flood mitigation and severe weather impact on tunnels
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FLOOD MITIGATION AND SEVERE WEATHER
IMPACTS ON TUNNELS
Dr Q. J. Yang
Queensland Transport 2012
Brisbane, 25th-26th July 2012
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
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
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
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
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
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
SHAFT AND ADIT CONSTRUCTION IN HONG KONG
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
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
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
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
TUNNEL AND U/G STRUCTURE -SINGAPORE
Consideration of tunnels or
stations against water
/flooding pressure and
floatation
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
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
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
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
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
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.”
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.
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
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
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
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
BRISBANE CITY FLOOD LEVELS AT CITY GAUGE (AHD)
0123456789
Current Q100
Current defined
flood level
January 2011 flood
event
1974 without
Wivenhoe Dam
1893 without
Somerset and
Wivenhoe Dams
INUNDATED EXTENT PEAK DISCHARGE OF 12,000
M3/S AT PORT OFFICE GAUGE - WHOLE BRISBANE
INUNDATED EXTENT MAP - BRISBANE EAST
INUNDATED EXTENT MAP – BRISBANE WEST
INUNDATED EXTENT MAP – BRISBANE SOUTH
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
TEMPORARY FLOOD MITIGATION DAM
FLOOD DRAINAGE OR STORAGE TUNNEL
Drainage / Storage Tunnel Option
WATER DIVERSION TUNNEL OPTION
Long Tunnel/Cavern Option
Short Tunnel/Cavern Option
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
ACKNOWLEDGEMENTS
Brisbane City Council for public information
All from information from various sources on the website
I am grateful to support from Hyder.
THANK YOU FOR YOUR ATTENTION
Questions?
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