Dam management, drainage keys to flood prevention

 

In terms of the overall management plan, in areas which are sources of the water, the middle areas and lower areas, what needs to be understood when the seasonal peak tides come?

There are plans in place, which are subject to changes on a daily basis, starting from the sources of the water – how much dams can trap rainwater, and later how much catchment areas can hold water, and the lower areas, down from Ayutthaya, can cope with the leftover [water]. The main principle is how the water should be drained when it travels to the lower areas, and the other key is how to manage the dams’ operations to retain much of the water.

 

Did the heavy flooding last year result from water in the upper or lower areas?

Both. Rainwater volume was excessive in areas north of the dams, while the volume in lower areas [the Central plains] during the seasonal peak tide was very high.

Around 10 billion cubic metres (units) can be trapped by the dams, while the rest in the plains must be managed to keep the water at two metres for around 20 days to over a month in the plains, totalling about 4.6 million rai, which will gradually accommodate the 10 billion units, in order to slow down the current so that it would cause the least damage.

 

Which area will be hit hardest?

The 4.6million rai plains, but the severity will not be as bad as last year, if rainwater volume decreases, because waterways in the lower areas have been dredged.

To slow down the floodwater, we have to make sure how many days Phichit and Uttaradit can be allowed to be flooded. In a special area designated as a slope, the water can stay up to 20 days, while other areas where the water does not go, we may negotiate with farmers to ask them to plant the first two crops, while they will decide whether to do a third crop.

 

What are plans for rainwater volume in areas downstream of dams?

In the Chao Phraya basin, there are irrigation networks in place in provinces southward from Nakhon Sawan, but they are fewer in Phichit, which are however still manageable. The key is to cut out the excess water in Ayutthaya, which is the final line of defence. A key problem resulting in heavy flooding last year was the water from the swelling Pa Sak River crossed the Chao Phraya River to flood the plains on its east. To solve this problem, improvement to waterways connecting to Rangsit Canal have been made to drain water southward to pumping stations as quick as possible, while more flood barriers are being built and more pumps provided.

The main strategy is to keep the water north of dams in the dams – slowing down the water in the plains and making use of it the most. And the efficiency of flood drainage in the lower areas is maximised through building floodways, flood barriers, doubling roads as flood barriers, and drilling holes in roads or railways that block currents.

We have to think what to do if these projects, numbering more than 100, cannot be done in time. How do we drain water out of eastern areas of Bangkok? How do we do it in the west of Bangkok? By relying on natural waterways and increasing drainage capacity with more pumps and getting rid of natural obstacles?

If everything is done, no floodwater will reach Bangkok?

A. Some may, if flood barriers are demolished by people, or collapse by themselves. The new barriers don’t need to be concrete, but in short term they should be heightened, or roads which double as barriers be heightened. Building new barriers within three months is out of question. It’s not possible. The key worry is about barriers being demolished by people. But what can we do about it?

 

Q. What scenario will be likely or presented to the public?

A. It’s up to rainwater volume, both in areas north and south of dams. No one knows about it now, but we can do an estimate in per centtime volume, whether it will increase or decrease from last year. For example, if it’s 5 or 10 per cent less than last year, what scenario and management methods would be likely or used. What do we do if it rains when it should not, or rains at different volumes, in areas north or south of dams?

Q. Then there are many scenarios.

A. No. What I say is designation in parameters, and working out scenarios is based on the use of many parameters, and also on three other factors, or dimensions, which are time, volume and locations. Working out scenarios is also based on these three factors.

Q. The management has been planned from the aspect of the central government, what about local administrations, like the BMA?

A. The government has coordinated with local administrations, and given to them a Bt1billion budget for dredging waterways. I could feel their enthusiasm, for the first time, and I am following the progress of their works, which they will report back to the government within two weeks.