JICA proposed the revised master plan for Chao Phraya River Basin flood prevention to Royal Irrigation Department Director-General Lertviroj Kowattana.
Yusuke Amano, a JICA academic, said the agency conducted an aerial survey on areas hit by the devastating 2011 flood for accurate calculation and analysis of the flood prevention plan.
The existing system and facilities must be fully and efficiently utilised, in particular all dams, which need systematic management and assessment, he said.
According to the aerial imagery, more appropriate water bypasses and floodways will help drain water from low-lying areas, affected by flooding.
Diverting water to the east and the west sides of the river basin does not help much to alleviate flood impacts.
However, JICA advised an additional 20km bypass through Ayutthaya, north of the capital, will reduce water volume in an amount that does not exceed the holding capacity of the Chao Phraya River and prevent large amounts of water from flowing into business areas in the lower central provinces including the capital.
Regarding water retention areas, an unspecified number of such zones must be maintained more systematically, Mr Amano said.