Hinksey Flood Alleviation Scheme Sink or Swim

Transcription

1 Hinksey Flood Alleviation Scheme Sink or Swim Hinksey Flood Alleviation Scheme Sink or Swim; Enhancing asset resilience a case study in tackling flooding on the railway Presented by: Paul Armitage, Project Manager Network Rail November November

2 Agenda 1. Hinksey geography 2. The problem of flooding and the impact on the railway 3. The reason to improve flood resilience 4. Option selection using flood modelling 5. The Hinksey flood alleviation scheme scope of works 6. Planning the possession 7. The 16 day blockade

3 Introduction Hinksey Flood Alleviation Scheme Sink or Swim 3

4 Geography Area of consideration To Didcot Parkway and London 4

5 The Network 1. Key strategic passenger and freight line from Didcot to north 2. Used by 7.5m passengers annually 3. Freight line supports high value automotive traffic for export 4. 2 track railway, signal controlled with track circuits, 90mph line speed 5

6 The problem The whole area floods 6

7 The whole area floods all the time Telegraph 11 times in the last 14 years 7

8 The business case Train delays in the area are roughly 400 per minute. In the last 3 years Hinksey has flooded causing in excess of 16 Million per year Politically VERY sensitive This job was a top 10 urgent requirement from David Cameron Network Rail was funded to deal with flooding at 10 key sites in the Western region. Hinksey is number 1 So what did we do 8

9 Hinksey Flood Alleviation Scheme Project Aim: 1. To increase the resilience of the railway in the Hinksey area to flood events 2. Works shall minimise the impact on the flood risk to third party properties and businesses 3. Implement the works as soon as possible The Telegraph

10 Area of consideration Residential Residential A34 NSC Depot & Sidings Fowles Bridge Abingdon Road Bridge Cold Harbour Campsite Dairy Depot Strouds Bridge Southern By Pass (A423) Residential

11 Network of watercourses Hinksey Lake Hinksey Stream Hinksey Brook Redbridge Stream Weirs Mill Stream River Thames Hinksey Ditch Abingdon Road Bridge Hinksey Drain

12 Why does the railway corridor flood at Hinksey? Hinksey Drain Indicative Cross-Section Looking Towards Oxford Hinksey Stream Oxford Abingdon Road Overbridge South-West By- Pass Overbridge Fowles Underbridge Indicative Longitudinal Track Profile Stroud s Underbridge Peak Flood Level

13 Typical flooding extents

14 Project options March 2008 Feasibility Report: Looked at various flood mitigating measures including: Do nothing Sheet piling along the embankment Raise the track levels above the flood line Widen and enlarge existing culverts Holding reservoir High capacity pumping Report concluded that the preferred solution was to raise the existing track levels

15 Preferred solution Oxford Abingdon Road Overbridge South-West By- Pass Overbridge Fowles Underbridge 400mm MIN Stroud s Underbridge Peak Flood Level Indicative Longitudinal Track Profile

16 Impact of the proposed solution A significant track lift required to raise the existing tracks above peak flood levels - Effectively building a dam across an existing flood plain The existing flood plain will be reduced on one side - how will this affect lineside neighbours? - There is a need to understand the flood dynamics both prior to and after the implementation of the proposed design

17 Flood modelling stages Stage 1- Form Baseline Flood Model Review and validate EA Oxford Flood Risk Mapping Models Stage 2- Design and model the Raised Track Understand the effects of raising the railway track to the existing flood plain Stage 3- Identify and Assess Flood Mitigation Measures Assess various flood mitigation measures to offset any increase in flood envelope or depth Define the Scope of the Overall Project

18 Stage 1 - Baseline model Hydrology embedded in the Environment Agency model (January 2014) included the following return periods: 5yr 20yr 75yr 100yr 100 plus Climate Change (20%) 1000yr

19 Stage 2 flood model conclusions Results of modelling stage 2 show: The proposed track lifting scheme is effective and will improve the flood resilience of the main lines (but the lines will still flood during the more severe flood events greater than a 1 in 20 storm) What does this mean? In terms of the past 11 flood events the proposed track lifting would have kept the rail corridor open on eight occasions The duration of the line closure for the remaining three events would have been significantly less, as the peak water flows would recede below the rail levels much quicker Is this a satisfactory solution?

20 Flood depth differences existing vs raised track (1 in 5 Fluvial Event)

21 Flood depth differences existing vs raised (1 in 20 Fluvial Event)

22 Flood depth differences existing vs raised (1 in 100 plus climate change)

23 Flood modelling stage 3 mitigation measures Basic Requirement: Need to increase the conveyance of water through the railway corridor Problem: The volume of water to be conveyed varies considerably for each fluvial event Options: Single Culvert Multiple Culverts in different locations Open up Abingdon Road bridge and the divert water southwards

24 Culvert positioning Abingdon Road ridge

25 Final culvert design Twin-box culvert. Each box 3.6m wide by 1.8m deep. Overall length 82m Steel Orifice plate fitted to inlet to be removed when the WCC implemented and operational

26 Development of the culvert design New Issues: The proposed works now extend outside the railway corridor and as such would be subject to Planning Consent The proposed site is located within a Flood Zone 3 as defined by the National Planning Policy Framework and Strategic Flood Risk Assessment. As such no increase in flood risk would be permitted A number of scenarios were run with varying widths, depths and invert levels to ascertain the optimum design across all fluvial events No solution produced a zero impact in regards to increasing flood levels in the surrounding area The flood modelling confirmed an optimum solution of a twin-box culvert, each unit being 2.1m wide by 1.5m deep (internal dimensions)

27 Strouds underline bridge main line decks Main Line Bridge Decks Effect of proposed track lift

28 Strouds underline bridge down goods deck Bridge Span under Down Goods Line

29 Strouds underline bridge scope Redundant freight deck replaced Goods loop deck renewed and raised Main line decks refurbished and raised

30 Raised track design Constraints to Track Lifting: Need to raise the track above the peak water levels BUT provide provision for future OLE Clearances to Abingdon Road Bridge Location of S&C Junction and connection to NSC Depot Location of Stroud s Bridge Track formation considerations and construction time

31 Summary of the flood mitigating measures Track lift of 430mm beneath Abingdon Road, tapering out to 250mm at Strouds bridge, including ballast retention and significant track formation works Renewal of 9 S&C units Install a 82m long twinbox culvert to the north of Abingdon Road Replace down goods line bridge deck at Strouds Lift main line bridge decks at Strouds Replace existing redundant span at Strouds bridge with a combined foot and cable crossing structure Raise all signalling and E&P lineside assets onto platforms above flood level Just a simple track lifting scheme!

32 Planning the blockade Agreement was made with TOCs and FOCs to complete works in a blockade. TOCs preferred a period of continuous disruption and the complexity of works lent to a complete rail closure 16 day blockade from Saturday 29 th July to Monday 15 th August 2016 Shared possession with other key projects in the area 32

33 Planning the blockade To aid with compliance of the CDM regulations we made sure principle contractor roles and responsibilities were clearly defined for the two main principle contractors for track and civils works Multiple stakeholders involved with and influenced by Hinksey Travelling public Lineside neighbours Commercial neighbours Manage risks weather (high winds and rain) 33

34 Construction during the blockade Manpower 2 x 12 hour shifts. Over 100 people working at any time Different plant in use requiring careful planning and on site coordination 34

35 Specialist plant utilised PEM LEMs Tamper Kirow crane Crawler crane 35

36 Informing the public 36

37 Achieved within blockade 9 S&C units replaced; 200metres of plain line renewed; thousands of tonnes of ballast dropped; 44 culvert units installed; 2 main line bridge decks removed, refurbished and reinstalled; 1 new foot bridge installed; S&T modifications and reinstalled 37

38 Culvert 38

39 Culvert 39

40 Culvert 40

41 New S&T raised platform 41

42 Country end of renewal 42

43 London end of renewal 43

44 16 days in 220 seconds (This video is hosted in the the PWI Technical Hub) 44