Mr Wim said there is now a large volume of water in the Yom River basin because of continuous rain in the upper North and there are no reservoirs to take the excess water in that part of the country, unlike in the Wang, Ping and Nan river basins.
Bhumibol Dam in Tak province takes water from the Wang and Ping river basins, while Sirikit Dam in Uttaradit and Naresuan Dam in Phitsanulok province can absorb water from the Nan River basin.
Therefore, it was necessary to divert water from the Yom River basin to the Nan River basin to reduce the quantity of water flowing southwards.
Mr Wim said the water is now being diverted through Khlong Hok Bat passing rice and lotus fields in Phichit and Phitsanulok provinces to swamps already prepared for this purpose with a budget of 120 billion baht. They include Bung Rakam, Bung Takhreng, Bung Raman and Bung Khi Raeng in Phitsanulok province.
The Royal Irrigation Department has a plan to use the Chao Phraya Dam in Chai Nat province to drain water as quickly as possible out to the sea. It has been instructed to issue a warning for people living along the river to keep the situation under watch.
According weather forecasters there will be heavy rain in the North and Central regions from Sept 13-17. This will result in more water flowing into the Chao Phraya River.
The Royal Irrigation Department plans to release water through the Chao Phraya Dam at the rate of 1,800 - 2,000 cubic metres per second to push existing water in the river to the sea.
Therefore, the water level in the Chao Phraya River in Chai Nat, Sing Buri, Ang Thong, and Ayutthaya would rise by between 20 and 50 centimetres.
The department has sent a warning to Nakhon Sawan, Uthai Thani, Chai Nat, Sing Buri, Ang Thong and Ayutthaya, telling people to be ready for possible flooding and to move their belongings to high ground in advance, Mr Wim said.
The Bangkok Metropolitan Administration has put all 50 districts in the capital on alert for possible flooding, Bangkok deputy governor Malinee Sukvejvorakij said on Thursday.
Dr Malinee said all districts were told to install water pumps in flood-prone spots, so that rainwater could be quickly drained away.
People in 27 communities, involving more than 1,200 households in 13 districts, not protected by floodwalls along the Chao Phraya River should be ready to remove their belongings to higher places.
The BMA had earlier drained water from some major canals, including Khlong Saen Saep, particularly the parts running through Phetchaburi, Sukhumvit and Khlong Tan roads.
In Sukhothai, the floodwaters have started to recede, as damaged levees along the Yom River have been repaired, reports said on Thursday morning.
More than 500 soldiers had installed gabions (rectangular wire mesh baskets filled with rocks, concrete or sand and soil) to reinforce the barrier of big bags, weighing about 2.5 tonnes each, the reports said.
About 1,000 sandbags were also used to strengthen the flood barrier.
Authorities brought in more than 50 large pumps to drain water in flooded areas of the lower northern province.
Vehicles can now use many of the roads hit by flooding and many merchants had resumed business, the reports said.
At 11am Thursday, Prime Minister Yingluck Shinawatra boarded a helicopter for a flight to inspect inundated areas in the central province of Ayutthaya, and visit affected people there.
Ms Yingluck was then due to travel to Nakhon Sawan and Sukhothai to assess the flood situation and the repaired levees. In Sukhothai, she was to be briefed on the overall situation by Natural Resources and Environment Minister Preecha Rengsomboonsuk.
Overflow from the Yom River swept into Sukhothai early Monday morning, breaking through eroded levees beneath flood walls and swamping parts of the city.