Three eastern provinces may endure flooding for another month

Residents in three eastern provinces could face another month of flooding as about 1.7 billion cubic metres of water remains to be drained, with natural waterways and high tides limiting the flow into the Gulf of Thailand.

Despite assessments by the National Water Resources Office (ONWR) and the deputy prime minister on when the region might return to normal, residents continue to struggle with extensive floodwater that has yet to recede.

Thai PBS joined Assoc Prof Seree Supratid, an expert on climate change and disasters, to survey drainage routes in the East. They found several natural bottlenecks that are slowing the movement of water.

If the entire 1.7 billion cubic metres were drained through the Bang Pakong River alone, the process would work best during low tide. More than 100 million cubic metres could be discharged a day under favourable conditions, but high tides in October are making natural drainage slower and more difficult. The sea level falls only twice a day, limiting the periods when water can flow out efficiently.

One proposed engineering solution is to divert some of the floodwater through the Chaiyanuchit and Samrong canals towards large pumping stations along the coast. These stations have a combined pumping capacity of 65 million cubic metres a day, although the route also faces physical constraints.

Seree said natural drainage could move more water under favourable conditions, but it was difficult to overcome the effects of high tides. He said authorities should instead use available engineering solutions to divert water through the canals towards the Gulf of Thailand.

Paitoon Kengkarnchang, deputy secretary-general of the ONWR, said water management required engineering measures to drain the floodwater as quickly as possible. The situation would improve if there were no further rainfall, he said.

One major obstacle to diverting water towards the Gulf is the area known as Khlong Lang Tao, an underwater ridge near the boundary between Bangkok and Samut Prakan. The submerged landform acts like an underwater weir, slowing the flow of water. Pumps must push water over the ridge to reach large pumping stations farther downstream.

Paitoon estimated that it could take about 30 days for floodwater in the eastern region to recede. Nakhon Nayok may recover sooner because of its steeper terrain, while water levels in Prachin Buri are expected to fall gradually. Some areas of Bang Nam Priao district in Chachoengsao could take another 10 to 20 days, he said.

Chachoengsao Governor Monsit Paisalthanawat said Bangkok, Samut Prakan and Chachoengsao needed to coordinate efforts to push water into the sea. Authorities also needed to find ways to drain water through both the Chao Phraya River and coastal canal routes.

Managing more than 1 billion cubic metres of water will take time, while pumping equipment must be allocated carefully, the report said. Prolonged flooding that forces residents to live with water for weeks or months should not be allowed to become the norm.

Although pumping water over the underwater ridge towards large coastal stations is more challenging, it could shorten the duration of flooding compared with relying solely on natural drainage through the Bang Pakong River, which is hindered by high tides.

The pace of recovery will ultimately depend on rainfall and cooperation among government agencies to coordinate pumps and other equipment, with the aim of reducing the impact on residents and restoring flooded areas as quickly as possible.