Some questions on floods in south west Sri Lanka

2017-06-17
The  of June 1 gives on Page 14 a discussion of rainfall predictions in the current season. Talking with an Irrigation Engineer cum Hydrology specialist, who has also a role in international consultancies, I raised some questions, which I would like to share, as well as the answers given by him.
This consultant has also worked on the study of water in the Kalutara District and on the design of the Colombo Katunayake Expressway.
Though he does not wish to give his name his views are well worth listening to. I have worked with him when we were both Government functionaries in land and irrigation, he as Irrigation Engineer and I as District Land Officer, in the early years of our public service.
Does it function as a barrier for the flow of water from the interior to the coast and thus cause floods in the interior?
We discussed a question which I raised as to why there was, in the interior of the Kalutara District, high flooding (Matugama etc.) while at the same time the coastal area, like the Kalutara town and other areas a few miles inland did not suffer from it.
I am a Kalutara person (home town etc) and have memories of the lagoon in front of our home rising and the sand bar being cut to release the water into the sea. Our own property and its surrounding lands, which according to survey maps are below the Kalu Ganga flood levels and were inundated readily, were not affected this year but lands in the interior, a few miles to the east were under water.
My driver is from Matugama, born and bred, and even in the last couple of years he was expressing surprise that certain parts of the Matugama town and adjoining areas which, in his memory, were normally not flooded, were subject to heavy flooding.
Is there enough space in the culverts or are there enough culverts to take the water across to the sea, in whatever way?
My engineer friend (Let’s call him GM) however pointed to the extremely high volumes of rains in recent years as evidenced by the rainfall forecast for April, May, June 2017 as shown on Page 14 of the  of June 1 2017, presented by Kelum Bandara,  journalist, from an interview with someone in the Meteorology Department.
GM said that these figures, depicting the intensity of the rainfall, were more than adequate explanation for the severe inundation of the interior of the Colombo, Kalutara, Galle and Matara districts.
Rainfall forecast for April, May and June 2017 ( 1 June P 14)
AVERAGE RAINFALL (mm) Kalutara 1233 Galle 1019 Matara 763 Hambantota 245, Colombo 942 Ratnapura 939, Kegalle 1,142 (selected data for western / southern area of SL from table).
Without making too much of a fuss however I am tempted to propose a further question. How come then that the coastal areas of these districts were relatively free of flooding?
As a tentative answer worth talking about may I bring up the existence of the Southern Expressway, which is in existence only for a couple of years. Does it function as a barrier for the flow of water from the interior to the coast and thus cause floods in the interior?
The raised earthworks and concrete works of the Expressway, running parallel to the coast 10 TO 20 MILES INLAND can also be seen as a dam blocking the easy flow of water from east to west in the south-western area of the country. And thereby causing floods. Another aspect of the Southern Expressway is that it runs through developed lands such as rubber, tea and other plantations, located more often than not on slopes.
The Expressway track runs along the bottom of the land, often, in its course i.e. in a ravine where the water will collect anyway. Because of this the water will fill up alongside (unless there are enough culverts to take it to the other side). But since on the other side too there is an upward slope the water will collect so that the Expressway will be a kind of long dry road sitting on top of a water body running north south, separating the coast from the interior. This is an observation made by another engineer friend. Is this a true description?
Thus to repeat the point of view: The raised earth and concrete works of the Expressway, running parallel to the coast 5/10 TO 20 MILES INLAND can also be seen as a dam blocking the easy flow of water from east to west in the south-western area of the country and thereby causing floods. That is the general question. It can be broken up into further details: Are there sufficient culverts at the bottom of the highway for water to go under the highway from east to west? If not, the blocking of water will contribute in a major way to creating floods in the interior of the south west.
Is it possible to create more space for the water to pass through? If the answer to the previous question is “Yes” then how can it be done and how much will it cost and what are the implications?
In contrast to the experience of the Southern Expressway the Colombo Katunayake Expressway has within the short period of its existence not caused problems.
But at the initial stages, when the sand foundation was being created south-north there was an event in Ja-ela which raised an issue. There was an existing watercourse running east-west taking water to the lagoon and the sea.
When the sand/earth bar was being created north-south, as a raised platform for the highway, there was sufficient room left for the water course to function, taking the water across the course of the sand bar. Despite this, when the rains came there were unprecedented floods in that area, though room had been left for the existing watercourse. It was then clear that water moved not only along the watercourse but around it too towards the sea and this caused a flood even before the road itself was built.
The residents of the area created a stir and either for this reason or whatever the project was abandoned by the then President Chandrika Kumaratunga. It was taken up later after a lapse of many years and now functions well. It’s very likely that it was redesigned with the earlier experience in mind.
This experience may be relevant to the current happenings in the south west. Is there enough space in the culverts or are there enough culverts to take the water across to the sea, in whatever way?
My friend tells me that the intensity of the current rainfall could never have been anticipated when the infrastructure was designed. These are outliers.  Was this inability to use info about the local scene due to the haste with which it was constructed?
What was the status of interaction between the foreign contractors and the local expertise?
Lots of questions to ask about the past with the hope of making room for the future. Are these pertinent questions to ask before more Expressways are given as contracts to foreign companies without local inputs and collaboration?
Can one excuse such outcomes as the interior flooding found in the southwest as being caused by unprecedented rains?
Surely we have records going back a hundred years.
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