Colombo’s Flood Protection — a response

The recent article by Dr Ratnasiri, in The Island, certainly provides interesting reading, to a novice, on this subject. But, the absence of a suitable plan makes it difficult if the article is to have any practical value to a reader who can be a professional engineer. The mention of my name prompted me to pen this response.

The Madiwela East Diversion, remaining dry most of the time, as mentioned, may be due to its wrong location, too far upstream of the Kelani Ganga about 10 miles above the historic Nagalagam Street outfall. Even during floods of the Kelani Ganga, this outfall No 1 (See plan) has to be closed, long before Nagalagam Street outfall closing at +5.00 ft MSL, the accepted minor flood level for Colombo, negating the very purpose for which this canal was built. I have had reports that many groundwater wells, too, had dried up during the construction of this canal.

1. The learned doctor has not noticed the extent to which the Thalangama Tank had silted up, reducing the capacity to retain flood water (about 50 ac.ft) entering the Parliament lake, which contributes to the flooding of the Parliament lake. The flood of 1992, referred to in the said article, which caused havoc to the city of Colombo, which flooded the Parliament for the first time, was further aggravated because of a gate, constructed by SLLRDC, at the premises of Irrigation Department’s flood control unit, at Nagalagam Street, that could not be opened because of the missing gate operator. It was finally based on information given by me to President Premadasa that the President had this gate cut down by the Navy.

2. This gate was constructed at ID’s flood control premises to pump water from the Kelani Ganga to the Beira Lake, for the purpose of cleaning the lake, under a different project called MEIP, costing US$ 87 million, funded by the World Bank. The project ceased soon after the flood. Strangely, no inquiry was made. It was all swept under the carpet.

3. Dr. R’s reference to the Beira Lake, too, needs some clarifications. The Beira Lake is not a natural lake. It is an artificial lake also kept at an artificial level, of 6.00 ft above mean sea level, by the Beira Spillway, and two other control points; the control gates on the spillway have been sealed and no longer adjustable, preventing the lowering of the lake level to induce gravity flow, as suggested in my proposals.

4. I have always opposed pumping, recommending it as a last resort because it costs a lot of money to install, operate, maintain and find replacements as was our experience at the Nilwala Ganga and the Gin Ganga; which a poor country, like Sri Lanka, cannot afford. Colombo can well be without pumping, mentioned in Dr. R’s article.

5. Ignoring many other references, contained in Dr R’s article, let me now say a few words about narrowing of bridges, mentioned in it. This is not a matter of life and death, as made out to be. Any hydrologist will agree that within the narrowed section, the velocity will increase to make up for the constriction. I am not sure whether Dr. R has been informed of other matters such as hydraulic jumps, etc.

6. I would request Dr. R to study the Sri Lanka’s River Basin Map, showing the 103 river basins of our country. He will then realize that Colombo is in River Basin No 1, while the adjoining basin, named as Bolgoda, appears as basin No 2. If, as proposed, the southern diversion takes place, such a canal would become a “trans-basin diversion” let alone the new outfall getting pushed about 20 miles, down south, to Panadura; not to mention reversing the natural flow direction, within the Madiwela catchment, and aggravating the already existing problems, within Bolgoda. Then what about the environmental damages caused in constructing this canal? If what is contained in the article is supported by a plan, all these deficiencies will get highlighted.

7. I am unable to contribute further because two different River Basins have got mixed up and several independent catchments, too, have gone the same way, not to mention the mix up of proposals of three foreign consultants, under GCFC&EIP by Atkins (British), JICA & Nippon Koe (Japan) and Western Region Proposal consultants, from Singapore, possibly working under three different TORR. All my work I have confined myself strictly to one river basin, namely the Kelani Basin

The proposals, I have been making for more than 30 years, do not go against nature, no damage to environment by digging new canals, no underground tunnels of large diameter, no widening of bridges, and no pumping, all of which will require foreign consultants and contractors and cause heavy borrowing

I am fully convinced that this is a subject better left in the hands of our own trained engineers with proven experience on the subject. Any foreign input may be in the form of investors for which they can receive all the benefits they are entitled to .

Eng. ANTON NANAYAKKARA