1 Strategic Options Report Cover - Thames Water...water from toilets, bathrooms and kitchens. 2.1.2 There are over 1700 properties across parts of the London Borough of Hammersmith

Protecting residents from flooding

Strategic Sewer Site Assessment Stage 1: Strategic Options Report

Document Number C680-TW-00503-RP

March 2014

Counters Creek Strategic Sewer Flood Alleviation Scheme

COUNTERS CREEK STRATEGIC FLOOD ALLEVIATION SCHEME

STRATEGIC SEWER SITE ASSESSMENT STAGE 1: STRATEGIC OPTIONS REPORT

Document Ref C680-TW-00503-RP Status Draft Document Type Report Title/Subject Strategic Sewer Site Assessment Stage 1: Strategic Options

Report Project Counters Creek Strategic Flood Alleviation Scheme Authors TWUL Keywords Mund Street Site Suitability Report

REQUIRED APPROVALS

Co-ordinator Reviewer Approver (for publication)

Chris Colloff Associate, Savills

Mark Mathews

Town Planning Manager, TWUL

Martin Bennett

Project Lead, TWUL

Date 31.03.14 Date 31.03.14 Date 7.11.14

Counters Creek Strategic Sewer Stage 1 Strategic Options Report

COUNTERS CREEK STRATEGIC FLOOD ALLEVIATION SCHEME

STRATEGIC SEWER SITE ASSESSMENT STAGE 1: STRATEGIC OPTIONS REPORT

LIST OF CONTENTS

PAGE 0 EXECUTIVE SUMMARY 1

1 INTRODUCTION 2

1.1 PURPOSE OF THIS REPORT 2

2 BACKGROUND 3

2.1 WHY THE SCHEME IS NEEDED 3

2.2 CAUSES OF FLOODING 4

2.3 INVESTIGATING THE EXTENT OF FLOODING AND UNDERLYING CAUSES

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3 DEVELOPING A SOLUTION TO FLOODING 6

3.1 DEVELOPMENT A SOLUTION TO FLOODING 6

3.2 IDENTIFYING THE MOST COST EFFECTIVE PROGRAMME 8

3.3 SUSTAINABLE DRAINAGE SYSTEMS 10

3.4 ENGINEERING OPTIONS FOR THE NEW STORM RELIEF SEWER 11

4 SELECTED COUNTERS CREEK SCHEME 17

4.1 OVERVIEW 17

4.2 THE FIVE ELEMENTS OF THE PROPOSED PROGRAMME 18

5 DELIVERY OF THE PROPOSED PROGRAMME 20

5.1 THE NEW STORM RELIEF SEWER AND THE SEWER UPGRADE WORKS

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5.2 LOCAL SEWER UPGRADE WORKS 20

5.3 FLIPS 20

5.4 SUDS 20

6 NEXT STEPS 21

7 INDEPENDENT SCRUTINY 23

8 STAKEHOLDER AND CUSTOMER SUPPORT 24

APPENDIX 1

APPENDIX 2

Strategic Sewer Stage 1 Strategic Options Report

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0 EXECUTIVE SUMMARY 0.1 The Counters Creek Strategic Flood Alleviation Scheme is required to protect

properties from basement flooding within the Counters Creek catchment in the London Borough of Hammersmith and Fulham and the Royal Borough of Kensington and Chelsea. The present Counters Creek Flooding Register1 shows that over 1,700 properties are subject to flooding.

0.2 A number of strategic solutions are being pursued, each of which plays a role in

providing the relief necessary to guard against basement flooding. The strategic solutions comprise the provision of flooding local improvement projects (FLIPS), the introduction of pilot Sustainable Drainage Systems (SuDS) schemes, the implementation of sewer upgrade works and the construction of a strategic storm relief sewer.

0.3 In July 2013, Thames Water agreed with Ofwat to invest a further £26m to

progress the proposed programme of works including the installation of further FLIPs, commencement of sustainable drainage systems pilots and design development of the major network improvement works required. This report summarises the work undertaken to identify the strategic solutions required to address the issue of basement flooding in the Counters Creek catchment ( the proposed programme ). The report sets out:

how the need for a strategic storm relief sewer was identified; how the interception locations on the existing sewers were identified; how the proposed programme of works was developed; the options considered for a new strategic storm relief sewer to connect the

interception locations; the reasons for choosing the outline design for the proposed strategic

storm relief sewer; and the scrutiny provided in developing the range of strategic solutions required

to address basement flooding in the Counters Creek catchment.

0.4 The report also sets out the further actions necessary in order to progress the delivery of the proposed programme identified as being required. These actions include the further design and development of the strategic storm relief sewer including site selection work to identify sites for construction.

1 The Counters Creek flood register is a register of all the properties in the Counters Creek Catchment that have been recorded as being flooded at some point in the past. This register is in turn taken from the Thames Water Sewer Flooding History Database (SFHD). Properties are added to the register based on reported flooding incidents. Incidents are assessed to confirm whether or not the flood event was caused by an operational problem (i.e. a blockage), an extreme rainfall occurrence (greater than the current design criteria), or by a lack of capacity in the sewer.


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1 INTRODUCTION / PURPOSE OF REPORT 1.1 The purpose of this report

1.1.1 The Counters Creek Strategic Flood Alleviation Scheme is required to protect

properties from basement flooding within the Counters Creek catchment in the London Borough of Hammersmith and Fulham and the Royal Borough of Kensington and Chelsea. The present Counters Creek Flooding Register shows that over 1700 properties are subject to flooding.

1.1.2 The Counters Creek Flood Alleviation Scheme comprises a proposed programme of works including the installation of Flooding Local Improvement Projects (FLIPs); delivery of Sustainable Drainage Systems (SuDS); delivery of local sewer upgrade works; and the delivery of a new strategic storm relief sewer and associated sewer upgrade works.

1.1.3 Identification of the above components within the proposed programme of works

has required a detailed process of analysis, investigation and review of the options available to meet the need mentioned above.

1.1.4 This report sets out the options considered, and how the components of the proposed programme were selected with particular regard to the requirement for the new strategic sewer. This report also summarises the independent scrutiny and stakeholder engagement which has been undertaken in the development of the scheme.

1.1.5 This report represents Stage 1 in the Site Selection Methodology for the strategic

sewer.


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2 BACKGROUND 2.1 Why the scheme is needed

2.1.1 Counters Creek is one of the lost rivers of London and is situated on the boundary

of the London Borough of Hammersmith & Fulham and the Royal Borough of Kensington & Chelsea. This former river and its catchment now form part of the sewerage network, draining surface water from buildings and roads, as well as foul water from toilets, bathrooms and kitchens.

2.1.2 There are over 1700 properties across parts of the London Borough of Hammersmith & Fulham and Royal Borough of Kensington & Chelsea that are subject to flooding. It is believed that the number of properties subject to flooding exceeds this figure as new reports of flooding are being received to this date. In some areas, the flooding problem is acute with some customers having been flooded up to six times in recent years. This large 'cluster' of flooded properties sits within the boundaries of both Boroughs and the properties share many similar characteristics - they are generally located in low lying areas, there are no local water courses and there is a very high density of properties with basements. This 'cluster' therefore naturally forms a study boundary. The location of the Counters Creek catchment is shown in Figure 1.

Figure 1: Location of the Counters Creek Catchment

2.1.3 After the storms of 2007, which severely tested sewerage

network, a detailed review of the flooding that had affected many local properties in the Counters Creek area was undertaken. The catchment is large and served by a number of large interconnecting sewer systems developed over many years. It was established that this scheme requires separate consideration, outside the current sewer flooding programme, due to the scale and the complexity of the problem.


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2.2 Causes of flooding

2.2.1 There are approximately 44,000 properties with basements in the Counters Creek area, of which some 30,000 lie within the London Borough of Hammersmith & Fulham and Royal Borough of Kensington & Chelsea (the study area). Many of these basements have been converted to being habitable since the reduction in risk of fluvial flooding due to the construction of the Thames Barrier in the early 1980s.

2.2.2 There are several key factors contributing to sewer flooding in the Counters Creek area which make it unique in the Thames Water region: A significant proportion of properties have basements. The vast majority of

these are of the older type buildings (Victorian). The basements were generally built down to levels close to the sewer levels. The basements were generally used as coal stores. Flap valves installed within the trunk sewers at the connection point from properties indicate that basements were indeed subject to flooding in those days as well. The coal stores are now converted into habitable areas. The area has the highest density of properties with basements per square kilometre in the UK. Basement developments are continuing.

ace) over the last 40 years, and now has a high coverage of impermeable surfaces (e.g. buildings and roads), resulting in more rainwater entering the sewer network.

There are no local watercourses in the area to divert surface water to all storm waters have to be taken by the sewer system.

The sewer system over the years was extended northwards as areas further to the north (Ealing, Camden, Acton) grew. At that time the flows that needed to be managed were calculated using simplistic methods and standards. The sophisticated computer models available these days for analysing such vast, complex and interconnecting networks had not been developed. Consequently, the sewer overloading problem could not be accurately quantified.

The network in the Counters Creek catchment is wholly combined, making it prone to flooding following heavy rain, much more so than separate or partially separate systems where a significant proportion of rainwater does not enter the foul sewer system.

2.3 Investigating the extent of flooding and underlying causes

2.3.1 A significant amount has been learnt about the sewerage network in the Counters Creek catchment since the widespread flooding in July 2007. Since 2007, Thames Water has been undertaking a detailed research of both the number of customers affected and the underlying causes.

2.3.2 The above research was to:

identify the number of properties affected by sewer flooding; ; identify alternative solutions, that reduce the risk of flooding more sustainably

for the future; and


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design a programme of work that offers the most protection to customers, but which is still affordable.

2.3.3 Thames Water has carried out over 3,000 door-to-door surveys taking physical

measurements of basements and sewer level and ground level assessments. As a result, it has been possible to provide:

an updated sewer flooding database for Counters Creek; clear information on the causes of flooding; a more accurate view of the extent, location and depth of affected property

basements; and identification of high-to-low risk properties and the size and scale of affected

areas.

2.3.4 The main causes of flooding were identified to be:

a) Deep basements: some property basement levels were found to be very close or at the same level as the sewer. So, as soon as the flow levels rise during a rainfall, the flows back up the connection pipework into the basement areas.

b) Inadequate capacity in the sewers: this results in water levels within the sewer network to rise when it rains. This rise in water level can result in flows backing up the connection pipework serving the properties and then into the basement areas.

c) Large flows from upper catchment: the deep storm relief sewers fill up following rainfall from the flows coming from the upper catchment, leaving insufficient capacity to relieve the trunk sewer network in the lower catchment (namely Hammersmith and Fulham and Kensington and Chelsea).

d) Inadequate capacity in the local sewer as well as large flows from the upper catchment: these properties flood because of both b) and c) above.


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3 DEVELOPING A SOLUTION TO FLOODING

3.1 Developing a solution to flooding

3.1.1 In 2009, Thames Water presented the flooding problem and the results of the initial investigations to Ofwat. In 2010, full investigation works started followed by options development.

. 3.1.2 To arrive at a viable option, the following process was adopted:

Step 1 Step 2

Step 3

Step 4

Step 5

3.1.3 The above process enabled a solution for each cluster to be identified and then the

solutions combined and rationalised across the areas to reduce cost and construction disruption.

3.1.4 The above process showed that the combined and rationalised solutions were either

too expensive or not practical to implement.

How does each property flood? a) Is it because the basement level is similar to sewer level resulting in the

flows to back up into the property as soon as water levels rise during a storm?

b) Is it because the storm relief or trunk sewers are filled up by flows from the upper catchment not allowing drainage of the local areas resulting in flooding?

c) Is it because the local sewers have inadequate capacity? d) Is it because of both b) and c) above?

Divide catchment into small sub-drainage areas. For each area, cluster the properties that flood for each reason identified in step 2.

Identify options to resolve flooding for each cluster in each area

Combine the solutions across the areas to rationalise and optimise

Investigation to identify properties at risk of flooding (see section 2.3)


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3.1.5 One important conclusion from the above process was that the underlying cause of flooding was identified (namely the large flows from the upper catchment causing overloading of the existing storm relief and trunk sewers). This issue had to be dealt with first to allow practical and viable solutions for the clusters to be developed.

(8th December 2011) where it was shown be alleviated without a more strategic, catchment-wide solution. In essence, this meant that the flows in the larger storm relief sewers and trunk sewers had to be intercepted at strategic locations to allow the existing systems to drain freely and allow one major cause of flooding to be removed. As such a need was established for a new strategic storm relief sewer (strategic sewer).

3.1.6 By mapping out the overloaded storm relief and trunk sewers, it was then possible to identify the hydraulic pinch points through hydraulic modeling to determine the required interception points. Details of the four hydraulic interception locations identified are described below:

The Lots Road interception point has been identified to remove the restriction created on the Walham Green Storm Relief Sewer (SRS) due to the pumping capacity on the Walham Green side of Lots Road Sewage Pumping Station.

- Brook Green Branch The interception point along the Brook Green Branch has been identified to stop the excess flows from the upper section of the storm relief sewer surcharging the sewer further downstream and hence drowning the lower weirs. The storm relief sewer has been split between the local Goldhawk Road overflow and the Lena Gardens overflow. In conjunction with this new interception point, the trunk sewer connection between Goldhawk Road and Hammersmith Grove can be disconnected to stop the main flow draining past a low section of basements.

Creek Branch Interception Points These two interception points work in tandem. There are three incoming storm relief sewers draining into the duplication sewer downstream of the Upper Addison Gardens overflow. By putting in the two new interception points this removes two of the incoming storm relief sewers and leaves the final storm relief sewer (North Kensington SRS) able to drain down the existing Hammersmith SRS duplication sewer.

The four interception points are shown on Figure 2 below.


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Figure 2: interception locations of overloaded storm relief and trunk sewers

3.2 Identifying the most cost effective programme

3.2.1 The results from basement surveys identified a number of properties whose

connections were at or below the nearest pipe soffit level. It is not possible to drop the water levels in the sewers to below basement level in these cases without relaying the whole sewer network with connection to every property at a lower level to allow free gravity discharge. Clearly relaying the whole sewer systems with connection pipework to every property would not be a viable solution. For such properties the only viable solution was FLIP installation (a small package pumping station which isolates the property from the sewer and pumps the flows into it). In addition, for certain individual properties located away from the clusters, a solution like sewer relaying, storage or other similar measures were not viable when considering the benefits (namely flooding protection to only one or two properties for a large expenditure). FLIP installations were identified as the most viable solution for such instances as well.

Interception location

Locations subject To flooding

Existing Storm Relief Sewers

Existing Trunk Sewers


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3.2.2 The following process was therefore followed to identify the solutions:

Is the basement below pipe soffit? i.e. Is the cause of flooding item a) step 2 under 3.1.2 above?

Install FLIP

Is flooding due to overloading of larger trunk or storm relief sewers? i.e. Is the cause of flooding item b) step 2 under 3.1.2 above?

Resolve by the new strategic sewer intercepting the existing network at strategic locations

Can it be resolved by sewer upgrade works, once the new strategic sewer is constructed and has taken the major flows away? i.e. Is the cause of flooding item d) step 2 under 3.1.2 above?

Resolve by sewer upgrade works

Can it be resolved as a local sewer upgrade scheme independent of the new strategic sewer? i.e. Is the cause of flooding item c) step 2 under 3.1.2 above.

Yes

No

Yes

No

Yes

No

Yes

Resolved by local sewer upgrade works No or not a viable solution

available i.e. away from clusters of flooding, therefore high cost, low benefit (paragraph 3.2.1)

Install FLIP


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The following solutions were identified by following the above process: 1- FLIP installations for deep basement properties or individual properties

away from clusters. 2- New strategic sewer 3- Sewer upgrade works (which require the new strategic sewer) 4- Local sewer upgrade works

Hydraulic analysis was undertaken to look into the possibility of implementation of Sustainable Drainage Systems (SuDS) in respect of the above works.

3.3 Sustainable Drainage Systems 3.3.1 A key part of the process was the investigation of the potential for sustainable

drainage systems (SuDS) across the Counters Creek catchment to reduce surface water run-off and alleviate flood risk.

3.3.2 Hydraulic modelling indicated that flow reduction from SuDS influences flood

water levels to a greater extent when they are located at the top of drainage catchments. This is because at the downstream end, flood water levels are heavily influenced by overflows at Lots Road and Hammersmith pumping station. In these areas, removing flow at the surface has a negligible effect on flood water levels, as any space created in local sewers is simply filled up from trunk sewers. In other words, because of the vast and interconnecting sewer network in the two boroughs, it was found that implementation of SuDS in each area is mainly ineffective as the flows from the upper catchment and other areas fill up the sewer resulting in negligible changes in water levels and no flooding protection.

3.3.3 The modelling, however, identified that in one area SuDS may work subject to the

new strategic sewer being implemented. This scheme has been included as part of the above programme.

3.3.4 Retrofitting of SuDS measures in an urban area can be problematic and their

performance is unknown: During sustained periods of rain, when the ground becomes saturated,

surface water run-off could cause flooding. London clay clearly does not help this situation.

There is no track record of their performance in an urban environment (i.e. actual flow reduction over a long period of time) and hence their effectiveness in flood protection is not proven.

The extent of maintenance required for SuDS in an urban environment is uncertain.

Certain SuDS measures like green roofs to old Victorian houses would mean new heavier roofs which can affect their foundations resulting in structural damage.

3.3.5 In view of the above, Thames Water has decided to undertake SuDS trials where

the performance of SuDS can be better understood. This is being undertaken in consultation with the local councils. The results from the trials will feed into the scheme identified in 3.2.3.3 above. In addition, the results would enable the programme to be expanded into the future in collaboration with the other stakeholders in order to prevent further increases in impermeable areas and ensure future sustainability of the project.


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3.3.6 The solution identified under 3.2.2 above was therefore developed to include

SuDS:

FLIP installations for deep basement properties or individual properties away from clusters.

New strategic sewer Sewer upgrade works (which require the new strategic sewer) Local sewer upgrade works SuDS retrofit trials followed by SuDS scheme

3.4 Engineering options for the new storm relief sewer

3.4.1 As the location of the hydraulic interception points was fixed through the hydraulic modelling, various engineering options were then appraised to connect the interception points together using a strategic sewer.The new sewer was designed to store the flows. This means that the storm volumes are stored and then passed forward for treatment after storm subsidence. In intense storms, the volumes of flows can become very large and impractical to store. For such situations a pumping station near an existing outfall was required to allow excess storm flows to discharge into the river. The storage in the system was optimised as far as possible which meant a significant reduction of approximately 650,000 tonnes of sewer discharge into the river in a typical year when compared with the existing situation.

3.4.2 Four options for a strategic sewer were developed and appraised. Details of the

four options are provided in figures 3-6. All four schemes require a new pumping station at Lots Road and all options are required to capture flows from the same interception locations. However, three of the options would result in the storm flows being split with some flows taken to a new pumping station at Lots Road with the remaining flows taken to a further new pumping station at Hammersmith Pumping Station; at Hyde Park or at Cadogan Place.

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3.4.3 Option 4 was selected as the preferred route for the new strategic sewer element

of the programme for the following reasons:

it was the most cost effective option in comparison with the other options; it allows an additional cluster of flooded properties at Mund Street

(additional interception point) to be connected to it to alleviate more properties from flood risk;

it requires fewer pumping stations than other options; it allows potential for the river to be utilised for materials transport,

minimising disruption to residents; and it offers opportunities for potential integration with the Thames Tideway

Tunnel should the Thames Tideway Tunnel obtain consent.


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4 SELECTED COUNTERS CREEK SCHEME

4.1 Overview

4.1.1 As mentioned in Section 3, the following five elements of work constitute the proposed programme for the Counters Creek Sewer Flood Alleviation Scheme:

A new strategic sewer and pumping station Sewer upgrade works (which require the new strategic sewer) Local sewer upgrade works FLIPs SuDS trials, the results of which will then feed into a SuDS scheme.

4.1.2 In July 2013, Thames Water agreed with Ofwat to invest a further £26m to

progress the proposed programme of works including the installation of further FLIPs, commencement of sustainable drainage systems pilots and design development of the major network improvement works required. Full Ofwat funding for the development of the proposed programme is expected in December 2014.

4.1.3 Figure 7 shows the properties that have reported sewer flooding which will benefit

from the above elements of the proposed programme.


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Figure 8: Schematic of the Counters Creek catchment showing properties alleviated by components of the proposed programme

4.2 The five elements of the proposed programme

4.2.1 The new strategic sewer and the new pumping station:

The outline solution design is to provide a new storm relief sewer to intercept

the four interception points (including the additional Mund Street interception point) within the catchment and to transfer flows to Lots Road where a further interception point can be captured. The new sewer is designed to store the flows. This means that under storm conditions, the flows are intercepted and stored in the new storm relief sewer. A new pumping station at Lots Road will be constructed to pump the flows back into the existing sewer system to be passed forward for treatment following storm subsidence. Under intense storms, the volumes of rainwater can become very large (some 750,000m3). Under these circumstances, it would not be practical to store all the flows. The pumping station at Lots Road will therefore include storm pumps to pump the excess storm water into the river.

Flooding locations to be protected: To be protected by FLIPs To be protected by SuDS To be protected by local sewer upgrade works To be protected by the new storm relief sewer and sewer upgrades


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The proposed strategic sewer would store a significant amount of combined sewage, but would not replace the need for the Thames Tideway Tunnel to control the Lots Road Pumping Station CSO discharges at Cremorne Wharf Depot.

4.2.2 Sewer upgrade works:

As a consequence of constructing the new strategic sewer, the overall

hydraulic headroom in the system increases as water levels are lowered. This lowering allows a number of sewer upgrade works to be undertaken to remove existing hydraulic constraints and pass flows to the new strategic sewer.

4.2.3 Local sewer upgrade works:

In the certain areas of the Counters Creek catchment, the new strategic sewer

would not contribute to alleviation of the risk of flooding as the mechanism of flooding has been identified as being predominantly local, i.e. caused by the hydraulic constraints in local system only and largely unaffected by the storm and trunk systems. In these areas local sewer upgrade works solutions have been identified.

4.2.4 FLIPs:

FLIPs will be installed at properties where the reduction of water levels in the

sewers will not provide flooding protection due to their deep basement levels. Also FLIPs will be installed for properties away from the clusters, where expensive local upgrade works would only protect a few properties (i.e. they would not be cost beneficial).

4.2.5 SuDS:

Hydraulic analysis has shown that in one area (Lillie Road) SuDS measures

can provide flooding protection as long as the large flows are intercepted by the new storm relief sewer. However, prior to implementation of this scheme, a SuDS trial is required to assess the performance of such measures and the actual flow reductions that can be achieved. The results of this trial can then feed into the Lillie Road scheme. It is intended that the trial will also assist with future implementation of schemes by all stakeholders in order that the increase in the impermeable areas can be stopped or even reversed. By encouraging the delivery of SuDS through working with the London Borough of Hammersmith and Fulham and the Royal Borough of Kensington and Chelsea, as they develop their surface water management plans, the long term performance of the sewerage network in terms of future growth and climate change can be safeguarded.


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5 DELIVERY OF THE PROPOSED PROGRAMME

5.1 The new storm relief sewer and the sewer upgrade works

5.1.1 The provision of the strategic sewer and sewer upgrade works requires further design development to refine the outline design. Further 3rd party consultation, design progression and ground investigations are now required before the proposed tunnel alignment can be confirmed and any necessary planning permissions sought. The construction works are programmed to start in early 2017 and be completed in 2020.

5.2 Local sewer upgrade works

5.2.1 The local sewer upgrade works can start in 2015 as these are independent of the main works. These works also require further design development but may be delivered using Thames Waters permitted development rights. Where necessary planning permission will be sought for any elements of the local sewer upgrade works which require planning permission.

5.3 FLIPs

5.3.1 The programme of FLIPs installations will continue in 2014 and 2015.

5.4 SuDS

5.4.1 Three SuDS pilots will be implemented in 2014/2015. The SuDS pilots will provide information to use in the design of the Lillie Road SuDS proposals to allow the proposals to be completed by 2020.


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6 NEXT STEPS

6.1 Strategic Sewer and Sewer Upgrade Works

6.1.1 As set out above, there is a requirement for further design development of the strategic sewer to ensure that the horizontal and vertical alignments do not conflict with existing below ground infrastructure and constraints.

6.1.2 A review of the route alignment will be undertaken in parallel with site selection

work to assess potential construction sites against planning, environment, property and engineering criteria.

6.1.3 The further design development will feed into the site selection methodology. The

culmination of this work will be the identification of preferred construction sites and a preferred route alignment. The preferred sites and route will then be subject to a public consultation and discussions with stakeholders in Autumn 2014.

6.1.4 Following the 1st consultation and discussions with stakeholders on the preferred

route and construction sites detailed design will be undertaken before a 2nd stage public consultation in mid 2015. The 2nd stage public consultation will confirm the proposed construction sites and provide greater level of detail of the proposed works.

6.1.5 Any necessary planning applications for the works will be sought in late 2015 with

an aim to be able to commence construction at the start of 2017.

6.1.6 Further modeling and design development will also be undertaken of the sewer upgrade works. This work may identify sewer upgrades works which deliver sufficient independent flood alleviation to justify delivery in advance of the strategic sewer with further flood alleviation benefits being realised following the completion of the strategic sewer.

6.1.7 Thames Water is seeking consent for the Thames Tideway Tunnel (TTT) which is a major new infrastructure project which would tackle the current problem of combined sewer overflows (CSOs) discharging untreated sewage into the tidal River Thames during wet weather. The TTT would capture the overflows and transfer the sewage flows for treatment at Beckton Sewage Treatment Works. One of the CSOs which would be controlled by the TTT is the Lots Road Pumping Station CSO at Cremorne Wharf.

6.1.8 The proposed strategic sewer for the Counters Creek Flood Alleviation Scheme would store a significant amount of combined sewage, but would not replace the need for the Thames Tideway Tunnel to control the Lots Road Pumping Station CSO discharges at Cremorne Wharf Depot.

6.1.9 The design of the strategic sewer is required to deliver sewer flood alleviation.

Since the Thames Tideway Tunnel is not a confirmed scheme, the design of the proposals cannot rely on the provision of the TTT however, should the TTT obtain consent there will be opportunities for potential integration of the schemes to be investigated further.


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6.2 SuDS

6.2.1 Work will progress on the delivery of the SuDS pilot schemes in 2014 and 15. The outcomes of the SuDS pilot will assist with the design and development of the proposed SuDS scheme.

6.3 Local Sewer Upgrade Works

6.3.1 As the modeling has shown that the local schemes are independent of the requirement for the strategic sewer, these works will be delivered separately. Further design work will be undertaken to develop the schemes. Most elements of the schemes can be delivered using Thames Waters permitted development rights. Any consents that are required to deliver the local schemes will be sought separately from those for the strategic sewer.

6.4 FLIPs

6.4.1 The installation of additional FLIPs will progress throughout the remainder of AMP5 (which runs until the end of March 2015) and in AMP6 which starts in April 2015.


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7 INDEPENDENT SCRUTINY

7.1 Independent scrutiny is an important part of any project. It provides assurance over the accuracy of the proposals, as well as expertise from leading experts. In this case, Thames Water engaged with a number of industry experts and academics over the course of the process of developing the proposed programme to scrutinise key technical, financial and cost elements of the programme. Further information is provided below.

7.2 Independent Advisory Group

7.2.1 In September 2010, Thames Water established an Independent Advisory Group (IAG), made up of the following independent experts from industry and academia, who together with Ofwat, have reviewed and challenged Thames Water work:

Professor Bob Andoh, Director of Innovation at Hydro International and

Visiting Professor at Liverpool John Moores University Professor David Balmforth, Executive Technical Director at MWH, Visiting

Professor at Imperial College and Vice President of the Institution of Civil Engineers

Professor Adrian Saul, Professor at the University of Sheffield and leading academic in the Flood Risk Management Research Consortium

7.2.2 The terms of reference were for the IAG to undertake a review of the work that

Thames Water has undertaken to understand the cause of sewer flooding in the Counters Creek catchment and the sustainable options that should be explored to alleviate this risk.

7.2.3 Thames Water has addressed their challenges to the data acquired, the overall

approach, and the scope and extent of identified solutions. They also encouraged Thames Water to explore options that have until recently not been applied by the UK water sector (such as green infrastructure), drawing upon experiences from other countries to make this programme more sustainable. In response, Thames Water have produced deeper analysis, commissioned studies, completed more complex modelling and conducted further detailed reviews. A statement of support from the IAG is provided in Appendix 1.


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8 STAKEHOLDER AND CUSTOMER SUPPORT

8.1 Customer support

8.1.1 for the Counters Creek Flood Alleviation Scheme and their

views, feedback and willingness to pay have been central to developing the strategy in the Counters Creek catchment. Thames Water can demonstrate customer support for this programme at a number of different levels:

local customer support for the scheme in the Counters Creek area; evidence of support from the wider customer base which identifies the

importance that customers place on sewer flooding; and illingness to pay across the range of income groups

to alleviate sewer flooding.

8.1.2 With over 1700 properties at risk of flooding in a densely populated urban environment, Thames Water has had significant customer feedback, both directly and following property surveys. There has been on-going engagement with customers around developing a solution. The result is a group of customers who have a good understanding of the issues surrounding the problem, the potential solution and the development process that needs to be followed. The project has benefitted from listening to the concerns and providing updates through the formal and informal networks developed with these customers.

8.1.3 In order to develop this programme, Thames Water has:

contacted over 6,000 customers to investigate sewer flooding risk; completed over 3,000 customer door-step interviews and measuring the

depth of property basements; since 2008 invited over 3,000 customers to ten half yearly public meetings held one-to-one sessions and group meetings with key influential

stakeholders who include affected residents, local interest groups (Kensington Society), CC Water and local or central authorities (GLA, TfL etc.); and

delivered a FLIPs programme and started a sustainable drainage pilot. 8.1.4 Thames Water has also worked closely with officers and councillors from both the

London Borough of Hammersmith & Fulham and the Royal Borough of Kensington & Chelsea to both understand the challenges that they face in relation to flooding, but also to develop a solution that is acceptable to customers. The Boroughs have been very supportive in the process of developing the solutions.

8.1.5 Thames Water has been holding public meetings every six months since 2009 at

Council offices at Hammersmith and Fulham and Kensington and Chelsea as requested by customers to update them on the progress of the project.

8.2 Consumer Council for Water

8.2.1 The Consumer Council for Water has attended many public meetings to hear at first hand the concerns of customers affected by sewer flooding. On 23 January 2013 Thames Water met the Consumer Council for Water to brief them on the proposed programme and the intention to use the Change Protocol process to


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agree additional funding with Ofwat during AMP5. The Consumer Council for Water has provided a statement of support for Change Protocol application in relation to Counters Creek. This is given in Appendix 2.


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Appendix 1: IAG Statement of Support

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Appendix 2: Consumer Council for Water Statement of Support (4th April 2013)

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Documents

1 Strategic Options Report Cover - Thames Water...water from toilets, bathrooms and kitchens. 2.1.2 There are over 1700 properties across parts of the London Borough of Hammersmith