures are generally permanent methods or techniques that can be carried out at property level i.e. inside a property, to minimise damage caused by floodwaters that have entered a property. Such measures can be fitted to both existing properties and to new build in flood prone areas. As with resistance measures good quality workmanship in installation is important. Full effectiveness of flood resilience hinges on total coverage by resilient membranes or materials of surfaces, sealed joints and closed outlets. The occupant must be made aware that the measures must be maintained in good order and regularly checked. Figure 6.1 illustrates a number of resilience (and some resistance) measures as well as the building surfaces potentially vulnerable to the inflow of water.



Figure 6.1: Schematic illustrating a number of res ilience (and some resistance) measures To illustrate the potential vulnerability of building surfaces to the inflow of water, Table B6.1 lists examples of the typical air spaces for some common surfaces, some of which are shown in Figure 6.1.

Table 6.1: Area of typical openings on building su rfaces

Approximate Area of Openings Typical Building Surface Type

(sq mm) (sq cm) External Door: Gaps at sides and along threshold

PVC door in reasonable condition 4050 40.5 Wooden door in poor condition 8250 82.5

Air brick openings 3650 36.5 Unsealed perimeter around pipe

50mm diameter 314 3 75mm diameter 471 4

100mm diameter 628 6 Wall cracks / porous brickwork (2mm x 500mm) 1000 10

1mm construction gap between vertical wall and floor (floor length 5000mm one side)

5000 50

Ground floor pipework open at both ends Shower tray outlet 38mm (ground floor) 1134 11

Toilet outlet 75mm (ground floor) 4418 44



Sumps and pumps Sump and pumps are installed in domestic properties at a low point so that floodwater may be pumped away faster than it enters. This will assist cleaning and draining after a flood. Most pumps are automatically triggered and may require a power supply separate from the normal domestic supply. Manufacturers of temporary products may need to install the sump and pump system if this is to remove floodwaters which enter the sub floor area. Sealing of floors/internal walls -“tanking” Tanking basements, cellars or ground floors with water resistant membranes can be an effective method of reducing flood damage but involves specialist fitters and can be relatively expensive because the whole area has to be fully sealed. Plaster is removed from floor to ceiling before installation. Some systems incorporate plastic barriers or coatings that fit behind sacrificial plasterboard on internal walls and beneath floors. It can often have the appearance of bubble wrap or egg boxes so that any floodwater reaching the inside of the external walls (from outside) or from beneath the floor is directed behind the plastic membrane to a sump at the lowest point in the property and automatically pumped out. This measure is normally appropriate for flood depths up to 600mm and should be used in conjunction with other measures such as raised electric sockets, flood boards, flood resistant doors, resilient floors etc. Even shallow floodwater inside a property is usually absorbed by plaster above skirting boards. A practical option to make a wall more resilient may be to apply tanking on the inside of every internal wall up to approximately 450mm by removing plaster, apply water resistant render, apply tanking compound (GRP resin based water resistant), and finish with render on top. Plastic skirting is a more resilient measure to replace standard wooden skirting. Additional measures for floors include:

• Replacement of sand-cement screeds on solid concrete slabs. Where screeds are damaged in floods, resistance to future damage may be improved by replacement with a denser proprietary concrete screed;

• Replacement of chipboard flooring with treated timber floorboards. Chipboard has to be replaced if there is any chance of contamination. Other treated floorboards are more resilient to floodwater;

• Replacement of floors including joists with treated timber to make water resistant/repellent. The timber is less likely to absorb water, enabling the floor to dry out more quickly and be more resistant to rot or distortion; and

• Replacement of timber floor with solid concrete and provide tiled finish with falls to allow draining to a sump and pump.

Additional measures for walls include:

• Replacement of gypsum plaster with more water resistant material, such as lime plaster or cement render. This reduces the extent to which water will penetrate and significantly increases the probability that a wall will survive a flood without damage. In the photo shown here, the walls have been re-plastered up to one metre above floor level



with lime-based renovating plaster to limit dampness seeping into the walls;

• Installing a chemical damp-proof course below joist level. This helps minimise the amount of dampness that gets above the damp-proof course, potentially reducing the damage to the property and the amount of repair work that must be done above this level;

• Replace doors, windows, skirting boards, doorframes and window frames with fibreglass, plastic or UPVC or other similar water-resistant alternatives. These do not absorb water or warp, and so are more readily functional after a flood. The photo opposite shows where new internal doors, door frames and linings have been fitted to make them easier to remove, and ceramic tiles replace carpets.

Internal fixtures and fittings Flood damage to any electrical system in a property usually involves not only the electrical sockets, TV points and telephone points but also consumer units, which may be at low level. The following measures can aid property resilience:

• Electrical sockets, fuse boxes, controls and wiring should be raised to at least 1.5 metres above floor level. If rewiring, cables should be brought down the wall to the raised socket so that cabling isn’t affected. (Basements or situations where depth of flooding could be more than 1m would require special consideration);

• Boilers should be mounted to the wall above the level that floodwater is likely to reach;

• Service meters should be moved to at least one metre above floor level (or well above likely flood level) and placed in plastic housings;

• Washing machines should be moved to first floor rooms if the layout of the house is suitable. Washing machines are heavy and impractical to move before a flood and are expensive to replace after one;

• Shelving: irreplaceable or valuable items should be placed on high-mounted shelves above likely flood level;

• Home entertainment: audio-visual equipment, for example TV and hi-fi, should be mounted to the wall about 1.5 metres above floor level (or above likely flood level);

• Kitchen and bathroom: water-resistant materials such as stainless steel, plastic or solid wood should be used rather than chipboard-based units. Where possible fridges and appliances should be raised on plinths.

• The photo opposite shows a kitchen which is fitted with all main appliances on plinths, and incorporates new steel kitchen units with base units raised off the ground and electrical points placed above likely flood level.



B6.3 Assessment Template

Outline Assessment

Table 6.2 summarises the various resistance and resilience measures described above and provides a broad indication of measures which are likely to be suitable for different circumstances. It is emphasised however that a pre- installation survey (see following section) should always be undertaken to determine appropriate measures in each situation and specific requirements. Table 6.2: Assessment Guide for pluvial flood resis tance and resilience measures 12

Type of Property Likely Depth of Flooding Costs (€) Measure

Detached Multiple (Block) Basement Up to

0.3m Up to 0.6m

Up to 1m

Up to 0.3m

Up to 0.6m

Up to 1m

Units

Resistance �

Bunds or walls � � � (or more)

50 Per m²

�

Threshold raising � � (pavement level step)

� 1500 - 2200

Per door

Storm porches � � � 70 Per m

External renders and facings � � � � 70 90 Per m

Demountable / free standing barriers

� � � � 2500 2600 3700 Per 5m

Aperture covers / flood guards � � � � 100 - 200 Per Property

Flood skirts � � 100 - 200 Per Property

Anti-flood valves � � � � 60 - 120 Per Unit (valve)

Resilience Sumps and pumps � � � � 550 Per unit (pump)

Resilient finishes to walls and floors and tanking

� � � � 40 - 60 Per m²

Raised fixtures and fittings � � � � 700 Per Property

12 All measures are only suitable for relatively short duration flooding. Contaminated floodwater may require special consideration.



Pre-Installation Survey

Any application of flood resistance and resilience measures in individual properties should be preceded by a survey by professionals with the requisite skills and experience. The pre-survey process generally comprises of six elements:

1. Assessment of the depth, duration and frequency of possible flooding around a cluster of properties.

2. Assessment of the elevation of building thresholds and of ground-floor levels, basement levels and the elevation of under-floor spaces.

3. Assessment of the likely routes of ingress of floodwaters for each particular property.

4. Evaluation of potential means of protecting or making more resilient the structure and content of each particular property.

5. Recommendations for approved protection and / or resilience measures to reduce the impact of future floods. (In the UK such products are normally British Standard approved.)

6. Requirements for post implementation quality assurance inspections, at each property, of any measures that are installed.

All technically suitable and affordable resistance and resilience solutions should be considered. Where resistance alone protection is not practical, resilience can offer an alternative, or additional approach as resistance protection measures may not prevent all ingress of floodwaters. Once the full range of possible options has been identified the survey should set out those protection and / or resilience measures considered most suitable for the circumstances pertaining in each property. This should include consideration of the following:

• The cost-effectiveness of measures;

• The suitability of measures for the anticipated type of local flood risk;

• The suitability of measures for the lifestyle of the occupiers;

• The ability of the occupiers to successfully deploy any measures in the event of a flood warning;

• The aesthetic impact of the measures (particularly on listed buildings or in conservation areas);

• Any possible negative impacts on the health and safety of residents (e.g. access and escape during a flood; trip hazards; the risk of injury during the deployment of measures);

• The preferences of residents / landlords;

• Any impacts on the ability of the community to act collectively in response to a flood or flood warning; and

• Any possible negative consequences of the measures on the structure or condition of the building (e.g. condensation; damp; structural integrity during a flood).



It is desirable to protect the property against flooding as far as protection measures and structural safety allow. The benefit in terms of reduced insurance premiums or even on the availability of insurance should be considered. The opportunity should also be taken to incorporate improved resistance and resilience measures as a part of reinstatement following a flood event. Reporting Following the implementation of the measures, properties must be inspected in order to check that the measures implemented meet the performance specification in the original survey report. This also gives an opportunity to ensure the property owner is aware of how to deploy the product(s). Achieving consistency in the degree of flood resistance and resilience provided across any one area is important. This can be undertaken directly by the local authority (for example Dublin City Council) or with the assistance of community and business groups who can act in a coordinating capacity. The local authority can maximise feedback on the performance and effectiveness of resistance and resilience measures and obtain detailed information on specific flood events which can be of considerable value in planning for and further strengthening the response to future flood events. A simple on-line pro-forma could be developed to gather information on the performance of measures. The same pro-forma, or a parallel linked pro-forma could gather information on the nature of flooding, timing and any damage sustained as well as for upload of images and video-clips which can also provide valuable information. Community and business groups could again play an important coordinating role in assisting and encouraging the gathering of such information from individual householders and businesses. It is important that this feedback is available to the community and business groups themselves as well as the local authority (Dublin City Council). Reporting can also gather information on the extent to which regular practice exercises are undertaken – in addition to promoting familiarity with resistance and resilience products and practices and implementation procedures these help to ensure that flood awareness is maintained. Again community and business groups can be used to plan and coordinate such exercises. Through these exercises any weaknesses in deployment or responses can be identified and addressed.

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