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?