Reservoir operation and flooding

Former Director General of Irrigation, G.T. Dharmasena, in an article, titled "Revival of Innovative systems for reservoir operation and flood forecasting" in The Island of 17 December, 2025, starts out by stating:

- BY NEVILLE LADDUWAHETTY

"Most reservoirs in Sri Lanka are agriculture and hydropower dominated. Reservoir operators are often unwilling to acknowledge the flood detention capability of major reservoirs during the onset of monsoons. Deviating from the traditional priority for food production and hydropower development, it is time to reorient the operational approach of major reservoirs operators under extreme events, where flood control becomes a vital function. While admitting that total elimination of flood impacts is not technically feasible, the impacts can be reduced by efficient operation of reservoirs and effective early warning systems".

Addressing the question often raised by the public as to "Why is flooding more prominent downstream of reservoirs compared to the period before they were built," Mr. Dharmasena cites the following instances: "For instance, why do (sic) Magama in Tissamaharama face floods threats after the construction of the massive Kirindi Oya reservoir? Similarly, why does Ambalantota flood after the construction of Udawalawe Reservoir? Furthermore, why is Molkawa, in the Kalutara District area, getting flooded so often after the construction of Kukule reservoir"?

"These situations exist in several other river basins, too. Engineers must, therefore, be mindful of the need to strictly control the operation of the reservoir gates by their field staff. (Since) "The actual field situation can sometimes deviate significantly from the theoretical technology... it is necessary to examine whether gate operators are strictly adhering to the operational guidelines, as gate operation currently relies too much on the discretion of the operator at the site".

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