Flood Risk Assessment

Crossrail Line 1 Mott MacDonald Assessment of Water Impacts Technical Report Cross London Rail Links Limited

Appendix H: Flood Risk Assessment

203357/31/Final/February 2005 Appendix dividers H.doc

Crossrail Line 1 Mott MacDonald Flood Risk Assessment - Surface Water Crossings Cross London Rail Links Limited

Cross London Rail Links 1 Butler Place London SW1H 0PT United Kingdom

Crossrail Line 1 Flood Risk Assessment – Surface Water Crossings

Crossrail Reference: 1E0321-GOE00-00006

February 2005

Mott MacDonald Demeter House Station Road Cambridge CB1 2RS UK Tel : 44 (0)1223 463500 Fax : 44 (0)1223 461007

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Crossrail Line 1 Mott MacDonald Flood Risk Assessment - Surface Water Crossings Cross London Rail Links Limited

Summary

The proposed Crossrail route extends from Maidenhead in the west to Shenfield and Abbey Wood in the east. The route crosses a number of watercourses ranging from minor brooks to substantial main rivers.

There are concerns that the proposed works may increase the potential for flooding at the crossing sites and in surrounding areas. There are also concerns that the Crossrail route may itself be affected by flood events at the crossings. Flood Risk Assessments have therefore been carried out in accordance with the procedures set out in the Government Planning Policy Guidance Note 25 (PPG25). These have been set out in this report, with the exception of Pudding Mill Lane (Route Window C13) where, because of the extent of the works proposed within watercourses, a more detailed Flood Risk Assessment has been carried out and is reported separately.

In carrying out the required Flood Risk Assessments, reference has been made to the ‘Flood Map’, which is shown on the Environment Agency (EA) website as of 7 October 2004, and is the primary source of publicly available flood risk information. At those locations where there is shown by the EA Flood Map to be a potential impact on flood risk, a more detailed assessment has been undertaken, and a more detailed determination of flood risk established.

These local Flood Risk Assessments have made use of any available detailed modelling, backed up by analysis using Flood Estimation Handbook (FEH) procedures. Flood levels have been taken from existing models where possible.

Detailed topographic data gathered for the Crossrail alignment has also been used where possible.

For the locations where there was assessed to be a risk of exacerbating flooding and/or encroachment on the floodplain, further study has been carried out to determine how such risks may be mitigated.

The conclusions of the Flood Risk Assessments are summarised in Table S.1 which shows that there is no significant residual risk at any of the sites. It has been assessed that there is no risk of flooding of the Crossrail line at any of the named sites. The only exception to this is Gidea Park where levels from the most recent EA modelling indicate that there is a small risk of flooding to the existing railway. The proposals for Crossrail would not increase this risk.

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Table S.1: Summary Conclusion of Flood Risk Assessment

Route Watercourse Residual risk Ref Flood related impacts window after mitigation

NE4 Ilford Station Alders Brook • None Not Significant

NE9 Romford River Rom • None Not Significant Station & Depot (East)

NE11 Gidea Park River • There may be minor filling of the floodplain and displacement of flood Not Significant Stabling Ravensbourne storage. This is subject to model output verification and detailed Sidings design.

• There would be a small headloss (afflux) due to the increase in culvert length. This can be mitigated by improvements to the entry and exit conditions to the culvert.

W13 West Drayton Fray’s River • Construction of the new road bridge would have an impact on upstream Not Significant Station water levels. This can be mitigated by provision of hydraulic streamlining at the new bridge and between the new and existing bridge.

3 • Reduction in available flood storage of up to 150 m during the 100- year+20% flood event. This can be mitigated by providing compensation storage.

• Temporary encroachment of floodplain during construction workswould need to be managed to minimise the volume of storage taken up and the duration of the works.

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Route Watercourse Residual risk Ref Flood related impacts window after mitigation

W15 Dog Kennel Horton Brook • Reduction in available flood storage of up to 715 m³ during the 100- Not Significant Bridge year+20% flood event due to widening of the embankment. This can be mitigated by providing compensation storage.

• Minor headloss (0.08 m) due to increase in culvert length of 7 m. This can be mitigated by provision of streamlining at the entry and exit transitions.

C11 Isle of Dogs Docks • Available flood storage volume within the dock system would be Not Significant Station reduced, with potential for minor increases in the risk of flooding elsewhere in the vicinity. Effective mitigation should be possible, but cannot be guaranteed at this stage.

SE7 Church Wickham • None Not Significant Manorway Valley Bridge Watercourse

NE8 Romford Two non-main • None Not Significant Depot (West) rivers

Various Other sites River Thames • As the stations and shafts are within the Thames protected floodplain, Not Significant located within which is protected to the 1000 year event, they are considered to have the Thames no flood related impacts for the purpose of this study. Protected Floodplain • At Maidenhead there may be a minor temporary impact due to the construction works. This should be managed to minimise the volume of storage taken up and the duration of the works.

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Crossrail Line 1 Mott MacDonald Flood Risk Assessment - Surface Water Crossings Cross London Rail Links Limited

List of Contents Page

Chapters and Annexes

1 Introduction 1

2 Route Window NE4 – Ilford Station 2 2.1 Existing Conditions 2 2.2 Proposed Works 3 2.3 Flooding Assessment 3 2.4 Mitigation 6 2.5 Conclusions 6

3 Route Window NE9 – Romford Station & Depot (East) 7 3.1 Existing Conditions 7 3.2 Proposed Works 9 3.3 Flooding Assessment 10 3.4 Mitigation 11 3.5 Conclusions 11

4 Route Window NE11 – Gidea Park Stabling Sidings 12 4.1 Existing Conditions 12 4.2 Proposed Works 13 4.3 Flooding Assessment 14 4.4 Mitigation 15 4.5 Conclusions 16

5 Route Window W13 – West Drayton Station 17 5.1 Existing Conditions 17 5.2 Proposed Works 19 5.3 Flooding Assessment 19 5.4 Mitigation 21 5.5 Conclusions 21

6 Route Window W15 – Dog Kennel Bridge 22 6.1 Existing Conditions 22 6.2 Proposed Works 24 6.3 Flooding Assessment 24 6.4 Mitigation 26 6.5 Conclusions 26

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7 Route Window C11 – Isle of Dogs Station 27 7.1 Existing Conditions 27 7.2 Proposed Works 27 7.3 Flooding Assessment 28 7.3.1 EA’s Concerns 28 7.3.2 British Waterways Concerns 28 7.3.3 Temporary Works 29 7.3.4 Permanent Works 29 7.4 Mitigation 30 7.5 Conclusions 30

8 Route Window SE7 – Church Manorway Bridge 31

9 Romford Depot (West) 32

10 Other Thames Sites 33 10.1 Tidal Floodplain 33 10.2 Fluvial Floodplain 34

11 Conclusions 35

Annex A: Topographic Survey Data A

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Table of Figures

Figure 2.1: Route Window NE4 – Ilford Station 2 Figure 2.2: Alders Brook as it passes under existing tracks 3 Figure 2.3: EA Flood Map – Ilford Station 4 Figure 2.4: Approximate Dimensions of Alders Brook at site 5 Figure 2.5: Alders Brook Barrage 5 Figure 3.1: Route Window NE9 – Romford Station & Depot (East) 7 Figure 3.2: Area to West of Romford Station 8 Figure 3.3: River Rom Culvert Beneath Railway Tracks 8 Figure 3.4: Position of Platform Extension at River Rom Culvert Entrance 9 Figure 3.5: EA Flood Map – Romford Station & Depot (East) 10 Figure 3.6: Approximate Dimensions of River Rom Channel at Culvert 11 Figure 4.1: Route Window NE11 – Gidea Park Stabling Sidings 12 Figure 4.2: River Ravensbourne near Crossrail Route 13 Figure 4.3: Ravensbourne Culvert at Gidea Park Sidings 13 Figure 4.4: EA Flood Map – Gidea Park Stabling Sidings 14 Figure 5.1: Route Window W13 – West Drayton Station 17 Figure 5.2: Fray’s River passing under railway tracks 18 Figure 5.3: Area Proposed for West Drayton Stabling 18 Figure 5.4: Lower Colne Model Flood Outline 19 Figure 5.5: Approximate Dimensions of Fray’s River 20 Figure 6.1: Route Window W15 – Dog Kennel Bridge 22 Figure 6.2: Horton Brook near Chequer Bridge 23 Figure 6.3: Chequer Bridge 23 Figure 6.4: EA Flood Map – Dog Kennel Bridge 24 Figure 6.5: Approximate Dimensions of Horton Brook 25 Figure 6.6: Approximate Dimensions of Horton Brook Culvert 25 Figure 7.1: Route Window C11 – Isle of Dogs Station 27 Figure 8.1: Route Window SE7 – Church Manorway Bridge 31 Figure 9.1: Route Window NE8 – Romford Depot (West) 32

Table of Tables

Table 5.1: West Drayton Sidings Flood Levels and Topographic Information ...... 20 Table 11.1: Summary of Flood Risk Assessments...... 35

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1 Introduction

The proposed Crossrail route extends from Maidenhead in the west, through Whitechapel to Shenfield in the north east and Abbey Wood in the east. The route crosses a number of watercourses ranging from minor brooks to significant main rivers.

There are concerns that the proposed works may increase the potential for flooding at key sites identified during a preliminary scoping undertaken to identify works potentially affecting the hydraulic performance of watercourses or works within floodplains. Flood Risk Assessments have therefore been carried out in accordance with the procedures set out in the Government Planning Policy Guidance Note 25 (PPG25). These have been set out in this report, with the exception of Pudding Mill Lane (Route Window C13) where, because of the extent of the works proposed within watercourses, a more detailed Flood Risk Assessment has been carried out and is reported separately.

Reference has been made to the ‘Flood Map’, which is shown on the EA website as of 7 October 2004, and is the primary source of publicly available flood risk information. These maps have been compiled based on a nationally consistent methodology which utilises a new digital terrain model, accurate to +/- 50 cm in level, together with a hydrological flow spreading model based on FEH, the standard UK flood estimation methodology. On the Flood Maps dark blue shows the area that could be affected by flooding from rivers if there were no flood defences. This area could be flooded from a river by a flood that has a 1% (1 in 100) or greater chance of happening each year. Light blue shows the additional extent of a more extreme flood. These areas are likely to be affected by a flood with up to a 0.1% (1 in 1000) chance of occurring each year.

In some cases where more accurate modelling is available, the EA have included the outputs in the new dataset, and it is planned that further improvements will be made to the maps with a revised set being issued at three month intervals. The January 2005 update was received too late to be addressed within this assessment.

At those locations where it is determined from the EA Flood Map that the Crossrail works would have a potential impact on flood risk, a more detailed assessment has been undertaken and a more detailed determination of flood risk established.

When further details of temporary works are available these will be assessed for flood impact and proposals for mitigation put forward with the approval of the EA.

Levels given in this report are referred to as Above Tunnel Datum (ATD). This is the general level datum being used by Crossrail and is also the level datum used by London Underground. It is used to avoid the need for negative values. To convert to Above Ordnance Datum (AOD), 100 m should be subtracted from the ATD values.

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2 Route Window NE4 – Ilford Station

2.1 Existing Conditions

This route window covers the route alignment between Gloucester Road and Hainault Street.

Figure 2.1 shows the main features within the route window.

Figure 2.1: Route Window NE4 – Ilford Station

The main work elements within route window NE4 are the provision of a new station building accessible from Cranbrook Road, York Place and Ilford Hill, and temporary tunnel fit out sidings on derelict land at the Aldersbrook sidings site to the west of the North Circular Road. The works to Ilford station would be undertaken within a railway cutting.

The proposed Crossrail alignment follows the route of the existing rail tracks and crosses the Alders Brook via a bridge approximately 700 m to the west of Ilford Station. Beneath the bridge Alders Brook is regulated by a control structure as shown in Figure 2.2. This spans the full width of the channel and is fitted with an adjustable penstock gate. It appears that this structure acts to hold back high flows and this forms part of a flood alleviation scheme. Alders Brook is a tributary of the River Roding. The brook branches off from the River Roding some 815 m north-west of the Crossrail alignment and rejoins it just south-east of the crossing of the Crossrail alignment.

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Figure 2.2: Alders Brook as it passes under existing tracks

2.2 Proposed Works

The proposed works of relevance to the Flood Risk Assessment are described in this section. Crossrail would rebuild the disused Aldersbrook sidings to the west of Ilford station. These would be used during the construction phase as a tunnelling logistics site. The railway training school building would be demolished and a new road access would be provided, including the possible replacement of the existing under-strength road bridge over the Alders Brook with a new structure that replicates the hydraulic characteristics of the old structure. This would need to be discussed with the EA to ensure that it supports the overall flood management strategy for the area. When rebuilt, the site would consist of six sidings, a widened embankment and a hard standing area.

Works at the Aldersbrook sidings logistic site would be carried out from within the existing fenced boundary of the railway and also on the adjacent disused training school site to the south of the GEML adjacent to the existing track towards London.

Although in initial assessments it was considered that an extension to the railway bridge may have proven necessary at the site, this is now not considered to be necessary. As it is not part of the Hybrid Bill proposals, it has not been covered in this assessment.

2.3 Flooding Assessment

Figure 2.3 shows the combined Alders Brook and River Roding floodplain from the EA Flood Map. The proposed site for the Ilford Station sidings encroaches on the Alders Brook floodplain, which indicates that further Flood Risk Assessment work is required.

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Figure 2.3: EA Flood Map – Ilford Station

It is understood that hydraulic modelling of the Lower Roding system is on-going for the EA. Outputs from this work, however, are not currently available. FEH procedures have therefore been used to provide an estimate of the flows and levels at the site during the 100-year+20% flood event. As a branch of the River Roding, the Alders Brook catchment is not represented separately within the FEH dataset. In order to determine values of water levels and flows for the 100-year+20% flood event, FEH parameters have been used for the full Roding catchment at the site. The catchment is classified as Rural and has an area of 305.1 km2 at the railway crossing. From hydrological analysis using ISIS the critical storm duration is 30 hours and the 100-year+20% flood flow is 166.1 m3/s.

Figure 2.4 shows the approximate dimensions of Alders Brook as it approaches the rail tracks, at the location shown in the photograph in Figure 2.5.

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Figure 2.4: Approximate Dimensions of Alders Brook at site

Figure 2.5: Alders Brook Barrage

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Assuming a bank slope of 1:10 on the right hand side of the brook, Manning’s n equal to 0.03 and taking an estimated channel slope at the site of 0.001 m/m, the approximate depth of flow in the Alders Brook channel, in the event that it was required to take 20% of the full flow from the River Roding catchment during a 100-year+20% flood, is 2.2 m. This implies that during the 100-year+20% event, the watercourse would rise to a depth of up to 2.2 m, and overtop its western bank. From the site survey the estimated bed level of the brook at the site is 102.5 mATD. A conservative equivalent water level for the 100-year+20% event is therefore 104.7 mATD.

Further analysis of this area will be carried out to give more accurate results when the River Roding model becomes available from the EA.

Annex A includes topographic data for the site. The area designated for extension of the sidings is at a general elevation of 107 to 108 mATD. This is some 3 to 4 m above the level of the Alders Brook banks and 2 to 3 m above the estimated water level for the 100- year+20% flood event.

2.4 Mitigation

No mitigation is required at this site.

2.5 Conclusions

Using very conservative assumptions for the flow in the Alders Brook, the area designated for extension of the sidings is significantly above the assessed level of the 100-year+20% flood event. There is therefore no significant risk that the proposed works would impact the floodplain of Alders Brook.

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3 Route Window NE9 – Romford Station & Depot (East)

3.1 Existing Conditions

This route window covers the route alignment between Sheringham Avenue and Carlisle Road.

Figure 3.1 shows the main features within the route window.

Figure 3.1: Route Window NE9 – Romford Station & Depot (East)

The main work elements within route window NE9 would consist of a new depot and stabling sidings located on the old goods yard site to the west of Romford station and on the south side of the GEML. In addition, the works would include a rebuild and extension to Romford station.

The River Rom runs to the west of the station, between the station and Waterloo Road as shown in Figure 3.1. The area to the west of the existing platform is shown in Figure 3.2. The River Rom currently flows beneath the tracks in a large Victorian culvert as shown in Figure 3.3.

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Figure 3.2: Area to West of Romford Station

Figure 3.3: River Rom Culvert Beneath Railway Tracks

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3.2 Proposed Works

The proposed works of relevance to the Flood Risk Assessment are described in this section. To accommodate longer Crossrail trains, platform five would be extended westwards by 18 m to 205 m, to accommodate an overall train length of 200 m. The island platforms three/four would be extended by 21.5 m. A new ticket hall and associated staff accommodation would be developed as an extension to the original ticket hall. A new access road would be constructed over the River Rom to the south of the railway tracks and downstream of the culvert.

The platforms would be extended over the entrance to the existing culvert to the north of the railway tracks by constructing a new deck to span between the existing sidewalls. The existing culvert is shown in Figure 3.4. It is understood that the construction of the crossing over the River Rom would be carried out without the need for any intrusion into the existing channel.

Figure 3.4: Position of Platform Extension at River Rom Culvert Entrance

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3.3 Flooding Assessment

Figure 3.5 shows the River Rom floodplain from the EA Flood Map. The proposed area of the Romford Station platform extension encroaches on the River Rom floodplain. However it is known that the Flood Map has been derived without taking account of man-made features such as the railway embankments. It is clear that in order to produce a more accurate definition of the floodplain, further Flood Risk Assessment work is required.

Figure 3.5: EA Flood Map – Romford Station & Depot (East)

The River Rom is a tributary of the River Beam. From previous hydraulic modelling work carried out for the EA on the River Beam catchment, the 100-year flood level for the River Rom just downstream of where the Crossrail route crosses the watercourse (National Grid Reference: 551256, 188370) has been determined as 111.56 mATD. Figure 3.6 shows the approximate dimensions of the River Rom at the culvert.

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Figure 3.6: Approximate Dimensions of River Rom Channel at Culvert

Annex A includes topographic data for the area around Romford Station. The track level at the existing culvert is approximately 122 mATD and the culvert invert level is approximately 110 mATD. The culvert soffit is approximately 3 m below the track level at 119 mATD. All proposed work to extend the platform would take place above this soffit level, and would thus be more than 7 m above the modelled 100-year flood level of 111.56 mATD. The works would have no effect on the hydraulic performance of the culvert.

The access road bridge would be constructed parallel with the railway tracks and to the south, downstream of the culvert. It has been assumed that the level of the bridge soffit would be approximately 116 mATD, and that it would therefore not impinge on the existing channel or floodplain of the River Rom. If this is the case, there would be no effect on the hydraulic characteristics of the river.

3.4 Mitigation

Provided temporary works for construction of the platform extension and the downstream access road bridge does not impinge on the existing channel or floodplain of the River Rom, no mitigation is required at this site.

3.5 Conclusions

Since the platform extension and the road bridge are significantly above the level of the 100- year+20% flood event, there is no significant risk that the proposed works would impact on the floodplain of the River Rom.

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4 Route Window NE11 – Gidea Park Stabling Sidings

4.1 Existing Conditions

This route window covers the route alignment between Brentwood Road and Briars Walk.

Figure 4.1 shows the main features within the route window.

Figure 4.1: Route Window NE11 – Gidea Park Stabling Sidings

The main work elements within route window NE11 are the extension of existing sidings and provision of new sidings in order to provide stabling for Crossrail trains.

The River Ravensbourne crosses under the Crossrail route east of Gidea Park station as a small brook as shown in Figure 4.2. The river approaches the tracks in a concrete channel and data from EA model studies indicate that the watercourse passes under the tracks in a sprung arch culvert structure. The length of the existing culvert is approximately 54 m and the cross section is as shown in Figure 4.3.

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Figure 4.2: River Ravensbourne near Crossrail Route

Figure 4.3: Ravensbourne Culvert at Gidea Park Sidings

4.2 Proposed Works

The proposed works of relevance to the Flood Risk Assessment are described in this section. The existing sidings, which lie in a shallow cutting to the east of Upper Brentwood Road, would be rebuilt. The existing sidings would be extended northwards with three new tracks provided. In total, seven sidings would be provided for Crossrail trains, each 240 m in length. All works would be undertaken in existing railway land and a new retaining wall constructed on the northern boundary.

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It is proposed that the Gidea Park stabling sidings are built in the area where the River Ravensbourne passes under the existing tracks. The existing culvert would be extended to have additional tracks crossing it. In order to extend the existing culvert northwards (upstream) by some 16 m, it is proposed that the walls of the lined channel approaching the existing culvert would be adapted and a roof slab constructed to structurally link into the walls, forming a culvert. The extension would be of equivalent flow area to the existing culvert, with smooth transitions sections from channel to culvert to minimise hydraulic head losses at entry.

4.3 Flooding Assessment

Figure 4.4 shows the River Ravensbourne floodplain from the EA Flood Map. The proposed area of the Gidea Park stabling sidings encroaches on the River Ravensbourne floodplain. However it is known that the Flood Map has been derived without taking account of man- made features such as the railway embankments. It is clear that in order to produce a more accurate definition of the floodplain, further Flood Risk Assessment work is required.

Figure 4.4: EA Flood Map – Gidea Park Stabling Sidings

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The River Ravensbourne is a tributary of the River Beam. The EA have provided two alternative hydraulic models for the Beam system, both of which include this reach of the Ravensbourne. The data from the two models at the entrance to the culvert under the Crossrail route can be summarised as follows:

100-year level 100-year flow

Beam 1999 Model 128.51 mATD 2.7 m3/s

Washlands 2004 Model 130.09 mATD not available

Annex A includes topographic data for the area around the Crossrail crossing of the River Ravensbourne. The track level at the existing culvert is approximately 129.5 mATD. The culvert soffit level, as shown on Figure 4.3, is 128.39 mATD. The area designated for the construction of sidings to the west of the river crossing is at a general level of between 130.5 m and 132 m ATD. This is above the 100-year flood level produced by both models and would not therefore be detrimental to floodplain storage. The area designated for the construction of sidings to the east of the river crossing is at a general level of between 129.3 m and 131 m ATD. This is above the 100-year level from the 1999 model, but partly below that from the 2004 model. The proposals for the site involve the laying of railway tracks at a similar level to the existing ground.

With respect to flow through the culvert, the additional 16 m length proposed would potentially cause an additional headloss (afflux) due to increased losses to hydraulic friction. The 100-year flow from the 1999 model has been used to calculate losses through the culvert, with and without the 16 m extension.

Using Manning’s equation with a culvert roughness, n, of 0.015 the friction headloss for the existing 54 m long culvert flowing full is calculated as 0.03 m. The additional 16 m of culvert length would increase this friction headloss to 0.04 m.

At this stage it is not known which of the two models is more accurate at this location. In the event that the 2004 model indicates a larger flow than the 1999 values, the additional headloss would increase accordingly. Repeating the above calculation with a flow of 5.4 m3/s (100% increase on the 1999 value) shows that the 16 m culvert extension increases headloss through the structure from 0.11 m to 0.14 m.

4.4 Mitigation

Although the additional headlosses calculated above are very small, it is proposed that streamlining works are carried out at the entrance to, and potentially also to the exit from, the culvert, in order to reduce headlosses due to rapid changes in flow area.

Such works could be designed to reduce overall headloss at the culvert to more than compensate for the small additional friction headloss produced by the culvert extension.

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4.5 Conclusions

There are two existing hydraulic models covering the Ravensbourne crossing which give different 100-year levels.

Taking the 1999 model, all the proposed works to the sidings are above the flood level and there would therefore be no work carried out in the floodplain. Taking the 2004 model, part of the sidings to the east of the river would be constructed on land currently below the 100-year level. However, the nature of the sidings work is such that there may be minor filling of the floodplain and displacement of flood storage. This is subject to model output verification and detailed design.

With respect to the culvert extension there would be a very small increase in headloss due to the additional 16 m length. This increase can be more than offset by improvements to the entry and exit conditions to the culvert which would reduce headlosses due to rapid changes of flow area.

In view of the above it can be concluded that the works to Gidea Park station would have no significant impact on the River Ravensbourne floodplain.

It should be noted that if the 100-year level from the 2004 model is considered representative, then the existing railways, part of the proposed sidings and significant area of housing upstream of the culvert are currently at risk of flooding. Provided that mitigation is adopted as discussed above, the proposals for Crossrail works would not increase their risk.

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5 Route Window W13 – West Drayton Station

5.1 Existing Conditions

This route window covers the route alignment between the west bank of the River Colne and the Roberts Close development.

Figure 5.1 shows the main features within the route window.

Figure 5.1: Route Window W13 – West Drayton Station

The main works in this route window comprise the construction of the new West Drayton Stabling Sidings, works to West Drayton Station and West Drayton Goods Loop. The proposed works to West Drayton Station and the West Drayton Goods Loop are remote from any watercourse and would have no impact on flooding.

Fray’s River passes under the railway tracks just west of West Drayton Station where the new West Drayton Station Sidings would be constructed. Fray’s River passing under the railway tracks is shown in Figure 5.2. The site of West Drayton sidings is shown in Figure 5.3.

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Figure 5.2: Fray’s River passing under railway tracks

Figure 5.3: Area Proposed for West Drayton Stabling

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5.2 Proposed Works

The proposed works of relevance to the Flood Risk Assessment are described in this section. The site proposed for the 22 new siding berths is currently occupied by EWS sidings and a coal depot. Staff accommodation, depot buildings and carriage washing facilities would be provided. Extensive works to the sidings would be required including new drainage.

A retaining wall would be constructed at the road kerb in the west of the site. A new bridge would be constructed for a new access road adjacent to the existing rail crossing over the Fray’s River.

5.3 Flooding Assessment

A detailed analysis of the River Colne and the Fray’s River was carried out as part of the EA Lower Colne Reappraisal Modelling Study which reported in August 2004. Figure 5.4 shows the 100-year+20% flood event outline from the Lower Colne Reappraisal Modelling Study. There is a small floodplain associated with the Fray’s River where it passes beneath the rail tracks to the east of the proposed site for West Drayton sidings. Figure 5.4 shows that the existing area of the sidings is raised above the level of the surrounding floodplain, and therefore should be unaffected by it.

Figure 5.4: Lower Colne Model Flood Outline

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The modelled flood levels for the 100-year+20% flood event from the Lower Colne Reappraisal Modelling Study have been compared with the site topographic data in Annex A. The results are summarised in Table 5.1.

Table 5.1: West Drayton Sidings Flood Levels and Topographic Information

100-year+20% Flood Event Area of Sidings Topographic Level (m ATD) Level (m ATD)

Western end 127.9 126.0

North west corner 126.0 126.5

Fray’s River (north east) 126.4 127.3

South eastern end 130.6 127.0

An estimation of flood levels and flows has been carried out using FEH procedures and local topographic data to give a comparison with the results given in the Lower Colne Reappraisal Modelling Study. The Fray’s River catchment is classified as Urban and has an area of 43.9 km2 at the railway crossing. From hydrological analysis using ISIS, the critical storm duration is 7 hours and the 100-year+20% flood flow is 79.2 m3/s.

Figure 5.5 shows the approximate dimensions of the Fray’s River. Assuming Manning’s n equal to 0.03 and taking an estimated channel slope of 0.001 m/m, the approximate depth of flow in the channel during a 100-year+20% flood flow is 2.4 m. This equates to a flood level of approximately 127.5 m ATD. This estimate is based on a much less detailed analysis than the Lower Colne Reappraisal Modelling Study.

Figure 5.5: Approximate Dimensions of Fray’s River

The levels in Table 5.1 indicate that the area to the north west of the sidings where the retaining wall would be constructed and the area where the site crosses the Fray’s River in the north east of the site would be within the floodplain for the 100-year+20% flood event. The current proposal would lead to a reduction in available flood storage of up to 150 m3 during the 100-year+20% flood event.

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At the point where the Fray’s River crosses the Crossrail route the topographic data shows that the track level is some 3 m higher than the 100-year+20% flood level of the Fray’s River.

5.4 Mitigation

To mitigate against the impact of the construction of the new road bridge on the upstream flood levels hydraulic streamlining would be provided at the entry to the new bridge and between the new and existing bridge. This is likely to be required at both the entrance and the exit to the new bridge. The works would be designed to take into account both flood risk and other environmental concerns.

There would be some temporary encroachment on the floodplain during the construction of the road bridge and hydraulic streamlining works. This would have to be managed during the project planning to minimise the volume of flood storage taken up and the duration of the works.

The permanent reduction in flood storage of up to 150 m3 of the Fray’s River floodplain can be mitigated by providing compensatory flood storage within the existing sidings area. Potential areas for compensatory flood storage can be identified in the west and north-west of the site and it is therefore considered that this mitigation can be achieved. However, design of the access road and retaining wall, and the exact location for any compensatory storage areas, need to be considered in combination with further design for the site in consultation with the EA.

5.5 Conclusions

If the mitigation measures suggested above are adhered to, there would be no permanent impact on flood risk at this site and the temporary impact during construction would be insignificant.

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6 Route Window W15 – Dog Kennel Bridge

6.1 Existing Conditions

This route window covers the route alignment from the fence line between Maplin Park and Southwold Spur to Bathurst Walk.

Figure 6.1 shows the main features within the route window.

Figure 6.1: Route Window W15 – Dog Kennel Bridge

The main work elements would be the construction of new tracks, on a widened embankment, over half a mile and replacements of the Chequer and Dog Kennel Bridges.

Figure 6.1 shows Horton Brook crossing the Crossrail route approximately 150 m west of Chequer Bridge. Horton Brook close to Chequer Bridge is shown in Figure 6.2.

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Figure 6.2: Horton Brook near Chequer Bridge

Figure 6.3: Chequer Bridge

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6.2 Proposed Works

The proposed works of relevance to the Flood Risk Assessment are described in this section. The upgrading of the freight loop would require the construction of new single track over a length of half a mile between Langley East and Dog Kennel Bridge. The track would be constructed outside the existing railway corridor on a 7 m extension to the existing embankment to the north of the alignment.

The embankments at Chequer Bridge would be widened. The Horton Brook culvert to the west of Chequer Bridge would have to be extended and the brook would have to be moved to the north. The culvert would be kept straight and extended only enough to bring it out of the embankment, and the open watercourse upstream diverted to meet the new culvert entry point. Part of these works fall within Route Window W16.

6.3 Flooding Assessment

Figure 6.4 shows the Horton Brook floodplain from the EA Flood Map. The proposed area of the Crossrail route at Horton Brook encroaches on the Horton Brook floodplain, and indicates that further Flood Risk Assessment work is required.

Figure 6.4: EA Flood Map – Dog Kennel Bridge

An analysis has been carried out using FEH procedures and local topographic data to determine values of water levels and flows for the 100-year+20% flood event. The Horton Brook catchment is classified as Rural and at the crossing has a catchment area of 11.9 km2. From hydrological analysis using ISIS the critical storm duration is 13 hours and the 100-year+20% flood flow is 11.5 m3/s.

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Figure 6.5 shows the approximate dimensions of Horton Brook just upstream of the crossing.

Figure 6.5: Approximate Dimensions of Horton Brook

Assuming Manning’s n equal to 0.05, an estimated channel slope of 0.001 m/m and a conservative bank slope of 1:10 on either side of the brook, the approximate depth of flow in the channel during a 100-year+20% flood is 2.26 m. Therefore during the 100-year+20% event, the brook would overtop its banks.

The Crossrail topographic data of the area is included in Annex A. The brook bed level just downstream of the bridge is 125.31 mATD.

The approximate dimensions of the existing Horton Brook culvert are shown in Figure 6.6. The extension of the culvert should have dimensions similar to the existing culvert. There would be an additional friction headloss of 0.08 m due to the increase in culvert length from 54 m to 61 m.

Figure 6.6: Approximate Dimensions of Horton Brook Culvert

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The existing ground levels in the area have been used to assess the impact of the proposed embankment extensions on the existing flood storage capacity. It is estimated that the proposed widening of the embankments at Chequer Bridge would reduce the flood storage of the Horton Brook floodplain by some 715 m³ during the 100-year+20% flood event.

6.4 Mitigation

To ensure that the proposed Horton Brook culvert extension has no significant impact on upstream flood levels, the culvert should be kept straight and extended only enough to bring it out of the embankment. The open watercourse upstream should be diverted to meet the new culvert entry point. It is understood that this is part of the currently proposed design.

The minor additional headloss (afflux) of 0.08 m would be mitigated by the construction of streamlining to the entry and exit transitions from the channel to the culvert.

The 715 m3 reduction in flood storage of the Horton Brook floodplain can be mitigated by providing compensatory flood storage. There is a suitable area for provision of flood compensation north of the site which runs alongside Market Lane/Hollow Hill Lane and is on the west of the road, a provision suggested by the EA. The area is presently outside the floodplain but is within the LOD/LLAU area. It is understood that further design work is necessary to develop these proposals to the satisfaction of the EA.

6.5 Conclusions

The works to the Dog Kennel Bridge route window would have no significant impact on the Horton Brook floodplain, provided that the recommended mitigation measures are adhered to.

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7 Route Window C11 – Isle of Dogs Station

7.1 Existing Conditions

The route window covers the route alignment between Westferry Road and Blackwall Way.

Figure 7.1 below shows the main features within the route window.

Figure 7.1: Route Window C11 – Isle of Dogs Station

The main works elements in this route window are the Hertsmere Road Shaft, Isle of Dogs Station and the running tunnels. The Hertsmere Road Shaft is covered in Section 10 below.

7.2 Proposed Works

The proposed works of relevance to the Flood Risk Assessment are described in this section.

The main work element is the cut and cover box containing the station, crossover and overrun to be constructed within the West India Dock North, to the west of the station. On completion there would be two shafts, for access and ventilation; the dock being reinstated. The box would be constructed between diaphragm walls and an outer cofferdam of piles which would provide a cut-off through the overburden and allow a section of the West India North Dock to be emptied during construction of the Isle of Dogs Station.

The top of the station box would be approximately 90 mATD which is some 6 m below the bottom of the North Quay basin. The Blackwall Basin and Poplar Dock marinas would be

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closed for the duration of construction since the only navigation access, through Bellmouth Passage, would be closed off by the cofferdam in the North Dock.

7.3 Flooding Assessment

The West India North Dock is part of the extensive dock system in the Isle of Dogs, which includes the Millwall Docks. The only navigable link between the dock system and the Thames is via the lock into the West India South Dock. The docks are operated by British Waterways (BW).

7.3.1 EA’s Concerns

The EA consider the dock system to be essential for the overall management of flood risk in the Thames. During tides which are not high enough to trigger Thames Barrier closure, but higher than the retained level in the dock system, water will enter the docks via the mitre gates. The tide level at which the Barrier is closed is 104.72 m ATD.

If Crossrail construction causes a reduction in the surface area of water, then the docks would have less capacity for the storage of flood water and unless steps are taken to provide mitigation, there would be increased risk of flooding elsewhere.

7.3.2 British Waterways Concerns

BW seeks to maintain the water level within the docks at a level of 104.23 m ATD which represents the Mean High Water Spring Tide Level. This target level is maintained for a number of reasons.

Navigation: There is a need to maintain a depth of water for the boats in the dock to operate.

Stability of Dock Walls: It is perceived by BW that the lowering of dock water levels may endanger the structural integrity of the dock walls.

Operational Issues: The connection between the river and the docks is via three sets of mitre gates pointing into the dock. At very high tides, when the river level exceeds the level in the docks, the flow of water pushes the gates open and flow passes in. Following such a situation BW are concerned at the potential risk of the gates failing to close as the tide goes down. It is perceived that, if the gates stick open, the resultant lowering of dock water levels would endanger navigation and the integrity of the dock walls. For this reason BW have a significant investment in ensuring that the gates do shut, and they would resist any proposal to lower the target water level since this would involve the gates being pushed open by the tide more frequently.

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In order to maintain the target level within the docks BW pump water from the river to the dock system. The amount of daily pumping required will vary according to a number of factors including the tidal profile and the number of boat movements through the locks. Records show typical values of pumping to be 60 minutes per day to raise water levels by 0.1 m.

7.3.3 Temporary Works

The cofferdam required for station construction “occupies the whole of the West India Dock North plan area between the DLR bridge and the eastern end of the dock”. The plan area of the working space is approximately 33,000 m2. Over the period of construction the surface area of the dock system would therefore effectively be reduced by this amount. Note: as the cofferdam is built inside the dock walls there would be small water channels between the dock walls and the cofferdam. The north side of the Dock also contains a false quay. These extra volumes of water have not been included in the high-level calculations presented here.

The estimated surface area of the entire dock system (West India plus Millwall) is some 380,000 m2. The reduction due to the temporary works is therefore some 9% of the full area.

If it is assumed that flood storage in the dock system is provided between the target water level of 4.23 m and the maximum river level without Barrier closure of 4.72 m, then the storage range is 0.49 m. For the existing 380,000 m2 water surface this equates to a volume of storage of 186,200 m3.

If the temporary works reduce the surface area by 33,000 m2 , this would be equivalent to a reduction in available storage volume of 16,200 m3. In order to maintain the same volume of storage, the range of water levels would need to increase to 0.54 m. Hence the target water level would need to be reduced by 0.05 m to 104.18 mATD.

7.3.4 Permanent Works

On reinstatement of the North Dock the permanent shafts would occupy some 3,600 m2 of the dock water surface. This represents some 0.95% of the full area of the dock system, and is equivalent to a reduction in available storage volume of 1,760 m3.

With respect to maintaining the volume available for flood storage, from these calculations it is estimated that the range of water levels would need to increase to 0.496 m, that is, the target water level would need to be reduced by 0.005 m to 104.225 mATD.

Although Isle of Dogs Station is sited on the defended floodplain, it could become partially inundated under some flood defence breach or Thames Barrier failure scenarios. This can be mitigated by suitable design of the cill levels.

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7.4 Mitigation

One option to mitigate the impact on flood risk of reducing the open water area of the dock would be to reduce the target level at which water levels the docks are maintained. BW has indicated that they would strongly object to any such proposals because this would increase the frequency with which flows push the lock gates open and thus increase their operational concerns. They state that although the impact of the permanent works would be small they would still object. The target retained level was apparently previously lowered in connection with an earlier development and BW considers that any further lowering would be unmanageable.

The EA have suggested that mitigation might be provided by Crossrail acquiring alternative land in the vicinity of the docks and making this available for compensatory flood storage. Due to difficulties with availability of such land, it is doubtful whether this is a practical proposition.

If BW’s operating procedures were altered to allow a lower maintained level in the dock system then this would remove any residual increased flood risk. If the operating procedures were not changed then the temporary works would cause a minor increase in peak Thames flood levels in the vicinity of the docks.

The removal of 33,000 m2 of dock water surface area for the temporary works, and 3,600 m2 for the permanent works may be compared with the total River Thames water surface area of some 4 million m2 between Tower Bridge and the Thames Barrier. During the proposed temporary works, the potential loss of 16,200 m3 of storage volume, as discussed in 7.3.3 above, would equate to a rise in peak water level of some 0.004 m if spread over this reach. For the permanent works, the potential loss of 1,760 m3 of storage volume would equate to a level rise of the order of 0.0005 m.

7.5 Conclusions

It may be concluded that for the permanent works, the increase in flood levels due to the minor loss of storage capacity in the dock would not be significant.

Mitigation to offset the loss of storage capacity in the dock caused by the temporary works should be possible at this site, however this cannot be guaranteed. Even without mitigation it is assessed that the increase in flood levels due to the loss of storage capacity in the dock would not be significant.

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8 Route Window SE7 – Church Manorway Bridge

The route window covers the route alignment between Marmadon Road and De Lucy Road.

The figure below shows the main features within the route window.

Figure 8.1: Route Window SE7 – Church Manorway Bridge

The main work elements are works to the tracks and reconstruction of the bridges over the alignment at Church Manorway, Eynsham Drive and Bostall Manorway.

Wickham Valley Watercourse is a piped stormwater drain which crosses under the Crossrail route between Plumstead and Abbey Wood Stations from south to north. It runs parallel to the railway for several hundred metres before turning northwards towards its outfall in a lake, which feeds through one of the Marsh Dykes to Tripcock Pumping Station.

This section of working railway would be widened to accommodate both the existing railway and the new Crossrail line. This would require provision of earth retaining structures to provide additional width at formation level.

The site falls within the area protected by the Thames Barrier and its associated tidal flood protection works (see Section 10 below). These works provide tidal flood protection to a standard of greater than 1 in 1000 years, hence no further flood risk investigation is considered necessary at this site.

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9 Romford Depot (West)

The main works in this route window comprise the construction of a rail underpass in order to reduce conflicting movements between trains on the GEML and those moving to and from a new Romford depot. This would also require works to Jutsums Lane bridge.

The figure below shows the main features within the route window.

Figure 9.1: Route Window NE8 – Romford Depot (West)

As part of the Crossrail works, a small pipe culvert collecting flow from two streams near St Edwards School would be moved and may be converted into an inverted siphon underneath the Great Eastern Main Line. Options to reduce the siphon depth or avoid it altogether are being studied as of the date of this report. The design would be subject to EA approval in the detailed design phase. (Ref: Memo from Nadia Brannon of the EA, date 01/11/04).

The increased maintenance needs of a siphon may lead to flood risk associated with potential blockage of the surface water drainage route.

No floodplain for this watercourse is identified on the EA Flood Map. The watercourse has a catchment of less than 3 km2 and is not considered a ‘main’ river. As a result, no further flood risk investigation has been undertaken at this stage.

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10 Other Thames Sites

10.1 Tidal Floodplain

In addition to the Isle of Dogs Station, major works within the Thames Protected floodplain include:

• Hertsmere Road Shaft – Emergency Intervention Point (EIP) access shaft close to the Isle of Dogs Station

• Blackwall Way Shaft – EIP between Isle of Dogs Station and Victoria Dock Portal

• Limmo Shaft – EIP, ventilation and evacuation facility between Isle of Dogs Station and Victoria Dock Portal

• Victoria Dock Portal – tunnel portal

• Custom House Station – new station

• Connaught Tunnel – existing tunnel to be refurbished

• Thames tunnels – new twin tunnels constructed with entrance and exits at North Woolwich and Plumstead respectively. This includes the Plumstead Portal

• Warren Lane Shaft – EIP and ventilation shaft on the corner of Warren Lane and Beresford Street in Woolwich.

• Abbeywood Station and Turnback Sidings

• Manor wharf

All these sites are situated on the defended floodplain. The Thames Barrier and its associated tidal protection works provide tidal flood protection to a standard of greater than 1 in 1000 years. The standard quoted by the EA is a 1 in 1000 year level taking account of climate change to the year 2030. There is a concern that Crossrail tunnels could become partially inundated under some flood defence breach or Thames Barrier failure scenario. A risk analysis would be undertaken and suitable design measures incorporated into the design, possibly including flood gates at Victoria Dock Portal and North Woolwich or Plumstead Portal. Moreover, consideration would be given to suitable design of cill levels at shafts within the defended floodplain and Isle of Dogs Station.

The usual requirement of the EA for Flood Risk Assessments in such areas requires the consideration of potential breaches to the defences. It is known that “embayment studies” are currently being undertaken by others to provide an indication of the effects due to such breaches. It is proposed that the detailed design of all works in the Thames protected floodplain would take account of the outputs from these studies. In view of this, no further flood risk investigation is considered necessary at these sites at present.

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10.2 Fluvial Floodplain

Overhead electrification of the Great Western Mainline is proposed including on the bridge over the River Thames at Maidenhead (W24), where it may be necessary to use an island in the river for access to erect scaffolding for temporary works. This would have no permanent impact and should be managed to minimise the volume of storage taken up and the duration of the works. This does not affect the river beneath the bridge and no further flood investigation is considered necessary.

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11 Conclusions

The results of the Flood Risk Assessments undertaken at the selected sites where the Crossrail alignment crosses watercourses are summarised in the Table 11.1 below.

Table 11.1: Summary of Flood Risk Assessments

RW Site Watercourse Proposed works Flood related impacts Mitigation measures Residual risk

NE4 Ilford Station Alders Brook • Clearance of the site • None • None Not • Addition of new spur significant • New access road including possible replacement of bridge • New railway drainage • Temporary storage of excavated materials

NE9 Romford River Rom • Ticket hall upgrade • None • The works to the culvert must not Not Station & • New maintenance encroach on the River Rom significant Depot (East) depot floodplain, or constrict the River • Platform extension Rom in any way when in flood. • New bridge

NE11 Gidea Park River • Construction of new • There may be minor filling of the • Improvements to the entry and exit Not Stabling Ravensbourne sidings including a floodplain and displacement of conditions to the culvert and significant Sidings culvert extension flood storage. This is subject to consideration of flood storage/ model verification and detailed detailed design of the sidings. design. • There would be a small headloss (afflux) due to the 16 m increase in culvert length.

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RW Site Watercourse Proposed works Flood related impacts Mitigation measures Residual risk

W13 West Drayton Fray’s River • Construction of new • Minor impact on upstream flood • Hydraulic streamlining at the new Not Station sidings levels due to the construction of bridge and between the new and significant • New retaining wall the new of the rail bridge. existing bridge. • New access road • Permanent reduction in flood • Provision of 150 m³ of bridge storage of up to 150 m³ during compensation storage the 100-year+20% event. • Management of the temporary • Temporary reduction in works to minimise the volume of floodplain storage during storage taken up and the duration construction. of the works

W15 Dog Kennel Horton Brook • Embankment • Permanent reduction in flood • Provision of 715 m³ of Not Bridge widening storage of up to 715 m³ during compensation storage significant • Horton Brook culvert the 100-year+20% event due to • Provision of streamlining at culvert extension widening the embankment. entry and exit transitions • New single track • Minor afflux due to culvert railway bridge extension.

C11 Isle of Dogs Docks • Temporary works • Available flood storage volume • Reducing the impounded level in Not would require the within the dock system would be the docks could compensate for significant north dock to be reduced, potentially increasing the lost storage volumes, however emptied. the risk of flooding elsewhere in BW are hostile to this proposal. • Works would take up the vicinity. The analysis has • Provision of compensatory flood some dock area however shown that the impact storage at an alternative site in the of the permanent works is not vicinity to the dock would be significant. effective, but acquiring appropriate • Effective mitigation should be land probably prohibitive. possible, but cannot be • Amendments to operative guaranteed at this stage. procedures for the Thames Barrier could be considered but the EA are likely to oppose this as a solution • Suitable design of cill levels

RW Site Watercourse Proposed works Flood related impacts Mitigation measures Residual

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risk

SE7 Church Wickham • Wickham Valley • Site is located within the • None Not Manorway Valley Watercourse (piped Thames protected floodplain, significant Bridge Watercourse stormwater drain) which is protected to the 1000 crosses Crossrail route year event. It is considered to • Embankment to be have no flood related impacts widened for the purpose of this study. NE8 Romford Two non-main • A small pipe culvert • Increased maintenance needs • None at present Not Depot (West) rivers collecting flow from two of siphon significant streams would be • Not main river and no further moved and may be Flood Risk Assessment work converted into an has been carried out. inverted siphon various Other Thames River Thames • Hertsmere Rd shaft • As all the sites are within the • Risk analysis, possibly including Not sites - Tidal • Blackwall Way Shaft Thames protected floodplain, flood gates/suitable design of cill significant • Limmo Shaft which is protected to the 1000 levels • Warren Lane Shaft year event, they are • Victoria Dock Portal considered to have no flood • Custom House station related impacts for the • Connaught Tunnel purpose of this study. • Thames Tunnel (including North Woolwich and Plumstead Portals) • Abbeywood Station and turnback sidings • Manor wharf

W24 Other Thames River Thames • Electrification at • Possible minor temporary • Management of the temporary Not sites - Fluvial Maidenhead Railway impact due to the construction works to minimise the volume of significant Bridge works. storage taken up and the duration of the works.

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Annex A: Topographic Survey Data

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Crossrail Line 1 Mott MacDonald Flood Risk Assessment - Pudding Mill Lane Portal Cross London Rail Links Limited

Cross London Rail Links Limited 1 Butler Place London SW1H 0PT United Kingdom

Crossrail Line 1 Flood Risk Assessment - Pudding Mill Lane Portal

Crossrail Reference: 1D000-C1N00-01028

February 2005

Mott MacDonald Demeter House Station Road Cambridge CB1 2RS UK Tel : 44 (0)1223 463500 Fax : 44 (0)1223 461007

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Summary

The proposed route connecting Crossrail and the Great Eastern Main Line emerges from the ground via a portal located in the vicinity of the River Lea, near Pudding Mill Lane. The alignment runs roughly parallel with the Docklands Light Railway (DLR) corridor towards Pudding Mill Lane station. From Pudding Mill Lane station the alignment shares the existing surface railway corridor to the east. The proposed alignment crosses the City Mill River as it joins the Docklands Light Railway (DLR) corridor. The DLR will be re-aligned between the bridge over the River Lea and City Mill River to accommodate the Crossrail running lines and the ramp into the tunnel. This will include construction of a new DLR bridge over the City Mill River. Refer to Route Window C13.

Where the tunnel passes under the River Lea Navigation, ground conditions are expected to be poor. In view of this, it is proposed to temporarily close part of the Lea Navigation at this point while a concrete slab is placed in the river bed, in preparation for a tunnel being bored under the bed of the river. An area sufficient for free navigation of the river will remain open. It is also planned to temporarily restrict the width of the City Mill River to enable construction of the railway bridge. These restrictions, which are both considered in this document, may be carried out concurrently, or the timing could be staggered according to a number of considerations, including flood risk. On completion of the works to the bed and banks of the River Lea Navigation, the river channel will be returned to its original state. At the City Mill River Bridge the permanent works will result in a small reduction in channel width due to extension of the existing abutments.

There are concerns that the proposed works may increase the potential for flooding at the sites and in surrounding areas. The Environment Agency has therefore requested that a Flood Risk Assessment is carried out in accordance with the procedures set out in the Government Planning Policy Guidance Note 25 (PPG25).

A hydraulic model of the River Lea was first developed for the Environment Agency by the consultants Halcrow in 1997/98. This was revised in 2001/02 and again in 2004. These assessments consider both fluvial and tidal conditions and combinations thereof. In July 2004 Halcrow were commissioned by Mott MacDonald to carry out further modelling looking specifically at flood risk at the Crossrail construction site. Modifications were made to the model to generate worst design-case flood conditions at the proposed worksites. For this study Halcrow’s most recent work is considered to supersede all previous modelling work.

The scenarios analysed were the 100-year fluvial / 20-year tidal and 200-year tidal / 20-year fluvial flood events. These scenarios are acknowledged to be conservative; however they have previously been accepted by the Environment Agency as a reasonable approach for this type of analysis. Halcrow’s work has been reviewed and the model outputs have been used as the basis of an appraisal of current levels of flood risk at the sites. Calculations have been undertaken to determine possible increases in peak flood levels caused by flow constrictions of different widths. Observations made during site visits have been used, in conjunction with available information from British Waterways and previous studies, to assess the flood risk at the proposed work sites and in the surrounding reaches.

Provided the temporary channel width is maintained at a minimum of 8 m, at the tunnel portal site on the River Lea, it has been found that the increase in peak levels during flood events

i 203357/31/Final/February 2005/ AppH_2.doc Crossrail Line 1 Mott MacDonald Flood Risk Assessment - Pudding Mill Lane Portal Cross London Rail Links Limited will have no significant impact on flood risk locally. Further upstream there are reaches where the risk of flooding would potentially increase for the duration of the temporary works. This will need to be verified by topographic survey and, if necessary, temporary flood defences provided for the duration of the works. For the temporary 8 m channel width in the critical 100-year fluvial/20-year tidal case, the predicted peak flood level is 105.10 mATD.

At the City Mill Bridge site, provided the temporary channel width is maintained at a minimum of 5 m the increase in peak levels during flood events will have no significant impact on flood risk either at the site or in surrounding reaches. The predicted flood level in the critical 100- year fluvial/20-year tidal case is 105.15 mATD. The permanent works as planned for the City Mill Bridge will reduce the area of flow by less than 10%. This constriction will have no discernable impact on flood water levels; the computed increase in water levels is less than 5 mm and there will be no impact on flood risk.

The new DLR bridge over the City Mill River should be designed to be have appropriate headroom, span and soffit levels to ensure that the bridge has no impact on flood risk.

It is recommended that the top levels of the cofferdam for the works to place the concrete slab on the bed of the River Lea are set at a maximum level of 104.2 mATD. This level will mean that the works flood out before the River Lea overtops, thereby considerably reducing the flood risk upstream.

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List of Contents Page

Chapters and Annexes

Summary i

1 Introduction 1

2 Existing Conditions 4 2.1 General 4 2.2 Tunnel Portal on Lea Navigation 5 2.2.1 Existing Flood Defences on Lea Navigation 5 2.3 City Mill River Crossing 7 2.3.1 Existing Flood Defences on City Mill River 7

3 Proposed Construction Works 9 3.1 Temporary Works 9 3.1.1 Tunnel Portal at the River Lea 9 3.1.2 City Mill River Crossing 10 3.2 Permanent Works 10

4 Hydraulic Modelling 13 4.1 Previous Modelling 13 4.1.1 Halcrow 13 4.1.2 Symonds 14 4.2 Modelling Carried Out for this Flood Risk Assessment 14

5 Current Flood Risk 16 5.1 Current Flood Risk on Lea Navigation 17 5.2 Current Flood Risk on City Mill River 17

6 Hydraulic Analysis 18 6.1 Halcrow Model Output 18 6.2 Local Area Calculations for Other Widths of Constriction 21 6.3 Local Area Calculations Following Revised Constriction Cross Section 22 6.4 Flood Protection 23 (i) At the Tunnel Portal Worksite - Temporary 23 (ii) At the Tunnel Portal – Permanent 23 (iii) Upstream of the Tunnel Portal Worksite 24 6.5 Assumptions made in Hydraulic Modelling 24

7 Conclusions 25 7.1 Temporary Tunnel Portal Works on Lea Navigation 25 7.2 Permanent Works for Lea Navigation at Tunnel Portal 25 7.3 Temporary Works for City Mill Railway Bridge 25 7.4 Permanent Works for City Mill Railway Bridge 26 iii 203357/31/Final/February 2005/ AppH_2.doc Crossrail Line 1 Mott MacDonald Flood Risk Assessment - Pudding Mill Lane Portal Cross London Rail Links Limited 7.5 General Conclusions 26

Annex A: Site Photographs 28

Annex B: British Waterways Cross Sections at the Proposed Worksite 30

Annex C: Further details on constriction layout 31 C.1 Summary of works modelled on the City Mill River and River Lea 31 C.1.1 River Lea: Temporary works 31 C.1.2 River Lea: Permanent Works 32 C.1.3 City Mill River: Temporary Works 32 C.1.4 City Mill River: Permanent works 33

Annex D: Full Tables of Model Output 35

Annex E: Output from Symonds Modelling 36

Figures Figure 1.1: Location Plan ...... 3 Figure 2.1: Existing Flood Defences and Photograph Locations ...... 6 Figure 2.2: Cross sections on the City Mill River...... 8 Figure 3.1: Construction Plan at the Tunnel Portal on the River Lea Navigation ...... 10 Figure 3.2: Section of the Crossrail Railway Bridge at City Mill River ...... 11 Figure 3.3: Cross section at City Mill River Bridge ...... 12 Figure 5.1: EA Flood Map ...... 16

Tables Table 4.1: Baseline Conditions...... 15 Table 6.1: Temporary Works, Calculated Peak Levels during Flood Events ...... 18 Table 6.2: Permanent Works, Calculated Peak Levels during Flood Events ...... 20 Table 6.3: Temporary Works at River Lea Portal ...... 22 Table 6.4: Revised Afflux on the River Lea at the River Lea Portal ...... 23

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1 Introduction

The proposed route connecting Crossrail and the Great Eastern Main Line emerges from the ground via a portal located in the vicinity of the River Lea near Pudding Mill Lane. The alignment runs roughly parallel with the Docklands Light Railway (DLR) corridor towards Pudding Mill Lane station. From Pudding Mill Lane station the alignment shares the existing surface railway corridor to the east. The proposed alignment crosses the City Mill River as it joins the Docklands Light Railway (DLR) corridor. The DLR will be re-aligned between the bridge over the River Lea and City Mill River to accommodate the Crossrail running lines and the ramp into the tunnel. This will include construction of a new DLR bridge over the City Mill River. Refer to Route Window C13.

Where the tunnel passes under the River Lea Navigation ground conditions are expected to be poor. In view of this it is proposed to temporarily close part of the Lea Navigation at this point while a concrete slab is placed in the bed of the river. This concrete slab is to be constructed to protect the subsequent tunnel boring. An area, sufficient for free navigation of the river, will remain open. It is also planned to temporarily close part of the City Mill River to enable construction of the railway bridge. These closures may be carried out concurrently, or the timing could be staggered, according to a number of considerations including flood risk.

On completion of the works constructing the bed slab on the River Lea Navigation the river channel will be returned to its original state. At the City Mill River Bridge the permanent works will comprise a small reduction in channel width due to extension of the existing abutments.

The area around the proposed work sites is primarily industrial/commercial development. The locations of the sites are shown in Figure 1.1.

There are concerns that the proposed works may increase the potential for flooding at the sites and in surrounding areas. The Environment Agency (EA) has therefore requested that a Flood Risk Assessment is carried out in accordance with the procedures set out in the Government Planning Policy Guidance Note 25 (PPG25).

Any works affecting the channel are subject to approval by both the EA and British Waterways (BW). As the channel reaches involved are designated ‘main river’ the EA are responsible for the control of all the works therein. BW have particular responsibility for the maintenance of navigation in the River Lea system. In addition to the maintenance of navigation, it is required by British Waterways that the promoter of any works impinging on their waterways is able to deal with storm flows reaching the site at all times. This must be taken into account in the design of both temporary and permanent structures.

A hydrological assessment for the River Lea was first carried out for the EA by the consultants Halcrow in 1997/98. This was revised in 2001/02 and again in 2004. Symonds completed further modelling of the Lower Lea area in 2004; this work takes account of the previous studies undertaken by Halcrow. These assessments consider both fluvial and tidal conditions and combinations thereof.

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2 203357/31/Final/February 2005 AppH_2.doc Figure 1.1: Location Plan

Carpenters Lock

W a te r w o r k s R iv e r a e L r e iv R d Ol

v P i R u l d l rd di i n M g y t M i i l C l R iv e r

R iv e r L e a

Proposed City Mill River Crossing

City Mill

Lock T h r e e

i l l s

a l l

R i v e r r ive R Proposed ck Ba Pudding Mill Lane w Bo Portal

Proposed Crossrail Tunnel

L ea Nav igation © Crown Copyright

Legend Proposed Crossrail route DLR / GEML ± Lea River network Northern Outfall Sewer / Greenway

Crossrail Line 1 Mott MacDonald Flood Risk Assessment - Pudding Mill Lane Portal Cross London Rail Links Limited

2 Existing Conditions

2.1 General

As shown in Figure 1.1 the proposed Crossrail alignment crosses the River Lea in an area where flow is divided between three branches of the river.

The main conveyor of flows is the tidal Waterworks River which forms the eastern branch. The western and central branches are the River Lea Navigation and the City Mill River respectively. Between them these two watercourses typically convey less than 10% of the total flow passing through the river network. These latter two river channels have extremely flat hydraulic slopes with water levels being maintained for navigation by the system of British Waterway locks.

Carpenters Lock connects the Waterworks River to the City Mill River and the Lea Navigation via the short section of Old River Lea. However there are a number of closed derelict control structures in series at the lock site, and it appears that no flow can pass from the Waterworks River to the City Mill River except under high flood conditions. The December 2002 Halcrow ‘Technical Report on the Stratford Box River Lea Flood Study’ (Reference 2) discusses the operational arrangements at the site. The main source of water in the City Mill River is from the Lea Navigation, via the Old River Lea, and from the south end where the City Mill River joins with Bow Back River. Here the system is also linked to the Waterworks River/Three Mills Wall River via the City Mill Lock.

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2.2 Tunnel Portal on Lea Navigation

In the vicinity of the proposed tunnel portal works the Lea Navigation is typically a 20 m wide rectangular channel lined by sheet pile walls. The water level under normal conditions is controlled by the structures downstream at the Three Mills Lock complex (not shown in Figure 1.1) and is maintained at approximately 103.10 mATD.

The most recent river survey information relating to the site is the British Waterways section labelled as chainage 3050. The cross section at this point is given in Annex B. This is assessed to be located close to the site of the proposed portal. Photograph 1 in Annex A shows the view from the east bank towpath to the west bank at this location.

2.2.1 Existing Flood Defences on Lea Navigation

Figure 2.1 shows the location of existing flood defences and the nature of land use along the river banks in the reach upstream of the portal site.

Along the east (left looking downstream) bank there is a paved tow path, at a level of 104.0 - 104.2 mATD. Immediately upstream of the proposed tunnel portal construction site the channel is contained by sheet piling and concrete walls on the west bank with top levels noted on the BW survey as between 106.1 and 107.1 mATD. On the east bank flood defence walls rise from the towpath with a top level of around 106.5 mATD. These flood defences continue upstream on both banks to the Docklands Light Railway / Great Eastern Main Line (DLR/GEML) Bridge. Continuing further upstream, on the east bank the flood defences are replaced by a railway embankment, estimated top level 110 mATD, and on the west bank a gravel embankment, estimated top level 108 mATD. After a second smaller rail bridge, leading into a depot, the east embankment is replaced by a plant yard with made ground at an approximate level of 106 mATD. This level reduces after a further 100 m to almost towpath level (104.2 mATD) in an area where assorted rubbish is stored. The east bank then rises again above 106 mATD towards the Greenway and Old Ford Nature Reserve.

The west embankment drops to a level of approximately 104.7 mATD approximately 400 m upstream of the proposed works site, beyond the gravel embankment. The bank here is formed by a sheet pile wall with a concrete pilecap. There are several small factories/ warehouses close to the channel in this area which are accessed via Autumn Street. Photograph 2 in Annex A shows the general view. It was noted that many of the factories nearest the channel appear to be derelict. In some places there are areas of low earth banks in front of the wall with a level of around 103.5 mATD. Near the Old Ford Lock, the riverside properties have concrete or masonry bank protection at a height of 105.1 mATD. There is a natural ground slope up from the channel with most properties being set back at higher levels. Either side of the Northern Outfall Sewer/Greenway Bridge there are plots of land currently being developed. At the Old Ford Lock, the retained water level rises by approximately 2 m. Under normal flow conditions, discharges through the control gates at this site provide the main inflow into the Lea Navigation / City Mill River network.

5 203357/31/Final/February 2005 AppH_2.doc Figure 2.1: Existing flood defences and photograph locations

Carpenters

Lock W a te rw o rk s R iv e r

a e L r e iv R ld O

r e v i R

l l i

P M u y d t Old Ford d i in C g Locks M i ll R Photograph 3 iv e r

R iv e r L Photograph 2 e a Photograph 4

Proposed City Mill River Crossing

City Mill Loch

T h re

e r ve M k Ri c i a l B l Proposed ow s B Pudding Mill Lane W a l l Portal R i v e Photograph 1 r

Proposed Crossrail Tunnel L ea Nav igation ± © Crown Copyright Legend: approximate locations

Flood defences Areas Under Development Proposed Crossrail Route

Rubbish tip Gravel Embankment DLR / GEML

Plant yard Railway Embankment Northern Outfall Sewer / Greenway Nature Reserve Industrial Areas Crossrail Line 1 Mott MacDonald Flood Risk Assessment - Pudding Mill Lane Portal Cross London Rail Links Limited

2.3 City Mill River Crossing

The Old River Lea connects the City Mill River to the River Lea Navigation downstream of the Old Ford Locks. The City Mill River is approximately 20 m wide, has a concrete lining and a high towpath on the east bank with a level of approximately 105.3 mATD.

The river cross section in the vicinity of the proposed crossing changes significantly as it passes under the existing DLR/GEML Bridge and then the Greenway/Northern Outfall Sewer Bridge. Between these two existing structures there is a triangular shaped bay.

The most appropriate survey section available for analysis of the new bridge works is the BW section labelled as chainage 750. This is given in Figure 2.2, the channel width at this point is approximately 13 m. Photograph 4 in Annex A shows the view from the Northern Sewer to the DLR/GEML Bridge.

It should be noted that upstream of this area the width of the channel reduces to a minimum of 10.8 m. These narrower sections will reduce the impact, in terms of afflux, of any construction causing a channel constriction at chainage 750. This narrower cross section is also given in Figure 2.2 overleaf.

2.3.1 Existing Flood Defences on City Mill River

A sheet-pile and concrete flood wall protects industrial properties along the full length of the west bank of the City Mill River upstream from the DLR/GEML Bridge to the Old River Lea, close to Carpenters Lock. This wall appears to be in reasonable condition, although in places some damage has occurred. Photograph 3 in Annex A shows this wall. The top level of the wall is approximately 105.3 mATD.

On the east bank, the towpath is backed by a steep bank up to railway yards at approximately 108 mATD for the full length from the DLR/GEML Bridge to the Old River Lea.

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Figure 2.2: Cross sections on the City Mill River

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3 Proposed Construction Works

3.1 Temporary Works

The information given below regarding the construction plans for the temporary works is based on the current best available information.

On both rivers the width of the free channel and the shape of the constriction are not yet finalised for the temporary works. In the following analysis various configurations are investigated for the River Lea. The channel of the City Mill River is assumed to have been reduced to the minimum navigation width, 5 m.

3.1.1 Tunnel Portal at the River Lea

It is proposed to construct a protective slab in the bed of the River Lea at the point where the tunnel passes underneath. This is due to poor ground conditions, the necessary removal of an existing sheet pile wall on the west bank of the river Lea and also in order to minimise the risk of contamination. It is required by British Waterways that the River Lea must remain navigable during the works. In order to ensure this, they require that a navigation channel of a minimum 5 m wide and 1.5 m deep be provided. Under the present construction plans there is some flexibility for width of this channel to be increased. A schematic plan of the navigation channel is given below. After the construction in this area is completed, the river system will be returned to its original state.

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Figure 3.1: Construction Plan at the Tunnel Portal on the River Lea Navigation

3.1.2 City Mill River Crossing

It is proposed that the new bridge over the City Mill River will be constructed as a concrete portal frame structure beneath the existing bridge. During the temporary works, the greatest restriction will be due to the construction of a working platform. At present, the exact form of temporary works has not been finalised; however analysis has been carried out assuming a worst case scenario by which the width of the channel is temporarily reduced to the minimum navigable width of 5 m. The other scenario being considered is to place the working platform on top of large culverts within the channel, this is detailed further in Annex C.

3.2 Permanent Works

As noted above, on completion of the temporary works for the tunnel portal at the Lea Navigation crossing, the river channel will be returned to its original condition. Therefore there will be no long term impact on flood risk.

The new Railway Bridge over the City Mill River when complete will provide a slight impedance to flow. The permanent works will consist of 800 mm thick new abutments built within the brick abutments of the existing DLR/GEML bridge. The towpath will also be inset by 800 mm to retain the existing towpath width.

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Figure 3.2: Section of the Crossrail Railway Bridge at City Mill River

Within this study the above constriction is modelled as shown in Figure 3.3 below. The proposed constriction will reduce the area of flow during an extreme flood event by less than 10%.

The bridge soffit level has been estimated, from drawings and photographs, to be approximately 107.7 mATD. As given in Table 4.1 in the following section, the most current modelling work estimates the 100-year flood level to be 105.04 mATD at the City Mill Bridge site. Therefore, the current clearance from the peak 100-year water level to the bridge soffit is 1.7 m. Following the construction of the City Mill River Bridge this clearance will be reduced by 800 mm to 0.9 m. It should be noted that this is 50% greater than the 600 mm clearance from the 100-year+20% level usually requested by the EA. These levels are indicated on Figure 3.3.

The new DLR bridge over the City Mill River should be designed to be have appropriate headroom, span and soffit levels to ensure that the bridge has no impact on flood risk.

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Figure 3.3: Cross section at City Mill River Bridge

8 Existing Conditions 7 Permanent Works 6

100-year flood level 5

4 Elevation (mAOD) Elevation

0 2 4 6 8 10 12 14 16 18 20 Chainage (m)

In addition, although the headroom and width are being reduced in this specific location, just to the north of the new structure the channel width is less than the current design proposal, and just to the south, the headroom under the Northern Outfall Sewer Bridge, is significantly less than the current design proposal.

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4 Hydraulic Modelling

4.1 Previous Modelling

Due to the complex nature of this system, flood flows and levels are dependant upon a wide range of factors. Critical factors include:

• Timing of tidal and fluvial flood peaks

• Downstream tidal levels

• Operation of gates in the area, including British Waterways locks, and their impact on flows in the Lea Navigation network

A number of hydraulic models have been developed covering this area. These have previously been used to model different flood scenarios in order to assess flood risk in a range of locations.

4.1.1 Halcrow

In 1997/98 Halcrow consultants carried out hydrological and hydraulic modelling of the Lower Lea from Feildes Weir near Hoddesdon to its confluence with the river Thames at Canning Town, 1km upstream of the Thames Barrier. The results of this modelling are given in the Final Report for the work issued in April 1998 (Reference 1). Hydrological data for the design flood events used in this modelling were provided by the EA from their FRQSIM model.

Further fluvial modelling was carried out in 2001/02 by Halcrow as part of Rail Link Engineering Consultants for the Channel Tunnel Rail Link Flood Study for the Stratford Box. Changes are reported to have been made from the 1998 hydraulic model in terms of new survey, better estimates of inflows into the River Lea from tributaries and revised arrangements for Carpenters Road Lock and at Bow Lock. The hydrological inputs however were still based on the EA’s FRQSIM model. The results from the modelling are given in the Technical Report on the Stratford Box River Lea Flood Study revised to December 2002 (Reference 2).

Work carried out by Halcrow, in January 2004, further updates the modelling of the Lower Lea by using hydrological inputs from Flood Estimation Handbook (FEH) analysis. The FEH methodology is now the generally accepted procedure for the analysis of flood events in the UK. During investigations for this Crossrail Flood Risk Assessment, Halcrow have, by agreement of the EA, provided us with output from this January 2004 modelling for fluvially dominated events. The January 2004 run was carried out for Rail Link Engineering regarding a development at the Temple Mills site. This is upstream of Carpenters Lock from where the majority of flow in the River Lea is diverted into the Waterworks River.

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Symonds completed further modelling of the Lower Lea area in January 2004 (Reference 4). This work was carried out in connection with the 2012 Olympic sites and takes account of the previous studies undertaken by Halcrow. This new modelling includes the 100-year fluvial event with tide levels at the Thames Barrier Closure trigger level, 104.72 mATD. This level is just below a 20-year tidal level as given in the EA 2002 study ‘Tidal Thames - Hydrodynamic Modelling’.

4.2 Modelling Carried Out for this Flood Risk Assessment

As part of this Flood Risk Assessment, Mott MacDonald initially carried out some local area calculations (reported in Section 6.2) for Crossrail, and compared these to the Symonds modelling. The Symonds modelling produced lower peak flood levels and flows at the proposed work sites (see Annex E) and so this was not taken forward as the worst design case scenario.

The EA requested that Crossrail carry out analysis using the Halcrow model, and so Halcrow were commissioned to update their hydraulic model to assess flood risk at the proposed worksites. The Halcrow model contains FRQSIM generated inflows using FEH rainfall, which were provided by the EA. Two storm durations were supplied, a 16.0hr duration storm (Storm 10) and a 30.5hr duration storm (Storm 105). For this assessment, both storm profiles have been investigated.

In order to model the worst design case conditions at the proposed worksites a number of modifications were made by Halcrow to the previous versions of their model. Tidal levels at the confluence with the River Thames were updated from the EA Study 'Tidal Thames - Hydrodynamic Modelling’, 2002. The study defined the peak levels at the confluence with the Thames as 104.74 mATD (20 year) and 104.85 mATD (200 year). The timing of the fluvial flood peak and peak tidal level was adjusted to determine the highest water levels within City Mill River and the Lea Navigation. The change in downstream tidal levels led to more flow being diverted over Carpenters Lock from the Waterworks River to the Lea Navigation System than had been predicted by the version of the model used in January 2004 for analysis of the Temple Mills site.

The latest model has been specifically updated to generate the worst design case conditions at the Crossrail worksites. Therefore, this most recent modelling is considered to be the most conservative case and supersedes previous work.

The following flood events were considered:

• 100yr fluvial/20yr tidal

• 20yr fluvial/200yr tidal

These boundaries are acknowledged to be conservative and more than cover the usual allowances for climate change. They have been accepted by the EA as a reasonable approach for this type of analysis. When considering the 20-year fluvial / 200-year tidal flood scenario it is assumed that the Thames Barrier is closed. In addition, as the analysis has

14 203357/31/Final/February 2005 AppH_2.doc Crossrail Line 1 Mott MacDonald Flood Risk Assessment - Pudding Mill Lane Portal Cross London Rail Links Limited been undertaken predominantly to investigate the impact of temporary works the impact of climate change has not been considered.

Table 4.1 summarises the peak flows and levels at the two proposed construction sites for these events.

Table 4.1: Baseline Conditions

Lea Navigation Works Site

Flood Return Period (yrs) Max. stage Max. flow Freeboard to Freeboard to (mATD) (cumecs) towpath (m) defences (m)

200 Tidal / 20 Fluvial 104.85 13.40 -0.70 1.25

100 Fluvial / 20 Tidal 105.02 24.60 -0.87 1.08

City Mill River Works Site

Flood return period (yrs) Max. stage Max. flow Freeboard to Freeboard to (mATD) (cumecs) towpath (m) defences (m)

200 Tidal / 20 Fluvial 104.87 9.23 0.43 0.43

100 Fluvial / 20 Tidal 105.04 13.11 0.26 0.26

The existing ‘freeboard to towpath’ is calculated from towpath levels taken from the Crossrail Pudding Mill Lane Portal Location Plan, 2003. These levels compare favourably with river cross sections obtained from British Waterways which were surveyed in 2002 and 2003.

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5 Current Flood Risk

The Tower Hamlets Unitary Development Plan (UDP) (1998) designates the River Lea as within a Flood Protection Area and states that those areas known to be at risk from flooding will require consultation with the EA and Thames Water Utilities for all planning applications for new development.

The EA publishes flood maps for all significant watercourses throughout England and Wales. These extents are available to the public via the internet and also to Local Authorities and other concerned bodies on CD. The new flood maps supersede the indicative floodplains previously published by the EA. In addition to showing the “at risk” areas without defences, the flood maps indicate areas nominally “at risk”, but protected by significant defences, including the influence of the Thames Barrier. The flood map for the Pudding Mill Lane area is given below.

Figure 5.1: EA Flood Map

The hatched areas on the figure above are areas which benefit from flood defences. The flood defences are shown on the figure as dashed magenta lines. The dark blue indicates areas which would lie within the 100-year fluvial floodplain or 200-year tidal floodplain without these defences. The light green/blue indicates the extreme flood outline. It should be noted that this is not significantly greater than the 100-year fluvial or 200-year tidal outline.

The 2002 Halcrow report, Reference 2, notes that: “[Section 2.3] Extensive flood alleviation works were carried out on the River Lea during the late 1960’s and 1970’s as part of the Lower Lea Flood Alleviation Scheme ... [Section 4.1] Now that the River Thames Barrier excludes surge tides from the River Lea, the lower reaches ... are protected from flooding to 16 203357/31/Final/February 2005 AppH_2.doc Crossrail Line 1 Mott MacDonald Flood Risk Assessment - Pudding Mill Lane Portal Cross London Rail Links Limited a high standard (exceeding 1000 years return period). The reaches further upstream are less well protected and are subject to flooding during periods of high flow in the river system. The Stratford site is approximately at the transition between these two reaches of the river. It is also the upstream limit of the tidal defences that were effective before the tidal exclusion barriers were constructed.”

The Stratford site, as referred to above, is approximately 1 km upstream of where the Crossrail alignment crosses the River Lea.

5.1 Current Flood Risk on Lea Navigation

Reference to Section 2.2.1 indicates that the existing defences / embankments at the tunnel portal worksite, upstream to the DLR/GEML Bridge and for 350 m beyond are at such a level as to protect against the 100-year fluvial and 200-year tidal flood levels (Table 4.1).

In the area marked as a rubbish tip on Figure 2.1 there is no containment of any flood flow over the towpath level. In the Nature Reserve, either side of the Northern Sewer, the natural high ground offers protection up to the 100-year fluvial and 200-year tidal flood levels.

The industrial area in the vicinity of Autumn Street along the western bank to the Northern Sewer Bridge is protected to a maximum level of 104.71 mATD and is therefore at risk in both of the peak flood events analysed (Table 4.1). In the area between the Northern Sewer and the Old Ford Locks, brick or stone bank protection has been constructed to a height of 105.11 mATD. This area is therefore protected against both the events analysed.

5.2 Current Flood Risk on City Mill River

Current flood risk on the City Mill River is very low. Flows are contained within the channel by the west bank defences and there is substantial freeboard to the towpath on the east bank for all flood events analysed.

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6 Hydraulic Analysis

6.1 Halcrow Model Output

The following runs were carried out for the 100-year fluvial and 200-year tidal flood events:

• Baseline conditions, no constriction at either of the proposed worksites

• Temporary works, 8 m width constriction at the River Lea worksite and 5 m width constriction at the City Mill River worksite

• Permanent works, no constriction on the River Lea, overall width of channel cross section reduced by 1600 mm on the City Mill River.

Further details of the constrictions as they were modelled are given in Annex C.

It should be noted that this modelling assumes that the temporary works cofferdam is to a level of 105.56 mATD. A lower level for this cofferdam is now proposed. See Section 6.3 for further details.

The following results were extracted from the mode (Tables 6.1 and 6.2):

Table 6.1: Temporary Works, Calculated Peak Levels during Flood Events

River Lea

Design case Constriction Flood level without Predicted flood Predicted afflux period (yrs) width (m) construction level with temporary (m) (mATD) works (mATD)

200 Tidal / 20 8 104.85 104.89 0.04 Fluvial

100 Fluvial / 20 8 105.02 105.14 0.12 Tidal

City Mill River

Design case Constriction Flood level without Predicted flood Predicted afflux period (yrs) width (m) construction level with temporary (m) (mATD) works (mATD)

200 Tidal / 20 5 104.87 104.91 0.04 Fluvial

100 Fluvial / 20 5 105.04 105.15 0.11 Tidal

18 203357/31/Final/February 2005 AppH_2.doc Crossrail Line 1 Mott MacDonald Flood Risk Assessment - Pudding Mill Lane Portal Cross London Rail Links Limited Full tables of model output are given in Annex D. The relevant nodes are r12 on the River Lea and cmr800 on the City Mill River. These nodes are highlighted in Annex D. Modelling was carried out for storm durations of both 16.5 hours and 30.5 hours. The shorter duration event was found to be more critical, therefore results were extracted for this event only.

It can be seen that the greatest afflux at the tunnel portal construction site occurs during the 100-year fluvial flood; the predicted rise in level is 0.12 m for the 8 m constriction width. The new flood level is 105.14 mATD.

At the City Mill River Crossing the greatest afflux generated by the temporary works also occurs during the 100-year fluvial event. The predicted afflux is 0.11 m and the resulting peak water level is 105.15 mATD.

The results from the model show that afflux is expected to reach the peak level immediately upstream of each worksite. There will be a small reduction in this afflux in the upstream lengths of both rivers. Although the afflux will still be significant as far upstream as the Old Ford Lock, Halcrow’s modelling shows that, at the predicted flood levels, the flow remains entirely within modelled banks along both the Lea Navigation and the City Mill River.

At the City Mill River crossing the revised bridge soffit level is approximately 1.7 m above the 100-year fluvial level across the whole width of the bridge. This estimated headroom is conservative as it includes both the impact of afflux and assumes the concrete portal has been constructed. This distance is significantly greater than the usual EA requirement of a minimum clearance to the soffit of 600 mm during the 100-year event.

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Table 6.2: Permanent Works, Calculated Peak Levels during Flood Events

River Lea

Design case Current flood level Predicted flood level Predicted return period Constriction without construction post construction afflux (m) (yrs) (mATD) (mATD)

200 Tidal / 20 None 104.85 104.85 0.00 Fluvial

100 Fluvial / 20 None 105.02 105.02 0.00 Tidal

City Mill River

Design case Current flood level Predicted flood level Predicted return period Constriction without construction post construction afflux (m) (yrs) (mATD) (mATD)

1600 mm 200 Tidal / 20 width 104.87 104.87 0.00 Fluvial reduction

1600 mm 100 Fluvial / 20 width 105.04 105.04 0.00 Tidal reduction

For the permanent works there is no obstruction to flow along the River Lea Navigation. The ISIS model shows that the permanent constriction along the City Mill River generates less than 5 mm afflux. This is too small to be identified within the Halcrow model and is therefore considered to be negligible.

For the permanent works the revised bridge soffit level is approximately 1.8 m above the 100-year fluvial level across the whole width of the bridge. Again, this distance is significantly greater than the usual EA requirement of a minimum clearance to the soffit of 600 mm during the 100-year event.

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6.2 Local Area Calculations for Other Widths of Constriction

In order to investigate the impact of varying the width of the constriction at the River Lea worksite, a series of calculations have been carried out to determine afflux generated upstream of the proposed worksite. This was carried out for 5 m, 8 m and 9 m constriction widths in both flood events analysed using the following expression [Reference 3: Waterway Design, AustRoads (1994)]:

2 2 2 2 h = Kα2V /2g + α1V /2g [(A/Adownstream) - (A/Aupstream) ] Where h = headloss K = headloss coefficient V = velocity α = approach velocity coefficient g = gravity A = cross-sectional area at the bridge.

Cross-section data was received from both Halcrow and British Waterways. Some minor inconsistencies were noted between the sections attributed to slight differences in the locations of the cross sections. The more recent and detailed cross section data from British Waterways was used in the analysis for this assessment.

These calculations only model the area in the immediate vicinity of the constriction and do not take into account hydraulic characteristics of adjacent sections. In order to verify the accuracy of these calculations they are compared against the results from the Halcrow ISIS model. Results are tabulated below.

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Table 6.3: Temporary Works at River Lea Portal

Design Constriction Flood level Halcrow - ISIS Mott MacDonald case storm width (m) without - local model return construction period (yrs) (mATD) Predicted Predicted Predicted Predicted afflux (m) flood level afflux (m) flood level with with temporary temporary works works (mATD) (mATD)

200 Tidal / 5 104.85 - - 0.18 105.03 20 Fluvial 8 104.85 0.04 104.89 0.05 104.90

9 104.85 - - 0.03 104.88

100 Fluvial / 5 105.02 - - 0.54 105.56 20 Tidal 8 105.02 0.12 105.14 0.14 105.16

9 105.02 - - 0.10 105.12

Comparison with the afflux predicted by the Halcrow ISIS model and the afflux calculated by the local area calculation shows broad agreement for the 8 m constriction on the River Lea, with the local model predicting slightly higher affluxes.

The greatest affluxes at the tunnel portal construction site occur during the 100-year fluvial flood. This shows rises in levels ranging from 0.54 m for a 5 m constriction width to 0.10 m for a 9 m constriction width. The new peak flood levels on the River Lea would be 105.56 mATD and 105.12 mATD respectively.

6.3 Local Area Calculations Following Revised Constriction Cross Section

An assumption made in the initial modelling stage was that the walls surrounding the construction area are higher than the water levels reached in any extreme flood event. Following discussions with the EA this has been revised. As described in Section 6.4 the new level of protection to the worksite is just below 104.20 mATD, rather than 105.56 mATD as previously modelled.

The impact of this change in terms of reducing the afflux generated has been estimated using the local area calculations described in Section 6.2. Revised results for the temporary works on the River Lea are given in Table 6.4 below. Only the 100 year fluvial event is considered as this is the most critical.

22 203357/31/Final/February 2005 AppH_2.doc Crossrail Line 1 Mott MacDonald Flood Risk Assessment - Pudding Mill Lane Portal Cross London Rail Links Limited Table 6.4: Revised Afflux on the River Lea at the River Lea Portal

Design case Constriction Flood level without Mott MacDonald - local model return period width (m) construction (yrs) (mATD) Predicted afflux Predicted flood level (m) with temporary works (mATD)

100 Fluvial / 20 5 105.02 0.14 105.16 Tidal 8 105.02 0.08 105.10

9 105.02 0.07 105.09

It can be seen that the impact on the afflux level for the 5 m constriction is significant, a reduction of almost 75% from 0.54 m to 0.14 m. For the 8 m constriction, the afflux is predicted to reduce by about 30%, to 0.08 m.

6.4 Flood Protection

(i) At the Tunnel Portal Worksite - Temporary

The proposed temporary works are to be completed prior to any tunnelling or portal works. A standard EA condition on works within channels is that the worksite protection should be arranged so that the works flood out prior to the river overtopping.

The normal water level is taken to be marginally higher than the level of the Weir at Three Mills, 103.09 mATD. The towpath level is 104.20 mATD, and this is the level at which the river is taken to be overtopping. The revised proposed top level for the cofferdam is set at a level marginally below this, giving a freeboard in excess of 1.0 m to the normal water level. This results in the crest of any works protection being more than 0.9 m below the 200-year flood level of the 100-year fluvial / 20-year tidal event.

It should be noted that this revised freeboard will result in a less severe channel constriction during the 1 in 200 event and will therefore reduce the afflux generated. This is discussed further in Section 6.3 above.

(ii) At the Tunnel Portal – Permanent

The predicated peak flood level is 105.02 mATD. Whilst the portal and access shaft is above this level, suitable design measures should be incorporated to ensure protection of at least an additional 1 m above the predicted peak flood level.

23 203357/31/Final/February 2005 AppH_2.doc Crossrail Line 1 Mott MacDonald Flood Risk Assessment - Pudding Mill Lane Portal Cross London Rail Links Limited (iii) Upstream of the Tunnel Portal Worksite

There are a number of locations upstream of the tunnel portal worksite, notably the rubbish tip and the industrial areas, which were identified during the site visit as currently being at risk of flooding during the 1 in 100 year fluvial event. The degree of risk to the industrial area would be better defined by topographic survey. Any increase in flood level, however incremental will increase the flood risk at these sites.

The duration of the temporary works is expected to be between 9 and 12 months. It is proposed that through this period the vulnerable areas described above are protected by temporary defences. The crest of these defences would be set at 300 mm above the 100 year flood level, including the calculated afflux. If required, there are a number of potential methods of temporary flood defence, including sandbags or more sophisticated barriers.

In addition it should be noted that the rubbish tip area would be acquired and used by Crossrail for the period of the temporary works. Therefore any increased risk at this area can be considered not to be critical.

6.5 Assumptions made in Hydraulic Modelling

The following assumptions were made in both the local area calculations and the ISIS hydraulic model:

• Manning’s roughness coefficient, n, is equal to 0.03 in the channel.

• Cross sections up and downstream of the construction site are representative of the actual river cross section at that point. This was verified as far as possible during the site visit.

• The temporary works would be carried out within the next few years and therefore flood flows and levels will not be significantly affected by climate change

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7 Conclusions

7.1 Temporary Tunnel Portal Works on Lea Navigation

The analysis of water levels on the Lea Navigation shows that for the design conditions considered, peak affluxes and flood levels occur during the 100-year fluvial/20-year tidal event. Reference to Table 6.4 shows that constricting the flow at the portal site to a 5 m wide navigation channel results, for the design events considered, in a predicted peak afflux of 0.14 m. If the width of the navigation channel is increased to 8 m this peak afflux is significantly reduced to a maximum of 0.08 m above the previous flood levels. The resultant peak flood level is 105.10 mATD.

A rise in 100-year fluvial flood levels of 0.14 m at the tunnel portal will not in itself cause a significant increase in flood risk, since the existing defences to the A11 road on the west bank and to the industrial properties on the east bank give a further 1 m freeboard or more. However the rise at the portal site will propagate upstream. It is expected that the increase in water level will still be significant 500 m upstream, where a number of small factories/workshops on the west bank are assessed to already be at risk from any flood in excess of 104.7 mATD.

If an 8 m wide temporary navigation channel is adopted then the localised increase in the fluvial 100-year peak levels reduces to 0.08 m. The increased water level will again propagate upstream. This increase in level may have a minor impact upon the areas already identified as being at flood risk between the portal and Old Ford Lock. This is primarily the industrial area closest to the river with access via Autumn Street. Topographic survey will be undertaken to identify the potential increase in flood risk in these areas. If necessary, temporary flood protection could be installed for the duration of the works.

The Halcrow model predicts that the flood level will overtop the towpath, but will remain otherwise in-bank up to Old Ford Lock.

7.2 Permanent Works for Lea Navigation at Tunnel Portal

On completion of the works to the bed and banks, of the River Lea Navigation, the river channel will be returned to its original state. There will therefore be no impact on flood risk from the permanent works at this site.

7.3 Temporary Works for City Mill Railway Bridge

The analysis of water levels on the City Mill River shows that for the three design events considered, constricting the flow to a 5 m wide navigation channel results in a peak afflux of 0.11 m. This maximum afflux is generated during the 100-year fluvial event and leads to peak flood levels of 105.15 mATD. The existing defences to the industrial sites on the west bank and the towpath on the east bank give protection to a level of 105.3 mATD for the full length of the river upstream to Carpenters Lock. Therefore a rise in 100-year fluvial flood levels of 0.11 m at the City Mill Bridge should cause no significant increase in flood risk either at the site or in the reach upstream.

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Reducing the channel width by some 0.8 m on each bank, by enlarging existing abutments, reduces the total area of flow by less than 10%. The afflux generated by this reduction is minimal, less than 5 mm and not observable in the Halcrow hydraulic model. This afflux is so small because of the very low flows passing through the City Mill River, even during the extreme flood events considered. The predicted peak flood level therefore remains at 105.04 mATD.

As the area is protected to a level of 105.3 mATD, such a minor rise in peak flood levels at the City Mill Bridge will be contained by existing flood defences. It will therefore cause no significant increase in flood risk, either at the site or in the reach upstream.

The new DLR bridge over the City Mill River should be designed to be have appropriate headroom, span and soffit levels to ensure that the bridge has no impact on flood risk.

7.5 General Conclusions

The Flood Risk Assessment has shown that:

• With a temporary constriction at the tunnel portal site to a navigable width of 8 m, the afflux produced will be small enough such that there is no significant increase in flood risk at the site itself.

• With the temporary constriction in place there may be a small increased flood risk to low lying areas upstream of the portal worksite on the River Lea. The risk should be verified by topographic survey and, if necessary, vulnerable areas protected by temporary flood defences for the duration of the works.

• Increases in peak flood levels from the permanent bridge works proposed on the City Mill River are minimal. The temporary bridge works on the City Mill River, here assumed to block all but the minimum 5 m navigation channel, also produce no significant increase in flood risk.

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References

1. Term Consultancy Hydraulic Modelling Lower Lea. Final Report, April 1998. Halcrow Consultants for EA Thames Region.

2. Channel Tunnel Rail Link Technical Report No. 230-RUG-RLEAZ-00001-AH, Stratford Box River Lea Flood Study, December 2002. Rail Link Engineering (Halcrow) Consultants for Union Railways.

3. Waterway Design. A Guide to the Hydraulic Design of Bridges, Culverts and Floodways. Austroads 1994

4. Strategic Flood Risk Assessment, Lower Lea Valley Masterplan Area. Baseline Flood Risk Assessment Report for the London Development Agency Report No. LLV-OL-ENV-01-P-002, January 2004. Symonds Group Ltd.

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Annex A: Site Photographs

Photograph 1: Pudding Mill Lane Portal location, western bank

Photograph 2: River Lea, properties upstream of the worksite

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Photograph 3: City Mill River, western bank upstream of worksite

Photograph 4: City Mill River Crossing location

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Annex B: British Waterways Cross Sections at the Proposed Worksite

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Annex C: Further details on constriction layout

C.1 Summary of works modelled on the City Mill River and River Lea

C.1.1 River Lea: Temporary works

The temporary works along the River Lea are assumed to be given by an 8 m width sudden constriction.

This constriction is assumed to occur between cross sections RL11 and RL12 in the Halcrow model. The centre line of the constriction is approximately 50 m downstream of the GEML / Docklands light railway bridge, opposite Wrexham Road. The centre line is at approximately the same location as British waterways cross section 3050. The constriction is assumed to be approximately 50 m in length. Construction occurs on one side of the channel at a time therefore the constriction is skewed to one side of the channel.

1) Schematic plan:

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2) Cross section used in ISIS modelling by Halcrow and Mott MacDonald’s local area calculations to represent the 8 m constriction.

No overtopping is allowed from the 8 m wide channel through the constriction. The 8 m channel for the second stage of the temporary works on to the right of the river centreline has a slightly larger cross section and will therefore produce slightly less afflux.

River Lee - constriction

7.0

6.0 Blackwall Tunnel 5.0

4.0

Heron 3.0 Industrial Estate Level (m AoD) 2.0

1.0

0.0 -5 0 5 10 15 20 25 Chainage (m)

C.1.2 River Lea: Permanent Works

None

C.1.3 City Mill River: Temporary Works

The temporary works along the City Mill River are assumed to be represented by a 5 m width (minimum navigation width) sudden constriction. The centreline of this constriction is assumed to be at cross section cmr800 in the Halcrow model, immediately downstream of the GEML / Docklands Light Railway Bridge. The constriction is assumed to have 90o ends and vertical sides and to be approximately 50 m in length. As above, construction occurs on one side of the channel at a time therefore the constriction is skewed to one side of the channel.

Cross section as modelled at the DLR Bridge showing constriction (Original cross section is shown for reference):

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Temporary works modelled at City Mill River Bridge

8 5m channel to be constructed on either side Elevation - this shows the worst case constriction 6

0 0 2 4 6 8 10 12 14 16 18 20 Chainage

An alternative scenario which is currently under discussion involves placing large pipe culverts within the channel and constructing the working platform on top of these. Culverts would be placed in the channel between the GEML/DLR Bridge and the sewer crossing so that headroom would not be impacted upon. In such a case the culverts would be sized such that their impact on flood levels was no more severe than that caused by the reduction to a 5 m width. In the event of water levels rising above the culvert soffit level, flood waters will be able to flow freely across the top of the working platform.

C.1.4 City Mill River: Permanent works

The permanent works consist of 800 mm thick abutments built within the abutments of the existing DLR Bridge.

Cross section as modelled showing additional restriction in channel due to the addition of concrete portal (original cross section is shown for reference):

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Permanent works modelled at City Mill River Bridge

Elevation 6

0 0 2 4 6 8 10 12 14 16 18 20 Chainage

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Annex D: Full Tables of Model Output

35 203357/31/Final/February 2005 AppH_2.doc Cross Rail - Hydraulic Modelling Table 1 Existing Conditions - Peak water levels (mAOD) and Flows (cumecs) under the 1 in 100yr fluvial event and 200yr tidal event

Node 100yr Fluvial Event (including 20yr tidal peak) 200yr Tidal Event (including 20yr fluvial event) Label Storm 105 Storm 10 Storm 105 Storm 10 Max Flow Max Stage Max Flow Max Stage Max Flow Max Stage Max Flow Max Stage 1056d 180.73 5.54 183.65 5.57 167.20 5.38 169.09 5.38 Carp593 17.85 5.04 18.40 5.05 15.28 4.81 15.21 4.88 Carp523u 17.87 5.03 18.41 5.04 15.12 4.81 15.03 4.88 Carp523d 7.10 5.03 7.15 5.04 6.35 4.81 6.39 4.88 Carp500 7.11 5.03 7.16 5.04 6.30 4.81 6.30 4.88 Carp450 7.12 5.03 7.17 5.04 6.18 4.81 6.14 4.88 Carp400 7.12 5.03 7.17 5.04 6.08 4.81 6.03 4.88 Carp350 7.13 5.03 7.18 5.04 5.98 4.81 5.92 4.88 Carp300 7.14 5.03 7.19 5.04 5.87 4.81 5.79 4.87 Carp250 7.14 5.03 7.19 5.04 5.77 4.81 5.68 4.87 Carp200 7.15 5.02 7.20 5.03 5.67 4.80 5.57 4.87 Carp150 7.16 5.02 7.20 5.03 5.56 4.80 5.46 4.87 Carp100 7.16 5.02 7.21 5.03 5.45 4.80 5.35 4.87 Navigation d/s Carpenters Lock Carp50 7.17 5.02 7.21 5.03 5.33 4.80 5.24 4.87 Carp1 7.18 5.02 7.22 5.03 5.20 4.80 5.12 4.87 rl27 23.15 5.02 24.53 5.03 12.99 4.80 13.05 4.87 rl26 23.16 5.02 24.54 5.03 12.73 4.80 12.90 4.87 rl23 23.17 5.01 24.55 5.02 12.52 4.80 12.94 4.87 rl19 23.17 5.02 24.56 5.02 12.55 4.80 12.98 4.87 rl18 23.21 5.01 24.58 5.01 12.75 4.80 13.15 4.86 rl17 23.24 5.00 24.59 5.01 12.80 4.80 13.27 4.86 rl16 23.25 5.00 24.59 5.00 12.77 4.80 13.33 4.85

Lee Navigation rl12 23.26 5.00 24.59 5.00 12.75 4.79 13.37 4.85 rl11 23.28 4.99 24.59 4.99 12.88 4.79 13.42 4.85 rl10 23.29 4.99 24.59 4.99 13.15 4.79 13.44 4.85 cmr050 11.84 5.03 12.30 5.04 9.05 4.81 9.03 4.88 cmr100 11.87 5.03 12.33 5.04 8.85 4.81 8.83 4.88 cmr150 11.90 5.03 12.36 5.04 8.61 4.81 8.62 4.88 cmr200 11.95 5.03 12.40 5.04 8.58 4.81 8.62 4.88 cmr259 12.05 5.03 12.46 5.04 8.61 4.81 8.65 4.88 cmr319 12.14 5.03 12.55 5.04 8.63 4.81 8.73 4.87 cmr363 12.20 5.03 12.60 5.04 8.64 4.81 8.78 4.87 cmr400 12.25 5.03 12.65 5.04 8.65 4.81 8.82 4.87 cmr500 12.42 5.03 12.80 5.04 8.68 4.81 8.95 4.87 cmr550 12.51 5.03 12.87 5.04 8.69 4.81 9.01 4.87 cmr600 12.59 5.03 12.94 5.04 8.70 4.81 9.08 4.87 cmr650 12.67 5.03 13.00 5.04 8.70 4.80 9.14 4.87 cmr700 12.73 5.03 13.06 5.04 8.71 4.80 9.19 4.87

City Mill River cmr750 12.80 5.03 13.11 5.04 8.71 4.80 9.23 4.87 cmr800 12.85 5.02 13.16 5.03 8.71 4.80 9.27 4.86 cmr833 12.88 5.02 13.20 5.03 8.70 4.80 9.30 4.86 cmr850 12.92 5.02 13.23 5.03 8.70 4.80 9.32 4.86 cmr900 12.96 5.02 13.27 5.03 8.69 4.80 9.35 4.86 cmr950 12.99 5.02 13.30 5.03 8.68 4.80 9.38 4.86 cmr1000 13.04 5.02 13.35 5.03 8.67 4.80 9.41 4.86 cmr1050 13.08 5.02 13.39 5.03 8.65 4.80 9.44 4.86 cmr1139u 13.18 5.02 13.48 5.03 8.61 4.80 9.49 4.86 cmr1139d 17.76 5.02 18.58 5.03 11.17 4.80 10.89 4.86 bbr005 17.76 5.00 18.60 5.01 10.53 4.80 10.32 4.85 bbr004 17.77 4.99 18.61 5.00 10.07 4.79 9.85 4.85 bbr003 17.77 4.98 18.61 4.99 10.05 4.79 9.83 4.85 bbr002 17.77 4.99 18.61 4.99 10.00 4.79 9.78 4.85 Bow Back bbr001 17.77 4.99 18.61 4.99 9.84 4.79 9.62 4.85 Cross Rail - Hydraulic Modelling Table 2 Temporary Works - Peak water levels (mAOD) and Flows (cumecs) under the 1 in 100yr fluvial event and 200yr tidal event

Node Storm 10 (16.5hr Storm Duration) Storm 105 (30.5hr Storm Duration) Label 100yr Fluvial Event (including 20yr tidal peak) 200yr Tidal Event (including 20yr fluvial event) 100yr Fluvial Event (including 20yr tidal peak) 200yr Tidal Event (including 20yr fluvial event) Peak Flows (cumecs) Diff Peak WL (mAOD) Diff Peak Flows (cumecs) Diff Peak WL (mAOD) Diff Peak Flows (cumecs)Diff Peak WL (mAOD)Diff Peak Flows (cumecs)Diff Peak WL (mAOD) Diff Existing Temp Wks (cumecs) Existing Temp Wks (m) Existing Temp Wks (cumecs) Existing Temp Wks (m) Existing Temp Wks (cumecs) Existing Temp Wks (m) Existing Temp Wks (cumecs) Existing Temp Wks (m) 1056d 183.65 183.64 -0.01 5.57 5.57 0.00 169.09 169.09 0.00 5.38 5.38 0.00 180.73 180.69 -0.03 5.54 5.54 0.00 167.20 167.21 0.00 5.38 5.38 0.00 Carp593 18.40 18.38 -0.01 5.05 5.16 0.11 15.21 15.21 0.00 4.88 4.92 0.04 17.85 17.87 0.01 5.04 5.13 0.09 15.28 15.28 0.00 4.81 4.85 0.04 Carp523u 18.41 18.38 -0.03 5.04 5.15 0.11 15.03 15.01 -0.02 4.88 4.91 0.04 17.87 17.86 -0.01 5.03 5.13 0.09 15.12 15.08 -0.04 4.81 4.85 0.04 Carp523d 7.15 6.71 -0.44 5.04 5.15 0.11 6.39 7.35 0.97 4.88 4.91 0.04 7.10 6.79 -0.31 5.03 5.13 0.09 6.35 7.43 1.08 4.81 4.85 0.04 Carp500 7.16 6.71 -0.45 5.04 5.15 0.11 6.30 7.28 0.99 4.88 4.91 0.04 7.11 6.78 -0.33 5.03 5.13 0.09 6.30 7.37 1.07 4.81 4.85 0.04 Carp450 7.17 6.69 -0.48 5.04 5.15 0.11 6.14 7.13 0.99 4.88 4.91 0.04 7.12 6.77 -0.35 5.03 5.13 0.10 6.18 7.22 1.04 4.81 4.85 0.04 Carp400 7.17 6.68 -0.49 5.04 5.15 0.11 6.03 7.01 0.98 4.88 4.91 0.04 7.12 6.76 -0.36 5.03 5.12 0.10 6.08 7.10 1.02 4.81 4.85 0.04 Carp350 7.18 6.68 -0.50 5.04 5.15 0.11 5.92 6.88 0.96 4.88 4.91 0.04 7.13 6.75 -0.38 5.03 5.12 0.09 5.98 6.98 1.00 4.81 4.85 0.04 Carp300 7.19 6.67 -0.52 5.04 5.15 0.11 5.79 6.74 0.94 4.87 4.91 0.04 7.14 6.75 -0.39 5.03 5.12 0.10 5.87 6.84 0.98 4.81 4.85 0.04 Carp250 7.19 6.67 -0.52 5.04 5.15 0.11 5.68 6.61 0.93 4.87 4.91 0.04 7.14 6.74 -0.40 5.03 5.12 0.10 5.77 6.72 0.96 4.81 4.85 0.04 Carp200 7.20 6.66 -0.54 5.03 5.15 0.11 5.57 6.49 0.92 4.87 4.91 0.04 7.15 6.74 -0.41 5.02 5.12 0.10 5.67 6.60 0.94 4.80 4.85 0.04 Carp150 7.20 6.66 -0.55 5.03 5.14 0.11 5.46 6.35 0.89 4.87 4.91 0.04 7.16 6.73 -0.43 5.02 5.12 0.10 5.56 6.48 0.92 4.80 4.85 0.04 Carp100 7.21 6.65 -0.56 5.03 5.14 0.11 5.35 6.21 0.86 4.87 4.91 0.04 7.16 6.73 -0.44 5.02 5.12 0.10 5.45 6.34 0.90 4.80 4.84 0.04 Navigation d/s Carpenters Lock Carp50 7.21 6.64 -0.57 5.03 5.14 0.11 5.24 6.07 0.83 4.87 4.91 0.04 7.17 6.72 -0.45 5.02 5.12 0.10 5.33 6.20 0.88 4.80 4.84 0.04 Carp1 7.22 6.64 -0.58 5.03 5.14 0.11 5.12 5.92 0.80 4.87 4.91 0.03 7.18 6.71 -0.46 5.02 5.12 0.10 5.20 6.06 0.86 4.80 4.84 0.04 rl27 24.53 23.95 -0.58 5.03 5.14 0.11 13.05 13.70 0.65 4.87 4.91 0.03 23.15 22.69 -0.45 5.02 5.12 0.10 12.99 13.77 0.78 4.80 4.84 0.04 rl26 24.54 23.94 -0.61 5.03 5.14 0.11 12.90 13.63 0.73 4.87 4.91 0.04 23.16 22.69 -0.46 5.02 5.12 0.10 12.73 13.50 0.77 4.80 4.84 0.04 rl23 24.55 23.93 -0.62 5.02 5.14 0.11 12.94 13.65 0.70 4.87 4.90 0.04 23.17 22.69 -0.48 5.01 5.11 0.10 12.52 13.34 0.82 4.80 4.84 0.04 rl19 24.56 23.92 -0.64 5.02 5.14 0.11 12.98 13.66 0.67 4.87 4.90 0.04 23.17 22.69 -0.48 5.02 5.12 0.10 12.55 13.19 0.64 4.80 4.84 0.04 rl18 24.58 23.90 -0.68 5.01 5.13 0.11 13.15 13.70 0.55 4.86 4.90 0.04 23.21 22.68 -0.53 5.01 5.11 0.10 12.75 13.15 0.40 4.80 4.84 0.04 rl17 24.59 23.89 -0.70 5.01 5.12 0.12 13.27 13.73 0.46 4.86 4.89 0.04 23.24 22.67 -0.57 5.00 5.10 0.10 12.80 13.07 0.28 4.80 4.84 0.04 rl16 24.59 23.88 -0.71 5.00 5.12 0.12 13.33 13.74 0.41 4.85 4.89 0.04 23.25 22.66 -0.60 5.00 5.10 0.10 12.77 13.32 0.54 4.80 4.84 0.04

Lee Navigation rl12 24.59 23.87 -0.72 5.00 5.12 0.12 13.37 13.75 0.38 4.85 4.89 0.04 23.26 22.73 -0.53 5.00 5.10 0.10 12.75 13.47 0.72 4.79 4.84 0.04 rl11 24.59 23.86 -0.73 4.99 4.99 0.00 13.42 13.97 0.55 4.85 4.85 0.00 23.28 22.92 -0.37 4.99 4.98 0.00 12.88 13.74 0.86 4.79 4.80 0.00 rl10 24.59 23.99 -0.59 4.99 4.99 0.00 13.44 14.23 0.79 4.85 4.85 0.00 23.29 23.08 -0.21 4.99 4.98 0.00 13.15 13.98 0.83 4.79 4.80 0.00 cmr050 12.30 11.68 -0.61 5.04 5.15 0.11 9.03 7.75 -1.28 4.88 4.91 0.04 11.84 11.10 -0.74 5.03 5.13 0.09 9.05 7.68 -1.37 4.81 4.85 0.04 cmr100 12.33 11.68 -0.65 5.04 5.15 0.11 8.83 7.56 -1.28 4.88 4.91 0.04 11.87 11.11 -0.76 5.03 5.13 0.09 8.85 7.54 -1.32 4.81 4.85 0.04 cmr150 12.36 11.67 -0.69 5.04 5.15 0.11 8.62 7.48 -1.14 4.88 4.91 0.04 11.90 11.12 -0.79 5.03 5.13 0.09 8.61 7.40 -1.21 4.81 4.85 0.04 cmr200 12.40 11.67 -0.73 5.04 5.15 0.11 8.62 7.44 -1.17 4.88 4.91 0.04 11.95 11.16 -0.79 5.03 5.13 0.09 8.58 7.31 -1.27 4.81 4.85 0.04 cmr259 12.46 11.73 -0.73 5.04 5.15 0.11 8.65 7.42 -1.23 4.88 4.91 0.04 12.05 11.24 -0.81 5.03 5.13 0.09 8.61 7.29 -1.31 4.81 4.85 0.04 cmr319 12.55 11.79 -0.76 5.04 5.15 0.11 8.73 7.46 -1.27 4.87 4.91 0.04 12.14 11.32 -0.83 5.03 5.13 0.09 8.63 7.28 -1.35 4.81 4.85 0.04 cmr363 12.60 11.82 -0.78 5.04 5.15 0.11 8.78 7.48 -1.30 4.87 4.91 0.04 12.20 11.37 -0.84 5.03 5.12 0.09 8.64 7.27 -1.37 4.81 4.85 0.04 cmr400 12.65 11.86 -0.79 5.04 5.15 0.11 8.82 7.50 -1.32 4.87 4.91 0.04 12.25 11.41 -0.85 5.03 5.12 0.09 8.65 7.26 -1.39 4.81 4.85 0.04 cmr500 12.80 11.95 -0.84 5.04 5.15 0.11 8.95 7.55 -1.39 4.87 4.91 0.04 12.42 11.55 -0.87 5.03 5.12 0.09 8.68 7.22 -1.46 4.81 4.85 0.04 cmr550 12.87 12.00 -0.87 5.04 5.15 0.11 9.01 7.58 -1.43 4.87 4.91 0.04 12.51 11.61 -0.89 5.03 5.12 0.09 8.69 7.20 -1.49 4.81 4.85 0.04 cmr600 12.94 12.05 -0.89 5.04 5.15 0.11 9.08 7.61 -1.47 4.87 4.91 0.04 12.59 11.68 -0.91 5.03 5.12 0.10 8.70 7.17 -1.52 4.81 4.85 0.04 cmr650 13.00 12.10 -0.90 5.04 5.14 0.11 9.14 7.63 -1.50 4.87 4.91 0.04 12.67 11.74 -0.92 5.03 5.12 0.09 8.70 7.15 -1.55 4.80 4.85 0.04 cmr700 13.06 12.14 -0.92 5.04 5.14 0.11 9.19 7.66 -1.53 4.87 4.91 0.04 12.73 11.80 -0.94 5.03 5.12 0.10 8.71 7.13 -1.58 4.80 4.85 0.04

City Mill River cmr750 13.11 12.19 -0.93 5.04 5.14 0.11 9.23 7.67 -1.56 4.87 4.91 0.04 12.80 11.84 -0.95 5.03 5.12 0.09 8.71 7.11 -1.60 4.80 4.85 0.04 cmr800 13.16 12.21 -0.95 5.03 5.14 0.11 9.27 7.68 -1.59 4.86 4.91 0.04 12.85 11.87 -0.98 5.02 5.12 0.10 8.71 7.09 -1.61 4.80 4.85 0.04 cmr833 13.20 12.23 -0.97 5.03 5.03 0.00 9.30 7.69 -1.61 4.86 4.86 -0.01 12.88 11.88 -1.00 5.02 5.02 0.00 8.70 7.10 -1.61 4.80 4.80 0.00 cmr850 13.23 12.27 -0.95 5.03 5.03 0.00 9.32 7.69 -1.63 4.86 4.85 -0.01 12.92 11.91 -1.00 5.02 5.02 0.00 8.70 7.10 -1.60 4.80 4.80 0.00 cmr900 13.27 12.34 -0.93 5.03 5.03 0.00 9.35 7.70 -1.65 4.86 4.85 -0.01 12.96 11.95 -1.01 5.02 5.02 0.00 8.69 7.11 -1.58 4.80 4.80 0.00 cmr950 13.30 12.39 -0.92 5.03 5.03 0.00 9.38 7.70 -1.68 4.86 4.85 -0.01 12.99 11.99 -1.01 5.02 5.01 -0.01 8.68 7.14 -1.54 4.80 4.80 0.00 cmr1000 13.35 12.45 -0.90 5.03 5.03 0.00 9.41 7.71 -1.70 4.86 4.85 -0.01 13.04 12.02 -1.01 5.02 5.02 0.00 8.67 7.20 -1.47 4.80 4.80 0.00 cmr1050 13.39 12.52 -0.87 5.03 5.03 0.00 9.44 7.71 -1.73 4.86 4.85 -0.01 13.08 12.07 -1.02 5.02 5.01 0.00 8.65 7.27 -1.38 4.80 4.80 0.00 cmr1139u 13.48 12.66 -0.82 5.03 5.03 0.00 9.49 7.71 -1.78 4.86 4.85 -0.01 13.18 12.16 -1.02 5.02 5.01 0.00 8.61 7.41 -1.20 4.80 4.80 0.00 cmr1139d 18.58 18.73 0.15 5.03 5.03 0.00 10.89 9.87 -1.02 4.86 4.85 -0.01 17.76 17.79 0.03 5.02 5.01 0.00 11.17 9.96 -1.22 4.80 4.80 0.00 bbr005 18.60 18.72 0.12 5.01 5.01 0.00 10.32 9.32 -1.00 4.85 4.85 0.00 17.76 17.79 0.03 5.00 5.00 -0.01 10.53 9.36 -1.18 4.80 4.80 0.00 bbr004 18.61 18.71 0.09 5.00 4.99 0.00 9.85 8.78 -1.06 4.85 4.85 0.00 17.77 17.79 0.03 4.99 4.99 0.00 10.07 8.81 -1.26 4.79 4.80 0.00 bbr003 18.61 18.71 0.09 4.99 4.99 0.00 9.83 8.76 -1.07 4.85 4.85 0.00 17.77 17.79 0.03 4.98 4.98 0.00 10.05 8.79 -1.26 4.79 4.80 0.00 bbr002 18.61 18.70 0.09 4.99 4.99 0.00 9.78 8.70 -1.07 4.85 4.85 0.00 17.77 17.79 0.02 4.99 4.98 0.00 10.00 8.73 -1.27 4.79 4.80 0.00 Bow Back Back Bow bbr001 18.61 18.70 0.09 4.99 4.99 0.00 9.62 8.52 -1.10 4.85 4.85 0.00 17.77 17.79 0.02 4.99 4.98 0.00 9.84 8.54 -1.30 4.79 4.80 0.00 Cross Rail - Hydraulic Modelling Table 3 Permanent Works - Peak water levels (mAOD) and Flows (cumecs) under the 1 in 100yr fluvial event and 200yr tidal event

Node Storm 10 (16.5hr Storm Duration) Storm 105 (30.5hr Storm Duration) Label 100yr Fluvial Event (including 20yr tidal peak) 200yr Tidal Event (including 20yr fluvial event) 100yr Fluvial Event (including 20yr tidal peak) 200yr Tidal Event (including 20yr fluvial event) Peak Flows (cumecs) Diff Peak WL (mAOD)Diff Peak Flows (cumecs) Diff Peak WL (mAOD) Diff Peak Flows (cumecs)Diff Peak WL (mAOD)Diff Peak Flows (cumecs)Diff Peak WL (mAOD) Diff Existing Temp Wks (cumecs) Existing Temp Wks (m) Existing Temp Wks (cumecs) Existing Temp Wks (m) Existing Temp Wks (cumecs) Existing Temp Wks (m) Existing Temp Wks (cumecs) Existing Temp Wks (m) 1056d 183.65 183.66 0.02 5.57 5.57 0.00 169.09 169.09 0.00 5.38 5.38 0.00 180.73 180.73 0.00 5.54 5.54 0.00 167.20 167.20 0.00 5.38 5.38 0.00 Carp593 18.40 18.37 -0.03 5.05 5.05 0.00 15.21 15.21 0.00 4.88 4.88 0.00 17.85 17.85 0.00 5.04 5.04 0.00 15.28 15.28 0.00 4.81 4.81 0.00 Carp523u 18.41 18.38 -0.03 5.04 5.04 0.00 15.03 15.03 0.00 4.88 4.88 0.00 17.87 17.87 0.00 5.03 5.03 0.00 15.12 15.12 0.00 4.81 4.81 0.00 Carp523d 7.15 7.16 0.01 5.04 5.04 0.00 6.39 6.41 0.02 4.88 4.88 0.00 7.10 7.13 0.03 5.03 5.03 0.00 6.35 6.37 0.02 4.81 4.81 0.00 Carp500 7.16 7.17 0.01 5.04 5.04 0.00 6.30 6.32 0.02 4.88 4.88 0.00 7.11 7.14 0.03 5.03 5.03 0.00 6.30 6.32 0.02 4.81 4.81 0.00 Carp450 7.17 7.17 0.01 5.04 5.04 0.00 6.14 6.16 0.02 4.88 4.88 0.00 7.12 7.14 0.03 5.03 5.03 0.00 6.18 6.20 0.02 4.81 4.81 0.00 Carp400 7.17 7.18 0.00 5.04 5.04 0.00 6.03 6.05 0.02 4.88 4.88 0.00 7.12 7.15 0.03 5.03 5.03 0.00 6.08 6.10 0.02 4.81 4.81 0.00 Carp350 7.18 7.18 0.00 5.04 5.04 0.00 5.92 5.94 0.02 4.88 4.88 0.00 7.13 7.16 0.03 5.03 5.03 0.00 5.98 6.00 0.02 4.81 4.81 0.00 Carp300 7.19 7.19 0.00 5.04 5.04 0.00 5.79 5.81 0.02 4.87 4.88 0.00 7.14 7.17 0.03 5.03 5.03 0.00 5.87 5.89 0.02 4.81 4.81 0.00 Carp250 7.19 7.19 0.00 5.04 5.04 0.00 5.68 5.70 0.02 4.87 4.87 0.00 7.14 7.17 0.03 5.03 5.03 0.00 5.77 5.79 0.02 4.81 4.81 0.00 Carp200 7.20 7.20 0.00 5.03 5.04 0.00 5.57 5.59 0.02 4.87 4.87 0.00 7.15 7.18 0.03 5.02 5.02 0.00 5.67 5.69 0.02 4.80 4.81 0.00 Carp150 7.20 7.20 0.00 5.03 5.04 0.00 5.46 5.48 0.02 4.87 4.87 0.00 7.16 7.19 0.03 5.02 5.02 0.00 5.56 5.58 0.02 4.80 4.81 0.00 Carp100 7.21 7.21 0.00 5.03 5.03 0.00 5.35 5.37 0.02 4.87 4.87 0.00 7.16 7.19 0.03 5.02 5.02 0.00 5.45 5.46 0.02 4.80 4.80 0.00 Navigation d/s Carpenters Lock Carp50 7.21 7.21 0.00 5.03 5.03 0.00 5.24 5.26 0.02 4.87 4.87 0.00 7.17 7.20 0.03 5.02 5.02 0.00 5.33 5.34 0.02 4.80 4.80 0.00 Carp1 7.22 7.21 0.00 5.03 5.03 0.00 5.12 5.14 0.02 4.87 4.87 0.00 7.18 7.20 0.03 5.02 5.02 0.00 5.20 5.22 0.02 4.80 4.80 0.00 rl27 24.53 24.53 0.00 5.03 5.03 0.00 13.05 13.07 0.02 4.87 4.87 0.00 23.15 23.17 0.03 5.02 5.02 0.00 12.99 13.01 0.02 4.80 4.80 0.00 rl26 24.54 24.54 -0.01 5.03 5.03 0.00 12.90 12.93 0.03 4.87 4.87 0.00 23.16 23.19 0.03 5.02 5.02 0.00 12.73 12.74 0.02 4.80 4.80 0.00 rl23 24.55 24.54 -0.01 5.02 5.02 0.00 12.94 12.97 0.03 4.87 4.87 0.00 23.17 23.19 0.03 5.01 5.01 0.00 12.52 12.53 0.02 4.80 4.80 0.00 rl19 24.56 24.55 -0.01 5.02 5.03 0.00 12.98 13.01 0.03 4.87 4.87 0.00 23.17 23.20 0.03 5.02 5.02 0.00 12.55 12.58 0.03 4.80 4.80 0.00 rl18 24.58 24.57 -0.02 5.01 5.02 0.00 13.15 13.18 0.03 4.86 4.86 0.00 23.21 23.24 0.03 5.01 5.01 0.00 12.75 12.78 0.03 4.80 4.80 0.00 rl17 24.59 24.58 -0.01 5.01 5.01 0.00 13.27 13.30 0.03 4.86 4.86 0.00 23.24 23.27 0.03 5.00 5.00 0.00 12.80 12.83 0.03 4.80 4.80 0.00 rl16 24.59 24.59 -0.01 5.00 5.01 0.00 13.33 13.37 0.03 4.85 4.85 0.00 23.25 23.28 0.03 5.00 5.00 0.00 12.77 12.80 0.03 4.80 4.80 0.00

Lee Navigation rl12 24.59 24.59 0.00 5.00 5.00 0.00 13.37 13.40 0.03 4.85 4.85 0.00 23.26 23.29 0.03 5.00 5.00 0.00 12.75 12.78 0.03 4.79 4.80 0.00 rl11 24.59 24.60 0.01 4.99 4.99 0.00 13.42 13.45 0.03 4.85 4.85 0.00 23.28 23.31 0.03 4.99 4.99 0.00 12.88 12.92 0.03 4.79 4.79 0.00 rl10 24.59 24.61 0.02 4.99 5.00 0.00 13.44 13.47 0.03 4.85 4.85 0.00 23.29 23.32 0.03 4.99 4.99 0.00 13.15 13.18 0.03 4.79 4.79 0.00 cmr050 12.30 12.21 -0.08 5.04 5.04 0.00 9.03 9.01 -0.02 4.88 4.88 0.00 11.84 11.80 -0.04 5.03 5.03 0.00 9.05 9.03 -0.02 4.81 4.81 0.00 cmr100 12.33 12.24 -0.08 5.04 5.04 0.00 8.83 8.81 -0.02 4.88 4.88 0.00 11.87 11.83 -0.04 5.03 5.03 0.00 8.85 8.83 -0.02 4.81 4.81 0.00 cmr150 12.36 12.28 -0.08 5.04 5.04 0.00 8.62 8.61 -0.02 4.88 4.88 0.00 11.90 11.86 -0.04 5.03 5.03 0.00 8.61 8.59 -0.02 4.81 4.81 0.00 cmr200 12.40 12.32 -0.08 5.04 5.04 0.00 8.62 8.60 -0.01 4.88 4.88 0.00 11.95 11.91 -0.04 5.03 5.03 0.00 8.58 8.56 -0.03 4.81 4.81 0.00 cmr259 12.46 12.40 -0.06 5.04 5.04 0.00 8.65 8.63 -0.03 4.88 4.88 0.00 12.05 12.01 -0.04 5.03 5.03 0.00 8.61 8.58 -0.03 4.81 4.81 0.00 cmr319 12.55 12.47 -0.07 5.04 5.04 0.00 8.73 8.70 -0.03 4.87 4.87 0.00 12.14 12.10 -0.04 5.03 5.03 0.00 8.63 8.60 -0.03 4.81 4.81 0.00 cmr363 12.60 12.52 -0.08 5.04 5.04 0.00 8.78 8.75 -0.03 4.87 4.87 0.00 12.20 12.16 -0.04 5.03 5.03 0.00 8.64 8.61 -0.02 4.81 4.81 0.00 cmr400 12.65 12.56 -0.09 5.04 5.04 0.00 8.82 8.79 -0.03 4.87 4.87 0.00 12.25 12.21 -0.04 5.03 5.03 0.00 8.65 8.62 -0.02 4.81 4.81 0.00 cmr500 12.80 12.70 -0.10 5.04 5.04 0.00 8.95 8.92 -0.03 4.87 4.87 0.00 12.42 12.38 -0.04 5.03 5.03 0.00 8.68 8.65 -0.02 4.81 4.81 0.00 cmr550 12.87 12.77 -0.09 5.04 5.04 0.00 9.01 8.99 -0.02 4.87 4.87 0.00 12.51 12.47 -0.04 5.03 5.03 0.00 8.69 8.66 -0.02 4.81 4.81 0.00 cmr600 12.94 12.85 -0.09 5.04 5.04 0.00 9.08 9.05 -0.02 4.87 4.87 0.00 12.59 12.55 -0.04 5.03 5.03 0.00 8.70 8.67 -0.02 4.81 4.81 0.00 cmr650 13.00 12.92 -0.09 5.04 5.04 0.00 9.14 9.11 -0.02 4.87 4.87 0.00 12.67 12.63 -0.04 5.03 5.03 0.00 8.70 8.68 -0.02 4.80 4.81 0.00 cmr700 13.06 12.98 -0.08 5.04 5.04 0.00 9.19 9.17 -0.02 4.87 4.87 0.00 12.73 12.70 -0.04 5.03 5.03 0.00 8.71 8.69 -0.02 4.80 4.81 0.00

City Mill River cmr750 13.11 13.04 -0.08 5.04 5.04 0.00 9.23 9.21 -0.02 4.87 4.87 0.00 12.80 12.76 -0.04 5.03 5.03 0.00 8.71 8.69 -0.02 4.80 4.80 0.00 cmr800 13.16 13.09 -0.08 5.03 5.03 0.00 9.27 9.25 -0.02 4.86 4.86 0.00 12.85 12.81 -0.04 5.02 5.02 0.00 8.71 8.69 -0.02 4.80 4.80 0.00 cmr833 13.20 13.12 -0.08 5.03 5.03 0.00 9.30 9.28 -0.02 4.86 4.86 0.00 12.88 12.84 -0.04 5.02 5.02 0.00 8.70 8.68 -0.02 4.80 4.80 0.00 cmr850 13.23 13.15 -0.07 5.03 5.03 0.00 9.32 9.30 -0.03 4.86 4.86 0.00 12.92 12.87 -0.05 5.02 5.02 0.00 8.70 8.68 -0.02 4.80 4.80 0.00 cmr900 13.27 13.20 -0.07 5.03 5.03 0.00 9.35 9.33 -0.02 4.86 4.86 0.00 12.96 12.91 -0.05 5.02 5.02 0.00 8.69 8.67 -0.02 4.80 4.80 0.00 cmr950 13.30 13.24 -0.06 5.03 5.03 0.00 9.38 9.35 -0.03 4.86 4.86 0.00 12.99 12.95 -0.05 5.02 5.02 0.00 8.68 8.67 -0.02 4.80 4.80 0.00 cmr1000 13.35 13.29 -0.06 5.03 5.03 0.00 9.41 9.38 -0.02 4.86 4.86 0.00 13.04 12.99 -0.05 5.02 5.02 0.00 8.67 8.65 -0.02 4.80 4.80 0.00 cmr1050 13.39 13.34 -0.05 5.03 5.03 0.00 9.44 9.41 -0.02 4.86 4.86 0.00 13.08 13.04 -0.05 5.02 5.02 0.00 8.65 8.63 -0.02 4.80 4.80 0.00 cmr1139u 13.48 13.45 -0.02 5.03 5.03 0.00 9.49 9.47 -0.02 4.86 4.86 0.00 13.18 13.13 -0.05 5.02 5.02 0.00 8.61 8.59 -0.02 4.80 4.80 0.00 cmr1139d 18.58 18.54 -0.04 5.03 5.03 0.00 10.89 10.89 0.00 4.86 4.86 0.00 17.76 17.73 -0.03 5.02 5.02 0.00 11.17 11.17 0.00 4.80 4.80 0.00 bbr005 18.60 18.54 -0.05 5.01 5.01 0.00 10.32 10.31 0.00 4.85 4.85 0.00 17.76 17.74 -0.03 5.00 5.00 0.00 10.53 10.53 0.00 4.80 4.80 0.00 bbr004 18.61 18.55 -0.06 5.00 5.00 0.00 9.85 9.84 0.00 4.85 4.85 0.00 17.77 17.74 -0.03 4.99 4.99 0.00 10.07 10.06 0.00 4.79 4.79 0.00 bbr003 18.61 18.55 -0.06 4.99 4.99 0.00 9.83 9.83 0.00 4.85 4.85 0.00 17.77 17.74 -0.03 4.98 4.98 0.00 10.05 10.05 0.00 4.79 4.79 0.00 bbr002 18.61 18.55 -0.06 4.99 5.00 0.00 9.78 9.77 0.00 4.85 4.85 0.00 17.77 17.74 -0.03 4.99 4.99 0.00 10.00 9.99 0.00 4.79 4.79 0.00 Bow Back Back Bow bbr001 18.61 18.55 -0.07 4.99 5.00 0.00 9.62 9.62 0.00 4.85 4.85 0.00 17.77 17.74 -0.03 4.99 4.99 0.00 9.84 9.83 0.00 4.79 4.79 0.00 Crossrail Line 1 Mott MacDonald Flood Risk Assessment - Pudding Mill Lane Portal Cross London Rail Links Limited

Annex E: Output from Symonds Modelling

Table E1: Modelled Peak Flood Levels (mATD)

100yr 100yr 100yr fluvial / 100yr fluvial / 100yr fluvial / fluvial+20% / fluvial+20% / 10 year tidal 20 year tidal Barrier Closure 20 year tidal Barrier Closure

104.279 104.315 104.308 104.928 104.936

104.280 104.315 104.309 104.930 104.938

104.281 104.316 104.310 104.930 104.939

104.295 104.331 104.325 104.955 104.967

104.295 104.330 104.324 104.955 104.966

104.294 104.330 104.324 104.954 104.965

104.293 104.329 104.322 104.953 104.964

36 203357/31/Final/February 2005 AppH_2.doc