Excess water in Phetchaburi's Kaeng Krachan dam had crossed the spillway as of press time last night but the central municipality was not expected to be flooded due to the province's comprehensive flood-drainage and management plan.
Initial overflow from the dam was predicted to hit the municipality at midnight but fears of the Phetchaburi River bursting its banks had subsided by the early evening, said Samrueng Saengphuwong, deputy secretary-general of the Office of National Water Resources.
He said the situation was no longer deemed critical and remains manageable, noting that residents still had enough time to move their belongings to higher ground and reinforce flood dykes.
Spillover from the dam is expected to peak Wednesday or Thursday, with floods projected to strike late next Monday, he said, adding that without rain the floodwater level was unlikely to surpass 30cm.
But if the flow rate from Phetchaburi dam, which receives water from the Kaeng Krachan dam, exceeds 170 cubic metres of water per second, the level could rise to 50cm, he said.
With high tides expected over the weekend, efforts to drain the floodwater into the Gulf of Thailand may not happen as quickly as was originally hoped, he added.
Local irrigation officials are speeding up work to dredge four irrigation canals so more floodwater can be drained from Phetchaburi dam.
This is one of several measures to reduce the flow of water into the Phetchaburi River and minimise flooding in Phetchaburi's Muang municipality.
Thaweesak Thanadecho, deputy chief of the Royal Irrigation Department, said irrigation canals would be opened to receive water due to be drained into the sea from Friday.
The goal is to discharge water from the Phetchaburi Dam to 140-160 cu/m per second and minimise flooding in several districts, he said. Water pumps and water-propelling boats are working together to drain more water into the sea, he added.
The Royal Thai Navy is on standby and is ready to supply more boats to speed up the project.
Twenty boats are being deployed in the final section of the river in Ban Laem district to push the water out to sea at a rate of 2 million cu/m per day. They function optimally during low tides but high tides are forecast this weekend, officials said.
About 30 households living upstream in Kaeng Krachan district have reportedly already been flooded.
The flooding took place on Monday at Ban Phu Khem in tambon Kaeng Krachan. In low-lying areas, flooded streets saw water levels reach as high as 2 metres, officials said.
Residents in Amphoe Kang Krachan, one of the areas hit by floods, appeared calm Tuesday and confident the situation would be brought under control.
Mali Naknoi, who owns one of the resorts that was inundated in the province, said local authorities had warned her about the risk of spillover on Tuesday, giving her sufficient time to move her belongings to higher ground.
The resort was built on a part of the river that connects to one of the Kang Krachan dam's spillways.
The owner of another resort located nearby, who spoke on condition of anonymity, faulted the Royal Irrigation Department for not managing the flow of water effectively.
Thongbai Klaipetch, the 78-year-old owner of another resort that was partially submerged on Tuesday, urged local authorities to find better ways to resolve the flooding.
He said he doubted a planned inspection tour to the province Wednesday by Prime Minister Prayut Chan-o-cha would yield fruitful results.
Gen Prayut has called on residents in flood-prone communities to stay abreast of developments and brace for possible evacuation.
He said that while measures were in place to divert the floodwater, rainstorms could trigger flash floods and residents should take the necessary precautions.
The premier promised to provide more flood relief and rehabilitation measures during his visit.
Meanwhile, 50 provinces have been warned to brace for possible flooding and landslides due to heavy rainfall this week.
Chayapol Thitisak, chief of the Department of Disaster Prevention and Mitigation, said the danger zones include 15 provinces in the North, 15 in the Northeast, 11 in the Central Plains and nine in the South.
The department has alerted officials and ordered them to prepare rapid deployment units and equipment in case of an emergency.
In Kanchanaburi, two major dams discharged more water last week so they could handle more inflow in case the weather conditions and general situation worsen.
In Thong Pha Phum district, the Vajiralongkorn dam is releasing an average volume of 43 million cu/m of water a day, up from 38 million, this week for the same purpose.
The dam was holding 7.5 billion cu/m as of Tuesday, putting it at about 85% capacity. In Si Sawat district, the Srinakarin dam was discharging 20 million cu/m a day.