Flood mitigation and severe weather impact on tunnels

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Dr Jim Yang, Regional Technical Director – Geotechnics and Tunnelling, Hyder Consulting delivered this presentation at the 2012 Queensland Transport Infrastructure Summit.
The State Transport Infrastructure Series of events represent the leading forums in Australia to assess the future plans for transport infrastructure development and financing across Australia. For more information, please visit http://www.statetransportevents.com.au

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Flood mitigation and severe weather impact on tunnels

  1. 1. FLOOD MITIGATION AND SEVERE WEATHER IMPACTS ON TUNNELS Dr Q. J. Yang Queensland Transport 2012 Brisbane, 25th-26th July 2012
  2. 2. OUTLINE OF PRESENTATION  Factors that cause flooding  What can tunnels do - dealing with stormwater or flooding  Tunnel design Issues for various types of tunnels  Flood impacts on tunnel operation and services  Review of major Brisbane flood events up to 2011  Some thoughts on mitigating measures against Brisbane flooding  Summary  Acknowledgements
  3. 3. CAUSES OF FLOODING  Tropical storms – intensive rainfall within a short period of time.  Seasonal flooding – melting of snow due to global warming and/or increased rainfall.  Coastal flooding - resulting from sea level changes near shore from wind setup, barometric setup and wave setup.  Tsunamis - coastal flooding caused by long, low sea waves induced by volcanoes / landslides / earthquakes.  Flooding induced by explosion of water retaining structures such as tunnels  Climate change – have potential impact on all of the above
  4. 4. URBAN FLOODING CAUSES  Reduced natural landscape and increased hard surface  Heavy rainfall -large catchment-water courses  Poor drainage system in urban environment  Tail water impact - storm surge or tidal effect near sea
  5. 5. WHAT CAN TUNNELS DO?  Flood diversion tunnel – to divert flood water into the tunnel to alleviate the water level in watercourse  Drainage tunnels – to collect water from the source and divert it to downstream to control the water flow into the urban/suburban area  Storage tunnels/caverns – to temporarily store the surface water during storm event to reduce the water into the urban area and then pump it out when storm / flood ceases  Sewage tunnels – to divert the overflow to sewage tunnels / caverns to avoid flooding  SMART tunnels – a multifunctional tunnel / cavern for transport and flood mitigation
  6. 6. STORMWATER STORAGE CAVERN IN TOKYO  25.4 m tall x 78 m wide x 177 m long, the massive underground stormwater management system in the metropolitan area of the city of Saitama, Japan
  7. 7. HONG KONG WEST DRAINAGE TUNNEL  Two sections: 1) 5km long and 6.25m in diameter, Tai Hang to Aberdeen Tunnel 2) 6km long and 7.25m in diameter, Aberdeen Tunnel to Cyberport  35 intake shafts up to 180m deep, many in constrained sites  7.5km of connection adits
  8. 8. SHAFT AND ADIT CONSTRUCTION IN HONG KONG
  9. 9. NORTHSIDE STORAGE TUNNEL IN SYDNEY  20 km of sewage tunnels - diameter from 3.8 m to 6.6 m with a total useable storage volume of nearly 500 ML  Tunnel depth - 40 m underneath the Lane Cove and Scotts Creek overflow sites, to 100 m below sea level at the North Head Wastewater Treatment Plant U/G wastewater Treatment Plant
  10. 10. NORTH HEAD WASTEWATER TUNNELS  Standby mode – 300 to 330 days/year  Wet weather operating mode – 30 to 40 days/year  Main tunnel maintenance mode  North Head wastewater treatment plant bypass mode  Northern suburbs ocean outfall system (NSOOS) maintenance mode
  11. 11. SMART TUNNEL IN KUALA LUMPUR  Dual-purpose 9.5 km long tunnel with central section of 3 km (excavated by TBM of 13.2m diameter) utilized for two-deck motorway  Use of three operational modes – 1) Low storm; 2) Moderate storm; and 3) 1 in 100 year storm  Intake structure and storage reservoir, automated water gate for closure within 24 hours
  12. 12. FLOOD RELATED DESIGN ISSUES FOR TUNNELS  Design water level  How the flood level to be determined  Entrance protection  Pumping requirement – failsafe  Tunnel lining design for extreme water level
  13. 13. TUNNEL AND U/G STRUCTURE -SINGAPORE  Consideration of tunnels or stations against water /flooding pressure and floatation
  14. 14. TAIPEI METRO  Original Design:  Flood level at a return period of 200 years + 0.5m free board to prevent water intrusion to all entrances to stations, structural openings and depots.  All other entrances shall be a minimum of 0.15m above the flood level with a return period of 100 years, and also meet the requirement of a minimum 0.6 - 1.2m above the adjacent ground level  Now:  Flood level at a return period of 200 years plus an additional 1.1m, or the level of flooding recorded during Typhoon Nari (1255mm over 24 hours) plus additional height  Gaps between vital mechanical & electrical facility rooms and conduits & pipes shall be filled with watertight materials
  15. 15. SILICON VALLEY RAPID TRANSIT CORRIDOR (SVRT)  The retained cut sections, retained fill sections, station entrances, and access points – 100 year flood level + 0.15m to 0.3m freeboard (FB)  Traction power substations, gap breaker stations, train control buildings and vent shaft openings – 500 year flood level  Existing critical facilities to be raised above the 500 year flood level.  SVRT plain to be designed to convey the surface flow generated by a 10 year storm event or to the minimum requirements of the cities, whichever is greater
  16. 16. TUGUN TUNNEL – GOLD COAST Average Recurrence Interval (ARI) Ocean Level Combined Ocean and Flood Level 2000 +0.1m 2007 +0.3m 1 in 100 year 2.05 2.15 2.45 1 in 250 year 2.30 2.40 2.70 1 in 500 year 2.50 2.60 2.90  Cut and cover tunnel beneath runway  Consideration of flooding level  Impact of green house effect
  17. 17. TUNNELS IN SYDNEY AND MELBOURNE  East Link - 1 in 100 year average recurrence interval (ARI) and the use of 2005 flood to calibrate the model by flooding during construction  Sydney Metro Tender - Metro tunnel works from the 1 in100 year ARI flood event Flood Protection  Physical barriers that prevent stormwater ingress into the station shafts, station caverns and running tunnels  Blinding layer at the base of the station shafts constructed to fall towards the sump and prevent ponding
  18. 18. LONDON UNDERGROUND  Increased seepage in tunnel 30,000m3/day pumping from London Underground (LU) Tunnels /stations due to rise of groundwater table  Use of failsafe pumping system and floodgate for Jubilee Line Extension  Thames Barrier to protect the tidal surge and flooding to the LU network
  19. 19. TUNNELS UNDER HUDSON RIVER – NEW YORK  Metropolitan Transportation Authority in New York has considered putting floodgates in subway tunnels to “contain raging torrents that an explosion in an underwater tube might unleash.”
  20. 20. TUNNELS IN BRISBANE  Brisbane City Council requires that no development causes an adverse impact on adjacent properties for flood events up to and including the 1 in 100 year flood event  Air Port Link – 1 in 10,000 year flood immunity for tunnel portals (SKM feasibility Study, 2006)  Northern Link - A requirement for the tunnels to have 1 in 10,000 year flood immunity.  Brisbane Cross River Metro – flood gate for southern portal and Yee underground station. 1 in 10,000 year flood event that is sufficient to defend the Jan 2011 flood.
  21. 21. SUMMARY OF DESIGN FLOOD FOR TUNNELS Sydney CBD Metro 1 in 100 plus FB East Link 1 in 200 plus calibration against flood in 2005 M5 Filtration 1 in 10,000 plus FB Tugun 1 in 500 plus 0.3m FB SVRT 1 in 500 plus FB Airport Link / Northern Link 1 in 10,000 plus FB Taipei 1 in 200 plus 0.5m FB Revised to 1 in 200 plus 1.1m FB Brisbane Cross River Metro 1 in 10,000 plus FB
  22. 22. TUNNEL MITIGATION MEASURES Aus/USA London Taipei Singapore Raised Entrances Yes No Yes Yes Tunnel Sumps Yes Yes Yes Yes Entrance Barriers Yes No Yes No Floodgates Yes Yes Yes No
  23. 23. FLOODING IN BRISBANE  1893 Flood – prior to construction of Somerset Dam  1974 Flood -Victoria Bridge seen from the CBD side looking over to South Brisbane, prior to construction of Wivenhoe Dam (1985)  2011 Flood –Victoria Bridge
  24. 24. BRISBANE CITY – FLOOD FACTS  Brisbane River - total length, 345 km, total catchment – 14,000 km2  Regional and local flooding along the river catchment  Flood mitigation dams – Q100 6,000 m3/s and 12,000 m3/s
  25. 25. BRISBANE CITY FLOOD LEVELS AT CITY GAUGE (AHD) 0 1 2 3 4 5 6 7 8 9 Current Q100 Current defined flood level January 2011 flood event 1974 without Wivenhoe Dam 1893 without Somerset and Wivenhoe Dams
  26. 26. INUNDATED EXTENT PEAK DISCHARGE OF 12,000 M3/S AT PORT OFFICE GAUGE - WHOLE BRISBANE
  27. 27. INUNDATED EXTENT MAP - BRISBANE EAST
  28. 28. INUNDATED EXTENT MAP – BRISBANE WEST
  29. 29. INUNDATED EXTENT MAP – BRISBANE SOUTH
  30. 30. POSSIBLE MITIGATION MEASURES FOR BRISBANE  Construction storage or flood mitigation dams to reduce the water from upper catchment  Storage caverns/tunnels to collect the rainwater to reduce the amount of discharge of storm water into the Brisbane River  Water tunnels to divert the upstream water to downstream faster  Water gate to minimize the impact from the tidal or storm surge
  31. 31. TEMPORARY FLOOD MITIGATION DAM
  32. 32. FLOOD DRAINAGE OR STORAGE TUNNEL Drainage / Storage Tunnel Option
  33. 33. WATER DIVERSION TUNNEL OPTION Long Tunnel/Cavern Option Short Tunnel/Cavern Option
  34. 34. SUMMARY  Multiple factors causing flooding  Tunnels/caverns for mitigation of flooding  Extreme weather condition and climate change impact should be considered in the tunnel design  The flooding level and the mitigation measures - an integrated decision  Water gate/door could be one of solutions to allowing some level of flood water intrusion to tunnels  Pumping system within the tunnel – failsafe  Tidal impact on the water course or tunnels
  35. 35. ACKNOWLEDGEMENTS  Brisbane City Council for public information  All from information from various sources on the website  I am grateful to support from Hyder.
  36. 36. THANK YOU FOR YOUR ATTENTION Questions?

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