Ever since widespread floods hit the capital in 1971 the government has been implementing measures to increase the rivers’ capacity for coping with flood waters from upstream. But over time conventional methods such as channel widening and deepening had become inadequate and extensive urban development was making matters worse.
Detailed studies had led to the concept of a tunnel for stormwater storage, and then at design stage came the novel idea of using it to tackle traffic congestion. After approval by Malaysia’s government, development began by the MMC Engineering-Gamuda joint venture, with engineering support from SSP Consultants and Mott MacDonald.
The Mott MacDonald team designed the tunnels and underground structures, the hydraulics and storm water control systems, and the road tunnel ventilation, lighting and communications systems.
SMART’s major components include an upstream intake structure, holding pond and storage reservoir, diversion tunnel, twin box culvert and ingress/egress connectors to the motorway tunnel. Ground conditions dictated construction by tunnel boring machine (TBM),with two state-of-the-art slurry TBMs working in opposite directions from the middle of the tunnel alignment.
SMART, which officially opened in June 2007, works on a three mode system. Mode one operates under normal conditions or when rainfall is low such that no water needs to be diverted into the tunnel. Moderate storms activate mode two. This diverts flood water into a bypass tunnel in the lower section of the motorway tunnel which remains open to traffic.
During the once or twice yearly heavy storms, a switch is made to mode three when the tunnel is closed and the full tunnel section with a combined capacity of 3 million m3 becomes available to divert the dramatically increased flows. Extensive monitoring stations ensure sufficient time is allocated to allow the last vehicle to exit before the automated water-tight gates open.
The motorway re-opens to traffic within 48 hours of closure. We helped ensure that operational aspects of the change over between modes from vehicle to flood use are efficient.