application reference number: wwo10001 environmental … · 2016-05-05 · victoria embankment...

Environmental Statement Update Report Appendices - March 2014Victoria Embankment Foreshore Vessel Relocation

Doc Ref: APP208.01.22

Folder 261 11 March 2014DCO-DT-APP-ZZ200-080122

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Thames Tideway Tunnel Thames Water Utilities Limited

Application for Development ConsentApplication Reference Number: WWO10001

October 2013DDR5163-RT002-R02-00

Thames Tideway Tunnel Victoria Embankment Foreshore vessel relocation #100-RG-MDL-WALLI-0047_AB

Thames Tideway Tunnel

Victoria Embankment Foreshore vessel relocation #100-RG-MDL-WALLI-0047_AB

DDR5163-RT002-R02-00

Document information Document permissions Confidential - client

Project number DDR5163

Project name Thames Tideway Tunnel

Report title Victoria Embankment Foreshore vessel relocation #100-RG-MDL-WALLI-0047_AB

Report number RT002

Release number R02-00

Report date October 2013

Client Thames Tideway Tunnel Delivery Team

Client representative David Wilkins

Project manager J V Baugh

Project director T J Chesher

Document authorisation

Prepared Approved Authorised

© HR Wallingford Ltd

This report has been prepared for HR Wallingford’s client and not for any other person. Only our client should rely upon the contents of this report and any methods or results which are contained within it and then only for the purposes for which the report was originally prepared. We accept no liability for any loss or damage suffered by any person who has relied on the contents of this report, other than our client.

This report may contain material or information obtained from other people. We accept no liability for any loss or damage suffered by any person, including our client, as a result of any error or inaccuracy in third party material or information which is included within this report.

To the extent that this report contains information or material which is the output of general research it should not be relied upon by any person, including our client, for a specific purpose. If you are not HR Wallingford’s client and you wish to use the information or material in this report for a specific purpose, you should contact us for advice.

Document history Date Release Prepared Approved Authorised Notes

09 Oct 2013 02-00 JVB MAL TJC

10 Sep 2013 01-00 JVB MAL TJC



DDR5163-RT002-R02-00

Executive Summary The preferred route of the proposed Thames Tideway Tunnel, between Acton Storm Tanks and Abbey Mills pumping station, has a schedule of temporary and permanent works within the corridor of the River Thames. Some of these works are located within the river and therefore may influence the hydrodynamic and sedimentary regime in the area.

The designs for the sites at Victoria Embankment Foreshore submitted as part of the application for development consent for the project have been reviewed further to include more detailed design work, which has been undertaken as part of the design process. The application for development consent will be amended to reflect the design changes.

The amendments at Victoria Embankment Foreshore will involve change to the temporary and permanent relocation of the pub/restaurant vessel Tattershall Castle; the implications of the alterations for the hydrodynamic and sedimentary regimes in the area therefore require assessment.

The previous predictions of hydrodynamic effects and scour associated with the works are generally considered insensitive to the proposed change in the position of the Tattershall Castle vessel. The dredged areas may, however, slightly offset (reduce) the speed increases mid channel and may further reduce currents along the foreshore between the Tattershall Castle and the main works. There is potential for some fine sediment (silts and clays with D50 < 63 µm) accumulation in the proposed dredged areas.

The arrangement of a dredged area with sheet piling on its shore side is designed to hold the foreshore level and is atypical for the tidal Thames although this arrangement is in place at the existing Blackfriars Millennium Pier. Historical bathymetric analysis has shown that the bed level in the area can vary and so there is potential for the sheet piles to become proud of the bed level. However this risk is small and in removing the need for dredged slopes to be established and so maintaining foreshore levels this methodology is considered appropriate at this site.

Some sediment release during dredging will occur. It is anticipated that employing the usual best practice for dredging in the tidal Thames will reduce the rate of sediment release to a level that is extremely small compared to the natural sediment flux.



DDR5163-RT002-R02-00

Contents

Executive Summary

1. Introduction _________________________________________________________ 1 1.1. Background ....................................................................................................................................... 1 1.2. Comments from stakeholders ........................................................................................................... 1 1.3. Structure of this report ....................................................................................................................... 1

2. Predicted effects of works ______________________________________________ 2 2.1. Fluvial modelling ................................................................................................................................ 3

2.1.1. Temporary works ................................................................................................................. 3 2.1.2. Permanent works ................................................................................................................. 4

2.2. Scour ................................................................................................................................................. 6

3. Proposed amendments to the works ______________________________________ 6 3.1. Temporary works ............................................................................................................................... 8 3.2. Permanent works .............................................................................................................................. 9

4. Conclusions _________________________________________________________ 9

Figures Figure 2.1: Works as modelled ................................................................................................................... 2 Figure 2.2: Temporary works in the application for development consent ................................................. 2 Figure 2.3: Predicted effect of temporary works on peak ebb tide currents ............................................... 4 Figure 2.4: Predicted effect of temporary works on peak flood tide currents ............................................. 4 Figure 2.5: Predicted effect of permanent works on peak ebb tide currents .............................................. 5 Figure 2.6: Predicted effect of permanent works on peak flood tide currents ............................................ 5 Figure 3.1: Proposed amended relocation of Tattershall Castle for temporary works ............................... 7 Figure 3.2: Proposed amended relocation of Tattershall Castle for permanent works .............................. 8



DDR5163-RT002-R02-00 1

1. Introduction The preferred route of the proposed Thames Tideway Tunnel, between Acton Storm Tanks and Abbey Mills pumping station, has a schedule of temporary and permanent works within the corridor of the River Thames. Some of these works are located within the river and therefore may influence the hydrodynamic and sedimentary regime in the area.

1.1. Background The designs for the sites at Victoria Embankment Foreshore submitted as part of the application for development consent for the project have been reviewed further to include more detailed design work, which has been undertaken as part of the design process. The application for development consent will be amended to reflect the design changes.

The amendments at Victoria Embankment Foreshore will involve change to the temporary and permanent relocation of the pub/restaurant vessel Tattershall Castle and the implications of the alterations for the hydrodynamic and sedimentary regimes in the area therefore require assessment.

1.2. Comments from stakeholders Comments on the proposed relocation of the Tattershall Castle have been received from the Port of London Authority, from the Environment Agency and from the City of Westminster. In regards to hydrodynamic and sedimentary aspects of the relocation the comments can be summarised as:

Effects of the proposed dredging – any impacts on the river wall, Hungerford Bridge;

Effects of the vessel being closer to the navigation channel;

Accretion in the dredged areas;

Exposure of the proposed sheet piling to the rear of the dredged area;

Sediment release during dredging and backfilling.

1.3. Structure of this report This report is made up of three further sections. Section 2 summarises the fluvial modelling and scour predictions for the Temporary and Permanent works proposed at Victoria Embankment Foreshore. The suggested changes to the proposed works are described in Section 3 which then describes the implications of the predicted changes arising from the modifications on the hydrodynamics and scour at the site. Conclusions are provided in Section 4.



DDR5163-RT002-R02-00 2

2. Predicted effects of works Fluvial modelling and scour assessments have been performed for the proposed works as provided in drawing 100-DA-CNS-PWR3X-263010_AA (Figure 2.1). There are some differences between this layout and that shown in the application for development consent (Figure 2.2). Within the application for development consent it is indicated that the final layout of the works would be subject to further modelling to confirm that predicted effects will be broadly consistent for the layout shown in the application for development consent. It should be noted for the present assessment that no dredging has been included in the works layouts modelled previously (either temporary or permanent) as the need to dredge was not defined at that stage in the development of the project.

Figure 2.1: Works as modelled Figure 2.2: Temporary works in the application for development consent

Source: TTT 100-DA-CNS-PWR3X-263010_AA Source: TTT Environmental Statement Vol. 17 Figures

The revised arrangement is primarily a difference in the location of the Tattershall Castle vessel. In the application for development consent the channel side of the vessel was broadly in line with the edge of the temporary works cofferdam whereas in the layout modelled the vessel was slightly further towards the authorised channel. Furthermore the vessel was located slightly further south, away from the temporary works in the application for development consent compared to the case modelled.



DDR5163-RT002-R02-00 3

2.1. Fluvial modelling

2.1.1. Temporary works

The effects of the temporary works, including relocating the Tattershall Castle, on typical spring tide currents is shown for times of peak ebb and flood tide currents in Figure 2.3 and Figure 2.4, respectively. The upper frame of these figures shows the baseline conditions for current magnitude and the centre frame shows the current magnitude with the permanent works in place. The lower frame shows the difference in currents associated with the works with green to blue colours indicating speed reduction and yellow to red colours indicating speed increase.

As well as these figures assessment was made of the detailed currents and potential for accretion near the moored vessels – the Tattershall Castle and RS Hispaniola. The blockage associated with the vessels’ hulls was included in the modelling by local adjustment of the available water depth.

The predicted effects relevant to the present assessment were:

The works will reduce the flow cross-section by up to 13%;

A deflection of flow towards mid channel is predicted;

An increase in the predicted effects of the works in deflecting flood tide flow towards mid-channel is provided by the location of the due to the flood tide flow being directed towards the structure by the piers of Hungerford Bridge;

The predicted flow speeds along the north bank between Westminster and Hungerford Bridges with the works in place are predicted to be low enough to allow deposition of clays, silts and fine sands;

Current speed increases of the order of 0.1 m/s are generally predicted (8-10% increase). These cover the channel width adjacent to the works and within the spans of Hungerford Bridge;

Current speed increases of up to more than 0.4 m/s are predicted near the works (40-50% increase). These may result in some movement of the bed sediments in the area, (the resultant potential for scour is summarised in Section 2.2);

Noticeable changes to current direction are only predicted in the immediate vicinity of the temporary works;

Some cross flows are predicted at the site of the relocated Tattershall Castle. These should be considered during the mooring design;

Limited accretion is predicted in the vicinity of the moored vessels Hispaniola and Tattershall Castle: a significant build-up of sediment is not expected under the vessels.

The studies concluded that the overall effect of the works will be dominated by the effect of the flow blockage provided by the temporary works cofferdam; any effect associated with relocating the Tattershall Castle will be comparatively small.



DDR5163-RT002-R02-00 4

Figure 2.3: Predicted effect of temporary works on peak ebb tide currents

Figure 2.4: Predicted effect of temporary works on peak flood tide currents

2.1.2. Permanent works

Figure 2.5 and Figure 2.6 show the predicted effect of the permanent works on currents at times of peak ebb and flood tides. As for Figures 2.3 and 2.4 the upper frame of these figures shows the baseline conditions for current magnitude and the centre frame shows the current magnitude with the permanent works in place. The lower frame shows the difference in currents associated with the works with green to blue colours indicating speed reduction and yellow to red colours indicating speed increase.



DDR5163-RT002-R02-00 5

Figure 2.5: Predicted effect of permanent works on peak ebb tide currents

Figure 2.6: Predicted effect of permanent works on peak flood tide currents

The effects of the permanent works were also largely a factor of the final reclamation shape. No noticeable effect of the relocated Tattershall Castle was indicated. The predicted effects were summarised as:

The permanent works will reduce the flow cross-section by up to 8%;

Current decreases of 0.5 m/s to 0.75 m/s are predicted along the north bank between Westminster and Hungerford Bridges. These are sufficient to allow deposition of clays, silts and fine sands;

Current increases of more than 0.2 m/s are predicted adjacent to the end of the works;

Changes to current direction are only predicted in the immediate vicinity of the works;

Some potential for changes to the bed sediment distribution is predicted mid-channel adjacent to the works, for example, finer sediments may be removed from the mixed sediments found though without moving the coarser gravels bed lowering is not anticipated (the implications for scour are described in Section 2.2);

No accretion under the moored vessels is predicted;

Monitoring of the nearby areas (second bullet point above) that are predicted to be subject to accretion in the early stages of the permanent works is advised.



DDR5163-RT002-R02-00 6

2.2. Scour The scour predictions around the completed temporary works site gave a maximum scour depth of 0.3 m. This would place scour depth at this site in the lower range compared to scour predicted at the other sites of temporary and permanent works associated with the Thames Tideway Tunnel. Contraction scour – the average deepening of the channel cross-section in response to a blockage was calculated as less than 0.1 m. This magnitude was considered to be negligible in the context of natural bed variation at the site.

3. Proposed amendments to the works The proposed amended temporary and permanent relocations of the Tattershall Castle are shown in Figure 3.1. The associated areas of dredging proposed to allow mooring at these locations are shown in Figure 3.2.

The proposed changes to the temporary and permanent works compared to those presented in the application for development consent include:

Dredging the river bed to accommodate the vessels draught – approximately 750 m3 for the temporary position and 4,000 m3 for the permanent re-location of the vessel;

Installation of sheet piling between the dredged areas and the river wall as a means of reducing sediment loss from the foreshore fronting the river wall;

Installation of anchors for mooring lines for the temporary location;

The temporary position of the vessel 8 m further into the river channel.



DDR5163-RT002-R02-00 7

Figure 3.1: Proposed amended relocation of Tattershall Castle for temporary works

Source: TTT Drawing DCO-PP-16X-VCTEF-180028_Rev1



DDR5163-RT002-R02-00 8

Figure 3.2: Proposed amended relocation of Tattershall Castle for permanent works Source: TTT Drawing DCO-PP-VCTEF-180031_Rev1

3.1. Temporary works The amended location of the vessel during the temporary works, including its location being 8 m further from the bank-line, is closer to that modelled than that shown in the application for development consent therefore the effects of the presence of the vessel on tidal flows are likely to be very similar to that predicted by the modelling. The effects are negligible in comparison to the effects of the flow blockage associated with the temporary works cofferdam.

The inclusion of a small area of dredging bounded on the river wall side by a sheet pile wall will be expected to further reduce tidal currents. As the dredge site is in an area of low flow speed it is unlikely that the expected increases to the flow speed in mid-channel will be significantly modified by the increase in cross section associated with the dredging. Tidal currents in the dredged area are likely to be slightly reduced due to the increased water depth and there will be potential for fine silts and sands to accumulate. It is recommended that this area be included in any proposed monitoring programme and that a strategy for removal of unwanted sediment be considered.

As was the case for tor the modelled location of the vessel there is evidence of cross flows at the mooring site during the ebb tide. This should be taken into account when designing mooring arrangements etc.



DDR5163-RT002-R02-00 9

With the effect of the vessel relocation being shown to be marginal in comparison to the presence of the cofferdam, any change in the predicted scour will be similarly marginal.

The arrangement of a dredged area with sheet piling on its shore side is designed to hold the foreshore level and is atypical for the tidal Thames. Historical bathymetric analysis has shown that the bed level in the area can vary by up to a 1.0 m and so there is potential for the sheet piles to become proud of the bed level. However this risk is small and in removing the need for dredged slopes to be established and so maintaining foreshore levels this methodology is considered appropriate at this site.

During the dredge some sediment release during dredging will occur. The detail of the dredging activity will be subject to the plant used by the contractor and will require discussion with the Port of London Authority (PLA). Dredging licences from the PLA and the Marine Management Organisation (MMO) will be required. However, for the present assessment it is anticipated that using the present best practice for dredging in the tidal Thames will reduce the rate of sediment release to a level that is extremely small compared to the natural sediment flux.

3.2. Permanent works The amended layout for the permanent works will place the Tattershall Castle nearer the permanent reclamation than was modelled. A dredged area bounded by sheet piling along its river side boundary is proposed to achieve adequate water depth for the vessel without causing slumping / erosion of the foreshore adjacent to the river wall. The predicted effects of the permanent works on tidal currents are, in general, less that those predicted for the temporary works associated with the reduced blockage to flow in the permanent works case compared to the temporary works. The increase in cross-sectional area due to the dredge is likely to reduce the predicted speed increase during the flood tide.

The dredged area is larger than that for the temporary works with the expectation of it being deeper in relation to ambient bed levels. The dredged area is close to the permanent reclamation site and therefore low currents are anticipated in the deepened area with a potential to accumulate fine silts and sands – though this effect will typically be reduced by the presence of the vessel due to local current acceleration and small scale turbulence generation at the vessel hull.

With the vessel closer to the permanent reclamation than was originally modelled there is a possibility of cross flows occurring at the mooring site during the ebb tide. This should be taken into account when designing mooring arrangements etc. As for the temporary case the proposed arrangement of a dredged area with sheet piling on its river side boundary is atypical for the tidal Thames. There is a potential that the foreshore to the rear of the piling may lower as has occurred in the past and that the sheet piles may become proud of the bed level. However this risk is small and in removing the need for dredged slopes to be established and so maintaining foreshore levels this methodology is considered appropriate at this site.

As there will not be any significant flow regime change there is no mechanism for the scour predictions at the reclamation or in the river cross-section to be altered by the proposed amendment to the works.

4. Conclusions The designs for the sites at Victoria Embankment Foreshore submitted as part of the application for development consent for the project have been reviewed further to include more detailed design work, which has been undertaken as part of the design process. The application for development consent will be amended to reflect the design changes.



DDR5163-RT002-R02-00 10

The amendments at Victoria Embankment Foreshore will involve change to the temporary and permanent relocations of the pub/restaurant vessel Tattershall Castle. The implications of the amendments for the hydrodynamic and sedimentary regime in the area have been assessed.

The conclusion of the study is that the existing predictions of hydrodynamic effects and scour associated with the works are considered broadly insensitive to the proposed change in the position of the Tattershall Castle.

The proposed dredged areas may slightly reduce the predicted flow speed increases mid channel.

Some further reduction in currents along the foreshore between the Tattershall Castle and the main works is anticipated. There is potential for fine silts and sand accumulation in the proposed dredged areas.

The arrangement of a dredged area with sheet piling to its rear, designed to prevent slumping of the foreshore adjacent to the river wall, is atypical for the tidal Thames although a similar arrangement is in place at the existing Blackfriars Millennium Pier. Historical bathymetric analysis has shown that the bed level in the area may vary and so there will be a potential risk for the sheet piles to become proud of the bed level from time to time.

It is recommended that the areas of potential bed change (accretion and erosion) be included in the bed level monitoring plan for the project.

During the dredge some release of sediments will occur. The detail of the dredging activity will be subject to the plant used by the contractor and will require discussion with the Port of London Authority (PLA). Dredging licences from the PLA and the Marine Management Organisation (MMO) will be required. It is anticipated that employing the usual best practice for dredging in the tidal Thames will reduce the rate of sediment release to a level that is extremely small compared to the natural sediment flux.

Certificate No. EMS 558310

Certificate No. FS 516431

© HR Wallingford

HR Wallingford, Howbery Park, Wallingford, Oxfordshire OX10 8BA, United Kingdomtel +44 (0)1491 835381 fax +44 (0)1491 832233 email [email protected]

HR Wallingford is an independent engineering and environmental hydraulics organisation. We deliver practical solutions to the complex water-related challenges faced by our international clients. A dynamic research programme underpins all that we do and keeps us at the leading edge. Our unique mix of know-how, assets and facilities includes state of the art physical modelling laboratories, a full range of numerical modelling tools and, above all, enthusiastic people with world-renowned skills and expertise.

Copyright notice

All rights reserved. Any plans, drawings, designs and materials (materials) submitted by Thames Water Utilities Limited (Thames Water) as part of this application for Development Consent to the Planning Inspectorate are protected by copyright. You may only use this material (including making copies of it) in order to (a) inspect those plans, drawings, designs and materials at a more convenient time or place; or (b) to facilitate the exercise of a right to participate in the pre-examination or examination stages of the application which is available under the Planning Act 2008 and related regulations. Use for any other purpose is prohibited and further copies must not be made without the prior written consent of Thames Water. Thames Water Utilities LimitedClearwater Court, Vastern Road, Reading RG1 8DB The Thames Water logo and Thames Tideway Tunnel logo are © Thames Water Utilities Limited. All rights reserved.

Copyright © Thames Water Utilities Limited March 2014.

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