How it began
In 2001 the Malaysian government sought proposals for a way to let a typical flood of three to six hours pass without inundating central Kuala Lumpur. A group led by Gamuda engaged the Malaysian consultant SSP and Mott MacDonald UK to design a bypass tunnel with holding ponds at each end. Under pressure to cut cost, Gamuda asked whether the normally empty tunnel could also carry traffic and be tolled. The tunnel was built between 2003 and 2007.
Before it existed
Major floods hit the city center in 1926 and 1971. After rapid urban growth from 1985, flooding became almost annual: the average annual flood in the Klang river rose from about 148 cubic meters per second to 440 by 1995. The Klang Basin Flood Mitigation Project added holding ponds and wider river channels, but studies found these measures alone would not protect the commercial center.
How it works
The road occupies the central 3 km of the 9.7 km flood tunnel, on two decks, one for each direction. In small floods no water is diverted. In moderate floods, about ten times a year, water runs through the void under the lower deck while traffic continues. In a major flood, about once a year, traffic is cleared, gates at both ends of the road section are lifted and water fills the road decks. About 48 hours are allowed to drain, wash and reopen the road.
What changed first
Tunneling ran through karstic limestone with cavities and soft alluvium, so slurry mixshield boring machines were used, with a bore of 13.2 meters. The highway section was scheduled to open at the end of March 2007 and the flood tunnel at the end of June 2007. Toll income from the road reduced the need for government funding of the flood works.
Where it stands today
The builder states that the tunnel has operated since 2007 and addresses 45 percent of the major flood risks of the Klang Valley, protecting areas including Masjid Jamek, Dataran Merdeka, Leboh Ampang and Jalan Melaka. It continues to carry traffic in dry weather and to divert stormwater during heavy rain.
