External Review of Sewer Flooding Risk Registers...

External Review of Sewer Flooding Risk Registers Mott MacDonald

Water Services Regulatory Authority

247338/01/C - 15 October 2008


Centre City Tower

7 Hill Street

Birmingham

B5 4UA

External Review of Sewer Flooding Risk Registers

Report

October 2008

Mott MacDonald

Demeter House

Station Road

Cambridge CB1 2RS

UK

Tel : 44 (0)1223 463500

Fax : 44 (0)1223 461007



247338/01/C - 15 October 2008



247338/01/C - 15 October 2008

External Review of Sewer Flooding Risk Registers

Report

Issue and Revision Record

Rev Date Originator

Checker

Approver

Description

A 04/08/08 A Heather M Surendra P Chadwick First issue for comment

B 22/08/08 M Surendra A Heather Revisions and corrections

C 15/10/08 A Heather P Chadwick P Chadwick Final corrections

This document has been prepared for the titled project or named part thereof and should not be relied upon or used for any

other project without an independent check being carried out as to its suitability and prior written authority of Mott

MacDonald being obtained. Mott MacDonald accepts no responsibility or liability for the consequence of this document

being used for a purpose other than the purposes for which it was commissioned. Any person using or relying on the

document for such other purpose agrees, and will by such use or reliance be taken to confirm his agreement to indemnify

Mott MacDonald for all loss or damage resulting therefrom. Mott MacDonald accepts no responsibility or liability for this

document to any party other than the person by whom it was commissioned.

To the extent that this report is based on information supplied by other parties, Mott MacDonald accepts no liability for any

loss or damage suffered by the client, whether contractual or tortious, stemming from any conclusions based on data

supplied by parties other than Mott MacDonald and used by Mott MacDonald in preparing this report.



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List of Contents Page

Chapters

1 Introduction 1-1

2 Findings from Review 2-1

3 Summary of Main Observations 3-1

3.1 Comments from CCWater on ‘At Risk’ Registers 3-1

3.2 Company Understanding of the ‘At Risk’ Registers 3-3 3.2.1 Understanding of the Purpose and Issues 3-3 3.2.2 Understanding and Interpretation of the Nomenclature 3-4

4 Main Process Steps 4-1

4.1 Overview of the process 4-1

4.2 Developing the Register 4-1 4.2.1 On First Contact 4-1 4.2.2 During Clean-up Activity 4-2

4.3 Adding Properties to the Register 4-6 4.3.1 After Initial Investigation 4-6 4.3.2 After Detailed Investigation 4-9 4.3.3 During Investment Planning and Delivery 4-9 4.3.4 Addition of Properties Estimated as being at Risk 4-11

4.4 Keeping the Register Up to Date 4-11 4.4.1 The Link with Information Systems 4-11 4.4.2 Update Frequency 4-12 4.4.3 Recording Changes 4-12

4.5 Removing Properties from the Register 4-13 4.5.1 On First Contact 4-13 4.5.2 During the Clean-up Activity 4-13 4.5.3 After a long time without Flooding 4-13 4.5.4 After Company Action 4-13 4.5.5 As a Result of Better Information 4-13

5 Comments on the At Risk Register Approach 5-1

5.1 Register Name 5-1

5.2 Return Periods, Risk and Sub-registers 5-1

5.3 GSS Payments 5-1

5.4 Assigning Properties to the Register 5-2 5.4.1 First Time Flooding 5-2 5.4.2 Repeat Flooding 5-2

6 Recommended Process 6-1

7 Summary of Recommendations 7-1

7.1 Short-term recommendations 7-1



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7.2 Longer term recommendations 7-2

Figure 4.1: Proportion of companies asking customers about the severity of flooding, if neighbours are

known to be flooded, and if it is raining. 4-2 Figure 4.2: Adding Additional properties 4-3 Figure 4.3: Numbers of companies having exclusion rules for internal and external flooding. 4-4 Figure 4.4: Approaches to GSS payments and definitions of severe and extreme weather 4-6 Figure 4.5: Choice of registers for first-time flooding is reported, and treatment of severe weather 4-8 Figure 4.6: Proportion of companies claiming late additions as outputs 4-10 Figure 6.7: Link between flowcharts 4 Figure 6.1: Best practice process flow chart – identification 6-1 Figure 6.2: Best practice process flow chart – initial investigation 6-3 Figure 6.3: Best practice process flow chart – GSS payments 6-5 Figure 6.4: Best practice process flow chart – Adding to the register 6-6 Figure 6.5: Best practice process flow chart – detailed investigation 6-8 Figure 6.6: Best practice process flow chart – removal from register 6-9



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1 Introduction

Ofwat’s ‘At Risk Registers’ record properties that have flooded from sewers and are at risk of flooding

again. There are separate registers for internal and external flooding. Each register is split showing

the risk of flooding twice in ten years (2:10), once in ten years (1:10) and once in twenty years (1:20).

The 1:20 years register, generally used to record properties flooded for the first time, has been

introduced recently compared with the 2:10 years and 1:10 years registers that have been in place for

many years. Companies target investment to remove properties from the 2:10 years and 1:10 years

registers if there is a cost beneficial case for doing so or to mitigate the risk of flooding1 if not.

Investment is not normally targeted at properties on the 1:20 years register, but if properties suffer

repeat flooding, they are moved to one of the other registers and solutions to resolve the problem are

developed as appropriate. Properties flooded in severe weather (rare events) are recorded by the water

companies but do not go on to the registers.

The At Risk Registers are maintained by each of the ten water and sewerage companies in England

and Wales. Each year the companies report details of the numbers of properties and areas at risk of

sewer flooding, together with the number of incidents that year, to Ofwat through the annual June

return in tables 3 and 3a.

Two major outputs are monitored by Ofwat:

• The reduction in size of the 2:10 and 1:10 internal flooding register (the ‘net reduction’).

• The number of problems resolved.

A further measure is the number of properties subjected to flooding, which affects the wastewater

Overall Performance Assessment (OPA).

Ofwat publishes June Return Guidance which sets out information requirements and definitions of the

data required in each line of the June return tables. The manual aims to standardise reporting

definitions but it has become apparent, from comments by water companies, that information

requirements are interpreted differently by the various companies, and that these differences might

affect the number of properties added to the register.

To help understand the differences in approach and their effect on company At Risk Registers, Ofwat

commissioned Mott MacDonald to conduct a short study of each company’s approach to reporting.

The aims of the study were to:

• Identify and set out the various processes and procedures used to identify flooding, record it,

allocate properties and areas to the appropriate register and eventually remove properties from

the At Risk Registers as the risk of flooding is reduced by company action.

• Establish whether a flood would be allocated to the same At Risk Register irrespective of

which company’s methodology was used.

1 ‘Mitigate the risk of flooding’ means relatively minor investment that reduces the flood risk without providing a permanent

solution. Mitigation is appropriate where a permanent solution is too expensive to justify. It is also used to provide a

temporary solution to severe flooding when a permanent solution will take a long time to deliver. Mitigation does not

necessarily provide full protection from flooding and so properties protected by it are reported as a subset of the At Risk

Register.



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• Check alignment with reporting guidelines, identify the most common approach, and

recommend amendments to the guidance and/or processes to ensure consistency and promote

good practice.

• Establish the impact on the At Risk Registers if Ofwat adopts any recommendations arising

from the study.

The study took the form of a structured interview with each of the ten water and sewerage companies,

limited to a maximum of one day per company during June 2008. At this time most were compiling

June Return data and preparing business plans for their August 2008 submission to the 2009 periodic

review. Interviews were conducted in water company offices so that information systems and flood

records could be seen.

The authors would like to acknowledge the cooperation of the ten water and sewage companies in this

review, as well as the contribution of the Consumer Council for Water to the review.

It must be stressed that this was not an audit of company procedures. The field work was limited to

one visit per company and although companies presented procedures and individual records of sewer

flooding it was not possible to check that the procedures are followed ‘in the field’. It is also possible

that our understanding of company procedures, and hence our view on differences in approach, might

result from the different roles and knowledge of the people interviewed in different companies.

The discussion topics were developed as the main differences emerged between companies. Therefore

some items were not discussed at the earlier interviews. However, those items are mentioned where

more than one approach was seen, as this provides evidence of differences between companies.

Detailed quantification of the impact of differing approaches on the At Risk Registers was not

undertaken and in many cases would not be feasible. A general indication of whether different

approaches would have an upward or downward impact on the number of properties on the register is

made in the report where appropriate.

In this report, ‘flooding’ means sewer flooding, unless stated otherwise.



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2 Findings from Review

• All companies understand the At Risk Register and the nomenclature, but in matters of detail

there are some differences of interpretation between companies.

• All companies consider that they are adhering to the June Return reporting requirements, but

there are differences in interpretation of the Reporting Requirements.

• A flooding incident would not necessarily be allocated to the same register irrespective of

which company’s methodology was used. For example the availability and choice of data and

analytical technique influences the assignment of return period and hence the choice of

register. Since solutions are usually implemented for properties on the 2:10 years and 1:10

years registers, selection for a solution may depend on which company’s area the flooded

property is in.

• In most companies, the At Risk Register is compiled by automated reporting directly from job

management systems. In others, it is compiled as an off-line database or spreadsheet, using

more manual approaches to reporting from customer relationship management systems or job

management systems. Effective examples of both approaches were seen. On reliability of the

approaches, companies pointed out that both depend on the source data having a correct

classification of the incident. Hence all companies conduct manual checking of individual

records to check that the classification aligns with descriptions of the findings.

• Clarification of some aspects of the Reporting Requirements would help to improve the

comparability of company registers. Areas for consideration should include:

o The definition of, and approach to identifying, severe weather. Differences in

approach can affect whether flooded properties are added to the register, or excluded

on the grounds of severe weather. There are three aspects to this: clarifying the

definition of severe weather, strengthening the guidance on best practice assessment

of severe weather events, and ensuring that all companies apply best practice methods

of assessment and report using the same definition of severe weather.

o Clarifying the definition of internal flooding, especially for cellars and garages.

o Clarifying the approach to flood return period analysis and the addition of first-time

flooding to the At Risk Registers.

o Clarifying the approach to assessing repeat flooding, especially where some instances

are the result of severe weather and others are not.

o Clarify the approach for recording properties when flooding is discovered at a much

later date (through detailed investigations or anecdotal evidence from customers).

Current practice varies between companies as to whether such properties are added to

the register and count towards outputs.

o Separating the monitoring of properties that have mitigation measures installed, to

better reflect their true risk of flooding.

• There is agreement that the term ‘at risk register’ is misleading and ‘flooding incident

register’ or ‘unresolved flooding incident register’ would be a better description. There is also

support from some companies for the register to record the risk of individual properties



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flooding (frequency x severity), compared with the current approach which only records

internal or external flooding in large frequency bands.

• There is general concern from companies about the potential impact of at risk registers on

home information packs (HIPs) and property values. The inclusion of a measure of flood

severity as well as frequency might help alleviate this, as it would enable property owners and

buyers to distinguish between large risks and small ones. It would also enable the benefits of

mitigation measures, as well as network enhancements, to be recognised.

• The approach to dealing with ‘severe weather’ if there is repeat flooding differs between

companies. In some cases, all events are counted once it has been established that a property

floods when the weather is not ‘severe’. In others, severe weather is always excluded. The

former approach is simpler for customers to understand and may better reflect the risk to the

property, while also increasing the frequency recorded for that property.

• Sewer flooding is identified from physical signs at the site, such as the location of flood water,

debris, movement of access covers etc. Customer reports and sometimes photographs also

provide evidence of the origin of the flood water.

• All companies check if neighbouring properties have flooded at the same time as a reported

flood, but the extent of the check varies between companies. The evidence suggests that more

rigorous searches during the initial investigation will identify the greatest number of flooded

properties.

• Flooding is attributed to overloaded sewers if no other cause can be found. Where hydraulic

overload is suspected, the majority of companies conduct CCTV surveys after the incident to

check that there are no hidden obstructions in the pipe. However, the subsequent removals of

properties from the register, on the grounds of better information, suggest that this is not a

precise science.

• Some companies continue to operate exclusion rules despite Ofwat having stated that no

incidents should be excluded (for example the time taken to clean up after external flooding,

or damp patches on cellar walls). Even where a company does not have a formal exclusion

rule, it is clear that at the time of the initial investigation a judgement is made as to whether to

conduct further investigation or to close the case, and hence on whether to report the flooding.

• Properties are removed from the At Risk Register when companies have taken action to

resolve the problem; when it is found that the problem is not associated with water company

assets; or sometimes if the property does not flood again for a specified length of time.

Properties may be transferred between registers or removed when better information about the

cause becomes available, as may happen during detailed network investigation after the flood.



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3 Summary of Main Observations

3.1 Comments from CCWater on ‘At Risk’ Registers

As part of the review, we met a representative of the Consumer Council for Water (CCW) to obtain its

views on companies’ procedures with respect to sewer flooding and ‘at risk’ registers from a

customer’s perspective. The views of several CCW regions were collated and are summarised below:

(i) Acceptability

CCW research confirms that sewer flooding is not acceptable to customers.

(ii) Customer reporting

There is a perception that customers’ concerns about potential property blight leads them to under-

report sewer flooding incidents. Therefore, CCW expects companies to pay special attention to

identifying flooded properties, so that robust solutions can be specified.

(iii) Internal flooding definition

CCW is concerned that some companies define some types of flooding such as toilet overflows,

flooding of garages with no internal doors and below-floor flooding as external flooding. CCW would

like clearer definitions to ensure that theses are classified as internal flooding events.

(iv) GSS payments

Some companies are going beyond the statutory minimum requirement for GSS payments, which

CCW welcomes. CCW also welcomes prompt payment, provided the company also pays due attention

to preventing flooding.

(v) Hydraulic overloading and risk assessment

CCW feels that severity and frequency might be better measures of flood risk than the nominal

internal/external and banded return-period registers (some companies also suggested this/agreed with

this comment).

The level of risk is not currently meaningful to customers and CCW feels that companies hide behind

the technical classification. It is difficult for customers to understand why some flood events count and

some do not.

(vi) Cost benefit analysis

CCW feels that cost benefit analysis should be used as a prioritisation tool rather than for the ultimate

selection/rejection of a property for a solution.



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(vii) Mitigation

CCW suggests that if the result from implementing mitigation measures for a property is a lower level

of flood risk than neighbouring properties, then perhaps it does not need to remain on the register.

Companies should count properties where sewer flooding was only prevented by customers’ own

mitigation actions.

(viii) Garages and sheds

CCW believes that if garages and sheds are in regular use and they are flooded, they should be

counted as internal flooding. There is concern that companies are counting too many garages as

external flooding.

(ix) Design standards

CCW notes that different companies have different design standards with respect to designing their

networks to prevent flooding and wonders whether this is this equitable.

(x) Communications

CCW supports regular communication with customers on the register (for example, some companies

send an annual letter). Communications need to be sensitive and show what is being done, with

delivery dates.

(xi) Information flow

CCW contends that there is generally poor information flow between local authorities and water

companies. Customers often report flooding to the wrong agency and information is not always passed

on to the right one



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3.2 Company Understanding of the ‘At Risk’ Registers

3.2.1 Understanding of the Purpose and Issues

The At Risk Register enables Ofwat to monitor company performance in managing its network and

informs customers about network capacity issues. However, there were some comments on the

purpose of the register:

• The classes of risk (2:10, 1:10, and 1:20) may be considered as a measure of the need for a

solution, but in most companies, more sophisticated risk assessments or cost-benefit

assessments are now being used. In some companies the three frequency bands and the

differentiation for internal and external flooding are used for reporting purposes only. Some

companies advocate a more continuous risk scale based on an assessment of the frequency,

severity and scale of likely flooding, but not all companies would want to change from the

existing approach.

• The register has been considered a technical device used between the companies and the

regulators. Many companies stated that the introduction of Home Information Packs has made

house sellers and buyers more aware of flooding. They are concerned that reporting of 1:10

and 2:10 flooding through property searches might introduce housing blight. Companies feel

that this changes the emphasis on the At Risk Register and that great care should be exercised

in placing properties on the register. All companies said that they make the decision on what

properties to enter and they do not accept householder requests to be excluded from it, when

the company has evidence that the property is subject to flooding.

• Dealing with properties where mitigation reduces the risk but the properties remain on the

register. Companies generally agreed that there are benefits to maintaining records of which

properties have had mitigation measures installed. However there are situations where the

mitigation may reduce the flood return period to less than that of neighbouring properties

which are not on the register. For example, mitigation measures for a house on the 1:10

register may reduce the flood risk to 1:30, whereas the risk for neighbouring properties is

1:25. Yet searches by a prospective house buyer would show the house was at risk of flooding

– because it is on the 1:10 register – but not the neighbouring house. This could therefore

mislead a house buyer as to the true risk and also blight the value of the house.

• Although the severe weather exemption is a necessary acknowledgment of the design

limitations of the network, it can be confusing for customers, especially when their property is

flooded several times under differing weather conditions.

• Most companies acknowledge the differences in interpretation of the reporting requirements,

and would welcome more prescriptive guidance on reporting flooding.

• Adoption of private sewers: In the event that private sewers are transferred to the water

companies, reporting could become much more complicated. For example, there are currently

three frequency classes for both internal and external flooding, and if private sewer flooding is

reported separately this will result in a total of 12 register categories. This may reduce the

certainty of allocation and thus lead to more changes as better information is gathered during

the asset management process. Companies do, however, acknowledge the need to monitor the

impact of adopting private sewers on network management costs.



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3.2.2 Understanding and Interpretation of the Nomenclature

There was some debate about the meaning of At Risk Registers. Many companies pointed out that the

registers do not list all properties at risk of flooding, but rather are flooding incident registers, because

they list properties that have flooded. Several companies suggested that the term ‘at risk register’ is

misleading because customers may believe that their property is only at risk of flooding if it is listed

on the register. In practice, the register is mostly restricted to properties that have flooded and which

remain at risk of flooding in the future. Other properties may also be at risk of flooding due to

hydraulic overload as a result of changing demand or weather patterns, but a suitable trigger event

may not yet have happened.

‘Flooding Incident Register’ or ‘Unresolved flooding incident register’ may therefore be a better name

for the At Risk Register, although any description would need to explain that the properties are listed

because they remain at risk.

A further area of confusion relates to the term ‘sewer flooding’. Ofwat’s guidance defines a flooding

incident as an event of flooding from a public sewer, whether foul, combined or surface water. It

should perhaps be clearer that this definition excludes flooding incidents from sewers that are caused

by surface run-off, fluvial flooding, some types of highway drainage or other sources of flooding

where they are the responsibility of other agencies. Ofwat wishes to ensure that water customers only

pay for sewer flooding schemes that address problems arising from flooding that water companies are

clearly responsible for.

Despite this lack of clarity, companies do generally exclude flooding events where the cause is clearly

the responsibility of others, for example flood events arising from private sewers.

The problem arises where the cause of flooding is unclear at the point of flooding (perhaps because

there is a mix of overland flow and sewer surcharge) or the cause is remote from the point of flooding

(for example, where high river levels prevent downstream overflows from operating properly and

sewage backs up in the network). Companies’ assessments of such causes is generally limited to what

the clean-up team can observe at the flooding site, with limited follow-up analysis to confirm the

cause and identify the principal owner of the flooding problem. As companies adopt more holistic

solutions in partnership with other members of the drainage community, the identification and sharing

of flood risks between the responsible agencies will become more important.

Properties are not usually added to the register unless flooding has occurred, although one company

does add adjacent properties that it ‘assesses to be at risk of flooding’, even if they have not flooded at

the time of an incident being investigated.



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Conclusions and recommendations:

� ‘At risk register’ is confusing terminology and does not describe what the register is.

Although properties on the register remain at risk of further flooding, the ARR is not a

comprehensive list of properties at risk of flooding. Therefore ‘Flooding incident register’ or

‘Unresolved flooding incident register’ better describes it.

� The ‘at risk’ registers record frequency, but not severity of flooding, so they do not record

‘risk’ (probability x consequence). This can make it difficult to distinguish between small

internal flooding problems and large external flooding problems, for example. The impact

extends to home information packs (HIPs), where the presence of a property on a register can

have the same impact irrespective of its flooding ‘risk’, as it is conventionally understood. An

alterative approach that could be considered would be a measure of the frequency, severity

(depth, area) and location of flooding, rather than location and frequency alone. The result

would be a continuous risk scale that would more closely align with the cost:benefit

approaches now in use in most companies, although for reporting the risk would be grouped

into a few (e.g. five) categories.

� A risk-assessment approach also applies to mitigation, where interventions reduce the

frequency of flooding but do not eliminate the risk of flooding. Such properties currently

remain on the register after mitigation has been delivered (although they are reported as

having received mitigation). This can cause anomalies with neighbouring properties that are

not on the At Risk Register but have a greater flood risk than those with mitigation in place. A

risk measure could therefore include mitigation measures, to demonstrate the benefit that they

deliver.

� If properties on the registers had a full risk rating, it would enable a distinction to be made

between frequent small flooding incidents and infrequent large flooding incidents. It would

also enable the benefits of mitigation to be recognised, where a property would remain on the

register, but its risk rating would change. This would also reduce the potential impact of the

register on property value and recognise the efforts made by companies to manage flood risks,

when increasing the capacity of the network is not always cost-beneficial.

� Some companies already record flood severity information, (such as depth and extent of

flooding and duration) to inform their prioritization methods and flooding cost-benefit

assessments. Consistent methods of assessment would need to be agreed if this was taken

forward. We recommend that Ofwat considers reviewing these comments with the industry

and other stakeholders, to establish support for developing full risk registers, and what form

the measures should take. It would be important, for example, that the risk categorisation was

simple and easily understood by customers and property owners, and would require careful

consultation.

� We also recommend that a definition of sewer flooding is provided with a clear statement of

what it includes and what it excludes. This could also be the subject of consultation with the

industry and other organisations with responsibility for drainage. The aim would be to ensure

that all stakeholders in the management of flooding agree on a common definition and

understand the boundaries between water company responsibilities and their own. This could

help initiate or reinforce conversations that companies are already having with stakeholders in

the context of integrated urban drainage.

� Once a definition for sewer flooding is agreed, companies would need to review their

procedures for assessing and recording the cause of flooding and flood ownership. This is

likely to develop as integrated urban drainage becomes established as common practice.



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4 Main Process Steps

4.1 Overview of the process

This section reviews the main activities that create and manage the At Risk Register in four sections:

• Developing the register

• Adding properties to the register

• Keeping the register up to date

• Removing properties from the register.

There is an implication of a sequential process but in practice but the various activities are carried out as

they are required for each flooding case.

4.2 Developing the Register

4.2.1 On First Contact

All companies record all customer contacts through contacts centres and central call handling systems.

All companies attempt to identify the main causes of flooding and whether the problem is with a privately

owned sewer. In some companies the call centre staff can see electronic maps of the sewer networks and

this improves their ability to differentiate between company and private sewers. When flooding is caused

by private sewers, the customer is normally told that it is their responsibility, if it is clear that the sewer is

blocked or collapsed. Sometimes a problem with the public sewer – including hydraulic overload –

results in egress from a private sewer. Companies said that if there is any doubt about ownership or the

cause then they will visit the customer.

It is also common to ask customers if it is raining, the severity and location of the flood, and whether

neighbours are affected (see Figure 4.1). This helps in prioritising and allocating the best response. For

example, if a householder feels sure that no other properties are affected and it is not raining, then the

problem is more likely to be blockage or collapse, than if a house floods during heavy rain or several

properties are affected. This is not a definitive guide at this stage and in most companies is used to

inform the operational response rather than for full classification of the event.

Call handling software and the capability to forward information to field staff are variable. Although it is

possible that jobs might not be forwarded at this stage, we found no evidence of this during our visits to

companies. In some companies the call handlers have to learn the questions to ask customers, with scripts

or prompt sheets on their desks. In others ‘case based reasoning’ is used, in which the questions are

presented to the call handler on screen. Subsequent questions are presented by the software, dependent on

the preceding response. This decision-tree approach is highly consistent and results in a specific set of

actions appropriate to the reported incident. It appeared to be efficient and in some companies it is

directly linked to the job management system, GSS payment systems, and At Risk Register reporting.

The use of GIS maps linked to the call handling software allows cal centre staff to see the location of

recent calls, which helps in the early identification of wide area flooding.



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Figure 4.1: Proportion of companies asking customers about the severity of flooding, if neighbours are known to be flooded, and if it is raining.

Ask about severity of

flooding

Ask if neighbours affected Ask if it is raining

The uncertainties at the time of the initial call mean that most companies investigate more flooding than

their assets cause. Depending on circumstances they are probably also clearing some blockages of, and in

some cases carrying out minor repairs to, customers’ pipes.

At this stage in the process companies have an unverified list of reported floods and their nature. This is

the list which eventually becomes the basis of the at risk register, after investigation of the problem,

validation of the cause, and estimation of the likely frequency of flooding.

Best practice

� Case-based reasoning offers advantages over manually read or memorised scripts for consistent

and reliable evaluation of customer calls about sewer flooding, where establishing responsibility

for the problem is important.

� Visibility of electronic maps of the sewer networks improves call handlers’ ability to differentiate

between company and private sewers. By showing the location of recent calls it also helps to

identify emerging area-wide problems as calls come in.

� Simple questions about whether it is raining and are neighbours affected give early indication of

the nature of the problem.

� Direct linkage between the call handling software and the job management system and GSS

payment system is an efficient and reliable means of data handling.

4.2.2 During Clean-up Activity

All companies have targets for response times to investigate and clean up flooded properties. During the

visit the details recorded by the customer contact centre are reviewed to confirm that they are correct. All

companies provide for field staff to add comments and correct the details about the scale and location of

the flooding, and ownership of the assets. At this stage it is common to identify blockages and collapses

and to clear such problems immediately. Where no cause can be found it is assumed that the hydraulic

capacity of the sewer has been exceeded.



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In demonstrating their quality control procedures, some companies showed examples where field staff

had classified flooding as hydraulic overload, and subsequently noted the removal from the pipe of an

obstruction such as a brick. It might be that the obstruction was seen as resulting in reduced capacity and

hence hydraulic overload or that staff felt under pressure to attribute the problem to underlying capacity

rather than operational problems.

All companies have a quality control step after the initial investigation, in which all entries are reviewed

and their classification is checked. In the example above, the classification would be changed to blockage

or collapse, depending on what other information was available about the source of the brick.

The extent to which neighbouring properties are checked appears to vary significantly between

companies. In some cases leaflets are left with neighbours but in others neighbouring properties are only

checked if the clean-up staff can see evidence that they have flooded. This latter practice is likely to lead

to fewer properties being reported as flooded at this stage, with a potential benefit to companies’ OPA

measures.

Figure 4.2: Adding Additional properties

Search for Neighbouring

Properties

ExtensiveDepending on evidenceMinimal

Addition of Neighbouring

Properties

To current job To new job

All companies were able to show examples of how additional properties are added to their database

following initial clean-up. Some companies add them to special fields in the same job as the original

flood, others create new entries specifically for neighbouring properties. One company mentioned

anecdotal evidence that adding neighbouring properties to the original job requires less work and is

therefore more reliably implemented.

(i) Exclusion Rules

Ofwat’s reporting requirements state that all flooding must be recorded, and all companies do record

details of all incoming calls about flooding. When deciding whether to record flooding, some companies

operate exclusion rules, including a description of ‘surcharge’ if external flooding can be cleaned up

within 15 minutes and the exclusion of ‘weeping manholes not causing a nuisance’. Some companies

reported difficulty in deciding how to handle damp patches on cellar walls where there is insufficient

water to take a sample, and many will not record these as flooding until a sample can be taken.

In practice most companies are likely to use judgement in deciding whether to record a flood, especially

during heavy rain when surface water flooding is prevalent. If all discharges, however small, are reported

then the number of external floods is likely to rise significantly.



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4-4

The June Return Reporting Requirements already state that all flooding incidents should be recorded and

exclusion rules do not apply. The guidance lacks clarity in its definition of sewer flooding (as described

earlier) and although companies check that the problem arose from a public sewer not a private sewer,

checks on root causes and ownership of the flooding problem are variable.

There are also differences in the interpretation of ‘internal flooding’. Two companies consider garages to

be external if they do not have an internal door connecting them to the property, even when they are

integral to the building’s construction (see Figure 4.3). We consider this to be a misinterpretation of the

reporting guidelines – it is certainly not a common interpretation – which reduces the number of internal

flooding incidents being reported. Although garages tend to have low door sills and therefore be more

likely to flood than other parts of a building, we consider this is unlikely to make a big difference to the

size of register. Classifying integral garage flooding as external might make it more difficult to justify

investment for those properties where they flood.

The June Return Reporting Requirement provides a definition of internal flooding but it appears that two

companies consider internal garages with no connecting door to be external. The guidelines could be

modified to state: “However, garages forming an integral part of a property are classed as part of the

building, even where there is no internal door to the house, and are included, even if their prime purpose

is storage, etc.”

Some companies noted that customers often consider flooding of garages and cellars to be internal

flooding. It is therefore possible that the current June Return definition does not align with customer

preferences. This could be checked by inclusion in future customer perception or stated preference

surveys.

Figure 4.3: Numbers of companies having exclusion rules for internal and external flooding.

Exclusion Rules for External

Flooding

0

2

4

6

8

10

Overw helmed by w ater course

Time to clean

None

Exclusion Rules for Internal

Flooding

0

2

4

6

8

No

internal

door in

garage

Damp

patch on

cellar wall

None

No internal door in garage

Damp patch on cellar w all

None



247338/01/C - 15 October 2008

4-5

Best practice

� All flooding incidents should be recorded, as required by the guidance.

� Adoption of robust quality control procedures is essential to check that the call-centre details are

correct and to check for anomalies in work-order entries that might imply incorrect identification

of the cause of flooding.

� Prioritising the early capture (generally within two weeks of an event occurring) of information

about the number of neighbouring properties affected and other data on the causes and severity of

flooding is important to prevent loss of data. Information captured long after flooding has taken

place is likely to be more anecdotal and less certain of being correct.

� The allocation of flooded neighbouring properties to the same work order as the original flood

ensures a better data audit trail. This may also be achieved by a database link to the original work

order.

� Identification of the root causes and ownership of flooding problems is necessary to establish

responsibility for resolving them. With the exception of identifying ownership of private sewers,

practice in this area is variable.

� Flooding of garages should be categorised as internal flooding where the garage is an integral part

of the building, even if there is no internal door. This aligns better with customers’ perceptions of

internal flooding.

(ii) Link to GSS payments and the Estimation of Flood Return period

Some companies allocate GSS payments regardless of the flood return period, except in cases of wide

area flooding where it is obvious that extreme weather is likely to have contributed. Such companies

make more GSS payments than they are required to. Companies cited the difficulty in obtaining reliable

return period data and benefits of showing goodwill in a difficult situation as the main reasons for this

behaviour.

Some company areas are covered by high resolution rainfall radar and in these areas companies are able

to identify severe weather more quickly, therefore reducing the number of GSS payments. One company

fully models the sewer event return period, even though this might mean missing the GSS payment

deadline and having to make an additional penalty payment. Another company purchases weather

analysis where it considers that unusually high rainfall might have happened, this approach balancing the

cost of acquiring weather data and the cost of overpaying GSS. Anther calculates the return period of

rainfall in each 1km grid square evry night, so return period analysis is available the following day.

In addition to its effect on GSS payments, the assessment of flood return periods determines the register

to which the flood will be allocated. The approach to assessing flood return period varies and this leads to

differences in the allocation of properties to registers (see Figure 4.4.). Furthermore there is some

confusion between the definition of ‘extreme weather’ in the GSS guidelines and ‘severe weather’ in the

June Return reporting requirements for At Risk Registers.



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Figure 4.4: Approaches to GSS payments and definitions of severe and extreme weather

Definition of Exceptional

Weather

1:10 yr storm 1:20 yr storm

1:40 yr storm Not know n

Definition of Severe Weather

1:10 yr storm

1:20 yr storm

1:40 yr storm

GSS and severe weather

Normally paid before w eather data av ailable

Get w eather data if sev ere w eather suspected

Alw ay s get w eather data first

Note: “Not known” means that the subject was not discussed with company, or the contact for the study was not involved in the GSS process and was not certain of the company’ approach.

We understand that Ofwat is currently consulting on the definition of exceptional weather for use with

GSS regulations. We recommend that when this is complete Ofwat clarifies the severe weather and

exceptional weather definitions. This would help to ensure that service is described in the same terms for

all customers, regardless of where they live. There might also be potential to align GSS definitions and

entry of properties on the ‘at risk’ registers.

4.3 Adding Properties to the Register

4.3.1 After Initial Investigation

In most companies the initial investigation is carried out at the time of clean-up. It is common for minor

repairs to be carried out at the same time, for example clearing roots or repairing collapsed pipes. Most

companies conduct an initial investigation within a fortnight of the event occurring, except in extreme

cases of wide area flooding.

When the clean-up and initial investigation is complete, companies have a database of reported flooding

events, with follow-up details that confirm which appear to result from hydraulic overload, and which are

from other causes. In many companies this subset of the customer contact or job management database

forms the basis of the At Risk Register, although at this time the return period of the sewer event might

not have been estimated. In some companies the relevant records are extracted and added to a separate

flooding register, in a spreadsheet or local database. Companies having integrated information systems

generally referred to a ‘live’ register, where those with off-line approaches tended to update their registers

monthly or annually.

The definition of ‘severe weather’ is a source of confusion and there are many approaches to determining

if the flooding has resulted from severe weather, in part because of differences in the source data that are

available in different regions. The issues are:

• The determination of flood return periods is complex and requires detailed network data and

modelling.



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4-7

• Some companies use rainfall return period as a surrogate for flood return period, despite specific

guidance from Ofwat that ‘DG5 measures the frequency of flooding incidents and not the return

period of the storm that causes the flooding’.

• Some companies use the interval between repeat floods as a surrogate for flood return period.

• Some companies use weather radar data, but radar coverage is variable and not universally

available. (Water companies do not operate weather radar systems.)

• Some companies use Environment Agency local rain gauge data, which may also be combined

with data from other sources, but rain gauges are not necessarily near enough to the event being

investigated to give confidence in the results.

• There is some evidence that even Met Office analysts differ on the return periods of individual

rainfall events.

The analysis of return periods is also complicated by the effects of climate change, which means that a

weather event with a 1 in 20 return period today may have a shorter return period (i.e. be more frequent)

in the future. In addition, urban creep has led to a greater proportion of rainfall entering the drainage

system, exacerbating the effects of climate change. Simple methods of analysis are likely to miss these

effects and events assessed as ‘severe’ based on today’s data may become the norm in the future,

increasing the number of emerging flooding incidents. If the ‘at risk’ registers are to be comparable

between companies and geographical areas, a consistent approach is required. That consistency does not

exist at present.

At this stage the list will be classified for internal or external flooding, severity, and an initial assessment

of the return period. It forms the basis for reporting in the At Risk Register although it will be developed

over time as more information becomes available.

At this stage two issues influence the choice of register and lead to differences between companies: the

approach to the assessment of return period and the extent to which repeat flooding takes account of

severe weather.

• The true return period of a flood is not generally evident from a single event. Companies

typically use either the estimated return period of the rainfall event as a surrogate for the flood

return period, or add the property to the 1:20 register. The former approach allows properties to

be added directly to the 2:10 register if the rainfall return period is estimated as less than 2:10

years and tends to increase the relative size of the 2:10 and 1:10 registers. Most companies will

take account of customer statements that previous flooding has not been reported, which may lead

to the property being entered to the 2:10 or 1:10 register instead of the 1:20. One company builds

hydraulic network models to assess the return period of every internal flood event, and chooses

the register on the result of that modelling rather than the rainfall return period.

• The treatment of severe weather in repeat flooding events differs between companies. Flooding

events arising from severe weather are normally excluded from water company assessments, but

this can cause confusion and dissatisfaction among customers for whom flooding is frequent and

also occurs under ‘normal’ weather conditions. One company includes repeat flooding under

‘severe weather’ conditions in its frequency assessment, once it knows that the property has

flooded under ‘normal’ conditions. Another will retrospectively include previous flooding that

happened under severe weather conditions, if a repeat flooding occurs under normal conditions.

Both these approaches probably better reflect the actual flood risk, but they also increase the

reported flood frequency and hence change the register choice, compared with the companies that

do not adopt this approach.



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The number of companies adopting each approach to the two issues is illustrated in Figure 4.5

Figure 4.5: Choice of registers for first-time flooding is reported, and treatment of severe weather

Choice of Register on First Time

Flooding

0

2

4

6

1:2

0

un

less

Ra

infa

ll

retu

rn

1:20 unless evidence of previous f looding

1:20 register

Rainfall return period

Modelled

Severe Weather and Choice of

Register

0

2

4

6

8

10

Severe

weath

er

is

Doe

s n

ot

co

unt

seve

re

Severe w eather is counted in repeats

Severe w eather counted w hen previous

f looding under normal conditionDoes not count severe w eather at all

Best practice

� A rapid GSS payment to sewer flooding victims is commended, and whilst the difficulties of

analysing extreme weather events are acknowledged, payments should be made as quickly as

practicable.

� A range of techniques is applied to the assessment of the return period for sewer flooding

incidents. No one method stands out as best practice, as the type and availability of data varies

between companies. There is also inconsistency in the way that climate change and urban creep

(a gradual increase in drained area) are accounted for in the assessments. In the absence of a

consistent approach or clear best practice for identifying return periods, we recommend that

properties should be added to the 1:20 register on first flooding, unless there is credible evidence

that previous flooding has occurred but not been reported. Allocation to 1:10 or 2:10 registers

should be on the basis of observed flood frequency. We recommend that the assessment of return

periods should be subject of an industry-wide study to share information and establish consistent

yet workable methodologies which companies can apply in practice in their areas. This will

enable a consistent approach for allocation to be developed, when companies should then use the

method to assign properties to registers. The benefit will be to ensure that severe weather is

identified consistently, and that the selection of registers for repeat flooding is consistent between

companies.

� We recommend clarification of the meaning and use of ‘severe weather’ and ‘exceptional

weather’. This would enable service to be described in the same terms for all customers,

regardless of where they live.



247338/01/C - 15 October 2008

4-9

4.3.2 After Detailed Investigation

The approach to detailed investigation differs between companies and may be formed of one or several

steps. Where hydraulic overload is suspected, it is common to carry out more detailed review and

analysis of the network, including camera surveys and hydraulic modelling. This is commonly done to

determine the most appropriate long-term solution to the problem and leads into capital programming.

Companies reported issues with the use of cost-benefit analysis at this stage. In some cases it is difficult

to justify capital intervention on cost-benefit terms and yet the companies believe they will be subject to

criticism or legal action if a solution is not implemented. Many companies reported that some schemes

are not truly cost-beneficial but that they believe they have a moral obligation to deliver a level of service.

If the level of service is described as a social choice rather than an economic case, it is likely that benefits

have not been expressed at their true value. Some companies commented that this valuation is especially

difficult where willingness to pay is taken into account, as customers do not always value the service in

line with its costs. On a straightforward economic assessment this could lead to an increase in unresolved

sewer flooding until customers valued the service sufficiently to pay for it, but those companies

discussing the subject felt that would be the wrong approach.

The detailed investigation step identifies errors in classification and leads to updating of the At Risk

Register categories, typically reducing the number of floods attributed to hydraulic overload. The

changes result from wider surveys of the network identifying blockages and collapses, and from hydraulic

modelling showing adequate capacity. Some companies carry out more detailed rainfall investigation at

this stage, leading to further exclusions where severe weather caused the hydraulic overload.

Some companies carry out additional investigation of neighbouring properties at this stage (although most

do this either with the initial investigation or with the investment delivery). Searching for additional

flooded properties often results in new additions to the register. Hence the timing of this investigation is

important: if it is carried out early in the process it may affect OPA measures, but at the same time it

improves the prioritisation of the register for investment and increases the benefit in cost-benefit

assessment.

4.3.3 During Investment Planning and Delivery

All companies carry out more detailed assessment in the design of capital solutions to flooding. The

scope of this step depends on the extent of previous investigational steps. At this stage companies

generally check for additional flooded properties in the neighbourhood, and those that have not done a

substantial early search typically find between 20% and 60% additional properties.

During our visits to companies, some commented that flooding events were becoming more localised,

with only a few properties affected each time, rather than the larger groups benefiting from previous big

schemes. This is consistent with a mature flood risk register, where companies have been prioritising the

bigger problems for some years. We have not collected information on the number of properties per

event, so cannot comment on whether this applies to all companies.



247338/01/C - 15 October 2008

4-10

If companies are experiencing a diminishing number of properties/event, this makes it more difficult to

make a cost-beneficial case for increasing the capacity of the network and more likely that mitigation

measures will be proposed instead. Mitigation solutions might be effective for less than their design life

if the underlying problem results from gradually increasing drained area or climate change, because

increasing flow may render mitigation ineffective. In such situations more strategic investment would be

indicated in order to prevent the problem returning and possibly affecting more properties. Risk

assessments and the associated cost-benefit analysis therefore need to take account of the rate of change

of ‘demand’ so that appropriate long-term solutions are selected.

The scope of this project did not include a review of company procedures for designing network

investment and hence we are unable to comment on .examples of best practice.

Any additional properties identified during pre-design investigations may be added to the At Risk

Register in the year of delivery of the solution – the same year in which they are removed. They add to

the number of properties removed from the register as a result of company action, but do not support the

output of net reduction in the At Risk Register. One company notes such additions separately and does

not claim them in its outputs (although they would be included in the cost-benefit assessment), preferring

to measure outputs in line with the original quantities assumed in its business plan (see Figure 4.6).

The addition or removal of large numbers of properties from the register at this stage implies a poor

quality of initial investigation and reduces confidence in any year’s register values.

Reporting progress of the properties originally on the register – i.e. not allowing late additions to be

counted within the company’s outputs – might provide a more balanced incentive for better investigation

and addition of all flooded properties at the time of a flooding incident. But it might also encourage

companies to add too many at the initial stage and lead to large numbers of removals through better

information later in the process. Hence we recommend reviewing the links to other incentive mechanisms

before changing the reporting requirements.

Figure 4.6: Proportion of companies claiming late additions as outputs

Adding Neighbouring

Properties

Claim outputs

Don't claim outputs



247338/01/C - 15 October 2008

4-11

4.3.4 Addition of Properties Estimated as being at Risk

Most companies only add properties to the register when flooding has been experienced. One company

adds nearby properties if on investigating a flood, it considers they are at risk of flooding in the future,

even if they have not flooded at the time.

Best practice

� Detailed investigations, including CCTV and network modelling are essential to confirm the

initial investigation, assess the root cause of flooding and flood ownership and to inform

assessment of the flood return period. This needs to be done as soon as possible after the flood, to

ensure that all relevant information is captured whie it is available. Companies having good

coverage of their sewer network with verified models are in a good position to undertake this

quickly.

� The use of cost benefit analysis to justify expenditure on network enhancements to resolve

flooding problems is a relatively new requirement and some companies are questioning it. We

recommend a review of how companies have applied cost benefit analysis to sewer flooding

problems following PR09 to share experience and best practice. This should extend to the use of

CBA for mitigation schemes. If flood severity is introduced, (see above), then the value of

mitigation in reducing flooding risks will be more visible.

� Some companies are reporting a diminishing trend in properties per flood event. It would be

helpful if more facts were available on this to assess if it is an industry-wide experience. Late

additions should be included in the analysis.

� In assessing the benefits of a scheme to enhance network capacity to resolve flooding problems,

account should be taken of the effect of climate change and urban creep on future numbers of

properties affected should nothing be done. It is not clear that this is being done consistently and

thus benefits may be under-stated.

� The addition or removal of large numbers of properties from the register at the design stage

implies a poor quality of initial investigation and reduces confidence in any year’s register values.

� One company notes late additions at the design stage separately and does not claim them in its

outputs (although they are included in its cost-benefit assessment), preferring to measure outputs

in line with the original quantities assumed in its business plan. Extending this practice to the rest

of the industry might provide a more balanced incentive for better investigation and addition of

all flooded properties at the time of a flooding incident, when confidence in the data is more

assured.

4.4 Keeping the Register Up to Date

4.4.1 The Link with Information Systems

The quality and degree of integration of information systems varies significantly between companies. In

some companies the information systems are highly integrated and the current status of the At Risk

Register may be interrogated at any time. In others the systems are not integrated and the register is

compiled off-line.

We observed that companies with well integrated information systems tended to have most confidence in

demonstrating their At Risk Register process, and that the results would compare with those in the June

Return, although some companies with off-line processes also had good data management processes and

archives of the registers. In the companies with integrated systems, the At Risk Register was seen as a

simple report from the database, rather than a separate entity.



247338/01/C - 15 October 2008

4-12

There did not appear to be a link between the approach to information management and the number of

‘better information’ changes to the register entries over time. This suggests that these changes are a

function of the quality of the investigation processes rather than the approach to data management.

4.4.2 Update Frequency

Companies with integrated information systems can report the status of individual properties on the

register at any time during the reporting year, although most companies review the status of flooding on a

monthly basis.

Companies without integrated information systems review new flooding that occurs in each month

through internal reports, but the regulatory At Risk Register may be compiled on an annual basis.

Companies generally aim to settle on a confident register allocation by the June Return reporting deadline

for the year, but achieving this depends on the number of floods that occur in the last month of the

reporting year. However, the extent of additions to, and removals from, the registers as a result of ‘better

information’ is significant in some companies, suggesting low confidence in the reported allocations in

those companies. It would be expected that company confidence grades for the At Risk Register reports

should reflect the proportion of retrospective changes that companies are making to their registers.

4.4.3 Recording Changes

Most companies retain a full audit trail of the changes that are made to records of flooding and the

progress of an individual property from entry to the register to ultimate removal. Companies having

information systems that do not allow the full data history to be retained stated they were developing new

systems that will retain a full audit trail.

Best practice

� Integrated information systems provide greater confidence that data has not been lost and is not

subject to human error from manual handling of data between off-line storage systems and

applications and corporate systems.

� The status of the ‘at risk’ registers should be reportable at any time and updated on a monthly

basis at least. A full audit trail should be available for properties added and removed from the

register.

� The extent of additions to and removals from the registers as a result of ‘better information’ is

significant for some companies. It might be expected that the confidence grades for the ‘at risk

register’ reports for these companies would reflect this.



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4.5 Removing Properties from the Register

4.5.1 On First Contact

If it is clear during the initial customer call that the flooding has arisen on a private pipe, as a result of a

problem with that pipe, then the property will not be entered on the At Risk Register.

4.5.2 During the Clean-up Activity

During the initial visit and clean-up, the causes other than hydraulic overload are commonly identified.

These will be entered on the job record and the property will not be entered onto the At Risk Register.

4.5.3 After a long time without Flooding

The Flood Estimation Handbook provides for removal of properties from the At Risk Register if they

have not flooded for a pre-determined time. All companies were aware of the ‘time-out rule’ but it is not

in widespread use. Its most common use is in companies where properties assessed as being at risk were

added to the register, but have not flooded, and one company uses a shorter approach than the normal

‘95% confidence’ duration. Although there are differences in approach, relatively few properties are

removed from At Risk Registers using the time-out rule.

4.5.4 After Company Action

The majority of properties are removed from At Risk Registers as a result of company action to improve

network capacity.

4.5.5 As a Result of Better Information

All companies remove some properties from the At Risk Register as a result of better information about

the cause of flooding. In some cases this information only becomes available during preparation of

capital solutions. Where large numbers of properties are removed through better information, it may be

inferred that early investigations are insufficient to provide confidence in the entry onto the register.



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5 Comments on the At Risk Register Approach

Companies were invited to make their own suggestions of ways to improve the At Risk Registers.

5.1 Register Name

The term “At Risk Register” may be associated with other flood risk assessments – e.g. in surface

water management plans, when the issue is a risk of flooding in extreme weather conditions such as

1:100 storms, during which the underground system is effectively irrelevant.

A better title for the ARR might be “Flooding Incident Register” or “Unresolved Flooding Incident

Register”; the description would state that it’s a register of properties that have flooded, and which are

listed because they are at risk of flooding again if the circumstances are repeated.

5.2 Return Periods, Risk and Sub-registers

Some companies commented that the current division of the register is not particularly useful. For

example, there might be an overlap between customer perception of minor internal flooding (e.g.

water coming up in a shower tray but not leaving the shower tray) and severe external flooding.

Likewise the return period is hard to determine accurately and the exclusion of a flooding event for

severe weather for a property that has already flooded in the past under ‘normal’ conditions is

distressing for some customers.

An alternative suggested by some companies would be to list properties according to a measure of

observed risk – i.e. the frequency and severity. This would then be reported in categories such as high,

medium, and low risk. The definitions for property owners would, for example, be that a ‘high risk’

would be liable to flooding that causes significant disruption, on a regular basis. Other companies

disagreed with that approach, suggesting that ‘high’ would effectively be the same as internal 2:10.

When sewer flooding is identified, an emergency job is started. Most companies use field service

contractors and if internal flooding is being investigated the company’s sewerage manager or

supervisor will also attend. Companies stated that this demonstrates ownership to the customer. It was

also mentioned that the company manager provides a point of contact for the customer after the clean-

up is finished.

All companies check the extent of flooding at this stage, and all said that for internal flooding they

knock on neighbours’ doors if they believe the flooding might affect those properties.

Some companies have exclusion rules, which provide guidance for staff on what to class as flooding.

These rules apply to external flooding and include ‘puddle size’, ‘puddle depth’, ‘time to clean up’.

Since Ofwat amended its reporting guidelines to include ‘any escape from sewers’, most companies

have discontinued these exclusions. However, where there is no exclusion rule, companies agreed that

staff have to use their discretion at the time of the visit. The extent of this discretion is likely to

influence the number of external flooding incidents that are reported.

5.3 GSS Payments

All companies reported that except in the case of wide area flooding, it is generally difficult to identify

the flooding return period at the time of the customer call or initial investigation. Therefore GSS

payments tend to be authorised as soon as the site visit confirms that the flooding has taken place.

This means that companies are often paying more in GSS payments than they would have to if they

were able to make a strict application of the rules. Where a strict application of the rules is applied,

companies find it difficult to complete within the 20 day limit.



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5.4 Assigning Properties to the Register

Companies do not all follow the same approach to assigning properties to registers and this affects the

number that are added to each register. Some of the main differences are described below:

5.4.1 First Time Flooding

Ofwat’s June return reporting guidelines state:

“When a previously unreported property or external area is flooded, it should normally be considered

to be at risk and added to the 1 in 20 category unless:

- investigation clearly shows that it is at risk of flooding more frequently than once in ten

years, when it should be included in the one in ten year category;

- investigation clearly shows that it is at risk of flooding more frequently than twice in ten

years, when it should be included in the twice in ten year category;

- the storm was exceptionally severe and investigation shows that it is clearly not at risk of

flooding as frequently as once in twenty years and the severity of the storm can be

verified (e.g. by the Meteorological Office); or

- the cause was a blockage, etc”

The most common approach used by companies is to add first-time flooding to the 1:10 register, but

one company adds them to the 1:20 register, and one uses the rainfall return period to determine the

register. Another conducts a full hydraulic analysis of the local network response to rainfall and thus

derives a modelled return period for the flood event. These differences affect the proportion of

properties on different registers rather than the total number reported. The use of rainfall data leads to

many additions directly to the 2:10 register. Using rainfall data alone will add more properties directly

to the 2 in 10 register simply because there are many more rainfall events at 2 in 10 year return period

than 1 in 10 year return period. However the effect on the sewer network should be considered when

allocating risk. It is not clear why a sewer network would become overloaded from a 2 in 10 year

return period storm.

5.4.2 Repeat Flooding

All companies review a property’s position on the register when a repeat flooding incident occurs.

The period between flooding incidents is frequently used to determine if a property should be moved

to a ‘higher’ risk category.

Some companies mentioned that it is not clear how they should handle multiple flooding when some

instances are caused by severe weather. Some companies ignore the severity of the weather once it

has been identified that flooding occurs under normal conditions. In other companies, repeat flooding

is not counted if it is the result of severe weather. Companies commented that the latter approach is

difficult to explain to customers and can lead to an underestimate of the risk of flooding.



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6 Recommended Process

We set out the approaches approach to managing DG5 registers using a common generic

process flow-chart that allows comparisons to be made. From our assessment of company

processes and taking a comparative view, we have suggested a best practice approach in

Figures 6 to 11. The six flow-charts cover the following areas of practice:

• Identification of a flooding event from first contact with the customer.

• Initial investigation of a flooding event, establishing the cause and the number of

properties affected.

• Making decisions on GSS payments.

• Adding properties to the ‘at risk’ registers.

• Undertaking detailed investigations to inform the design of capital solutions.

• Processes for removing properties from the registers.

We have categorised processes as preferred (green), non-preferred (grey) and optional

(yellow). The latter applies particularly to the assessment of flood-event return period, where

a number of techniques are used according to the availability of local data and weather

analysis. We believe that this is an area of developing practice that is worthy of industry-wide

study to share information and establish consistent yet workable methodologies that

companies can apply in practice in their areas.

Commentary on the recommended processes and the potential impact of their adoption on the

‘at risk’ registers is given after each figure.



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6-2

Figure 6.7: Link between flowcharts

Chart B: Initial InvestigationChart B: Initial Investigation

Chart D: Adding to RegisterChart D: Adding to Register

Chart E: Detailed InvestigationChart E: Detailed Investigation

Chart F: Removal from RegisterChart F: Removal from Register

Chart A: IdentificationChart A: Identification

Chart C: GSSChart C: GSS



247338/01/C - 15 October 2008

6-3

Figure 6.1: Best practice process flow chart – identification

Ask about severity of flooding

Can see asset register

Automatic creation of work order Manual creation of work order

Chart A: Identification

Dispatch investigation/clean-up team

Ask about location of flooding

Can see GIS maps

Ask if neighbours affected

Check if it is raining

Check if private sewer

Manual Scripting

Call Handling

Record details of all calls

No

YesEnd

Check if repeat

flooding

Preferred process

Optional processes

Non-preferred process

At same time as first contactTelephone customer to confirm visit time

Case Based Reasoning

Legend



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Principal points:

• Case-based reasoning preferred to manual scripts.

• Access to GIS and asset register helps call-handlers identify private sewers.

• Simple questions establish nature and extent of problem early.

• Automatic set-up of work-order using integrated IT preferred to manual methods.

• Inform customer of expected time of arrival of clean-up team on first contact.

Impact on ARRs:

• Limited direct impact, but integrated systems likely to lead to fewer data losses and

improved audit trail for subsequent processes.



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Figure 6.2: Best practice process flow chart – initial investigation

Telephone customer to confirm visit time

Clean up and repair damage

Supervisor or

engineer attends

as well as field contractors

Identify cause

Complete Work Order (WO)

CCTV

Leave forms if unoccupied

Exclusions

(none)

Update WMS Update via paper form

Write to customer

Pay GSS2 2 = For companies who pay GSS without reference to severe weather analysis

Check neighbours only if evidence of flooding

Confirm not private sewer

Internal External

Blockage/Collapse Hydraulic Overload Equipment failure

Exclude

surcharges

Exclude non-

sewer flooding

Exclude non-integral

garages

Exclude1 damp

patches (internal)

Additional properties added to same WOAdditional properties added to new WO

Validate WO entries

Check all neighbours

potentially flooded

EndEnd

Unless already done on first contact

1= Where samples cannot be taken and patches may arise

from groundwater

Chart B: Initial investigation



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Principal points:

• Supervisor attends as well as clean-up team/contractors to ensure that procedures are

followed.

• CCTV undertaken for all flooding events unless information already available.

• Exclude non-sewer flooding (eg surface-water flooding) where responsibility for resolving

the problem lies wholly with others.

• Exclude damp patches if samples cannot be taken and cause could be groundwater.

• Undertake detailed investigation of neighbouring properties affected, including those in the

area that are unoccupied. The intention is to capture and report this information once and it is

not expected to be amended months later through better information.

• Add any properties subsequently confirmed to have been affected to the same work order

record to ensure clean data audit.

• Validate work-order entries through robust quality control procedures and update digital

records (not via paper forms).

• Make GSS payments where they apply, unless it is an exceptional wide-area flooding event

clearly resulting from severe weather.

• Inform customer in writing of the findings from the initial investigation and the company’s

proposed actions.

Impact on ARRs:

• Reporting all sewer-flooding incidents may increase the number of properties on the

registers for those companies applying exclusion rules in the past.

• Emphasising the need to capture information on properties affected at the initial

investigation stage should reduce the number of late additions through better information and

provide more confidence that the ARRs are correct and up to date.

• Validating work-order entries through quality control procedures and application of

integrated IT will ensure improved data audit trails. This should be reflected in improved

data confidence grades.

• Early payment of GSS payments is encouraged as a goodwill gesture, accepting that some

customers may be ‘over-paid’ by the strict interpretation of the extreme-weather rules. Some

companies already do this.

• It is only proper that companies write to customers to inform them of the findings from the

initial investigation and the company’s proposed actions to reassure them that their problem

is being addressed. It is acknowledged that this may raise expectations that a capital solution

or mitigation measure will be delivered when the company may not always be able to make a

cost-beneficial case for doing so.



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Figure 6.3: Best practice process flow chart – GSS payments

Flood confirmed by field team

Chart C: GSS

Check if ‘extreme’

weather

Automatic ID GSS Manual ID GSS

Confirm GSS payment

Check GSS paid (audit)

Write to customer confirming actions

High resolution radar data

Weather

Analysis

Met Office data

Pay if < 1:20

Pay if < 1:40

Pay if < 1:10

Aligned with ‘severe’ weather

Principal points:

• Automatic identification of customers potentially eligible for GSS payments linked to the

flooding incident report and work management systems ensures that eligible customers are

not missed, which is a risk with manual systems.

• A range of techniques for estimating the return period of the flooding event can be applied,

according to available data. Best practice in this area needs to be defined through separate

study.

• The criterion for ‘extreme’ weather should be reviewed to consider alignment with that for

‘severe’ weather used to assess the inclusion of properties on the ‘at risk’ register. The

criterion proposed is that adopted by most companies, which is 1 in 20 years return period.

GSS payments do not apply if the flooding event is more extreme than this. Companies that

have adopted a higher standard than this in the past (e.g. 1 in 40 years) may opt to continue

to apply this to GSS payments (though not to the ARR, to ensure national consistency).



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Impact on ARRs:

• Clarification of the severe weather definition to rarer than 1 in 20 years will affect the

number of properties on registers for those companies that have adopted a different standard

in the past.

Figure 6.4: Best practice process flow chart – Adding to the register

Does customer report previous flooding?Ignore

Rainfall intensity

determines register

Consistent rules

determine register

Event specific network analysis

determines register

Interval

determines register

Rainfall

intensity determines

register

Severe weather is counted

in repeats

Severe weather not counted

in repeats

Keep record of severe

weather floodingAdd neighbouring properties assessed as being “at risk”

NO

YES

Repeat

flooding

Accept

Check if severe weather

Anecdotal evidence from

customers flooded in the past informs

register

Model output for standard

storm events informs register

Anecdotal

evidence from customers

flooded in the

past informs register

Model output

for standard storm events

informs

register

Event specific

network analysis determine register

1:20 1:40

First time

flooding

If confirmed by

company records

If not

confirmed

From results of initial investigations

Add to register

2:10 1:10 1:20

Chart D: Adding to Register



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Principal points:

• A >1 in 20 year return period is used to check for severe weather, in accordance with

Ofwat’s guidance.

• Information from customers about previous flooding events can be accepted although there

should ideally be evidence to corroborate the information. It should be clear that it resulted

from hydraulic overload and not other causes. Anecdotal evidence from customers of past

flooding should not otherwise be considered in determining the appropriate register to place

the property.

• A consistent set of rules should be applied when assessing the return period of a flooding

event to decide which register to record the affected properties against. This should not be

determined by the return period of the storm alone.

• The decision may be informed by the results from verified network models from simulating

standard storm events. Such information may already be readily available. Companies may

also wish to model the storm event using verified models to try to replicate the flooding

event. This is more onerous and may not be justified for all flooding events.

• Most first-time flooding events are added to the 1 in 20 years register, unless there is

compelling reason why it should be added to the other registers.

• Records should be kept of severe weather flooding events, even though the effected

properties are not added to the register.

• For repeat flooding, the interval between flooding events informs which register to allocate

the properties to. This may be supported with network modelling.

• Where one of the flooding events results from severe weather, the severe weather event

should count towards the assessment of the register allocation. This represents a change to

Ofwat’s guidance (which excludes all events arising from severe weather) but aligns better

with customer perceptions.

Impact on ARRs:

• The use by all companies of a 1 in 20 year return period for assessing the occurrence of

severe weather will bring consistency in the number of properties excluded from the ARR

for severe weather.

• Disallowing anecdotal evidence of past flooding from customers unless company records

support it should reduce the number of new additions for some companies; effectively, if

customer claims it was flooded, but there is no record on the DG5 register of past event, then

assume it must be due to ‘other causes’ or it never happened.

• Focusing on the return period of the flooding event, rather than that of the storm, will

probably result in a reduction in the number of first-time flooding events to the 1 in 20 years

and other registers for some companies.

• Including severe weather events in the assessment of repeat flooding may increase the

number of properties on the 2 in 10 and 1 in 10 registers slightly for some companies, though

by definition, severe weather events are rare.



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Figure 6.5: Best practice process flow chart – detailed investigation

Chart E: Detailed investigation

Detailed rainfall

analysisCheck severe weather

Check neighbouring properties – door to door

Claim additional properties in

outputs

Update register

Check neighbouring

properties – letter survey

CCTV

Hydraulic modelling

To confirm analysis undertaken when properties were added to the register and to assess future weather patterns

To obtain additional information to that gathered for the initial investigation where required

To confirm analysis undertaken when properties were added to the register and to assess the impact of future weather patterns on solution design

Further checking of neighbouring properties

optional. This should have been established at the

initial investigation stage

Confirm cause

Principal points: • The purpose of the detailed investigations is to capture additional information to that

captured at the initial investigation stage to inform the development of capital solutions to

flooding problems.

• Further assessment of severe weather determines future weather patterns as well as current to

inform the design and cost-benefit assessment.

• Additional CCTV surveys (if required) and network modelling studies are undertaken to

confirm the initial analysis and to assess the impact of future weather patterns and growth in

flood volumes on proposed solutions.

• Further checking for neighbouring properties affected can be undertaken at this stage, but

this is expected to have been completed at the initial investigation stage.

• Late additions should not be allowed in outputs, which should reflect the original register

values, unless there are compelling reasons to the contrary.



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Impact on ARRs:

• The emphasis on identifying all affected properties at the initial investigation stage and only

allowing the claiming of late additions in outputs by exception should reduce the number of

late additions through better information.

Figure 6.6: Best practice process flow chart – removal from register

Chart F Removal

Separate register for mitigation

Remove as a result of company action

Demote via time-out rule

Remove via time-out rule

Better Information

Full audit trail of decision to remove

End

Remove if strong evidence that analysis undertaken when properties were added to the register was inaccurate (egdiscovered to be other causes). This should only occur on rare occasions



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Principal points:

• Full audit trail of decisions to remove properties from the register.

• Generally, properties are only removed as a result of company action. Removal for better

information remains possible, but should only occur on rare occasions.

• Separate register kept for properties protected through mitigation measures.

• Large numbers of properties would not normally be removed through time-out rules.

Impact on ARRs:

• A separate register for mitigation measures will not affect numbers on the ARR, but will

record the benefits that such measures bring.



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7 Summary of Recommendations

7.1 Short-term recommendations

• Clarification of some aspects of the Reporting Requirements would help to improve the

comparability of company registers. Areas for consideration should include:

o The definition of, and approach to identifying, severe weather. Differences in

approach can affect whether flooded properties are added to the register, or excluded

on the grounds of severe weather. There are three aspects to this; clarifying the

definition of severe weather, strengthening the guidance on best practice methods of

assessing severe weather events and ensuring that all companies report using the same

definition and applying best practice methods of assessment.

o Clarifying the definition of internal flooding, especially for cellars and garages.

o Clarifying the approach to flood return period analysis and the addition of first-time

flooding to the At Risk Registers.

o Clarifying the approach to assessing repeat flooding, especially where some instances

are the result of severe weather and others are not.

o Clarifying the approach for recording properties that are discovered at a much later

date, (through detailed investigations or anecdotal evidence from customers), that are

likely to have been flooded. Current practice varies between companies as to whether

such properties are added to the register and count towards outputs.

o Separating the monitoring of properties that have mitigation measures installed, to

better reflect their true risk of flooding.

• The name At risk register’ is confusing and it should be named the ‘Flooding incident register’

or ‘\Unresolved flooding incident register’.

• The definitions of ‘severe weather’ (sewer flooding) and ‘extreme weather’ (GSS) should be

aligned, to a 1:20 year return period.

• When a property floods under ‘severe weather’ and ‘normal weather’ conditions, the severe

weather flooding should be included in cost-benefit analysis (if it has a return period that

should be met by normal design standards), as this better reflects the customer experience and

hence the benefit of investment.

• The definition of sewer flooding should be strengthened with guidance on what is included

and excluded. This would reduce the range of interpretation and help to provide a more

consistent service between sewage company regions.

• Companies should not exclude ‘minor’ flooding from the sewer flooding register (for example

through the use of exclusion rules or judgement). Proper checks should be in place to ensure

that all flooding is recorded.

• Full checks for flooding of neighbouring properties should be made at the time of the initial

investigation. Although it is appropriate to add more neighbouring properties through better

information at the time of investment, the addition of significant numbers of properties at that



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stage suggests that companies are not making adequate checks at the time the flooding occurs,

and may indicate poor service to some customers who experience flooding.

A common approach to the assessment of flood return periods (or flood frequency if a full risk scale is

used) is required. His should ideally be developed by an industry-wide study or by consensus of the

sewerage companies.

When assigning June Return confidence grades, companies should take account of the number of

additions to and removals from the ARR. (Where there is a significant addition or removal rate

through better information, companies cannot have high confidence in the original data.)

7.2 Longer term recommendations

The flood frequency (2:10, 1:10, 1:20) and severity (internal, external, other flooded areas) categories

should be replaced with a risk scale taking account of the frequency and severity of flooding. This

would be better aligned with the benefit-cost analysis now common in planning solutions. For

reporting purposes, risk would be reported in categories.

If a risk scale is adopted, the impact of mitigation on the flood risk should then be taken into account

and used to re-assess the risk once mitigation is in place. This would provide clearer information to

customers on the impact of mitigation.

External Review of Sewer Flooding Risk Registers...

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