The full-scale planning would be conducted on the capital's entire footprint, including new districts that were incorporated in 2008. Experts have been asked to design a water drainage system that would function over the -3,350-sq.m area, home to about 6 million residents.

Planning for the water drainage system would have to comply with the city's master plan, the decision said.

City planners were asked to carry out a comprehensive study on the existing drainage system and to incorporate computer weather models into their analysis to offer a comprehensive solution for drainage management in the city.

One component of the planning would focus on rainwater drainage with the aim of mitigate flooding in central areas of Ha Noi and gradually preventing any floods due to heavy rainfall.

Bui Huu Doan, deputy head of the Ministry of Construction's Technical Infrastructure Department, said the existing drainage situation in Ha Noi was defective and inadequate, a fact that was acutely evident during periods of heavy rainfall.

Deputy General Director Nguyen Xuan Dieu of the Ministry of Agriculture and Rural Development's Irrigation Department said that in addition to the low capacity of pumping stations, another problem was the collection of stagnant water that could not flow into lakes or rivers due to blocked outlets.

Last July, a three-hour downpour dumped 130mm of rain and flooded many areas of the city, which clearly demonstrated the low capacity of the city's water drainage system.

However, the situation was far better than the flooding in early November 2008 when all city streets were submerged in water due to the record 500mm downpour in the urban area.

Doan said most projects were focused on renovating the existing system rather than creating an entirely new one.

The existing system didn't separate rainwater runoff and sewage. Nor did the designers of the old system take into account the maximum rainfall or drainage pressure, he said.

The committee must finish its tasks by June.