Royal Irrigation Department director-general Samart Chokanapitak said the prolonged inundation was caused by the physical nature of the Tha Chin River which had many bends.

Samart said the bends slowed the flow of the river, delaying the run-off into the ocean. A further impediment, he said, was at the mouth of the river in Samut Sakhon where sediment had built up. It would take a long-term plan to remove this obstacle after the flooding had died down.

Since October, a huge volume of water had been diverted from the Chao Phya and Tha Chin river basin to the central plains in order to protect Bangkok.

The Tha Chin is a tributary of the Chao Phya and runs from Suphan Buri through Nakhon Pathom before spilling into the Gulf of Thailand at Samut Sakhon.

The RID has been able to drain water from the plains on the eastern side of the Chao Phya River, mostly in Sing Buri, Lop Buri and Angthong. Only a few areas of the provinces are still inundated.

But problems remain in the provinces located to the west of the Chao Phya that are sandwiched by the Tha Chin.

With the Chao Phya on one side and the Tha Chin on the other, more than 694,000 rai of land in Ayutthaya, Suphan Buri, Nakhon Pathom and Nonthaburi had been inundated by water diverted from both rivers.

More than 100 RID water pumps had been installed in the central plains to divert water from farmland back to the rivers through tributaries and irrigation canals. Three tunnels were dug by the RID and Army engineers to link Thung Chao Ched and the Chao Phya River. Before the tunnels were created, the water in Thung Chao Ched could not run directly into the Chao Phya as it was blocked by the Sena-Bang Sai Road. For the Tha Chin, two tunnels were dug to link Thung Praya Bunleu and Thung Prapimol to the river.

Though he could not give an estimate of the volume of water covering the central plain, Samart expected the flooding in the northern areas to be gone by Sunday, while the southern areas should be clear by December 15.

Pennapa Hongthong

The Nation