KUALA LUMPUR, Oct. 29 -- To most motorists, the SMART Tunnel is a way to bypass traffic congestion on the southern approach to Kuala Lumpur's city centre. Its primary purpose, however, goes beyond moving vehicles.

The 9.7km Stormwater Management and Road Tunnel combines a 3km double-deck motorway with a flood-control system designed to divert excess water away from the city centre during heavy rain.

It channels water from the Klang-Ampang catchment to reduce downstream flood risks, including around the confluence of the Klang and Gombak rivers near Masjid Jamek.

According to Amanat Lebuhraya Rakyat (ALR), the holding company of the SMART Tunnel concessionaire and three other highway concessionaires, the system has a combined water-stor...