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Innovative Surveying Tool for Building Resilience Works Against Flooding

Info: 16343 words (65 pages) Dissertation
Published: 14th Feb 2022

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Tagged: Environmental Studies


Flood risk is a significant and growing problem for the UK. This risk will increase with climate change and urban development. The number of people at high risk of flooding could rise from 1.5 to 3.5 million by 2080. Currently 400,000 homes and 75,000 businesses in England have an annual chance of flooding. Many of these buildings have an historic interest. 15,000 homes in the UK have been flooded in winter 2015/16.

Therefore, people must be aware of their flood risk, but also be prepared for a flood event.

Today, that is the case for risks occurring currently or for the next 5 days, by consulting the Environment Agency Website. The public can also find relevant information and ideas in order to be prepared or to get help during a flood by visiting the flood section of the Environment Agency website or by reading the different guides written by their Councils.

However, it appears that it is not so easy for people to know if they have something to do specifically for their existing house to be prepared in advance.

With that in mind, and knowing that most commonly studies about flood impacts focuses on future constructions or targets professional buildings, it becomes important to inform people living in a flood area about the level of risk they are exposed to, and to give them a preventive and effective solution specifically designed for their existing house, in an autonomous way.

The challenge is to protect the house and all the family, against flooding and prior to it.

A tool has been designed:

An accessible and comprehensive tool has been designed so that everyone can know in what type of flood zone they are living in, and depending on how high the risk was, the tool helps the user to make his own assessment of the potential damages in case of a flood and the associated vulnerability. Over this operational diagnosis, the tool delivers a preventive work “to do list” to increase resilience of the house against flood.

It refers to the notions of damage and vulnerability of private housing before proposing the operational diagnostic methodology. It also offers several practical preventive solutions.

The tool has been tested by users:

To ensure the usefulness and the workability of tool, it was necessary to test it.

Around 40 users had been approached to use the tool and complete a questionnaire to give their opinion and suggestions about the tool. The questionnaire has been designed specifically for this research.

Despite some difficulty to recover the toolkit from Dropbox, it appeared that the users appreciated the value of the tool, that whatever the user profile, the level of guidance given was sufficient and the vocabulary used was understandable. The exhaustiveness of the tool was not raised as an issue, but users have suggested additional options to describe more precisely the characteristics of their home including other materials. This was predictable due to the choice of options was limited only to probable and significant damage.

There are always wishes for improvements in the ergonomics of the tool, although from the results of the questionnaires, it did not seem to be the priority of the users, who focused more on functionality and especially on the economic aspect of damages and works.

The first approached users confirmed the usefulness of the tool, as it made them realise the risk level of flood and the relevant preventive measures to protect their own house.

Consequently, the tool has been recommended and suggestions have been made to help the decision of the works to implement, with a costing section.

A tool to make existing buildings more resilient against flooding is now available!

Table of Contents

Click to expand Table of Contents

1. Introduction

1.1. Background

1.2. Rational for the research

1.3. Aim, objectives and research methodology

1.4. Scope and limitation

1.5. Outline of the thesis

2. Flood impacts and the associated adaptive works

2.1. Introduction to flood impacts

2.2. Structural and non-structural Impacts

2.3. Economic impacts

2.4. Conclusion to flood impacts

3. Research methodology

3.1. Introduction to research methodology

3.2. Type of research

3.3. Theoretical and practical development of the tool

3.4. The questionnaire

3.5. Summary of the research methodology

4. Development of the toolkit

4.1. Introduction to the development of the toolkit

4.2. Steps of the development

4.3. Finalisation of the tool

5. Findings

5.1. Introduction to findings

5.2. Results of the questionnaire

5.3. Summary of findings

6. Discussion

7. Conclusion

Reference list


List of figures

Figure 1 – NatCatService analysis of natural loss events in 2015

Figure 2 – Bath predicted flood zone (Environment Agency, 2017)

Figure 3 – Definition of water level, (P. Bowker, M. Escarameia, A. Tagg. 2007)

Figure 3 – General representation of a ground floor to 1st floor house

Figure 4 – Some elements with potential damages by flooding

Figure 5 – Suspended timber floor (The Office of Deputy Prime minister report, 2003)

Figure 7 – Ranked damages, (Schwarz and Maiwald, 2008)

Figure 8 – Tool defining the flood scenario

Figure 9 – Tool assessment of the potential damages

Figure 10 – Tool assessment of the vulnerability

Figure 11 – Tool identification of measures to reduce the vulnerability to flooding

Figure 12 – Installation of temporary devices to block water entry (The Office of Deputy Prime minister report, 2003)

Figure 14 – Population of consulted users

Figure 15 – Profile of consulted users

Figure 16 – User’s choice of improvements

Figure 17 – Hierarchy of flood risk investigation, SFRA

Figure 18 – Potential step for the tool to analyse the measures to undertake depending on the economic aspects

List of tables

Table 1 – Potential damages depending on threshold reached by the water level

Table 2 – The degree of vulnerability associated with the safety of persons

Table 3 – The degree of vulnerability associated with return to normal delays

Table 4 – Assessment of the vulnerability of each of the defined parts of the building against flooding depending on previously found potential damages

1. Introduction

1.1. Background

A civil engineer aims to shape the world to respond to a social and demographic demand to make living easier (Institution of Civil Engineers, 2017). As well as conforming the infrastructures to the environment, a civil engineer also needs to prevent natural events impacting society.

One of the most common natural disasters to occur in the world is flooding. Contrary to rare but deadly disasters such as earthquakes, flooding occurs throughout the year and is predicted to occur more and more due to climate change (Defra/Environment Agency R&D Programme, 2005). NatCatSERVICE (2015), a natural catastrophe loss database which currently records about 1,000 events each year (Fig.1), states that flooding is one of the biggest and costliest natural disasters across the world. From their analysis from 1980 and 2015, the biggest flood event cost £34.52 M and resulted in 813 fatalities. In the United Kingdom, the biggest flood was of £32 M overall costs.

Studies have estimated that the number of people at high risk from flooding could rise from 1.5 million to 3.5 million by 2080 (D. Pickles, 2015). Around 400,000 homes in England in 2015 were subject to river and coastal flooding due to their location.

Flooding is a dreadful experience leading to extensive economic and social impacts. It destroys homes generating short and long-term consequences for everyone concerned. In addition to the security of people which remain the principal matter of concern, property damages and rehabilitation costs can be extremely high, as well as rehabilitation delays for buildings. However, most of the population is not aware of their vulnerability towards the risk of flooding. (R. Soetanto, D. G. Proverbs, 2004).

Given the number of dwellings in flood-prone areas and the consequences of flooding on people and properties, it is essential to work on flood prevention at an early stage, by establishing a diagnose of the vulnerability of buildings and propose clear adaptations designed to bring back security in private houses and make them reusable as quickly as possible. Despite extensive researches on how to resist this natural catastrophe and the measures taking place for more resilient structures, a clear majority of existing construction techniques are still unsuitable for the risk of flooding (F. Harvey, 2016).

1.2. Rational for the research

Current studies analyse various protected measures and their efficiency for new designs making houses more adaptable to flooding. This research will focus on addressing existing buildings.

Flooding mitigation for individuals currently consists of employing simple measures such as placing sand bags at the bottom of doors without fully understanding the reason behind this and relying on professionals to carry out repairs after the flood event.

The purpose of this project is to give to individuals the means, without the intervention of professionals. to estimate the vulnerability of their own habitat against the flood risks and to propose adaptive solutions that they can implement preventively from flooding.

1.3. Aim, objectives and research methodology

The aim of this project is to investigate an innovative surveying method that can be used by residents to provide anticipatory protective measures based on the levels of risks to various building elements and functions. This surveying method needs to lead to a better level of safety of the occupants of the building, a reduction of damages to structural and non-structural elements which would decrease the time to return to normal occupancy of the house after the flood.

To do so, the objectives of the research will be as followed:

  • Enquire about the hazard present at the level of the construction concerned by conducting an in-depth study focusing on a specific type of flood and building based on a chosen region
  • Diagnose the vulnerability of construction to flood risk by developing a suitable methodology
  • Selecting, with the help of existing case studies, the most relevant protective measures to the identified hazard
  • Prove the tool’s workability

1.4. Scope and limitation

1.4.1. Scope

R. Soetanto and D. G. Proverbs defines in The Structural Survey (2004), that when looking at flood damages to properties, the two main factors to focus on are the flood characteristics and property characteristics. Due to the large number of protective measures for different types of building and floods, this study will focus on a specific type of flood and a designated region. Therefore, this report isn’t intended to be exhaustive.

For the selection of the region, it has been found that Bath was situated in a flood danger zone from the river Avon. In a 1 in 100 annual probability event, 930 properties in Bath were at risk in 2014 (Environment Agency, 2014). In 2015, the number had significantly reduced but still counts to over 500 properties at risk from flooding (Environment Agency, 2015). The Environment Agency has set three zones depending on the level of risk of flooding (Fig. 2). For simplicity, the study considers that:

  • Zone 1, the risk is too low to be considered. The annual probability is under 1 in 1,000.
  • Zone 2, has a medium probability between 1 in 1,000 and 1 in 100, the maximum water level in the habitats will not exceed 0.5 m and the duration of flooding is less than 2 days.
  • For Zone 3, has a high probability over 1 in 100, the water level may exceed 0.5 m and the duration of flooding may be longer than 2 days.

Bath is located a significant distance from the coastline and as such is not affected by a coastal flooding (Capita Symonds, 2008).

Figure 2 – Bath predicted flood zone (Environment Agency, 2017)

The region is also considered likely to be impacted by climate change. The predictions expect an increase of the 1% AEP (Annual Exceedance Probability) in a 100 years’ time but this will have no impacts on this study (Capita Symonds, 2009).

1.4.2. Limitations

The recommendations proposed in this document have no regulatory value. The technical elements of the works listed in this document do not replace the requirements of a prevention plan of the risks, technical standards or professional rules.

This study does not assess the cost of potential damage and of the measures that would reduce vulnerability. The analysis is essentially focused on the safety of people and the return to normalcy of the building.

The use of this tool cannot engage the responsibility of the organisations which contributed to its drafting nor of the professionals consulted for its elaboration.

1.5. Outline of the thesis

The aim of the project is to develop a tool for the public to perform in an autonomous way:

first, by informing them about the level of risk of flood they are exposed to;

then, by diagnosing the vulnerability of their dwelling based on its characteristics and localisation.

Consequently, it will give preventive and effective solution specifically designed for their house to protect it and their family against flooding.

To validate to usefulness of the tool, it is required to be tested by a sample of users, with a questionnaire to be completed and analysed.

From this analysis and comparison of existing solutions, the tool will then be put in perspective to put forward ways of improvement and extension to a more exhaustive solution.

2. Flood impacts and the associated adaptive works

2.1. Introduction to flood impacts

The parameters characterising a flood, when looking at building impacts, include the water height, the duration of immersion, the flood rise rate (flow velocity), the turbidity and the transport of contaminants (R. Soetanto, D. G. Proverbs, 2004).

The velocity of floodwater through Bath is expected to be fairly low (<0.5m/s) (Capita Symonds, 2009). Therefore, this study will not be looking at floods with high current velocity. It will also not consider turbidity nor floodwater contaminants, because the damages from these factors on the buildings are too complex and diverse. However, it is important to keep in mind that their input would influence the way the building will react to the flood.

The main parameters of water depth and duration of immersion will be retained. The Bath & North East Council has identified in 2009 the flood hazards of the region and its characteristics:

The level of water

The depth of water is one of the most important factors when assessing flood damages to a building. Indeed, an increase of water depth relates to an increase in damages to the infrastructure (R. Soetanto, D. G. Proverbs, 2004).

The definition of the maximum level of the water on site is considered as the maximum level of flood found in the zone, subtracting the ground level of the dwelling (Fig. 3).

The nature of the damages is significantly different when the level is over 1 m. Indeed, the pressure acting on the surfaces of the building can create chaos within the structure.

The strategic flood risk assessment analysed the flood depth in Bath, where model results were available. The deepest flood water is shown in the floodplain of the Lower Avon upstream and downstream of Bath, and along the eastern floodplain of the Lower Avon through Bath itself (Capita Symonds, 2008).

As this research aims to help the community in a recurring event, it is logical to get a level of flood that is most likely to happen keeping in mind that it must be high enough to have an impact on the houses for a tool to be tested. If the height is too low for the flood to impact the dwelling, a tool to assess the vulnerably and propose works will not provide enough data.

The duration of immersion

The duration of immersion is the next most importance factor after water depth when considering potential damages on a building (R. Soetanto, D. G. Proverbs, 2004). This is due to the different characteristics of the materials constituting the structure. Indeed, damages can occur after a certain amount of time if the material has a certain resistance to water or humidity and even collapse. It is considered that it is unlikely to block the penetration of the water in the building when the duration exceeds 48 hours, whatever the sealing modes employed.

A rapid flood is considered to have a rise time of less than 12 hours, a slow flood is defined beyond this threshold (P. Bowker, M. Escarameia, A. Tagg., 2007).  The warning delays (that is the time between the announcement of the flood to the time of the event) must be sufficient to allow time to install the measures.

2.2. Structural and non-structural Impacts

2.2.1. Identification of the impacts

Water is evidently a main enemy to the structures of buildings. Most materials used in the construction can be deteriorated at different rates by prolonged contact with water (M. Keppert, 2017). The damages that occur are lead from different mechanisms such as infiltrations, capillarity action and condensation. The guidelines for new constructions of public and private houses are currently elaborated to avoid such situations. A property that has been recently designed, well-constructed and well-maintained must not be attacked by these mechanisms. However, for existing constructions under former regulations, it is more complicated to mitigate this kind of situations.

It is important to define how the flood factors (water height and duration) impact the building. Water depth

The structure is affected by the water level through the pressure exerted on the surfaces resulting in destabilising and damaging the building (R. Soetanto, D. G. Proverbs, 2004). The importance of these damages evolves in stages depending on defined thresholds, represented in Figure 2 and described in Table 1, rather than linearly proportional to the level of water.

Case studies of the effects of floods shows that as soon as the height of the water exceeds that of the window seal, the quantity of damages of the ground floor is much more important (cliff effect). (The Office of Deputy Prime minister report, 2003).

Table 1 – Potential damages depending on threshold reached by the water level

Water Height Thresholds Water is likely to reach and damage
1 – From floor to plinth – Floor coverings and their supports,


– The plinths

2 – From plinth to window seal – Power outlets


– Wall coverings – partitions

– The walls in elevation

Depending on the height of their location:


– Electrical installations

– Heating installations

– Hot water installations

3 – From the window sill to the ceiling – Carpentry


– The glazing

– The luminaires

4 – From the ceiling to the 1st floor – Electrical conduits (strong currents or weak currents)


– Pipes passing through the top floor or false ceiling Duration of immersion

The degradation of materials varies greatly with the duration of contact with the water. The longer the flood, the more it promotes the diffusion of moisture in the walls by capillary phenomena, leading to swelling or hydrolysis. As with water depth, the relationship between the immersion time and the magnitude of the damage is not linear. It evolves in stages with specific building thresholds. In the case, for example, of a gypsum board, for an immersion time of (F. Palha; A Pereira; J. de Brito; J.D. Silvestre. 2011):

  • Less than a day: 20% chance of damages,
  • 2 to 3 days: 50% chance of damages,
  • More than 3 days: 100% chance of damages.

Water depth and duration of immersion parameters have major impacts when aiming to make a structure resilient to flooding, and can be mitigated by replacing or protecting exiting materials with materials more adaptable to water. Potential damages

Specific parts of a building need to be considered when assessing the vulnerability to flooding. Various existing assessment project such as “How to assess a Home for renovation” Home building & Renovation (2017), “Preparing for flood” by The Office of Deputy Prime minister report (2003) and “Improving the flood performance of new building” from P. Bowker, M. Escarameia, A. Tagg, (2007) have analysed damages. From gathering data from these existing documents as well as and many other case studies, a list can be set out on to which parts must be assessed for a general type of house.

1. Foundations

It is the nature of the soil that leads to a change of behaviour when flooding occurs and create potential damages to the whole structures (Property assure, 2017).

– A compact, cohesive soil (clayey) and already saturated with water before flooding will promote an absence of damage. Conversely, a clay soil that has endured a long period of drought will make the foundations more susceptible to damage.

– A variation in non-uniform water content throughout the construction, due to the local presence of plants (trees or shrubs), can lead to differential swellings and, consequently, to disorders.

– For a sandy, powdery or poorly coherent soil, there can be possible scouring when the exposed soil surface can be eroded by a current of water.

The movements of the foundation ground can lead to damage to the foundation footings and to the elements which they support the load-bearing walls.

Limestone and clays underlie bath, mainly Lower Lias, with some Upper Lias, Middle Lias and Inferior Oolite. Soils in the study area are shallow, lime rich and freely draining (Bath & North East Somerset’s Planning Services, 2003). Consequently, the impact on foundation is improbable in the research and will therefore not be included in the tool.

2. Crawlspace

Crawlspaces prevent the contact of the lower floor with the ground and thus limit the risks of rising dampness. To ensure ventilation, openings are provided in the masonry. However, this leads to entry of water during a flood, as well as various objects driven by the current. Since the crawlspace is very often limited to a few decimetres in height, it can be difficult to extract these objects after the backflow of water (Home building & Renovation, 2017).

3. Walls in elevation

Potential damages vary from cracks to even collapses in the cases of significant movement of the ground through deformation of wooden frames or crumbling of bricks. A coated masonry wall is impermeable to rain water. It is no longer true if it is cracked, or if the joints of the masonry are degraded. Furthermore, the passage of the external networks (pipes and cables) through the walls and the floors are other ways for the water to enter (Home building & Renovation, 2017).

4. Plaster and exterior cladding

Damages of plaster and exterior cladding consists of separation, cracking, stains or indelible spots from hydrocarbons suspended in water (ArchSD, 2012).

These damages are minor and do not affect the safety of persons or the reinstatement of premises. Therefore, they will not be considered in the tool.

5. Indoor wall Distribution and lining partitions

Prolonged contact with water degrades the qualities of the distribution walls, mainly when made of plaster-based elements (D. J. Lemieux and P. E. Totten, 2016).

The direct consequences can range from a simple detachment of the wall coverings to the collapse of the partitions.

Indirect consequences may relate to electrical or heating installations and equipment integrated into the partition.

6. Interior finishes and wall covering

Plaster and coatings can witness degradation, detachment, indelible spots, moulds with the contact of water and swelling and deformation for wood panels (ArchSD, 2012).

7. Floor support

For floors with metal joists and vaults in terra cotta, swelling and possible degradation of the joints between vaults can be caused. For wood floors (Fig. 5) with wood joists and particle board, deformation of the joists and panels, swelling of the panels will be the damages from contact with water (The Office of Deputy Prime minister report, 2003).

8. Flooring

Types of flooring vary between mineral products (tiles, stones), organic (wood) and synthetic (paint, plastic or textile coatings). Their methods of application or fixing to the floor (sealing, gluing, nailing) depend on their nature.

The type of degradation due to flood is generally the main cause of damage, but the support (floorboard, paving) may itself be affected by flooding causing collapse, deformation, cracking.

9. Ceiling

There is potential deformation of wooden suspended ceilings, plasterboard and mineral fibreboard. For glued ceiling, pieces of from the slab may detach and fall. Paint would also get degraded (EPA, Indoor Environment Division, 2013)

As ceilings considers heights that not likely to be reached in the set conditions of the flood, it will not be considered.

10. Interior Fittings

After contact with water, wooden interior joinery can undergo drying, deformation, swelling (of particle board or cardboard), detachment (plywood panels), and appearance of mould.

11. Interior stairs

For wooden staircase, the damage is related to the duration of the immersion. It corresponds to deformations of the silts and the steps. (R. Hunt, 2017).

12. Glazing and exterior joinery

After contact with water, wood joinery undergoes deformation, swelling, peeling, and appearance of mould during drying. In fact, after the event, they no longer perform their functions and it is necessary to replace them.

Another phenomenon is the breakage of the glazing which can occur solely under the effect of water pressure (G. A. Bell & Never Paint Again UK, 2017).

13. Shutting

Possible deformation, buckling of wooden shutters and degradation of electric motors.

Motors for shutting, which are the most vulnerable parts, are usually placed on the ceiling levels and will not be included in the tool (G. A. Bell & Never Paint Again UK, 2017).

14. Garage doors

For the door with leaf, overhead or sectional door with wooden panels, one can notice deformation, buckling, detachment of panels due to the flood impact, as well as deterioration of electrical motors.

15. Heating installations (hot water production included)

The equipment of climatic engineering including boilers, heat pumps and regulating devices is often expensive and can be seriously deteriorated by immersion. They are important as they can facilitate the return to normal, such as the drying of the walls (The Office of Deputy Prime minister report, 2003).

16. Ventilation

Risk of deterioration of the fan in the case of mechanical ventilation. Sludge can deposit in ventilation ducts, air intake or extraction vents (Home building & Renovation, 2017).

17. Air conditioner

Deterioration of electrical parts (motor) of mono-bloc or dual-unit air conditioners and fan coils associated with a centralized installation is the main concern here (Home building & Renovation, 2017).

18. Plumbing

Evacuation pipes can undergo dismantling, breaking, slopes in the crawlspace or on buried networks around the building. Mud deposits are common in pipes and manholes after a flood event.

These damages are minor and do not affect the safety of persons or the reinstatement of premises. Consequently, they will not be considered in the tool (P. Thornborough, 2017).

19. Electrical Installation

The electrical distribution network and related equipment are particularly vulnerable. They are essential for efficient drying (heating, ventilation) and cleaning which reduces the time required to return to the normal (P. Thornborough, 2017).

Water conveyed by flooding is often chemically aggressive, especially if it is salty. This can lead to corrosion, which can severely damage the electrical equipment and cause malfunctions. Flooding can pollute electrical installations by carrying sludge or even mechanically damaging equipment and possibly cables. Fire hazards also have a possibility of occurring upon return to service.

  • Incomer: deterioration of the meter and of the general switching and protection apparatus
  • Distribution board: deterioration of circuit breakers, protective fuses and equipment.
  • Conductors: insulation defects in ducts and conduits.
  • Cables: deterioration of cables not sealed.
  • Equipment, sockets, switches, luminaires: oxidation of contacts, deterioration.

2.2.2. Vulnerability

The vulnerability of a building to the risk of flooding is measured by the extent of the consequences of the aggressions that the building will undergo and what it contains (F. Messner; V. Meyer, 2005). Defining the vulnerability of the building to the risk of flooding is based on answers to the following questions about the damages to the building resulting from flooding,

  • Do they contribute on how the impacts on the building in the event of flooding can lead to the danger of human life?
  • Do they make increase the time required to return to normal operation of the building following the flood episode?
  • Can they generate domino effects on their immediate environment and other disturbance such as pollution?

The assessment can be made by forming a hierarchy based on the gravity of the impacts, such as the proposition by Schwarz and Mainwald (2008) (Fig. 7). Vulnerability related to personal safety

The vulnerability related to personal safety is the most important concern. Personal safety is defined as the protection of people from physical harm. It is not only the people who live or are present in the building at the time of the flood but also the rescue services, the personnel of the companies in charge of the restoration works and the volunteers who would intervene during or after flooding.

The characteristics of the building that make people vulnerable must be analysed during the diagnosis. Attention should be paid to:

  1. The capacity of the building to withstand the exceptional stresses due to the rise of water;
  2. The existence of an out-of-water zone: the possibility of offering refuge to people who may be surprised by the rise of water while waiting for help and the possibility for the emergency services to easily reach this area out of water to evacuate those who have sought refuge there;
  3. The risks associated with technical equipment:
    • Electrical shock due to electrical installations or electrical equipment switched on if the electrical panel which supplies them has been reached and the damaged circuit protective device,
    • Explosion due to leakage of gas because of pipe breakage,
    • Poisoning by polluting products (storage of hazardous materials) or by the presence of mould in certain parts of the building where the water has stagnated,
    • The presence of cadavers of animals or organic matter which may cause health risks;
  4. The risks associated with changes in the environment:
    • the collapse of the road network because of scouring or the formation of underground tunnels,
    • the collapse of walls and the fall of materials,
    • soils made slippery by deposits of fine, causing falls,
    • the presence of ponds, excavations, manholes, manholes, low areas or holes due to scour for which limits and depth are concealed by the presence of residual water (risks of falling, injury or even drowning). Vulnerability related to the return to normal

The vulnerability related to the return to normal is measured by the time elapsing between the event “flood” and the moment when the activity in the building may resume satisfactorily. This period consists of the cleaning and drying time of the premises, the furniture and equipment which may be retained and the duration of the restoration work if necessary.

The drying time itself depends, for example, on whether electricity is supplied, whether the heating system is operating, and whether the premises are well ventilated.

The return to normal will thus depend both on the importance of the damage to the real estate, on the structures and elements of the construction of the building, on the time required for their restoration, and on the restoration period of the utilities such as water, electricity, gas and sewage disposal. The domino effect vulnerability

The domino effect vulnerability is related to the impacts of building damage on its immediate environment. The flooding of a site can in fact create a succession of damages and inconveniences on buildings located nearby. These domino effects have important impacts for the building owner or manager. Its legal liability may be incurred (Messner & Meyer, 2005).

Domino effects are by nature difficult to measure in advance. Therefore, it will not be considered here.

2.2.3. Proposed solutions to reduce the vulnerability to flood risk

Reducing the vulnerability of a building means ensuring that the risks of harm to the public and that the normal return to normal regular operation of the building are as low as possible. There are two main strategies for reducing the vulnerability of an existing building: resisting and yielding. Resisting strategy

Opting for the strategy of “resisting” consists in obscuring and waterproofing all the ways through which water is likely to enter, for example:

  • Existing small openings such as air inlets, grid covers, cracks, defective joints, voids or cracks around joineries.
  • The walls: the longer the flood, the more the water will be able to soak the walls and therefore to go up by capillarity and to flood the interior of the building.
  • The sewage system: as soon as the water treatment facilities are flooded, water pressure can push the wastewater back to the buildings and make it come out by the evacuations of the sanitary facilities.

The installation of devices to delay or even prevent this water penetration into the building can be done via temporary devices such as plugging openings, cofferdams, movable barriers and sandbags, or via permanent installations. These devices have the advantage of keeping the building dry to a certain extent and sometimes reducing its vulnerability in terms of time to return to normal. Their use should, however, be reserved for certain specific circumstances and their implementation surrounded by multiple precautions. For example, a temporary perimeter barrier that protects a building from collapsing or a cofferdam limits the penetration of water but cannot be perfectly watertight, so it is necessary to accompany its implementation with complementary measures such as pumping, non-return valve, or elevation of goods inside the building. It is advised to implement a solution that will be useful in case of failure of these systems and entry of water (The Office of Deputy Prime minister report, 2003). Yielding strategy

The yielding strategy consist in letting the water enter the building, taking all necessary measures to limit the damage and reducing the time to return to normal.

To yield is to allow the water to enter the building which is fatal in the most cases. An anticipation of this event helps to limit the damage. This anticipation involves an adaptation of the works that will be potentially immersed and an organisation designed to allow, in due time, the shelter of valuable objects inside the building. It should be noted that this strategy is recommended for the buried rooms of the current buildings: leaving a cellar to fill allows balancing of the water pressures on both sides of the buried walls, which limits the risk of collapse (The office of deputy Prime minister report, 2003).

In the annex, a list of relevant preventative works has been drawn up for each part of the building. Some of them are specific to each strategy “resist/yield” and some are for both.

2.3. Economic impacts

The financial impacts are mainly due to the loss of valuables and the cost of rehabilitation. Furthermore, protecting a home from being flooded is not cheap, flood insurance is becoming extremely expensive. Figures from the Association of British Insurers (ABI) estimate that protecting a property against shallow flash floods will cost in the region of £2,000-£6,000, and protection against prolonged flooding requires bigger changes and could cost up to £40,000.

2.4. Conclusion to flood impacts

The structural and economic damages result in negative impacts upon lives. Indeed, a research study done published in 2013 from the British Red Cross about ‘The experience of flooding in the UK’ showed that flooding effects on health – both physical and mental – with 39% of people suffering physical effects and 67% suffering effects on their emotional health (M. Pitt, 2008). The emotional effects from flooding impacts are long lasting and sometimes may last a whole lifetime.

To keep safe and avoid the devastating results of flooding, it is fundamental to be prepared in advance and be aware of the potential consequences. Moreover, when a flood event has never occurred in someone’s life (or even if it had), it is almost impossible to know all the steps into protecting a house against it and having easy accessible guidance helps stay focused on what needs to be done.

3. Research methodology

3.1. Introduction to research methodology

The functionalities of the tool are to:

  • Define the flood conditions on which the diagnosis will be conducted
  • Determine the potential damage to each part of the building
  • Determine if this damage can have an influence on the safety of persons and the delay in normal operation of the building
  • Propose measures to reduce the vulnerability to be implemented in prevention.

The diagnosis will be based on:

  • Visual inspection of structures,
  • Information gathered from surveys from occupants of targeted type of house
  • The examination of typical house plans,

Then, to make sure the tool is valid and reliable, several people will test the tool and assess it through a pre-made questionnaire.

3.2. Type of research

As described in the step by step guide for beginners in research methodology by Ranjit Kumar (2011), this research observes and analyses the gathered data from a survey based on the tool efficiency, this is a qualitative study, with an unstructured approach to an empirical philosophy. From an application point of view, this is pure research that develops and tests the theory of this tool being efficient and responding to the need of people against flooding. From the view point of objectives, it is also seen as an exploratory study as the outcomes are not yet known.

This is an evidence-based practice (EBP) as the tool to be promoted is based on research evidence through the questionnaire. It will follow existing procedures that have been tested in the past and proven to lead to reliable findings.

3.3. Theoretical and practical development of the tool

3.3.1. Flood conditions

It is a matter of determining the conditions under which the building is likely to be flooded. This phase is of the utmost importance because it directly implies the potential consequences on the building and therefore the provisions to reduce its vulnerability.

As the study considers only the flooding resulting from a slow and gradual river flood, it is more precisely to determine the main parameters:

  • the potential water level in the building
  • how long the water is in the building.

These data come from historical documentary sources or from specific hydrological studies carried out to prepare risk prevention or crisis management plans.

3.3.2. Assessing the damages

The principle is to evaluate the potential damages, then deduce the dangers for the people and the difficulties to return to reoccupy the premises until the systems can work normally.

For a given flood, the damages depend on the characteristics of the buildings. Ideally the evaluation can be prepared from architectural plans “as realised” but which can be lacking, especially after the property passes.

The process therefore provides for an on-site survey. The tool must allow the individual to be able to do so in an autonomous way, thus simple with common materials.

This statement is therefore proposed as a checklist of all the parts of the building (index).

The tool automatically evaluates the potential damage as a function of the flood zone to which the flooding characteristics corresponds and the characteristics of the building.

To do this, the tool relies on a pre-established diagnosis for all types of work and flooding by an expert panel of insurance and construction individuals. To streamline, the tool considers only the most significant and most probable damages.

3.3.3. Assessing the vulnerability Vulnerability related to personal safety

To clarify the risk incurred by persons, a classification of vulnerability level related to their safety is established for each potential damage.

The following table provides a classification of the degree of vulnerability associated with personal safety. (Based on N. A. Renfroe, J.L. Smith, 2016).

Table 2 – The degree of vulnerability associated with the safety of persons

Level Degree of vulnerability Consequences of damage on the safety of persons
0 Null No damage.


No risk to the safety of persons.

1 Low At the origin of a slight accident such as contusions, shock, minor sprains, etc.
2 Medium Source of more serious accidents such as light fractures, etc.
3 High Source of severe accidents or deaths. Vulnerability related to return to normal

Similarly, a level of vulnerability associated with the return to normal is established for each potential damage.

The few examples following will illustrate the influence on returning to normal:

  • The hot water tank has been hit by water, causing the control box to be deteriorate. The lack of functioning of the tank is not crucial with respect to the return to normal, since it is possible to dispense with hot water for the time to replace the casing which would take a rather short time. On the other hand, if the tank itself is damaged, and must be replaced, the damage becomes important with respect to the return to normal, because the replacement time is much longer.
  • The water of a part of the crawl space cannot be evacuated. Stagnant water creates a risk of insalubrity, thus making it difficult to reintegrate the staff or the inhabitants.
  • The power supply cannot be restored from the transformer, itself flooded and damaged by flooding. The drying and cleaning time thus increases, if a generator is not available.

The following table proposes a classification of the degrees of vulnerability that may be reached in terms of the time to return to normal due to damage to the building. (Based on N. A. Renfroe, J.L. Smith, 2016).

Table 3 – The degree of vulnerability associated with return to normal delays

Level Degree of vulnerability Consequences of damage on the return to normal
0 Null No restraint to return to normal with delays of less than a few days.
1 Low Necessary repairs make the building unavailable for a few days.
2 Medium Necessary repairs rendering the building unavailable for a period of several weeks.
3 High Necessary repairs rendering the building unavailable for a period of several months.

The deadlines set out above are technical delays resulting exclusively from reclamation work, without taking account of the time taken to award contracts and the release of financing, the availability of construction companies, etc. These delays are likely to be greatly extended, but in poorly known proportions, in the case of widespread flooding over vast territories impacting, at the same time, tens of thousands of buildings.

3.3.4. Identification of measures to reduce vulnerability

The two options to reduce vulnerability to the penetration of water into the building are either a resisting or yielding strategy. The choice is not always easy. The “yielding” strategy is recommended when the flood height of more than 1m or its duration exceeds 48h.

Indeed, if the pressures exerted on the walls of the building for height exceed 1m, it can create major disorders on the structure.

Water cannot be prevented indefinitely from entering a building, regardless of the type of sealing used. Two days can be taken as an arbitrary time.

For simplicity, the tool combines the strategy of resisting for habitats in zone 2, whose characteristics of the flooding are coherent such as the height under 0.5 m and the duration under 2 days. Conversely, the tool combines the strategy of yielding for houses in zone 3.

From the list of damages identified by the tool, it gives the most relevant prevention work to reduce the vulnerability of the building.

These measures may have different effectiveness depending on the objective to be achieved:

  • Occupant safety
  • Reduction of the time to return to the dwelling
  • Reduction of damages

The option to choose the objective targeted by the individual was not chosen because the criteria of choice are not obvious to the user.

To select the relevant measures, it is necessary to check the suitability of the works with the specificities of the housing (e.g. not to secure swimming pools or lifts or tanks of hydrocarbons if the house does not have them).

This step allows the individual to quantify the solutions and to have his strategy defined.

3.4. The questionnaire

For the questionnaire to be valid and reliable, it must respond to a procedure (Diem, 2004).

Definition of the objective of the questionnaire is as followed.

The questionnaire is set out:

  • to measure the user’s satisfaction towards the tool they will be testing to get a level of overall satisfaction,
  • to understand what is appreciated,
  • to understand the user’s needs
  • to discover the main areas of improvement they would add to the tool and to characterise them

Construction of the questionnaire:

Definition of the sample:

For the results of the analysis of the data collected to be valid and reliable, it requires:

  • that the audience selected to complete the questionnaire must be concerned as much as possible by the risk of flooding and if possible in the scope of the research (experienced or exposed to a river flooding, living in Bath, etc.)
  • that the numbers of users must be large enough to be representative of the targeted users. Here, as the tool aims to help the wild public, the number of people that needed to be surveyed had been based on the availability of people around as this questionnaire requires as much answers as possible (Keith G. Diem, 2004). Indeed, having a large enough number of participants answering the survey will result to roughly the same as if the entire population took it. For this test, 40 people received the tool and the associated questionnaire.

Application of basic rules

  • Writing short, simple and specific questions to aid the reader understanding the type of answer required, therefore leading to better result for the intention of the survey.
  • Clarify the questions to ensure the relevance of the answers
  • Do not use negations in the questions
  • Avoid technical terms or otherwise explain them
  • Structure by themes with different colours
  • Size the questionnaire for a 10min duration to ease the filling of the questionnaire
  • Apply a numeric scale, or verbal scale (dissatisfied-neutral-satisfied-very satisfied)
  • Use Even scale to lead the user to a pro or con position
  • Use an odd scale to give the opportunity of a neutral position

Collection of the data:

The questionnaire will be sent by mail, one of the most common and efficient way to undergo a survey as Don A. Dillman states in his publication Mail and telephone Surveys (1978) (Choose a more recent publication). For a reason of ease, the collection of the data will be done by email by directly answering what has been previously sent. The survey will be anonymous as the interest rely only on the result and not the choice of participants. This will also help getting people to undergo the survey without having the pressure to reveal their identities.

As the questionnaire will be sent through without the author being present to explain each point, the layout needs to be clear and easy to understand with segments explaining the relevance of the questions where needed. Furthermore, to ameliorate the experience of this questionnaire and obtaining the most answer as possible it is best for it to be pleasant to the eye of the reader.

Before being sent to the public, the questionnaire has been field tested by a select few people whose own real survey is to communicate whether it meets all the necessary criteria such as ease of reading and understanding.

Analysis of results:

The results of this questionnaire should be able to determine, after analysing them, whether the tool proposed for flooding resilience works, is efficient and suitable to the problem.

The results are presented in chapter 5, Findings.

In conclusion, the satisfaction survey, well used, remains an excellent tool to improve the understanding of customer needs and thus to retain them, but also to improve the tool itself

3.5. Summary of the research methodology

The methodology is structured in two main parts:

  1. Designing the tool in four steps:
    • To consider the flood conditions depending on a flood zone
    • Identify the potential damages of the defined parts of the buildings
    • Estimate the vulnerability on the safety of people and the return to normal of the building
    • Propose anticipatory works.
  1. Testing the tool:

A sample of users directly validates the tool to get real situation results and a survey is made for their opinion through a questionnaire that will be analysed.

4. Development of the toolkit

4.1. Introduction to the development of the toolkit

The tool must be accessible in terms of ease of usage and understandable by the public. Therefore, it requires to be a simple format with clear information.

The tool would be of better accessibility for modern days under the form of an application. To make the tool adaptable to its specific application.

4.2. Steps of the development

4.2.1. Step 1: Defining the flood scenario

The principle is that the tool gives the characteristics of the flood directly from the place of residence selected by the user.

In its first development, the tool allows to directly obtain the flood zone by clicking on the map of the city of Bath.


From the existing data, the tool could indicate additional information on the characteristics of the flood to the user:

– Flood level

– Duration of the flood

– Duration of the warning before the event

– Duration of help after the event

The last two options were not chosen because the info of the zone is sufficient for the objective of the tool by means of the simplifications described in the methodology.

4.2.2. Step 2: Assessment of the potential damages

The tool makes the relationship between it and a pre-existing damage assessment table for each part of the building according to the flood zone in question.

It gives the nature of the potential damage to the dwelling considered.

4.2.3. Step 3: Assessment of the vulnerability

The tool selects the following pre-existing texts (Table 4) according to the damage list from the previous step.

These texts are dumped into the final balance sheet presented in table form.

From the vulnerability assessment methodology set out and the known potential damages we can analyse each part of the buildings.

Table 4 – Assessment of the vulnerability of each of the defined parts of the building against flooding depending on previously found potential damages

Building parts Vulnerability from the security of people point of view Vulnerability from return to normal point of view
Crawlspace 1 – A slight vulnerability exists for health reasons since the building’s wastewater spilled in the crawlspace may stagnate in this crawlspace for 1 or more weeks. 1 – The return to normal is conditioned by the fact that the water contained therein, such as wastewater, can be discharged. Requirement of effective ventilation and disinfection.
Walls in elevations 0 – Except in the exceptional case of cracks, lack of solidity or collapse, such potential damages do not affect the safety of persons. 1 – Works on the rehabilitation of walls in elevation do not affect the reintegration of the premises which is conditioned, first, by drying.
Indoor wall distribution and lining partitions 0 – No impact on personal safety. 3 – The operation is cumbersome as rehabilitation leads to replacement of all partitions. It compromises the reinstatement of the premises for months. This leads to the vulnerability of the return to normal to be strong.
Interior finishes and wallcovering 0 – No impact on personal safety. 2 – Complete rehabilitation impedes the rapid reintegration of the premises.
Wooden floorboards 2 – The wood floor must be part of the checklist as part of the general inspection before reinstatement. It influences the vulnerability linked to the safety of people. 3 – Work to restore or replace wooden floors is heavy work and conditions works on other parts of the building such as partitions and flooring. Consequently, damage to wooden floors is an element of high vulnerability to return to normal.
Flooring 1 – Low vulnerability with the risk of falling on deformed parquet or loose tiling. The working times are variable depending on the floor covering.
1 – low vulnerability for bonded tiles
2 – medium vulnerability for plastic, textile or glued flooring
3 – strong vulnerability to parquet flooring on joists
Interior Fittings 0 – No impact on personal safety. 1 – Low impact on return to normal.
Interior stairs 0 – No impact on personal safety. 1 – The staircase can condition the access to the out of water zone. However, it can be used temporarily despite its deformation, if the stability of the staircase is ensured. The effect on return to normal remains low.
Glazing and Exterior joinery 0 – No impact on the safety of persons, except for the breakage of glazing which is not likely to happen in the set conditions. 1 – Restoration work only conditions the reintegration of premises. Adjustment and replacement work can be done from the outside.
Garage door 0 –  No impact on personal safety. 0 – No impact on return to normal.
Heating Installations 2 – Water damage to the electrical parts of pumps, burners, control and regulating panels and convectors may affect the safety when protective devices are damaged. Vulnerability can be high. 2 – The operation of the heating system conditions the drying time. However, the heating of the premises may be provided by temporary means. The impact on the reintegration of premises therefore remains at an average level.
Hot water unit 2 – Like any electrical equipment, the water heater can be hazardous to people when protective devices are themselves damaged. Vulnerability can therefore be high. 2 – If the water heater is to be replaced, the vulnerability is at an average level.
Ventilation 1 – The ventilator present a hazard like any electrical equipment. However, it is generally not very accessible, so the impact on the safety of people is low. 1 – Ventilation can be done naturally by opening the windows. Otherwise, the replacement of the fan is a simple and fast operation. The impact on return to normal is low.
Air conditioner 2 – The electrical parts may present a hazard like any electrical equipment. However, the impact of the damage on the safety of people is related to the accessibility of the equipment. 1 – It is possible to withstand for some time the absence of air conditioning. Replacing the hardware is a simple operation. Vulnerability to damage on these facilities is low.
Electrical Installation 3 – Electrical installations are the most sensitive parts of the construction that can pose the greatest risk to the safety of persons in the event of flooding. However, this risk can be avoided by making a general cut to the electrical system prior to the rising of the water and carrying out a general inspection before reintegration. It is therefore easy to reduce the impact of this damage on personal safety. 3 – The rehabilitation of the electrical installations which conditions the reintegration of premises is a rather heavy operation when:


– the water reaches the distribution and protection tables,

– power supplies, such as power sockets and switches are made from the ground and not downwards.

In this case, the vulnerability to damages to these facilities is high.

4.2.4. Step 3: Identification of measures to reduce the vulnerability

From a list of pre-selected prevention works, see below, the tool proposes the measures according to the strategy and the potential damage for each part of the buildings.

In addition, it systematically proposes the collection of wastewater and the creation of a refuge zone as soon as the house is located in a flood zone.

To select the relevant measures, the user must verify the suitability of the work with the specificities of the accommodation resulting from the previous steps.

The following measures have been identified to mitigate the vulnerability and potential damages to the building. They can be set from P. Bowker et. Al. (2007) as well as the case studies mentioned in the damages. Some are yielding strategies and other are resisting one:

1. Protection of crawlspaces (resist and yield)

The objectives: The measure aims at preventing the penetration of objects while promoting the evacuation of water during reflux and the ventilation of the sanitary space.

The works: The measure consists of checking the presence or possibly creating at least two openings on the walls of the crawl space.

The opening must respect the following guidelines:

  • Avoid placing an opening facing the current in such a way as to avoid a massive entry of water, in particular in the event of runoff.
  • Avoiding placing them on the same wall, to favour the ventilation of the crawl space.

Must have effective ventilation, a minimum height of 0.8 m, with easy access and circulation.

2. Installation of temporary and removable sealing devices (resist)

The objectives: Doors and patio doors prevent rain from entering the dwelling. However, when subjected to water pressure during flooding the openings may even break.

Other waterways are possible through:

– Permanent openings of small dimensions such as which air inlets at the bottom of the walls;

– Passages of pipes and cables through walls, floors and floors;

– Wastewater ducts

The works (Fig. 12): To limit the penetration of water into the house by adopting the following measures:

– Placement of cofferdams in front of doors and windows: this is a device that partially closes the doorway of a door to greatly limit the penetration of water.

– Insertion of removable hoods in front of small openings (air inlets, ventilators etc.). It is imperative to remove the covers in front of the air inlets after the backflow of water so that the house can be correctly ventilated.

Despite these provisions, there may still be a residual water passage, which requires a residual water removal system such as a water pump or vacuum cleaner.

3. Clogging of waterways (resist)

The objectives: The purpose of this measure is to limit the penetration of water, which reduces the damage and the time to return to normal.

The works: Limiting the penetration of water into the house for the parts liable to be immersed, by adopting the following measures:

– Repair of faulty joints in exposed stone or brick masonry,

– Treatment of cracks,

– Clogging voids between ducts and pipes.

The filling can be ensured by mortars adapted to different situations. It must withstand the pressure exerted by water from outside the building.

4. Removal of remaining residues (yield)

The objectives: Permanently prevent water from entering the dwelling during a flood is impossible as temporary and removable sealing devices may have a leakage rate due to design, installation or quality of support of the device on the wall, leading the clogging of the waterways to be deficient.

It is therefore necessary to ensure the evacuation of the water to outside by various means adapted to each situation. Pumping completes the efficiency of the means, helps to limit the damage and delay of refurbishment. The pump can be operated manually or by an electric motor.

The works: The presence of a low point makes it possible to collect water to a suction point. If the process uses an electric motor, it requires the use of an electrical source, a power supply line and pumping equipment with all the safety guarantees to avoid electric shocks.

5. Rehabilitation to reinforced concrete floors (yield)

The objectives: The measure is aimed at replacing low floors that are more vulnerable to water, such as a wooden structure, by a reinforced concrete floor. This operation evaluates the possibility of raising the level of the initial floor to locate the new floor above the level of the highest known waters.

The works: The replacement of an existing floor deemed vulnerable by a reinforced concrete floor is an operation that can be envisaged during a major transformation of the building. It must pass through a structural engineering study that considers the other elements of the structure.

6. Reflection of distribution and duplicating partitions (yield)

The objectives: The objective of the measure is to facilitate post-flood restoration work.

The works: Use partitions that can be disassembled for repairs such as plasterboard attached to metal frame or waterproof plaster tiles. Avoid alveolar partitions and partitions made of wood-based materials.

In addition to their function of delegating and organizing the interior space of the dwelling, the partition walls also ensures the passage or fixing of equipment. If it has been damaged during the flood, it will be either retained after rehabilitation or replaced.

7. Replacement of thermal and acoustic insulation (yield)

The objectives: The measure concerns the choice of thermal and acoustic insulation to limit their degradation during flooding. The general recommendation is the replacement of insulation that has undergone flooding.

The works: The replacement of the insulation behind the partition walls requires the dismantling of these partitions.

Thermal insulation on the inside of the walls can be replaced through important work on the dubbing.

The thermal insulation present on the outside of the walls can be replaced without the need for access to the interior of the house.

8. Protection of climate engineering equipment (yield)

The objectives: As with electrical installations, a short-term immersion requires the replacement of all electrical and electronic equipment that has been in contact with water.

It is therefore important to avoid as far as possible that these elements are immersed.

The works: Putting water-powered equipment out of water.

This measure consists of raising, moving or arranging a permanent barrier to displace the heat production equipment (boiler, heat exchanger, heat pump) and domestic hot water, air conditioning and ventilation (extractors air, air intakes) as well as accessory equipment (pumps, control units, control panels). This can be achieved in several ways depending on the presence or not of an upper floor.

Implementation of this measure can quickly act against practical considerations concerning the actual possibility of raising and using the equipment under safety conditions required (electrical safety, access to equipment, evacuation of products of combustion, air required for combustion, etc.)

9. Replacement of floor coverings (yield)

The objectives: The measure concerns the choice of floor covering that would be little affected by the water at the level of the material itself or its method of fixing, and must consider:

– the behaviour of the material against prolonged contact with water.

– Its cost

– Its ease of replacement

The works: Floor coverings fall into several categories in terms of their behaviour during flooding:

– Coatings that are relatively inexpensive but must be replaced after flooding (e.g. carpets)

– Coatings requiring a higher initial investment but likely to behave better during a flood or otherwise quite easy to clean (e.g. tiling).

– Coating which method of attachment is sensitive to water, but the material itself will be slightly degraded (e.g. soft floors, glued floors).

– Coating which method of attachment may be moderately sensitive but whose material may be affected (e.g. traditional parquet).

10. Replacement of interior joinery (yield)

The objectives: Interior joineries are not designed for prolonged immersion. This exposure to water can cause damage. The choice of the constituent material is therefore essential.

The works: It is recommended to use materials that are not sensitive to water such as aluminium and treated steel. With these materials, careful cleaning followed by drying and possible replacement of the joints (foam, rubber) make it possible to restore satisfactory operation. As a result, the choice of metal frames makes it possible to replace only the internal doors damaged by the flood.

Preferring baseboards not sensitive to water and plinths made of PVC or ceramics are not very sensitive to water. This option allows to limit the consequences of the flooding, provided that the fixing of the skirting boards guarantees their maintenance during and after their immersion.

11. Replacement of exterior joinery and installation of door gates (yield)

The objectives: The aim is to choose materials that are not very sensitive to water such as metal or PVC.

The works:

  1. Using water-insensitive materials for doors, windows and shutters.

With these materials, a careful cleaning followed by drying and possible replacement of the joints (foam, rubber) is recommended to find satisfactory operation.

The prescription of materials that are not sensitive to water concerns the entire joinery (opening and window frame).

  1. Providing security grids in front of the doors to allow water to pass through.

In some areas where water is rising rapidly, it is recommended to allow water to enter the dwelling to balance the interior-exterior pressures and thus avoid damage to the structure of the building. For this purpose, an anti-intrusion grid could be installed temporarily in front of the doors and windows left open.

This measure also allows for more effective drying after flooding limiting the risks of intrusion and theft.

12. Redistribution of electrical circuits (yield)

The objectives: The objective is to limit the damage to the electrical circuits by modifying their path in the house.

A complete replacement of electrical equipment which has undergone a long event is necessary.

The works:

– Individualising the circuits between flooded parts and parts out of water to anticipate the consequences of the penetration.

From a technical point of view, there are two types of electrical design that allow the individual parts of the flood and the parts out of water to be identified:

1. Using circuits protected by the flood zone in the General Repair Chart. These circuits will be marked and cut before the flood. With this typology, the separation of the circuits is done by function and by zone.

2. By installing a divisional panel specific to the flood zone and external electrical installations. In this second case, the location is simplified. It will be enough to cut the protective devices that feeds the divisional table on the repair board.

The rehabilitation of the network in the flooded parts can thus be carried out without consequences on the network of the non-flooded parts.

– Using electrical circuits to avoid retention of water in ducts.

The power grid is a passage for water during the flood. It contains areas where water and moisture can stagnate (especially in ducts) after flooding, which poses a danger to users and may cause repeated breakdowns. In addition, difficulty accessing ducts and junction boxes is a problem to ensure drying. By lowering the grids from the ceiling and the upper parts of the dwelling to the ground, the risk of stagnation is greatly reduced, since the “self-draining” of the ducts by gravity is favoured as well as the drying of the network.

To the extent that the level of water rise is not excessively high, it is recommended to take advantage of the rehabilitation works to move sockets and switches at a height where they will be less likely to be submerged in the event of a flood. Electrical appliances will therefore be located, if possible, above the level of the highest known waters, while respecting accessibility for people with reduced mobility.

These measures concerning electrical installations and must be entrusted to a professional.

13. Dismantling distribution panels and cabinets (yield)

The objectives: The rehabilitation of the electrical installations which conditions the reintegration of the premises is a rather expensive operation when the water reaches the electrical panels.

These risky situations, which are difficult to detect visually, can however be ruled out by cutting off the general low-voltage switchboard before the rising water level and by having a complete inspection carried out by a professional (electrician or inspection bodies) before returning to service.

The works

– Disconnect the electrical distribution panels, the protective devices, and the various communication equipment.

The measure consists of positioning the electrical panels and the various electrical equipment above the level of the reference flood or the highest known waters.

The aim here is to avoid a possible replacement of the devices. However, this measure is only possible in the case of buildings with rooms above the level of the highest known waters.

These measures must be entrusted to a professional.

– Relocate the main incomer from the District Network Operator out of water zone.

Damage caused by the presence of water in the dispenser cabinet may require significant work and delay rehabilitation of the building. In a dwelling with several levels, the electrical panel will be preferentially installed on upper floors. In this case, a main power switch must be installed on the ground floor (at a height between 0.90 and 1.30 m). This measure therefore avoids this situation.

These modifications must be carried out by the District Network Operator.

4.3. Finalisation of the tool

The first phase of the development of the tool consisted of linking the elements of the building, the flood zone, the damage, the vulnerabilities and the implementation of the works. The product led to a single table that synthesises all these elements (annex).

This has led to a unique database that serves all stages of the tool (Appendix 1 and 2).

5. Findings

5.1. Introduction to findings

Forty people were consulted for the use of the tool and their opinion was asked through a pre-established questionnaire. The people consulted are between 20 and 60 years old with an average age of 30. 20% are students, of whom 5 are in civil engineering. The others are professionals who do not work in the field of civil engineering or flood risks, such as education, research, hotel and industry.

Very few consulted users have their habitat directly affected by the risk of flooding. Nevertheless, less than 40% of them are aware from experience or live in an exposed region, such as the south-east of France or the Amazon. For more representative results, users were encouraged to act as if they were Bath resident living in a significant flood zone (2 and 3).

Figure 15 – Profile of consulted users

100% of users’ habitats are over 20 years old and have therefore not been built according to the recent Construction Design Management regulations which take better account of the risks of flooding.

5.2. Results of the questionnaire

5.2.1. Tool usability

It appears from the questionnaires that it is not the use of the tool that is difficult but the recovery of the tool by Dropbox. Indeed, improvement of the design and ergonomics increased the size of the file and required the use of Dropbox for its provision to the users.

It has been found that the availability depends on the informatics configurations of each computer such as the existence of anti-virus which can block the download or opening of the application, the lack of access to Dropbox upstream and the lack of applications to unzip the file. All these operations had been previously validated and / or processed in the user guide. However, it was found that some users did not consult the guide. This encourages embedding the user guide in the tool for systematic knowledge or to modify the tool so that it is very intuitive. These disturbances influenced the time spent and user satisfaction. On the other hand, once the tool was available, the ergonomics were considered satisfactory, in particular the interactivity with the card on the first page, the possibility to go back and the colorization of the different degrees of the vulnerabilities.

As for the tool, the two criteria that emerge are the need for illustrations of the damages and the recommended works, and to have the display the totality of the pages of the tool whatever the size of the tool screen, to avoid hiding certain instructions.

5.2.2. Tool constitution and construction

Whatever the user profile, the level of guidance given was sufficient.

The exhaustiveness of the tool is not an issue. Indeed, no question was raised about possible missing parts of buildings susceptible to flooding. On the other hand, users have suggested additional options to describe more precisely the characteristics of their home including other materials. This was predictable due to the choice of options was limited only to probable and significant damage.

The vocabulary used was chosen so that it was understandable at all levels of users.

5.2.3. Usefulness of the tool

Most affected users understood the value of the work and were sensitive to the approach to protect themselves from the risk of flooding, especially since the subject is of current topic. On the other hand, their profile such as not being resident in bath, not exposed to the risk of flooding or not owner of their house meant that the motivation to follow up the proposal of works is difficult to appreciate.

5.2.4. Improvement or extension suggestions

To date, out of the 10 answers, the users’ wish is rather to develop the economic aspect of the research which shows their interest in the tool.

Figure 16 – User’s choice of improvements

5.3. Summary of findings

It is noted that the tool is sufficiently simple and popularised for its use for any type of user.

It is important to facilitate the provision of the tool independently of the electronic configuration of the computer and without requiring any specific informatics skills.

There are always wishes for improvements in the ergonomics of the tool but from reading the results of the questionnaires, this does not seem to be the priority of the users who focus more on functionality.

The users’ requests are rather oriented towards an extension of the tool on the economic aspect of damages and works, which will be taken up as a proposal of evolution in the following chapters.

6. Discussion

The innovations of the tool was to provide a mean for individuals to realise the risk of the flood and preventive measures to mitigate those risks on their own house, existing, without the help of a professional.

  • To raise awareness of the level of risk of flooding throughout the lifetime of their dwelling. The Environment Agency website tool gives the flood zone linked to the probability of the event (100 to 1000 years’ floods). The government website gives the risk of flooding in real time.
  • Protecting attitude towards flooding through preventing works instead of dispositions essentially for before and after the event that are mainly to manage properties.
  • Applied to individuals in terms of their localisation and habitat with specific works in contrast to the Council flood risk strategy that applies at the level of the region, city and neighbourhood.

The strategic flood risk assessment (SFRA) (Capita Symonds, 2009) investigated floods for each level of specificity. This tool has its place within the most detailed part in the site-specific flood risk assessments.

  • As mentioned earlier, a lot of research has been made to develop a set of regulations for new dwellings that are more adaptable to flood events and the increase of risks due to climate change (Communities and Local Government, 2007). The research behind the tool focuses on existing structures. The tool therefore completes the regulations as it brings more for the as built.

It is therefore made clear that the tool is an innovation when compared to the existing measures to protect the population from flood impacts and answer to different requirements.

7. Conclusion

Although the usefulness and validity of the tool has been proven, a solution such as this one always needs improvement to adapt to user’s recommendation and individual necessities. The necessities can be ranked from the return to questionnaire.

Tool design

The main aspects to improve would be to allow the use of the application on all electronic systems as there are currently compatibility issues depending on the type of computer used. The solution would be for example to recreate the content to a website system.

Enhancing the visual aspects with the aid of additional graphics that can be more informative on the measures and potential damages as well as for the page to fit automatically to the screen would lead to a better reading and usability.

As for now, explanations are included in an external user guide. The tool could carry a more explicit presentation within its content to explain the aims of the project and the way to use it.

Technical and content development

The tool can be developed for other locations. To do this, it would require changing the appropriate maps and adjust the parameters as the search for zones is done through the criteria of colour and brightness, or to change the way of input such as entering the address.

The ways of using the tool can be enlarged for example to set the type of vulnerability and its degree as a criterion to select the work to do. This option is for the case that the individual knows how to define the purpose of his work. It is still possible to do from the existing tool as the user can look only at the type of vulnerability he requires and choosing the associated work. However, the tool doesn’t do an automatic separation. It can be easily done by adding an extra possibility through option functions.

The verification of the technical efficiency of the measures could be done directly by the tool. It could go further by ranking the different measures according to their effectiveness depending on the risks. This requires a work on the evaluation of the efficiency of each works. Thus, one could distinguish the necessary and important measures.

Economic and social aspect

A fourth step of the tool could propose a strategy to put in place based on efficiency and cost.

Indeed, the tool doesn’t consider the economical aspect usually implied in the choice by the occupant. The output can be a graph of a cost and the reduction of the flood risks, plotting the position of each work. The tool will therefore aid the decision for optimising the choices.

The current way the tool regards the results made during the assessment of the diagnosis is to try to identify and implement measures to reduce the vulnerability of the building. However, it must not be an end in itself. An ultimate evolution would be to advise a choice in function of the contextual elements, such as taking advantage of works envisaged for a renovation of the dwelling or other factors which would lead to abandon or resale the premises. This last option becomes necessary, for example, when the potential impacts of flooding are high and potential technical solutions for reducing vulnerability are not sufficiently effective or unsustainable. Another possible option would be the “status quo”, which consists in leaving the building untouched. In the event of flooding, this means choosing a strategy of cleaning, replacing the damaged parts of the building by relying on insurance compensation. This would require data other than technical such as the cost/benefits analysis.

From this project, it seemed essential to consolidate the specification before the development of the tool. Consequently, it is necessary to insert additional steps before its expansion.

To feed this phase of specification, the results of the first questionnaires must be integrated and complemented by the needs of users who live in a flood-prone area or flooded areas.

In addition, at various stages of the development of the tool, it is desirable to have all the necessary skills such as computer scientists, graphic designers and flood specialists to contribute to the needs expressed.

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Appendix 1 – The tool’s inputs

Appendix 2 – The tool’s outputs

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