Raising the Kotmale Dam: Think again

Thursday, 12 November 2020 01:11 - - {{hitsCtrl.values.hits}}

The existing Kotmale Dam is 87 metres high, and they want to raise by another 30 metres.

Generally, it is known that the existing foundations have been designed to take up the water pressures, etc., for the existing full supply level of the Kotmale Reservoir.

As they plan to raise it by another 30 metres from the present level, the simple Hydrostatics Principles taught in school comes to my mind.

The pressure at the bottom of the dam increases in no small measure as we go higher, and completely new designs need to be done to incorporate the additions, which is not at all an easy task, and at what construction cost?

Further, I would like to mention that I had the chance to work on the preliminary investigations of this existing Kotmale Dam while it was in the planning stage in 1973. That was one of the first jobs I was assigned when I started work at the Irrigation Department just after graduation. I was sent from Irrigation Department to the Faculty of Engineering to work on this project directly under Dr. A.S Balasubramanium, a Ph.D. from Cambridge University who was an expert in Soil Mechanics (later he became a Prof. at AIT, Bangkok). In our investigations, we found that the existing dam site had a lot of problems. There were some geological problems. I remember at the dam site, at a depth of about 152 feet, there was a layer of limestone. Generally limestone is cavernous, and if they are interconnected, there could be solution channels which could make the cavities bigger, and may result in catastrophic outcomes. To prevent this from happening, the caverns in limestone are concrete grouted.

I think, especially at this Kotmale Dam site, they should not do any more raising of the bund. That is my personal view. These are public investment projects where we are spending public money, and there should be no room for this type of failure. If the foundation of a building is designed for three storeys, and after few years of use, if they want to make it a five-storey building by adding two more floors with the pre-existing foundation, you are asking for trouble. This is what happened at a hotel building at Lewella, Kandy just a month or so ago.

A former Engineer who was associated with the Mahaweli Diversion Program