The Thames Tideway Tunnel & Borough of Tower Hamlets: Assessment of the KEMP Foreshore & Heckford Options

CONTENTS

EXECUTIVE SUMMARY

1.0 INTRODUCTION ...... 1

2.0 & THE LONDON BOROUGH OF TOWER HAMLETS ...... 1 2.1 Overview...... 1 2.2 NESR CSO ...... 1 2.3 Site Selection methodology ...... 2 2.4 NESR CSO Options ...... 3 3.0 THE KEMP FORESHORE OPTION ...... 4 3.1 Summary Description ...... 4 3.2 Location & Access ...... 4 3.3 Construction Activities & Programme ...... 5 3.4 Air Management & Quality Control...... 5 3.5 Legacy Issues...... 6 4.0 THE HECKFORD OPTION ...... 7 4.1 Summary Description ...... 7 4.2 Location & Access ...... 7 4.3 Construction Activities & Programme ...... 8 4.4 Air Management & Quality Control...... 8 4.5 Legacy Issues...... 9 5.0 OTHER OPTIONS ...... 10 5.1 NESR Interception and Connection to Kings Stairs Gardens...... 10 5.2 Alternative Locations for the Vertical Shaft Site in LBTH ...... 10 6.0 COMPARISON & EVALUATION OF THE HECKFORD & FORESHORE OPTIONS ...... 12 6.1 Construction & Programme ...... 12 6.2 Engineering Issues ...... 13 6.3 Traffic & transport ...... 13 6.4 Environmental Impact During Construction ...... 14 6.5 Air Quality Management Post Construction ...... 17 6.6 Legacy Issues...... 18 6.7 Other Planning Considerations ...... 19 7.0 CONCLUSIONS ...... 22

London Borough of Tower Hamlets London Borough of Tower Hamlets Thames Tideway Tunnel

EXECUTIVE SUMMARY

Construction of the Thames Tideway Tunnel project aims to deliver significant environmental benefits by reducing the 39 m tonnes of untreated sewage discharged annually into the River. The North East Storm Relief (NESR) sewer enters the Thames below the King Edward Memorial Park and discharges on average over 784,000 m3 of effluent a year. This sewer along with many others will be intercepted by the scheme and outflow diverted via a shaft into the main Tideway tunnel.

Various construction sites for the interception of the NESR have been considered by . In their Phase 1 public consultation a site on the KEMP foreshore was proposed as the Preferred Scheme. Due to the impact of this option on the park and the involvement of local community groups, other locations have subsequently been considered. This report presents an assessment of the Foreshore Option and an alternative proposal to use the Heckford business site, the Heckford Option.

The Foreshore Option involves both interception of the NESR and construction of the shaft to the main tunnel in the KEMP foreshore. A minimum worksite area of 7,500 m2 will be required for 3.5 – 4 years to achieve this. The Heckford Option proposes a two worksites: one centrally located in KEMP of 1,750 m2 for 1.5 – 2 years to intercept the NESR, connected by a transfer tunnel to the Heckford business site where the shaft would be constructed in a site of 7,500 m2 requiring 3.5 – 4 years.

Although the Foreshore Option has some engineering advantages due to combining the interception and shaft sites, as well as the option of using the River for transporting some materials to and from the site, it will have a significant impact on the park during the construction stage lasting for up to 4 years. After construction a 2,000 m2 permanent legacy area will be left in the foreshore for ventilation and access structures, and various landscaping improvements to the park will be made.

The Heckford Option will require two worksites, but the area taken in the park will only be approximately 20% of the area of the Foreshore Option and be required for up to 2 years less time. The main shaft site at the Heckford business park will be required for the full 3.5 – 4 years during construction. After this time the area has the potential to be redeveloped for mixed commercial and residential use, although a 2,000 m2 legacy area is required.

Both options will require permanent ventilation structures in the form of columns from 0.3m - 1.6 m in diameter and between 4m - 6m high during operation of the system. It is currently proposed that the Foreshore Option has 4 ventilation columns, and the Heckford Option has 2 in the business park site and 3 in KEMP. Air will only be exhausted from the tunnel system during major storm events and the predicted air quality impact for both options is minor.

The Heckford Option requires the alignment of the main Tideway tunnel to be altered so that it intercepts the shaft below the business park. This will increase the potential for settlement to impact buildings in the Borough, particularly where the connection tunnel to KEMP is located over the main tunnel. There have been a number of major tunnelling projects beneath East London in the last 20 years including the Extension and Channel Tunnel Rail Link. Following these and other projects, the amount of settlement and its impact on surface buildings is now better understood and accurate predictions can be made. Based on initial calculations made by Thames Water it is assessed that the impact of tunnelling between KEMP and Heckford should not be significant, and that the impact of the main Tideway Tunnel on buildings within the Borough is likely to be minor.

Nigel Legge Associates Ltd London Borough of Tower Hamlets London Borough of Tower Hamlets Thames Tideway Tunnel

Together with the engineering appraisal of each option, a number of environmental aspects have also been considered. During construction the Heckford Option may involve a greater number of vehicle movements on the local road network than the Foreshore Option, as it does not have the possibility for water-borne transport. It should be noted however that the extent to which river transport will be used during construction of the Foreshore Option is not yet known, and is not guaranteed by Thames Water. The location of a site within the Heckford business park will also lead to air quality and noise / vibration impacts on a larger overall number of residential dwellings. These impacts will however be ameliorated and minimised during construction.

The Heckford Option will have significantly reduced impact on biodiversity than the Foreshore Option, and less impact upon townscape and local views. The impact of the Foreshore Option on the King Edward Memorial Park as a valuable amenity resource will be greater, and for approximately double the duration through the construction, compared with the Heckford Option.

The Heckford Option may lead to a temporary loss of local employment at the business park during the construction phase, and this will need to be addresssed. Following completion of the project there may be potential for enhancement of the employment offered in the area depending on redevelopment options.

In legacy, potential environmental issues include visual impact and odour. The Foreshore Option will marginally increase the overall area of park due to a permanent 2,000 m2 legacy area remaining in the foreshore, and will therefore be more ‘visible’ than the Heckford Option. Thames Water modelling predicts that odour during operation of the system is unlikely to be a significant issue for either option.

Both options have a number of beneficial and adverse aspects in terms of environmental and socio-economic impact. It is considered, however, that many of the adverse environmental and socio-economic impacts identified could be minimised to an acceptable level through appropriate mitigation.

From an engineering perspective it is concluded that both options are technically feasible, and according to Thames Water estimates the cost of both is similar. Due to the reduced construction requirements in KEMP of the Heckford Option, this will result in significantly less impact on the park compared with the Foreshore Option.

Nigel Legge Associates Ltd London Borough of Tower Hamlets London Borough of Tower Hamlets Thames Tideway Tunnel

1.0 INTRODUCTION

This report has been produced for consideration by the Cabinet of the London Borough of Tower Hamlets. It is an assessment of the impact of the Thames Tideway Tunnel project on the Borough, and in particular two options which are currently being considered for the location of underground structures and worksites during construction. These are the Foreshore Option in the King Edward Memorial Park, and the Heckford Option which would involve a smaller area in the park and a larger worksite in what is currently the Heckford business park.

The purpose of this report is to present the outcome of various meetings and discussions with Thames Water over the past several months concerning these options, and to assist members in their understanding of the relative merits of the two options.

This report is produced jointly by Nigel Legge Associates Ltd, who have been retained by the London Borough of Tower Hamlets (LBTH) to provide specialist engineering advice concerning the Thames Tideway Tunnel (TTT) project on the borough, and LBTH officers.

2.0 THAMES TUNNEL & THE LONDON BOROUGH OF TOWER HAMLETS

2.1 Overview The Thames Tunnel project is a major infrastructure scheme whose aim is to prevent the discharge of large quantities of untreated sewage into the Thames. Currently some 39 million tonnes of sewage are discharged into the River each year.

The existing sewer network was designed and built in the Victorian era. During storm events the network now regularly becomes overloaded, resulting in overflows of sewage directly into the .

The Thames Tunnel project involves constructing a deep tunnel from Acton in west London – the so-called Super Sewer - to intercept many of the existing combined sewer overflows (CSOs), so removing discharge into the River during storm events. Their flow will be intercepted and passed down shafts to the main tunnel, which runs at a depth of some 70 m below ground level, mostly beneath the Thames. The Thames Tunnel effectively operates as a very large collection or attenuation tank which is filled during storm events, and is then pumped out at Abbey Mills pumping station with the contents passed through the to the Becton sewage treatment works.

2.2 NESR CSO The North East Storm Relief (NESR) CSO drains a large area of north-east London (Figure 1) and passes beneath the King Edward Memorial Park (KEMP) to discharge into the Thames. Due to its catchment area the NESR CSO is a large gravity overflow to the Thames and on average discharges over 784,000 m3 of effluent a year, representing 2% of the annual total into the River.

Nigel Legge Associates Ltd Page 1 of 27

London Borough of Tower Hamlets London Borough of Tower Hamlets Thames Tideway Tunnel

KEMP

Figure 1 The Area Drained by the North East Storm Relief Sewer (Source: Thames Water)

2.3 Site Selection methodology In order to intercept existing CSOs, shafts and various other structures have to be constructed. Although most of the structures are below the ground and will not be visible during operation, relatively large sites are required during the construction stage.

The process of selecting sites is clearly described in Thames Water’s (Thames Water) report ‘Site Selection Methodology Paper’ May 2009. Sites are evaluated according to five main criteria:

1. Engineering 2. Planning 3. Environmental 4. Community 5. Property

Thames Water have stated that all of these criteria are given an equal weighting in the selection process.

Stage 1 of the process involves producing a long list of options, refining this to a short list and then determining a preferred list of sites. Sites on the preferred list were included in

Nigel Legge Associates Ltd Page 2 of 27

London Borough of Tower Hamlets London Borough of Tower Hamlets Thames Tideway Tunnel

the Phase 1 Public Consultation. Site Suitability reports have produced for all short-listed sites.

The process of site assessment continues in the form of ‘Back-Checking’ if additional information comes to light. This process is currently underway for NESR.

2.4 NESR CSO Options Following Thames Water’s initial site selection process their preferred site for the NESR CSO interception, published in the Phase 1 Public Consultation, was in the KEMP Foreshore.

In response to this the local community formed the SaveKEMP campaign and proposed several alternative options for the NESR CSO interception. One these involved the transfer of effluent from KEMP across the River to a main shaft site in ; a second option was to site the vertical shaft connection to the main tunnel in one of a number of brownfield sites adjacent to Butcher Row. Thames Water subsequently selected the Heckford business park, located 800m to the north west of KEMP, as the site for the vertical shaft.

These options are shown in Figures 2 & 4 at the end of this report.

Nigel Legge Associates Ltd Page 3 of 27

London Borough of Tower Hamlets London Borough of Tower Hamlets Thames Tideway Tunnel

3.0 THE KEMP FORESHORE OPTION

3.1 Summary Description Under the current Thames Water Preferred Scheme, the alignment of the TTT in the vicinity of the King Edward Memorial Park is under the Thames, with a combined interception of the NESR and construction of a vertical connection shaft on the KEMP foreshore.

Thames Water state that the reasons for the preferred status of this option are:

. direct interception of the NESR without the need for connection culverts/tunnels . to create a ‘drive-through’ shaft with safety implications for the main tunnel connection work . minimise surface impact in the urban environment from settlement by locating the TTT beneath the Thames . enable maintenance of the tunnel boring machine (TBM) to take place as it drives from the Abbey Mills Pumping Station to King’s Stairs Gardens in Southwark.

Outflow from the Holloway Storm Relief (HSR) sewer, which also runs through LBTH, was to have been intercepted at the Butcher Row site north of The Highway and run in a connecting tunnel to the main vertical shaft site on the KEMP foreshore. The HSR will now not be connected to the TTT and will be dealt with by indirect control.

Following construction of the Foreshore Option, in the legacy situation Thames Water are proposing a landscaping scheme in the foreshore area of KEMP to incorporate the various legacy structures into the park landscape.

3.2 Location & Access The Foreshore Option involves a minimum site area of 7,500 m2. The site would be located in two areas of KEMP: on the foreshore, where the CSO interception and shaft construction would take place, and in the current playing field area in the western area of the park where associated facilities including workshops, stores, offices, canteens and welfare facilities would be situated.

The main construction site on the foreshore would be located at the level of the park.

The main access to the site is from Glamis Rd in the west. The two site areas within KEMP would also be connected by an access road running through the park.

Nigel Legge Associates Ltd Page 4 of 27

London Borough of Tower Hamlets London Borough of Tower Hamlets Thames Tideway Tunnel

3.3 Construction Activities & Programme

The principal construction activities for the Foreshore Option are shown in the table below.

The period of construction would be 3.5 – 4 years. The current proposals by Thames Water indicate that the amount of space required in the park would vary throughout the construction period.

Table 3.1 Proposed Construction Activities: Foreshore Option

Year Activities 1 Mobilise, site clearance, early landscaping and relocating park facilities, temporary cofferdam, shaft d-wall

2 shaft excavation, complete shaft base, form tunnel eyes, allow for main tunnel passing through shaft, construct chambers

3 shaft secondary lining and internal structures, remove cofferdam

4 finish internal structures, chambers and valves, MEICA works, finishes, commissioning and reinstatement/landscape works

3.4 Air Management & Quality Control

An important aspect of the Tideway Tunnel project is ventilation, which involves managing the quality of air coming out of the tunnel in order to avoid nuisance odour releases and adverse effects on occupational and public health.

Thames Water has carried out comprehensive studies both of the whole system, and the inlet structures i.e. interception chambers and drop shafts, to assess air quality issues. As a result of these studies Thames Water claim that the quality of the treated air will be better than the ambient air at the outlet environment.

Air filtration is an important aspect of air quality management. Two types of filters could be used at interception and drop shaft structures:

1. Active filters in which air is driven through the filters, probably using compressors to create increased pressure, which would involve additional noise 2. Passive filters in which air is pushed through filters using only the increased pressure created in the tunnel by water movement, which are silent

For the NESR CSO air quality would be controlled by passive filters, which will have less impact on the immediate surrounding area than active filters which use machinery.

Nigel Legge Associates Ltd Page 5 of 27

London Borough of Tower Hamlets London Borough of Tower Hamlets Thames Tideway Tunnel

3.5 Legacy Issues

For the Foreshore Option there are two principal legacy issues:

1. A permanent area of 2,000 m2 on the foreshore would be maintained for ventilation, access and maintenance purposes. 2. A landscaping scheme will be undertaken in the park.

Four permanent ventilation structures would be situated in the 2,000 m2 additional area on the KEMP foreshore, including:

1. Two 1.6m diameter 4m high ventilation columns 2. One 0.225m diameter 6m high ventilation column 3. One 0.3m diameter6m high vent column

Nigel Legge Associates Ltd Page 6 of 27

London Borough of Tower Hamlets London Borough of Tower Hamlets Thames Tideway Tunnel

4.0 THE HECKFORD OPTION

4.1 Summary Description The Heckford Option involves two separate sites within LBTH (Figure 2). One site in the Heckford business park would be required for the vertical drop shaft to the main tunnel, the largest structure to be constructed.

Within KEMP a smaller site would be required for construction of the CSO interception chamber above the NESR. Due to the alignment of the NESR, density of urban housing and lack of open spaces to the north of The Highway, it has been concluded that the only feasible location for the CSO interception chamber to be constructed within KEMP. A connection is also required to transfer effluent from the CSO interception site in KEMP to the drop shaft site located north of The Highway in the Heckford business park. This will require construction of a 4.2m external diameter connection tunnel.

4.2 Location & Access The main site in the Heckford business park would require an area of 7,500 m2, and access to this site would be off The Highway.

The site required within KEMP is smaller at 1,750 m2, equivalent to 42m x 42m. The location proposed for this site is near to where the NESR crosses The Highway. The site would be close to and may incorporate the Memorial Steps. Access to the site would be via Glamis Rd and within the park a one-way temporary road is required for construction traffic to travel to and from the construction area. Direct site access to The Highway is not feasible due to the difference in elevation between the main road and the park.

Other locations for the site along the route of the NESR within KEMP which are less central have been considered. Moving the CSO interception site to the SE corner of the park would place it close to the tunnel which passes below the NESR. The proximity to the could result in difficulties for construction of the connection tunnel to Heckford St. In addition, longer access would be required to a site in the south-east corner of the park, as a temporary road to The Highway past the Free Trade Wharf building is not feasible.

Other options for the site within KEMP have been considered including separating the CSO interception site and connection tunnel sites to reduce the overall impact on the central area of the park (Figure 3). It is considered that this option has little merit and will involve significant and more extensive disruption to the park during the construction period.

Nigel Legge Associates Ltd Page 7 of 27

London Borough of Tower Hamlets London Borough of Tower Hamlets Thames Tideway Tunnel

4.3 Construction Activities & Programme

The principal construction activities for the Heckford Option are shown in the table below. The period of construction would be approximately 3.5 – 4 years at the Heckford business site, and 1.5 to 2 years within KEMP.

Table 4.1 Proposed Construction Activities: Heckford Option

YEAR ACTIVITIES

Heckford Site 1 mobilise, site clearance, shaft d-wall and excavation

2 complete shaft base, form tunnel eyes, allow for main tunnel passing through shaft, start construction of chambers, erect TBM and start drive tunnel to KEMP North

3 finish tunnel drive to KEMP North, line tunnel to KEMP North, shaft secondary lining and internal structures

4 finish internal structures, MEICA works, finishes, commissioning and reinstatement

KEMP

1 mobilise, site clearance, piling and chamber excavation, chamber base, receive TBM, start internal structures

2 other chambers and valves, MEICA works, finishes, commissioning and reinstatement/landscape works

One of the requirements for this option is that the alignment of the main Tideway Tunnel is altered to intercept the vertical drop shaft in the Heckford business park site. This will involve the main tunnel passing below the urban area of LBTH for a greater distance.

The required connection tunnel to the main shaft would be constructed from the Heckford site to KEMP, minimising the required site area and impact on the park. Thames Water’s current proposals shows the alignment of the connection tunnel directly above the main Tideway Tunnel. There will be some surface settlement associated with the construction of these tunnels, but initial assessments show this will not be significant.

4.4 Air Management & Quality Control

For the Heckford Option, both the Heckford business park and KEMP sites would require ventilation structures to ensure adequate air quality management of the underground infrastructure. As for the Foreshore Scheme, air quality would be controlled by passive filters.

The permanent ventilation structures required for this option include:

1. At Heckford two 1.6m diameter 5m high ventilation columns

Nigel Legge Associates Ltd Page 8 of 27

London Borough of Tower Hamlets London Borough of Tower Hamlets Thames Tideway Tunnel

2. In KEMP two 1.2m diameter 4m high ventilation columns, plus one 0.225m diameter 6m high ventilation column.

4.5 Legacy Issues

For the Heckford Option the two principal legacy aspects following construction of the Tideway tunnel are:

1. Permanent ventilation structures, including their maintenance, at both the Heckford and KEMP sites 2. Access to the various underground structures for maintenance purposes 3. After construction there is a possibility that the Heckford Site will be redeveloped to include mixed commercial and residential use

Nigel Legge Associates Ltd Page 9 of 27

London Borough of Tower Hamlets London Borough of Tower Hamlets Thames Tideway Tunnel

5.0 OTHER OPTIONS

5.1 NESR Interception and Connection to Kings Stairs Gardens

A further option, proposed by the SaveKEMP group, involved intercepting the NESR outflows in LBTH, then transferring effluent via a connection tunnel across the Thames to an existing vertical drop shaft at King’s Stairs Gardens or Chambers Wharf in Southwark (Figure 4). The technical requirements for this option have been assessed by both Thames Water and Legge Associates.

Thames Water carried out detailed numerical and physical modelling tests for the whole Tideway Tunnel system under gradually varying and transient flow conditions and assessed the issues of air entrainment, air quality (odour) management and ventilation. It was concluded that this option was not feasible because of unstable hydraulic and pneumatic conditions it would introduce into the system. This work was independently assessed on behalf of LBTH by Professor Maksimovic, a specialist in hydraulic engineering from Imperial College London. Professor Maksimovic was also of the opinion that various hydraulically unfavourable conditions were associated with this option.

A 1640m long connection tunnel would be required from KEMP to the main shaft site in Southwark. Due to the existing Thames Tunnel between Wapping and Rotherhithe, and also a planned UK Power Networks electricity cable tunnel, the vertical alignment of the connection tunnel would need to be relatively deep at ~35m. This in turn would require a 16m diameter reception shaft to be located in KEMP, a major structure which would need a 5,000 m2 site area during construction for up to 3 years and involve significant disruption to the park.

Possibly the most significant issue associated with this option is that Thames Water estimated that to construct it from the main shaft site, the overall prolongation of the whole Tideway project is an additional 1 year. This would have substantial cost implications for the project as a whole.

Professor Maksimovic and Legge Associates agree with Thames Water that this option is not feasible either on hydraulic engineering, construction or cost grounds.

5.2 Alternative Locations for the Vertical Shaft Site in LBTH

Due to the requirement for a 7,500 m2 worksite associated with the main vertical shaft, Thames Water have identified the Heckford Street Business Centre as the only feasible alternative site north of The Highway.

During their site selection process Thames Water identified a number of other possible locations for vertical shaft connections in LBTH (Figures 2& 5). Several potential sites were identified north of The Highway in addition to the Heckford Street Business Centre including the Cemex site occupied by a concrete batching plant, Cable Street and the Studio site consisting of a Victorian brick warehouse subdivided into business units. These were rejected on the basis they were not large enough and that combining them, e.g. the Cemex and Studio site was not feasible. It was also considered there were implications for the local economy of closing down the Cemex site, and difficulties to relocate this facility elsewhere.

Nigel Legge Associates Ltd Page 10 of 27

London Borough of Tower Hamlets London Borough of Tower Hamlets Thames Tideway Tunnel

Thames Water considered were the Shadwell and Limehouse basins. As the Shadwell and Limehouse basins are surrounded by residential properties, and would also have access problems for site construction traffic, they were also not considered suitable shaft locations.

A further technically possible option would be to identify another foreshore site located away from KEMP. There are access issues for site construction traffic with alternative foreshore sites in LBTH, and it is understood there may be resistance from both the Authority and the Environment Agency.

Considering the various constraints within LBTH it is concluded that the only viable alternative shaft site to the KEMP foreshore is the Heckford Street site.

Nigel Legge Associates Ltd Page 11 of 27

London Borough of Tower Hamlets London Borough of Tower Hamlets Thames Tideway Tunnel

6.0 COMPARISON & EVALUATION OF THE HECKFORD & FORESHORE OPTIONS

6.1 Construction & Programme

Due to the urban density and lack of open spaces along the alignment of the NESR in LBTH, the only feasible location for intercepting this CSO is within KEMP.

From an engineering perspective, the Foreshore Option has the advantage of combining interception of the NESR with the vertical drop shaft to the TTT, requiring a single work site rather than two. Locating the combined worksite on the foreshore minimises impact on the urban environment and enables arisings from the shaft construction and tunnelling work to be transported away on the river by barge. The foreshore site also enables the main tunnel to be located beneath the Thames for a greater distance before the alignment turns north below the Limehouse Cut towards the Abbey Mills pumping station, therefore minimising settlement-related impact.

The principal issue with this option however is its impact on KEMP, an issue which is addressed further below. The entire 7,500 m2 work site would be located in KEMP including a large area of the foreshore, an access road and associated facilities including workshops, stores, offices, canteens and welfare facilities located in the western area of the park.

Thames Water has stated that the required area for the Foreshore Option is 7,500 m2. It is not currently known how large the actual shaft site on the foreshore will be, this will be decided by the contractor when he is appointed. The total required area including access and associated facilities in the park may therefore exceed 7,500 m2. The worksite would exist for 3.5 to 4 years, although Thames Water have indicated that its size would vary during the construction process.

The Heckford Option involves two sites: a 7,500 m2 worksite for the vertical shaft located away from KEMP in what is currently a business park, and a smaller 1,750 m2 site to intercept the NESR in KEMP. A 4.2m diameter tunnel would connect the two sites.

Feasibility studies have shown that the Heckford business park is the only site in the area with the required area for the main shaft site. The KEMP interception worksite is currently located centrally within the park. It has been shown that other locations within the park, e.g. to the south east towards the River and the Free Trade Wharf flats, are not feasible due to the alignment of the Rotherhithe road tunnel which would interfere with the required connection tunnel. This location would also require a longer access road within the park, as access to the Highway along the side of the Free Trade Wharf is not feasible. With this option the Heckford site would be required for 3.5 to 4 years, and the KEMP site for 1.5 – 2 years.

The principal difference between these two options is their impact on KEMP. With the Foreshore Option the entire construction process occurs within the park, although there are some efficiencies due to combining the shaft and CSO interception sites at one location and it is likely the contractor will use the River for some transportation, probably of excavated material away from the site. The Heckford Option requires a site area within KEMP which is only 23% the size of the Foreshore Option, and which could only be required for 1.5 years compared with 4 years for the Foreshore Option. The Heckford

Nigel Legge Associates Ltd Page 12 of 27

London Borough of Tower Hamlets London Borough of Tower Hamlets Thames Tideway Tunnel

Option does however require a further worksite in the Borough away from the park which currently is 7,500 m2.

It is noted that the location and layout of the site area in KEMP for the Heckford Option could be optimised, and its impact potentially reduced, if the King Edward memorial was professionally dismantled and stored during the construction. This is recommended.

A cost comparison by Thames Water of the two options has shown that they are comparable. Thames Water have also stated that the Heckford Option is technically feasible.

6.2 Engineering Issues

Settlement

The Heckford Option requires realignment of the main Tideway Tunnel to intercept the vertical drop shaft at the Heckford Street business park. The new alignment will require passing beneath the urban environment of LBTH to a greater extent, and raises the issue of ground settlement and its impact on buildings.

With the depth of the main Tideway Tunnel at ~70m below ground level and modern underground construction technology using tunnel boring machines, the amount and form of any settlement is likely to be limited, which in turn will reduce the risk of impact to surface structures. Additional surface settlement will occur however where the connection tunnel runs above the main tunnel between KEMP and the Heckford site.

There have been a number of major tunnelling projects beneath East London in the last 20 years including the Jubilee Line Extension and Channel Tunnel Rail Link. Following these and other projects, the amount of settlement and its impact on surface buildings is now better understood and accurate predictions can be made. Initial calculations made by Thames Water indicate that the impact of tunnelling between KEMP and Heckford will not be significant, and the impact of the main Tideway Tunnel on buildings within the Borough is likely to be minor.

6.3 Traffic & transport

Vehicle Trip Numbers

The Heckford Option would increase the number of vehicle trips to the area overall as they would not be able to access the site directly from the River Thames meaning that water-borne transport would not be a feasible/viable alternative.

It should be noted however, that if Thames Water are for some reason unable to use river transport during the construction of the KEMP Foreshore Option, the traffic movements needed to construct the coffer dam will lead to a significantly higher number of traffic movements during this period compared to the Heckford Option. The use of river transport throughout the entire construction period for the KEMP Foreshore Option, is likely to be ultimately decided upon by the appointed contractor and therefore is in no way assured.

However this being spread between two sites may reduce the impact on the Glamis Road / Highway junction which has a poor safety record. It is difficult to reach a more definitive conclusion without details of HGV movement numbers.

Nigel Legge Associates Ltd Page 13 of 27

London Borough of Tower Hamlets London Borough of Tower Hamlets Thames Tideway Tunnel

Effects on Glamis Road

The KEMP Foreshore Option would have a greater impact on Glamis Road. It is likely to require the suspension/relocation of the bus stops in Glamis Road to allow access for construction traffic. These stops are currently served by the D3 and the temporary loss/relocation of these stops would have a detrimental impact upon local residents who use these stops and those who use the stops in order to travel to the park.

It is also likely that the existing coach and permit parking bays on the west side of Glamis Road would need to be suspended while the construction works are taking place in order to allow access for construction vehicles. This again would have a detrimental impact on those who currently use these bays, although this may not be a valid concern as Glamis Road does not currently experience high levels of parking occupancy/stress (the Borough wide parking stress surveys show that Glamis Road experiences a 20% occupancy during the day and a 50% occupancy overnight).

There are no height or weight restrictions along this section of Glamis Road which would prevent or prohibit construction traffic using it as part of their route to the site.

Effects on the Highway

The Heckford Option would allow the possibility of HGV's entering and exiting the site in a forward direction by using left in / out onto The Highway which would be less disruptive to traffic on the TfL Road Network (TLRN) than the increased use of the Glamis Road signals, which would increase delays to TLRN traffic (accepting there would still be some level of increased use of these signals with the Heckford Option too).

The Heckford Option also seems to have less impact on the Rotherhithe Tunnel air shaft and the current access to it which would presumably be preferable for TfL in terms of regular maintenance and emergency access arrangements.

6.4 Environmental Impact During Construction

Local Air Quality

The Heckford Option will see a larger number of sensitive receptors likely to be impacted, as well as potentially greater local air quality impacts (i.e. worse air quality and dust impacts at the facades of the receptors) than the KEMP Foreshore Option due to the proximity of sensitive receptors.

The KEMP Foreshore Option would involve works at a greater distance from sensitive receptors; and potentially affecting a lesser number of sensitive receptors. These works would occur for similar period of time (3.5 - 4 years).

It should be noted, however, that emissions from construction traffic are likely to have less of an impact through the Heckford Option due to high background levels on the Highway.

Noise and Vibration

The Heckford Option will see a larger number of sensitive receptors likely to impacted, as well as potentially greater noise / vibration impacts (i.e. louder at the facades of the

Nigel Legge Associates Ltd Page 14 of 27

London Borough of Tower Hamlets London Borough of Tower Hamlets Thames Tideway Tunnel

receptors) than the KEMP Foreshore Option due to the proximity of sensitive receptors to the construction sites.

The KEMP Foreshore Option would involve works at a greater distance from sensitive receptors; and potentially affecting a lesser number of sensitive receptors. These works would occur for similar period of time (4 years).

It should be noted, however, that noise from construction traffic is likely to have less of an impact through the Heckford Option due to high background levels on the Highway.

Archaeology

The construction site within KEMP for the Heckford Option will lie within an Area of Archaeological Importance or Potential (AAIP), along with the southern part of the main construction site within the Heckford Business Park. This is a local designation.

Whilst the KEMP Foreshore Option does not lie within this AAIP, the Thames foreshore is well known for its potential for archaeological finds.

It is considered that both options will have a similar direct impact upon any potential unknown archaeology assets.

Additionally, it is considered that the KEMP foreshore option may have an impact upon buried archaeology elsewhere in the Thames foreshore if the proposed land extension alters the current and flow characteristics of this part of the river in anyway (due to changes in scour patterns).

Land Contamination

The Heckford Business Park is a possible High Risk site in terms of land contamination and receptors are close in the event that contaminated soil becomes airborne.

The KEMP Foreshore site is also a possible High Risk site in terms of land contamination but the potential receptors are further away.

In both options, effective mitigation measures should be employed to minimise this risk (as is standard practice in such worksites).

Ecology

KEMP has recently been proposed as a Site of Borough Grade II Importance for Nature Conservation (SINC), primarily because of its range of habitats, including wildflower meadows, small area of developing woodland which has been underplanted with native woodland wild flowers, pond with good population of frogs and the number of mature trees.

In terms of direct impacts upon ecology, the Heckford Option involves a construction site that will occupy an area of the park which is of limited biodiversity value and is also a smaller site area occupied for less time.

The main Heckford site is composed of buildings and hard standing and is of very limited biodiversity value.

The construction site for the KEMP Foreshore Option occupies an area of KEMP (proposed as a SINC), but also occupies a large area of the Thames foreshore which is

Nigel Legge Associates Ltd Page 15 of 27

London Borough of Tower Hamlets London Borough of Tower Hamlets Thames Tideway Tunnel

designated as a Site of Metropolitan Importance for Nature Conservation, i.e. of higher biodiversity value than KEMP itself. The construction site will also be in operation for a longer period of time than the site in KEMP for the Heckford Option.

It is therefore likely that the Heckford Option will have less impact upon biodiversity than the KEMP Foreshore Option.

It should be acknowledged that due to the likely nature of the construction for each option (periods of elevated noise and vibration), impacts upon any biodiversity in the wider KEMP area can be expected. This period of disturbance would be less for the Heckford Option due to the shorter construction period within the park.

Townscape and Visual Impact

Details of construction plant to be used at each site are not known at this stage, however, it is likely that all sites will need a number of structures which may be visually intrusive including stacked cabins and cranes.

For the purpose of this high level assessment, it is assumed that all sites will involve a similar scale of construction plant.

The Heckford Option will involve a smaller site within the park nearer the memorial. Being in the central area of the park, it will affect the townscape setting of the park for park users (see comments on Open Space), and short range views within the park itself.

The main construction site within the Heckford Business Park will be situated within an area of low current townscape value and is unlikely to significantly impact the local townscape. Local views in the vicinity may be affected as the current existing buildings are low-rise, however, given the height of some of the surrounding residential and hotel blocks, any impacts are likely to be slight.

The construction site for the KEMP Foreshore Option, will also impact upon the setting of the park as the Council sees the affected area of park as one of the most important parts to its users. Views from park users out to the river (a view which appears to be particularly important for the local community) will be significantly compromised for a greater period time.

Mid-range views of users will also be significantly affected (one of the main user groups of the park). Views from those residential properties to the north east of the proposed foreshore site will also be significantly affected during the construction period.

On balance, officers consider that the Heckford Option is likely to have less impact upon townscape and local/mid range views than the KEMP Foreshore Option (and for a shorter period).

Accepting the statement above, it should be noted that townscape and visual impacts of both options (construction related only, see section 6.6 for legacy impacts) are likely to be considered slight within the Thames Tunnel EIA as the impacts are temporary and no national, regional or local townscape or view designations are affected.

Nigel Legge Associates Ltd Page 16 of 27

London Borough of Tower Hamlets London Borough of Tower Hamlets Thames Tideway Tunnel

Socio-Economic Impacts

The primary socio-economic impacts associated with this type of infrastructure project are likely to relate to employment, affordable housing provision and impact upon public open space.

In terms of employment effects, the Heckford Option will lead to the displacement of businesses in the Heckford and Highway Business Parks. These businesses would need to be given assistance to relocate and actual job losses may be minimal.

Upon completion of the Thames Tunnel project, the same or more commercial / industrial floor space will need to be reprovided. So the employment impact would be temporary (approx 4 years). It is also a possibility (given a number of recent pre- application meetings) that some amount of housing might be developed on the site once the Thames Tunnel project was completed, as part of a mixed use development. This would be a beneficial effect in terms of affordable housing provision (assuming the redevelopment was of a certain size).

The KEMP Foreshore Option is unlikely to lead to any loss of employment, temporary or permanent. This option, however, does not provide any potential for increasing commercial / industrial floorspace, or providing new affordable housing.

Both options may provide some temporary local employment in construction and this should pursued by the Council in any consultation with Thames Water.

The Heckford Option will have a slight temporary adverse impact on local employment during the construction period, however, upon project completion it offers the potential for enhancement of the local industrial / commercial employment offer as well as some level of affordable housing provision if a mixed use development is bought forward.

It should be noted that any redevelopment of the site will be subject to the plans and intentions of the land owner at that time.

Parks are provided free at the point of entry and fulfil a much needed role in a borough where 83% of residents have no access to a private garden.

With high levels of child poverty and overcrowding the value of high quality open space cannot be overestimated.

In terms of impacts upon open space during the construction, the KEMP Foreshore Option will have a major negative impact on the park for up to 4 years whilst the alternative Heckford Option has a lesser impact on the park and only for 1.5 - 2 years.

6.5 Air Quality Management Post Construction

The Main Tideway tunnel and CSO interception system will be ventilated during operation through column structures up to 6m high. For the Foreshore Option these will all be four of these structures, and with the Heckford Option there will be two at the Heckford site and three in KEMP.

Nigel Legge Associates Ltd Page 17 of 27

London Borough of Tower Hamlets London Borough of Tower Hamlets Thames Tideway Tunnel

For the majority of the time there will be no exit of air through these columns when the system is not in operation. When the system is in operation but only partially full, air will actually be drawn in through the external ventilation structures not released.

It is only when the tunnel fills more completely during major storm events effecting large areas of London, a relatively rare occurrence, will foul air be forced out of the main tunnel through the ventilation columns. Thames Water estimates this will occur on average for 34 days a year.

Given the above information and the results of modelling tests, Thames Water consider that it is unlikely that odour will be a significant issue for either option.

Accepting this, if emissions were however to occur, the Heckford Option would have increased risk of odour nuisance to nearby receptors due to its more urban location – this could be ameliorated by the siting of the ventilation structures. The position of the KEMP Foreshore Option ventilation columns close to the River would be expected to better facilitate dispersion of any odorous emissions, although it is noted there is a residential development within relatively close proximity to the proposed site.

6.6 Legacy Issues

Both options will require residual structures to be left at the separate worksites. These structures and the reconfiguration of the affected areas of park will have an impact upon the use of the open space by the public as well as potential townscape and visual impacts, and odour impacts.

Legacy impacts upon Open Space (KEMP)

Sections 3.5 and 4.5 describe the legacy structures to be left for each option. The Heckford Option will involve some ventilation shafts and an equipment kiosk situated near the memorial. The ‘hardstanding’ area needed for maintenance around these vents and access points can be overlain by reinforced grass, or normal grass can be used and boarding can be place over it when maintenance is needed.

Further structures will be needed within the Heckford Business Park site, which may restrict the layout of future buildings on the site, however, these could conceivably be located within a car parking area (which would consequently provide the required hard standing).

The KEMP Foreshore Option will require a permanent land extension into the Thames foreshore, and the ventilations shafts and kiosk would be located within it. This option would extend the area of the park, although the actual extension would be mostly hard standing with benches etc (i.e. limited planting).

Officers are unable to comment further in terms of the impact of each option on the value of KEMP as a public open space upon completion of the scheme, as it has been Council’s position not to discuss with Thames Water, the potential for enhancements to the park achievable through the KEMP Foreshore Option.

Nigel Legge Associates Ltd Page 18 of 27

London Borough of Tower Hamlets London Borough of Tower Hamlets Thames Tideway Tunnel

It should be noted that Thames Water have indicated a willingness to allow the Council to influence the legacy left by the KEMP Foreshore Option through consultation.

Legacy impacts upon Townscape and Visual Impact

The park should be reinstated largely as it was before with the Heckford Option. A number of vents would be present, whilst the kiosk might be set back into the embankment wall at the back of the park. It is considered that this option, in legacy, is likely to lead to only limited impact upon townscape and local views within the park.

The legacy structures within the Heckford Business Park site should not have a significant impact upon townscape in the area (with the context being a business park). Any future redevelopment of the site will need to take these structures into account. The scale of structures will not have a significant impact upon views given the medium to high rise context of the area around the business park.

The land extension that would be required for the KEMP Foreshore Option legacy would be very visible from both the park and the residential developments to the north east of the site. The legacy would change the shape of the park and the Thames Path. Whilst it is accepted that there would be no level change with the park, the vent and kiosk structures may be more visible on the land extension than they would be with the Heckford Option.

The overall impacts upon townscape and views of the two options in legacy is unsure, however, it is clear that the legacy of the KEMP Foreshore Option is likely to be more visible than the Heckford Option and will also change the shape and possibly character of the park.

6.7 Other Planning Considerations

Industrial Locations

Core Strategy Policy SPO6 identifies the Highways Business Park as one of the Borough's 'Local Industrial Locations'. Together with 'Strategic Industrial Locations' these areas have been designated to safeguard and intensify industrial land. This needs to be considered within a wider context where a significant amount of industrial land across the Borough as a whole is being released for residential led development.

Unlike Strategic Industrial Locations, the Core Strategy identifies the potential for mixed use intensification of Local Industrial Locations, but only where: there is no overall net loss of employment floorspace; there is no detrimental impact on the quality and usability of that floorspace; and where access arrangements and environmental impacts have been properly addressed.

The Sites & Place Making DPD defines the boundaries of each of the Local Industrial Locations. The Heckford Business Park forms the central part of the Highway Business

Nigel Legge Associates Ltd Page 19 of 27

London Borough of Tower Hamlets London Borough of Tower Hamlets Thames Tideway Tunnel

Park Local Industrial Location with the boundary extending to the sites immediately to the east and west.

Demolition of the Heckford Business Park and its use for a works site to facilitate the Thames Tunnel would be contrary to LDF Policy if it resulted in an overall loss of employment floorspace within the wider Highway Business Park Local Industrial Location.

It is acknowledged that the works would be for a fixed period of time and the vast majority of the site would not need to be retained by Thames Water beyond this. Nevertheless, if on balance the Council determined that the works could be permitted on the site to facilitate the safeguarding of public open space at King Edward Memorial Park, it is considered that adopted and emerging LDF Policy would require as a minimum:

1. the re-location of existing businesses to an appropriate and accessible location, preferably within the Borough;

2. demonstration that access to, and operation of, the remaining industrial units would not compromised during the works period;

3. a commitment to ensure that the industrial floorspace lost from the Highways Business Park Local Industrial Location is re-provided following completion of the works to safeguard and strengthen its long term operation as a Local Industrial Location.

Public Open Space

Policy SP04 (subsection 1) within the Council’s Core Strategy 2025 (adopted September, 2010) states the need to protect and safeguard all existing open space such that there is no net loss.

This policy supports the Heckford Option in so far as it will involve less area of park for a shorter period than the KEMP Foreshore Option.

It should be noted that the net loss of open space may be minimal with both options, and indeed the KEMP Foreshore Option may even increase the area of open space slightly.

Affordable Housing

There have been a number of pre-application discussions with the current owners of both the Highway Business Park and Heckford Business Park. The potential for redevelopment of the site with a mixed use development has been explored (reproviding all employment uses).

The Heckford Option therefore may facilitate this redevelopment and the potential for some level of affordable housing provision.

Nigel Legge Associates Ltd Page 20 of 27

London Borough of Tower Hamlets London Borough of Tower Hamlets Thames Tideway Tunnel

In terms of the potential to redevelop the Heckford Business Park site as a mixed use development, the emerging policy direction is stated within the Development Management DPD Engagement Document, Policy 18 (May, 2011).

This direction being that there should be no net loss of industrial employment floorspace and that any residential use within the scheme should not compromise the integrity of the industrial designation.

Nigel Legge Associates Ltd Page 21 of 27

London Borough of Tower Hamlets London Borough of Tower Hamlets Thames Tideway Tunnel

7.0 CONCLUSIONS

Assessment of various options for the construction of the Thames Tideway Tunnel project in the London Borough of Tower Hamlets has involved extensive discussions and meetings with Thames water, as well as the involvement of technical experts from Imperial College in London.

Due to the urban density and lack of open spaces in Tower Hamlets, the only feasible location to intercept the NESR is within KEMP. Thames Water’s Foreshore Option combines interception of the NESR and construction of a shaft to the main tunnel level, requiring 3.5 – 4 years construction time and a likely minimum site area of 7,500 m2. This will have a significant impact on the park as an amenity during this time. Following construction landscaping improvements will be made to the park and a permanent ~2,000 m2 area will remain on the foreshore.

An alternative option supported by local community groups proposes a smaller site within KEMP to intercept the NESR, required for 1.5 – 2 years, connected by a tunnel to the main shaft located in what is currently the Heckford business park. This option will involve less impact on the park during construction and for a shorter period, and no permanent additional legacy area. The impact of losing a significant part of the business park during the 3.5 – 4 year construction phase will need to be assessed by LBTH’s planning officers and Members in consultation with those affected. Following construction however the business park may be redeveloped for mixed commercial and residential use.

Permanent ventilation structures will be required for both options – for the Heckford Option these will be in KEMP as well as within the business park site. The impact of these on air quality in the local environment is predicted to be minimal as they will only exhaust air from the tunnel system during major storm events affecting large areas.

For the Heckford Option, settlement due to tunnelling between the park and the business site may have an impact on buildings. Based on an initial assessment it is concluded that this impact should not be significant, and that the impact of the main Tideway Tunnel on buildings within the Borough overall is likely to be minor.

During construction the Heckford Option will generate more air quality and noise / vibration than the Foreshore Option. These impacts could be minimised through effective mitigation measures. The Heckford Option would, however, result in less impact on biodiversity, and have less visual and overall impact in KEMP as a valuable local amenity resource.

It should be noted that depending on the amount of river transport used during the construction of the Foreshore Option, local traffic impacts would be less than through the Heckford Option. The proportion materials transport by river is not yet known, and its use is not guaranteed by Thames Water.

From an environmental and socio-economic effects perspective, it is concluded that both options will have a number of different adverse impacts, although after mitigation, none are likely to be significant enough to rule out either option.

Nigel Legge Associates Ltd Page 22 of 27

London Borough of Tower Hamlets London Borough of Tower Hamlets Thames Tideway Tunnel

From an engineering perspective it is concluded that both options are technically feasible, and according to Thames Water estimates the cost of both is similar. Due to the reduced construction requirements of the Heckford Option in KEMP, this will have less overall impact on the park both in terms of construction area and time compared with the Foreshore Option.

Nigel Legge Associates Ltd Page 23 of 27

London Borough of Tower Hamlets Thames Tideway Tunnel

Figure 2 NESR Location & SaveKEMP Option 1 Proposed Sites

Key: Foreshore Option

Heckford Option

Alternative sites considered

Page 24 of 27

London Borough of Tower Hamlets Thames Tideway Tunnel

Figure 3 Heckford Option 1A

Option to split the worksite in KEMP

Page 25 of 27

London Borough of Tower Hamlets Thames Tideway Tunnel

Figure 4 Alternative Proposal for a Connection Tunnel to Southwark

Option to connect the NESR to Kings Stairs Gardens

Page 26 of 27

London Borough of Tower Hamlets Thames Tideway Tunnel

Figure 5 Thames Water Shaft Site Options in Zone 7 - LBTH

Page 27 of 27