Kuala Lumpur, Malaysia, sits at the confluence of the Klang and Gombak rivers, making it notoriously vulnerable to flash flooding caused by tropical monsoon rains. To combat devastating urban inundations and crippling traffic congestion, engineers constructed the Stormwater Management and Road Tunnel (SMART Tunnel), which opened in 2007. Spanning 9.
7 kilometers, it is the longest stormwater tunnel in Southeast Asia and features a unique 3-level operational design. Under normal weather conditions (Mode 1), no floodwater enters, and the top two levels serve as a dual-deck motor vehicle highway while the bottom level stays open for minor drainage. During moderate rainfall (Mode 2), floodwaters are diverted into the lowest channel while cars continue driving on the upper two levels.
However, when extreme storms threaten the city with major flooding (Mode 3), the entire system switches into full flood management mode. Automatic traffic control systems activate, water-tight gates seal off the entrance ramps, and traffic is completely evacuated from the upper decks within 17 minutes. Huge automated sluice gates then open, allowing up to 3 million cubic meters of floodwater to roar through all three levels of the tunnel.
Once the storm passes, high-capacity pumps drain the tunnel, automated sweepers and pressure washers clean debris from the roadways, and the tunnel reopens to vehicular traffic within 48 hours.